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View Full Version : Air Arms 400/500 series exhaust valve head extrusion, muzzle energy loss and general crapness..



cloverleaf
10-12-2013, 23:32 PM
In the past I've dealt with quite a few under-powered 400 series rifles (this applies to the S510 too). It seems that over time the guns not only lose muzzle energy, but the number of useable shots decreases and the velocity "sweet spot" moves down the cylinder pressure range.


What's the crack?

I stumbled across the suspected cause of this problem by accident when replacing a leaking exhaust valve. The gun that had previously only given me 36 good shots from an ideal fill of 140bar was now giving 65 good shots from a fill of 190bar.

When later looking at the old exhaust valve I noticed a raised portion in the centre of the sealing face of head. The image below shows an old valve (left) compared to an unused item. On the used valve, note the circular raised middle section on the valve sealing face, concentric with the valve stem:

http://img.photobucket.com/albums/v96/theboymike/Shooting%20II/SMALL_IMG_4487a.jpg (http://smg.photobucket.com/user/theboymike/media/Shooting%20II/SMALL_IMG_4487a.jpg.html)


It appears that this raised area develops over time due to the cylinder pressure forcing the valve against it's seat. As a result of the load on the valve, it's head compresses and displaces where it meets the seat / the centre section of the head extrudes down the valve throat. This step only usually stands proud of the sealing face by around 0.1mm, but it can have a profound effect on the output of the gun.

An undamaged valve only has to lift a fractional amount for airflow to begin and pressure on the output side of the valve to equalise with cylinder pressure; reducing the force attempting to close the valve to a fraction of that when the valve is closed.

When the valve head is partially extruded down the valve throat, the valve has to travel the depth of the extrusion before any significant flow can occur - this takes substantially more striker energy and has the effect of limiting effective valve lift and duration. This reduces muzzle energy, useable shots per charge and "sweet spot" pressure.


Testing..

Although I've already got data that supports this theory I wanted to try it again in isolation to see if I got the same results. Today I was presented with a 2005 .22 S410k that was, according to it's owner, a bit gutless. At a fill of 160bar it was giving around 7ftlb over the chrono with AA Field pellets; something was definitely amiss!

The gun was a bit of a shed so it was stripped and cleaned. The valve pot was reset to the magic 57mm, the striker rail polished and it all went back together fitted with a TDR air cylinder (0.6 times the capacity of the standard carbine item) and a new exhaust valve. The gun was set up over the chrono to give around 11.5ftlb with the AA pellets - it actually needed throttling back a bit :p

This was the state of the exhaust valve that came out - the step measured around 0.2mm deep and is the worst I've seen:

http://img.photobucket.com/albums/v96/theboymike/Shooting%20II/SMALL_IMG_4770a.jpg (http://smg.photobucket.com/user/theboymike/media/Shooting%20II/SMALL_IMG_4770a.jpg.html)

http://img.photobucket.com/albums/v96/theboymike/Shooting%20II/SMALL_IMG_4775a.jpg (http://smg.photobucket.com/user/theboymike/media/Shooting%20II/SMALL_IMG_4775a.jpg.html)


With the new valve fitted a full string was fired over the chrono, from 180 to 80bar. The gun was then stripped and the original exhaust valve refitted (with everything else kept the same) then another string fired over the chrono - this time from 180 to 40bar.

The velocity versus shot-count results can be seen in the graph below:

http://img.photobucket.com/albums/v96/theboymike/Shooting%20II/20131210VelocityTestingS410k054373_Shots.jpg (http://smg.photobucket.com/user/theboymike/media/Shooting%20II/20131210VelocityTestingS410k054373_Shots.jpg.html)


..and velocity versus cylinder pressure (assuming the pressure falls linearly with the shot count which it doesn't, but still gives an idea..):

http://img.photobucket.com/albums/v96/theboymike/Shooting%20II/20131210VelocityTestingS410k054373_Pressure.jpg (http://smg.photobucket.com/user/theboymike/media/Shooting%20II/20131210VelocityTestingS410k054373_Pressure.jpg.ht ml)


Muzzle energy versus shot count:

http://img.photobucket.com/albums/v96/theboymike/Shooting%20II/20131210EnergyTestingS410k054373_Shots_1-1.jpg (http://smg.photobucket.com/user/theboymike/media/Shooting%20II/20131210EnergyTestingS410k054373_Shots_1-1.jpg.html)


..and muzzle energy versus cylinder pressure (again, estimated):

http://img.photobucket.com/albums/v96/theboymike/Shooting%20II/20131210EnergyTestingS410k054373_Pressure_1.jpg (http://smg.photobucket.com/user/theboymike/media/Shooting%20II/20131210EnergyTestingS410k054373_Pressure_1.jpg.ht ml)


Observations

Most interestingly, referring to the last graph it can be seen that:

- The old extruded valve managed a maximum muzzle energy of 10.34ftlb at around 85-90bar cylinder pressure.

- The new, un-deformed valve made a maximum muzzle energy of 11.72ftlb at about 120bar cylinder pressure.


Additionally, from the data collected:

- The old valve gave 28 good shots (those within 1.5% of the max. velocity) from an ideal fill pressure of around 100-110bar.

- The new valve gave 41 good shots from an ideal fill pressure of between 160 and 170bar.

- Scaling up the shot count with the old valve to reflect Carbine cylinder capacity gives a figure of 46 good shots per charge.

- Scaling up the shot count with the new valve to reflect Carbine cylinder capacity gives a figure of 67 good shots per charge.

- The new valve gives around 45% more shots per charge than the old one.

- The new valve favours a fill pressure of nearly 60% higher than the old one.


Conclusions

From the information collected from this experiment, it's clear that deformation of the valve head over time has a significant effect on the performance of the rifle.

To put this into perspective, lets say you buy your new rifle and run a string over the chrono. This shows 65 shots at between 11.4 and 11.7ftlb from a 165bar fill. You use the rifle, put it away for a few months, generally stop tinkering with it..

When you come back to the gun you expect the same performance, but by filling to 165bar you're now getting 65 shots that begin at just over 7ftlb and climb to just past 10ftlbs at the end of the string. I'm sure we can all agree that 3ftlb or 30% variation in muzzle energy is not going to do accuracy any favours..

This situation could be made worse if you're blindly filling to 190bar as the handbook suggests.

A natural response to finding that one's rifle is under-performing is to crank out the screw that shall not be named - this may increase the muzzle energy at it's peak, but will further reduce the pressure at which this occurs; giving even fewer shots per charge.


A few final thoughts

Air Arms used to make the 300/400/500 series exhaust valve heads from (white) Nylon; a harder material than the current (black) Polyurethane(?), but this was dropped possibly for production reasons and the fact that it was attacked by moisture (not good if you're using a pump). I've never seen this issue in earlier (white valve) guns.

This problem appears to be a gradual process that gets all "black valve" guns to some extent. The three worst ones I've had have been around 8yrs old, however I had a similar issue in a 2yr old gun recently.

The only apparent ways to sort the problem are to:

a) Replace the valve with a standard item, knowing that it will deteriorate again over time
b) Replace the valve with a harder item (Air Arms tuning afficianodo Roger Moy apparently makes these)
c) Modify the existing valve by removing / back-cutting the affected area. Once everything has settled I suspect this might kill the problem, however you'll need a lathe to get this done.

Finally, this illustrates the importance or regularly checking a full velocity string from the rifle (be the rifle a new or used purchase); and if faced with problems don't make the assumption (as I did initially) that an exhaust valve is fine as long as it seals - there's evidently more to them than that ;)

roy0110
10-12-2013, 23:48 PM
very informative post...thanks!

Jackroadkill
11-12-2013, 00:01 AM
You are the man...

Don't suppose you have a youtube channel with stripdown guides?

cloverleaf
11-12-2013, 00:09 AM
Thanks chaps - glad the information (and the 7-odd hours it took to collect, compile and present it) is appreciated :)

I don't have a youtube video - I'm more a words and pictures man I'm afraid :p

Geordie
11-12-2013, 00:25 AM
Top class post Clover.

Fantastic detail on the pics of the valve seat:up::up::up:

Jackroadkill
11-12-2013, 00:39 AM
Thanks chaps - glad the information (and the 7-odd hours it took to collect, compile and present it) is appreciated :)

I don't have a youtube video - I'm more a words and pictures man I'm afraid :p

Right, I'll have to commission you to come round to my house and demonstrate the techniques in person...

cloverleaf
11-12-2013, 01:25 AM
Top class post Clover.

Fantastic detail on the pics of the valve seat:up::up::up:
Ta :D



Right, I'll have to commission you to come round to my house and demonstrate the techniques in person...
There's a thought - perhaps I could run some sort of travelling workshop, where we could all gather round cross-legged in someone's living room surrounded by bits of communally-stripped rifle :p

wonky donky
11-12-2013, 02:54 AM
I have seen the same thing on the odd occasion, Air Arms say it's because the rifle was over filled at some point in time? Personally I don't have an opinion I just change the valve, which i keep in stock, or make a new one. I don't machine the old one back as it will alter the valve spring pressure which will have a knock on effect to which, if I'm honest, can't be brothered to get into unless I'm putting a regulator in the gun.

That's a lot of good work though, does my head in just looking at the graphs.................I'm old & grumpy though! ;);)

gracole
11-12-2013, 08:02 AM
very good observation cloverleaf i applaued you for the many hours you spent nice when you get results. one question you say the magical 57 mm for the firing pot i have been led to beleive that its best to keep the ventura open as much as possible and adjust power with the pot what do you think atb

mark112
11-12-2013, 09:28 AM
Hi,

I had exactly this issue with my S410k which exhibited the same 'loopy' power curve as in cloverleaf's graphs. In my case I changed hammer spring, pot spring and valve at the same time. The springs were changed just 'cos gun was in bits and for a few quid I might as well! Fitting these flattened out the power curve of my rifle but looking at my old valve it was just like the one in cloverleaf's photo and showed the same extrusion. It was cloverleaf that put me onto this as being the potential culprit at the time so many thanks again.

Mark

Andy006
11-12-2013, 10:44 AM
Excellent and superbly informative post. Just what the airgun magazines should be printing. Well done Cloverleaf. As an S400 shooter (GML) fan I find this type of information really useful. I thank you.

Akita177
11-12-2013, 13:03 PM
very good observation cloverleaf i applaued you for the many hours you spent nice when you get results. one question you say the magical 57 mm for the firing pot i have been led to beleive that its best to keep the ventura open as much as possible and adjust power with the pot what do you think atb

I would guess that could improve air efficiency unsure how it may effect consistency though?
With the magical 57mm wouldnt a .22 be a little less with it not needing as much air as .177?

cloverleaf
11-12-2013, 15:35 PM
Thanks again all :)



I have seen the same thing on the odd occasion, Air Arms say it's because the rifle was over filled at some point in time? Personally I don't have an opinion I just change the valve, which i keep in stock, or make a new one. I don't machine the old one back as it will alter the valve spring pressure which will have a knock on effect to which, if I'm honest, can't be brothered to get into unless I'm putting a regulator in the gun.

That's a lot of good work though, does my head in just looking at the graphs.................I'm old & grumpy though! ;);)
Yes, it seems pretty common in my experience. At least you got some response out of AA - when I asked they pretty much flatly denied that the issue existed at all.

I hadn't considered the possibility of the deformation resulting from over-filling; of course this is plausible (all the guns I've had issues with have belonged to others or have been used purchases, so I can't be sure they haven't been abused in the past). That said of course it's convenient for Air Arms to be able to attribute the issue to user error rather than poor material choice on their part ;)

I appreciate your point on machining the old valves.. my approach would be to leave the existing sealing face intact and just remove / back cut the bit that sticks into the valve throat. This shouldn't affect the valve return spring load (as it would if the whole thing was refaced and shortened) although wouldn't necessarily prevent the issue happening again. Making a new valve (or head) to the original dims (and from a harder material) is probably the way to go, though :)



very good observation cloverleaf i applaued you for the many hours you spent nice when you get results. one question you say the magical 57 mm for the firing pot i have been led to beleive that its best to keep the ventura open as much as possible and adjust power with the pot what do you think atb
Thanks :)

Keeping the venturi as open as possible probably reduces losses somewhat, but will also push the ideal fill pressure down the range; incurring lower efficiency and the sort of problems encountered with the old valve in this example. Altering the venturi affects the rate at which air flows through the system (volume flow rate) while altering the striker spring or valve return spring affects the valve displacement and duration; so IME (although I've not tried it) adjusting the pot (within it's permitted range) will only have a similar effect to varying the striker impact energy and momentum.

FWIW I tend to run the venturi wound in as this pushes the full pressure up the range; giving more shots per charge.



I would guess that could improve air efficiency unsure how it may effect consistency though?
With the magical 57mm wouldnt a .22 be a little less with it not needing as much air as .177?
My gut tells me that a longer valve return spring with more pre-load would potentially flatten out the latter half of the shot string, but that's an experiment for another day :p



Hi,

I had exactly this issue with my S410k which exhibited the same 'loopy' power curve as in cloverleaf's graphs. In my case I changed hammer spring, pot spring and valve at the same time. The springs were changed just 'cos gun was in bits and for a few quid I might as well! Fitting these flattened out the power curve of my rifle but looking at my old valve it was just like the one in cloverleaf's photo and showed the same extrusion. It was cloverleaf that put me onto this as being the potential culprit at the time so many thanks again.

Mark
Thanks for chipping in Mark - always good to have one's own experiences backed up by that of others :)



Excellent and superbly informative post. Just what the airgun magazines should be printing. Well done Cloverleaf. As an S400 shooter (GML) fan I find this type of information really useful. I thank you.
Excellent, cheers. Sadly though I think this is precisely the sort of stuff the mags would shy away from, since it goes directly against the "every gun is the best one ever" mantra they constantly seem to be pushing..

sharpsman
11-12-2013, 16:20 PM
Well done Cloverleaf i enjoyed reading that you need a big pat on the back for the time and effort you put into writing that,i have always replaced the valve or refaced them the worst ones i have seen is were the owners have been stupid and over filled to 230 ish bar regularly.It stands to reason the more pressure that is put on the face of the stem the more it will pressure destort but as you say the older white ones did not distort no where near as much as the black ones do.Once again well done.

wonky donky
11-12-2013, 17:05 PM
Thanks again all :)



Yes, it seems pretty common in my experience. At least you got some response out of AA - when I asked they pretty much flatly denied that the issue existed at all.

I hadn't considered the possibility of the deformation resulting from over-filling; of course this is plausible (all the guns I've had issues with have belonged to others or have been used purchases, so I can't be sure they haven't been abused in the past). That said of course it's convenient for Air Arms to be able to attribute the issue to user error rather than poor material choice on their part ;)

I appreciate your point on machining the old valves.. my approach would be to leave the existing sealing face intact and just remove / back cut the bit that sticks into the valve throat. This shouldn't affect the valve return spring load (as it would if the whole thing was refaced and shortened) although wouldn't necessarily prevent the issue happening again. Making a new valve (or head) to the original dims (and from a harder material) is probably the way to go, though :)



I was in NSP for a day or two working with the Falcon guys, I had a S410 in for repair so took it with me to let Air Arms do it saving me the bother, it was then they said the rifle had been over filled? I must admit I've never noticed this deformation on other Delrin/acetal valves made by myself or others!

Yes I think your correct about the new valve/material.

cloverleaf
12-12-2013, 16:17 PM
Well done Cloverleaf i enjoyed reading that you need a big pat on the back for the time and effort you put into writing that,i have always replaced the valve or refaced them the worst ones i have seen is were the owners have been stupid and over filled to 230 ish bar regularly.It stands to reason the more pressure that is put on the face of the stem the more it will pressure destort but as you say the older white ones did not distort no where near as much as the black ones do.Once again well done.
Thanks - makes it all worthwhile to know that people find the information interesting and/or useful :)

I agree that consistently over-filling could only make this problem worse.. but in the absence of doing so I there's still a problem to be addressed IMO.



I was in NSP for a day or two working with the Falcon guys, I had a S410 in for repair so took it with me to let Air Arms do it saving me the bother, it was then they said the rifle had been over filled? I must admit I've never noticed this deformation on other Delrin/acetal valves made by myself or others!

Yes I think your correct about the new valve/material.
Cool - as above it figures that the worst examples will be those that have been over-filled.

Talking of the material; I've been told that the standard valve material is Acetal, although (in my very limited knowledge of synthetic materials) it seems a bit soft (could maybe be a harder grade of PU..?). Have you ever removed the head from a standard valve? I think I've got one somewhere that's beyond redemption that I might "disassemble" with a view to fitting a new head.

Another thing I'm yet to try is to measure the dynamic deflection of the valve under load - it's all good looking at the amount of extruded material that remains in place when the load is removed and valve taken out; I wonder how much the head deforms elastically when the reservoir is pressurised.. will try and measure this on the next gun I strip :)

wonky donky
13-12-2013, 02:30 AM
Cool - as above it figures that the worst examples will be those that have been over-filled.

Talking of the material; I've been told that the standard valve material is Acetal, although (in my very limited knowledge of synthetic materials) it seems a bit soft (could maybe be a harder grade of PU..?). Have you ever removed the head from a standard valve? I think I've got one somewhere that's beyond redemption that I might "disassemble" with a view to fitting a new head.

Another thing I'm yet to try is to measure the dynamic deflection of the valve under load - it's all good looking at the amount of extruded material that remains in place when the load is removed and valve taken out; I wonder how much the head deforms elastically when the reservoir is pressurised.. will try and measure this on the next gun I strip :)

It would be interesting to do a hardness test on some Acetal & a AA valve but the cross section may be too small to achieve an accurate result?
I can't remember stripping a valve but may well have done just to reuse the stem as I'm always looking for an easier way to do things! ;)

terry1001
13-12-2013, 09:42 AM
A very informative and useful thread. My first thought was that the valve seat could just be faced off in a lathe but then I wondered how much damage may have been done to the structure of the seating material and then if it has deformed that badly was it poor quality in the first place?
Have you checked or looked at the area this seats onto? Is there any visible deformation and are they all machined perfectly in the first place?
So many questions waiting to be answered, it can make your brain ache at times!

Chinnymonster81
13-12-2013, 10:08 AM
An interesting post. When mine start playing up I know the first place to look. Cheers.

Rabbit Sniper
13-12-2013, 11:55 AM
These are precisely the type of threads that I enjoy reading, because they are both technical in nature and insightful. Thanks Mike!

The S400 series action craves to be tinkered and experimented with - I'm very tempted to do so!

Adam

Truckcab79
13-12-2013, 14:36 PM
Very interesting, and beautifully photographed as your posts always are. I wished I'd read it ages ago as about a year back I spent a long time and many disassembles chasing low power issues on my S400, with advice across 3 forums. Eventually got it up to 11.4 with new seals, hammer and valve springs, spring spacer, and new transfer port, (and this was with the Venturi wound fully out). I wonder if this was the issue all along. That said, mines a 2002 model so I'm guessing it's the earlier, harder material anyway. Can't recall, but might take it apart again for a look-see.
Thanks again.

cloverleaf
13-12-2013, 15:03 PM
It would be interesting to do a hardness test on some Acetal & a AA valve but the cross section may be too small to achieve an accurate result?
I can't remember stripping a valve but may well have done just to reuse the stem as I'm always looking for an easier way to do things! ;)
Absolutely - was thinking exactly the same. I suspect you might get a reasonably accurate reading by facing off the front end and performing the test in it's centre. Do we know anyone with a Shore Durometer? If not the indenter looks pretty simple (http://www.substech.com/dokuwiki/doku.php?id=shore_durometer_hardness_test) to knock up if you have a lathe and I'm sure an approximation of the test could be lashed up with a few workshop tools. That said, there are a few testing rigs and gauges on ebay for around £50..

I'm glad I'm not the only one cheap / lazy / sustainability-obsessed enough to consider reusing the valve stems :p



A very informative and useful thread. My first thought was that the valve seat could just be faced off in a lathe but then I wondered how much damage may have been done to the structure of the seating material and then if it has deformed that badly was it poor quality in the first place?
Have you checked or looked at the area this seats onto? Is there any visible deformation and are they all machined perfectly in the first place?
So many questions waiting to be answered, it can make your brain ache at times!
Thanks :)

My thought with the material was the opposite; if it's crept (and strain-hardened perhaps, if plastics do) it might be a bit more resistant to further deformation in future.. I wouldn't call the material poor quality; just potentially badly-specced. The valve seats are left as-machined and in the white; there are usually some radial tool marks (which no-doubt could be polished out) although I'm not sure how much use this would be (I suppose removing radial ridges would aid low-lift valve flow).

I've never known the seats to deform; the only occasional problem being sealing issues due to contamination and subsequent damage, which can usually be lapped out with an old valve.

Yes, it can make one's brain ache but at least it's arguably both interesting and constructive :p



An interesting post. When mine start playing up I know the first place to look. Cheers.
Ta ;)



These are precisely the type of threads that I enjoy reading, because they are both technical in nature and insightful. Thanks Mike!

The S400 series action craves to be tinkered and experimented with - I'm very tempted to do so!

AdamThanks - same as that. Dicussions like this are why I really value the forum; don't think I'd bother if it was all ".177 or .22" :p


In other news I've today managed to separate a valve head from it's stem; with promising results. Will get some pics up later if nobody's around for a pint!

terry1001
13-12-2013, 17:24 PM
I wondered if some valves (maybe the odd batch) were substandard rather than the material being generally unsuitable. I would be concerned that deformation migh mean that the material has been over stressed and more liable to fail again in the near future but my understanding of plastics is very poor.
The design of the valve and seat is very basic, obviously it works well at least for some time but it's not very impressive (in my opinion). I do have an S410 and I'm very pleased with it and haven't noticed any issues with the valve when I've had it apart. No doubt it will be torn down again in the near future so I'll check it carefully then.

cloverleaf
13-12-2013, 18:57 PM
Very interesting, and beautifully photographed as your posts always are. I wished I'd read it ages ago as about a year back I spent a long time and many disassembles chasing low power issues on my S400, with advice across 3 forums. Eventually got it up to 11.4 with new seals, hammer and valve springs, spring spacer, and new transfer port, (and this was with the Venturi wound fully out). I wonder if this was the issue all along. That said, mines a 2002 model so I'm guessing it's the earlier, harder material anyway. Can't recall, but might take it apart again for a look-see.
Thanks again.
Cheers, and sorry I didn't reply to this earlier - my post was a long time in the making :p

Glad you got the issue sorted in the end - my records show that the guns didn't get the black valve until '04 at the earliest, so if original yours should have been white. Of course this doesn't mean that the valve might not have been replaced at some point; if you do have it apart I'd be interested to hear what you find.



I wondered if some valves (maybe the odd batch) were substandard rather than the material being generally unsuitable. I would be concerned that deformation migh mean that the material has been over stressed and more liable to fail again in the near future but my understanding of plastics is very poor.
The design of the valve and seat is very basic, obviously it works well at least for some time but it's not very impressive (in my opinion). I do have an S410 and I'm very pleased with it and haven't noticed any issues with the valve when I've had it apart. No doubt it will be torn down again in the near future so I'll check it carefully then.
It's certainly possible that the valves vary in hardness and the worst are more badly affected than the rest. I think the stress thing could go either way - my knowledge of plastics is similarly sketchy to yours :p

I agree about the valve - as much as I love the 400 series it's pretty basic and inefficient in some areas. IMO the throat is too large (in both diameter and length), as is the valve stem. In addition an angled valve seat might provide better flow at low lift (but would of course be more expensive to make). In contrast Daystate and FX seem to very nicely designed valves..

bigtoe
13-12-2013, 19:59 PM
ertalyte tx or bearing grade peek is what I would be using over acetal....also how much does the hammer bounce on the 4xx and 5xx?

terry1001
13-12-2013, 20:09 PM
ertalyte tx or bearing grade peek is what I would be using over acetal....also how much does the hammer bounce on the 4xx and 5xx?
Cloverleaf has done a very good thread about this which is well worth reading (like most of his stuff to be fair). I've got a design for an anti bounce hammer from the AAOC forum and it's on my list of worthwhile projects, unfortunately I don't have the kit to check for the problem. Like most other projects it's likely to be more time consuming than at first expected but it will be done!

cloverleaf
13-12-2013, 21:11 PM
ertalyte tx or bearing grade peek is what I would be using over acetal....also how much does the hammer bounce on the 4xx and 5xx?
Thanks -not familiar with ertalyte, but good call on the PEEK - IIRC this is what Daystate use for their valve seats.

And yes, the striker bounces a lot - typically 2-3 times in addition to the first strike IIRC. Air efficiency appears to be lagging pretty much all of the competition at the moment; largely because of this problem I suspect :rolleyes:



Cloverleaf has done a very good thread about this which is well worth reading (like most of his stuff to be fair). I've got a design for an anti bounce hammer from the AAOC forum and it's on my list of worthwhile projects, unfortunately I don't have the kit to check for the problem. Like most other projects it's likely to be more time consuming than at first expected but it will be done!
Thanks :)

I've been considering how to make a decent anti-bounce striker for the 400 for literally years.. the issue is achieving a working system without detrimentally affecting other characteristics. Sven's striker on the AAOC works very well at cutting bounce, but it's also heavier than the standard item and wastes a fair amount of striker energy compared to the standard setup, so doesn't do lock time or cocking effort any favours.


Earlier I attempted to remove the head from a (very dead) valve. Knowing it was most likely molded to the stem, that went in the vice and I tried to drift off the head with a block of wood; which failed. I cracked out the junior hacksaw and did my best to section the head (badly); doing the final bit with a knife before levering the two halves apart with a screwdriver.


I was surprised to be greeted with a threaded valve stem:

http://img.photobucket.com/albums/v96/theboymike/Shooting%20II/SMALL_IMG_4791a.jpg (http://smg.photobucket.com/user/theboymike/media/Shooting%20II/SMALL_IMG_4791a.jpg.html)


Heartened by this I managed to unscrew the valve head, intact, from another valve (the badly extruded example shown in the first post). The stem was held in the vice and the head unscrewed by hand - it was stiff at first but soon got easier..

http://img.photobucket.com/albums/v96/theboymike/Shooting%20II/SMALL_IMG_4783a.jpg (http://smg.photobucket.com/user/theboymike/media/Shooting%20II/SMALL_IMG_4783a.jpg.html)

http://img.photobucket.com/albums/v96/theboymike/Shooting%20II/SMALL_IMG_4789a.jpg (http://smg.photobucket.com/user/theboymike/media/Shooting%20II/SMALL_IMG_4789a.jpg.html)


It certainly looks like the valve heads are molded onto the stem and that the thread is probably just a convenient way of achieving this. It certainly makes the prospect of testing different valve head designs and materials a lot more promising, plus potentially makes it a possibility to remove the head, recut the extruded section with a shallow countersink and refit.

Finally, before completely butchering the first valve I managed to convincingly remove an extruded section and back-cut the area using a pillar drill and hand-held Stanley knife; which was nice :p

terry1001
13-12-2013, 21:35 PM
If the stems are threaded then making a replacement is much easier, the head would be simple to turn and you could be sure that the sealing face would be properly square to the stem. I'm not at all familiar with the materials mentioned so wouldn't know where to get the stock. Still I do know where there's a stock of spare valve stems!
Is there any difference if the weight of the complete valve is changed?

cloverleaf
14-12-2013, 12:19 PM
Absolutely. I've just had a look into Acetal and PEEK - from Direct Plastics (http://www.directplastics.co.uk/) 10mm OD PEEK bar is £28.33/m, while the Acetal is £1.51/m - I think a factor of nearly 20 on the price is enough to warrant trying the cheaper material first!

I'm not sure about valve mass. Half of me thinks that an increase in mass might be a good thing; as the valve will contain a higher proportion of the overall system's momentum; meaning more is lost when it returns to it's seat and less is retained in the striker to cause bounce. Not sure what the drawbacks of a heavier valve would be, though. In any case, the mass of the valve stem will be significantly more than that of the head, so I wouldn't worry about changes in mass caused by changing the head alone.

The more I casually fiddle with the valve I stripped, the more I think that the head's not Acetal. Through my constant screwing on and of the head's worn significantly on it's surface, taking on a dull, rubbery sheen. In addition to this it feels a little soft, tacky and rubbery to the touch or if you drag a finger nail over it. I suspect it may be something significantly softer. Acetal should be similarly hard to Nylon; this is definitely softer than the old Nylon head.

Very tempted to buy a hardness tester, now :p

mark112
14-12-2013, 20:15 PM
Hi folks,

Sorry for butting on your thread but I have a question or two. Why was the change made from the old Nylon valve heads to the newer 'Black' ones? Do the new type Black ones have better sealing properties? I'm guessing that the harder (less elastic I suppose) the valve is the less it deforms into the valve seat and more likely it is to pass air (oh err). Would some sort of hard valve head with an ultra thin 'elastic' or softer coating offer the best of both worlds .. non-deforming but excellent sealing. Am I talking from the bit between my waist and the chair? Is the typical pressure in your average PCP enough to seal with most materials?

Anyway just my first thoughts. Enjoying the thread as anything technical gets my interest ... but I'm not a geek honest :D

Mark

terry1001
14-12-2013, 20:38 PM
My thought is that the valve seat is not easy (read cheap) to get right so a valve with a soft face is more likely to seal. I'm certain that with a bit of cash thrown at it a much more efficient and long lastin valve could be made.

ratman60
15-12-2013, 10:31 AM
hello, without hijacking thread, as always cloverleaf has done and written some interesting reports as this and previous threads, my thoughts are is there a good solution to reduce the internal noise of a PCP even with a good silencer fitted ?, as many know using a pcp can never be whisper silent but if can be done, HOW!!!

Truckcab79
15-12-2013, 10:35 AM
Another hijack then if you wouldn't mind, though valve related. I've seen high performance valves offered on eBay. They look similar, though slightly waisted. They are also stainless steel. Apart from the anti-corrosion benefits, any reason to fit them or are they simply a thinly veiled advert for those wanting to upgrade to FAC legally or otherwise?

cloverleaf
15-12-2013, 15:49 PM
Hi folks,

Sorry for butting on your thread but I have a question or two. Why was the change made from the old Nylon valve heads to the newer 'Black' ones? Do the new type Black ones have better sealing properties? I'm guessing that the harder (less elastic I suppose) the valve is the less it deforms into the valve seat and more likely it is to pass air (oh err). Would some sort of hard valve head with an ultra thin 'elastic' or softer coating offer the best of both worlds .. non-deforming but excellent sealing. Am I talking from the bit between my waist and the chair? Is the typical pressure in your average PCP enough to seal with most materials?

Anyway just my first thoughts. Enjoying the thread as anything technical gets my interest ... but I'm not a geek honest :D

Mark


My thought is that the valve seat is not easy (read cheap) to get right so a valve with a soft face is more likely to seal. I'm certain that with a bit of cash thrown at it a much more efficient and long lastin valve could be made.
Mark - as Terry points out above a softer material will be more tolerant of irregularities in the seat surface, plus less affected by particulate contamination (the one I removed most recently had a large bit of ally swarf stuck in it's sealing face, yet the gun was still holding air.

In addition as mentioned some materials are easier (and cheaper) to process (injection moulding onto the valve stem rather than turning and manually fitting) plus greater moisture resistance in the face of increasing pump useage.



hello, without hijacking thread, as always cloverleaf has done and written some interesting reports as this and previous threads, my thoughts are is there a good solution to reduce the internal noise of a PCP even with a good silencer fitted ?, as many know using a pcp can never be whisper silent but if can be done, HOW!!!
Try here (http://www.airarmsownersclub.com/viewtopic.php?f=3&t=51529), courtesy of our very own Audiguypaul ;)



Another hijack then if you wouldn't mind, though valve related. I've seen high performance valves offered on eBay. They look similar, though slightly waisted. They are also stainless steel. Apart from the anti-corrosion benefits, any reason to fit them or are they simply a thinly veiled advert for those wanting to upgrade to FAC legally or otherwise?
This is an interesting one. I'm aware of the valves you mention; for a start I think the standard AA valves have stainless stems (I've never known one corrode), plus some of those I've seen are clearly modified standard items.

The idea of the waist is to improve flow by offering a larger cross sectional flow area at the throat; however this is more complicated than it might initially seem. Assuming a stem diameter of 4mm and a throat diameter of 6mm gives an effective throat flow area of 15.7mm. Given an effective valve throat circumference of 18.8mm, this means that between zero and around 0.85mm valve displacement, flow is limited by valve lift rather than throat area.

At higher lift values the throat area theoretically becomes the local limiting factor, however it must be remembered that the transfer port is by far the most restrictive part of the system (3mm diameter gives a flow area of around 7mm; far less with the screw wound in as most are).

So in summary, I think waisted valves on 12ftlb rifles are a waste of time. They might potentially have more use on FAC rifles where the transfer port is larger; but I'd want hard figures before parting with cash.


This does bring us round to the FAC valves; which appear to be the same material but have a larger sealing face - perhaps in an effort to accomodate the rigours of higher fill pressures and possibly greater valve lift encountered on FAC guns - it would be interesting to see how these compare to standard valves in 12ftlb applications.

Finally, I found my old white Nylon valve last night (removed due to the ravages of moisture) - this showed next to no extrusion at it's sealing face, despite having been fitted to the rifle for the best part of 10yrs (although it could possibly have relaxed a little since being removed from the gun).

I'm also very tempted by a cheapo £18 shore hardness tester from China courtesy of ebay!

Truckcab79
15-12-2013, 21:45 PM
Thank you. Think I'll save my money, and if on next strip-down I find any deformation then I'll replace with a standard AA version.

cloverleaf
28-12-2013, 16:33 PM
Cool :)

cloverleaf
16-01-2014, 17:00 PM
For those who are interested I recently measured the protrusion of the rear end of the exhaust valve stem from the rear of the exhaust valve block on a couple of 400 series rifles, at different cylinder pressures.

While the numbers in isolation are fairly meaningless, when considered with respect to each other they give a good indication of how much the exhaust valve head becomes compressed under cylinder pressure.

Firstly was an untouched rifle of 2005 vintage; still with the original valve:

[Cylinder Pressure, bar] [Valve Protrusion, mm]

145 bar: 2.22mm
125 bar: 2.22mm
100 bar: 2.20mm
70 bar: 2.19mm
50 bar: 2.17mm
0 bar: 2.14mm


Next was the same rifle, with a brand new exhaust valve fitted:

0 bar: 1.94mm
10 bar: 1.94mm
50 bar: 1.95mm
75 bar: 1.96mm
100 bar: 1.97mm
125 bar: 1.97mm
150 bar: 1.98mm


Finally, another (2007) rifle with it's original valve (rifle had been standing with around 50bar in it prior to testing):

0 bar: 1.92mm
50 bar: 1.94mm
100 bar: 1.96mm
150 bar: 1.98mm


So, broadly speaking it can be seen from the above that between cylinder pressure of 0 bar (atmospheric pressure) and 150 bar the compression of the valve heads varied by between 0.04 and 0.06mm.

With respect to the problem of the valves extruding into the valve throat and causing performance issues; potentially we apparently have two or more different issues to consider:

i. Elastic deformation - i.e. deflection or compression of the valve head when under pressure, which disappears when the the load is removed and the head returns to it's original dimensions.

ii. Plastic deformation - that which permanently alters the shape of the valve head; i.e. the valve head remains compressed / deformed once the load has been removed - taking a permanent "compression set".

A third thing to consider is the time dependent nature of this behavior (i.e. creep) - manifested by a slow, continued increase in deflection over time as the valve is left under load.


I suspect that when a new valve is fitted and the cylinder is pressurised, the valve mainly undergoes elastic deformation (can't say for certain though as I didn't test the new valve by depressurising the rifle); perhaps with a bit of elastic, non-time dependent deformation thrown in.

Given that I've seen valves with extruded section up to 0.2mm deep and considering the results earlier in this post, it seems legitimate to suggest that damage of this magnitude must result from creep; resulting from the valve being left under pressure for a significant time (I've seen extrusion on guns ranging from 2-9yrs of age).

It seems clear that creep is our biggest enemy here. I'm not sure how much of a role elastic deformation plays in exhaust valve behavior; although I think the valve is only open for typically 1-2ms every time the gun is fired - not sure if this is long enough for the valve head material to relax back to it's original shape.

One final factor to consider is the effect of repeatedly firing the gun; since this subjects the valve head to impact loading in the seat area.

Ultimately it seems obvious that the performance of the rifle (both in the long and short terms) would benefit from a significantly harder (and more creep-resistant) valve head :)

sharpsman
16-01-2014, 17:20 PM
If it was made harder it may not seal as efficiently it needs to have a little elastisity to allow for any inperfections on the valve body face.

Soximus
16-01-2014, 20:39 PM
Just want to say what an outstanding post :up: ...

rkr
05-02-2014, 13:54 PM
I guess I need to dig this up. Does anyone know how the valve stem is attached to the plastic seal? Is it screwed on, glued on or injection molded? I'm just wondering if it would be possible to turn a seal from a better material and then attach it to the standard stem?

mark112
05-02-2014, 17:25 PM
I guess I need to dig this up. Does anyone know how the valve stem is attached to the plastic seal? Is it screwed on, glued on or injection molded? I'm just wondering if it would be possible to turn a seal from a better material and then attach it to the standard stem?

See post #27 on page 3 of this thread. This is the information you are looking for ...... obwan. :)

terry1001
05-02-2014, 21:15 PM
I'm not sure that there is a definite answer on how the valve is made. Is the head moulded or screwed onto the stem? For a diy job I would use an appropriately sized cylinder of the chosen material, tap a thread to match the stem and screw the 2 parts together with a suitable adhesive. The assembly could then be turned in a lathe to ensure that the size is correct and that the mating/sealing face is exactly true to the stem. It would be possible to profile the seating face if required.
I would not expect the thread on the original stem to be capable of ensuring that the seat is correctly aligned, it must be machined after the parts are assembled.

cloverleaf
05-02-2014, 23:07 PM
I'm pretty sure the heads are injection moulded onto the stem (the internal profiles fit exactly, there are no machining marks and there's a "gate" mark on the end of the valve ;))

I agree that the most accurate way will be to fit a blank to the stem and machine it as one.. that said I'm lazy and like the idea of serviceability, so will look into getting some standalone heads machined at some point..

terry1001
05-02-2014, 23:45 PM
I'm pretty sure the heads are injection moulded onto the stem (the internal profiles fit exactly, there are no machining marks and there's a "gate" mark on the end of the valve ;))

I agree that the most accurate way will be to fit a blank to the stem and machine it as one.. that said I'm lazy and like the idea of serviceability, so will look into getting some standalone heads machined at some point..
You're almost certainly correct about the original manufacturing method, as long as the material has the correct properties for moulding it would produce a reasonably accurate valve, I just can't see that a screwed joint would be accurate enough nor would it be mechanically sound.
I think that I have a new valve laying around somewhere so, if I can remember, I'll check it for run out and see how well the plastic and metal parts are aligned.

rkr
06-02-2014, 07:08 AM
That valve seal is so small that I think it should be relatively easy to make. Just get a piece of PET-T/Ertalyte or PEEK, thread it to match the stem (M4?), screw the stem on with some glue or red locktite. Attach it in a lathe or bench drill from the stem and make a new seal.

Chinnymonster81
06-02-2014, 09:41 AM
If you are going to the trouble of machining a new head on the lathe then you might as well looking at changing the profile to improve airflow. You never know as you may just get the perfect after market valve.

Soximus
06-02-2014, 10:19 AM
...Keeping the venturi as open as possible probably reduces losses somewhat, but will also push the ideal fill pressure down the range; incurring lower efficiency and the sort of problems encountered with the old valve in this example. Altering the venturi affects the rate at which air flows through the system (volume flow rate) while altering the striker spring or valve return spring affects the valve displacement and duration; so IME (although I've not tried it) adjusting the pot (within it's permitted range) will only have a similar effect to varying the striker impact energy and momentum.

FWIW I tend to run the venturi wound in as this pushes the full pressure up the range; giving more shots per charge....

Cloverleaf, as you are without doubt "The Man" when it comes to this highly informative and interesting material do you know what the range of FPS is with your setup from the venturi closed to fully open.

I have my S400 set to run with the venturi fully open and have used the pot to set the levels at 11ft/lb so it can be reduced but not increased with JSB Heavies. Hopefully keeping the rifle under with any other heavier weighted pellets.

Once again brilliant work and write up....and superb images too :up:

lone wolf
06-02-2014, 10:56 AM
Honestly cloverleaf thats a great read and its great that you took the time to share it let alone do it.

Very informative and well written,if i knew half of what you know about airguns id be a very content person within my hobby,always nice to read your findings and great pics by the way!:)

Gaz

Targetmark
09-02-2014, 15:47 PM
I recently(yesterday) had need to strip my old S400 due to a leak. So whilst in bits had a look at the valve,it is one of the early white ones. Had a look under a magnifer and could not see the sort of wear as shown on the black valves. This rifle has had several thousand pellets through it so goes to show the old style were very hard wearing indeed.
I had a new black valve with spring that I had bought ages ago and noticed that the new spring was 3 or 4 mm longer. Would this be due to being compressed for a few years in the firing pot or maybe the old springs were shorter anyway ?

Cheers
Mark

cloverleaf
09-02-2014, 16:15 PM
You're almost certainly correct about the original manufacturing method, as long as the material has the correct properties for moulding it would produce a reasonably accurate valve, I just can't see that a screwed joint would be accurate enough nor would it be mechanically sound.
I think that I have a new valve laying around somewhere so, if I can remember, I'll check it for run out and see how well the plastic and metal parts are aligned.
Totally appreciate your point about alignment (something that would become more critical the harder and more unyielding the material becomes) however I wouldn't worry about mechanical integrity - if you think about it all of the forces involved in holding the valve shut are confined to the valve head; the stem is pretty much just ineffectually hanging out the back of the head when the valve is closed.

When the valve is opened the interface between the head and the stem takes the axial load required to lift the valve from it's seat; which shouldn't be enormous; and at any rate in this respect we know the setup already works with the existing valve and soft head.



That valve seal is so small that I think it should be relatively easy to make. Just get a piece of PET-T/Ertalyte or PEEK, thread it to match the stem (M4?), screw the stem on with some glue or red locktite. Attach it in a lathe or bench drill from the stem and make a new seal. As above this would be the most accurate method, if not necessarily the most viable for mass production..



If you are going to the trouble of machining a new head on the lathe then you might as well looking at changing the profile to improve airflow. You never know as you may just get the perfect after market valve.
Indeed; bear in mind though that flow will rapidly choke at the transfer port restrictor screw, so increasing the flow potentential through the valve will have limited effect. That said; improving flow at low valve lifts is definitely a worthy goal IMO. I think you're reasonably limited as to what you can do to the valve without having to alter the seat to accomodate them; though..



Cloverleaf, as you are without doubt "The Man" when it comes to this highly informative and interesting material do you know what the range of FPS is with your setup from the venturi closed to fully open.

I have my S400 set to run with the venturi fully open and have used the pot to set the levels at 11ft/lb so it can be reduced but not increased with JSB Heavies. Hopefully keeping the rifle under with any other heavier weighted pellets.

Once again brilliant work and write up....and superb images too :up:


Honestly cloverleaf thats a great read and its great that you took the time to share it let alone do it.

Very informative and well written,if i knew half of what you know about airguns id be a very content person within my hobby,always nice to read your findings and great pics by the way!:)

Gaz
Thanks to both of you - not that I do it for the attention, but knowing my tinkering is appreciated / of interest certainly encourages me to continue posting :)



I recently(yesterday) had need to strip my old S400 due to a leak. So whilst in bits had a look at the valve,it is one of the early white ones. Had a look under a magnifer and could not see the sort of wear as shown on the black valves. This rifle has had several thousand pellets through it so goes to show the old style were very hard wearing indeed.
I had a new black valve with spring that I had bought ages ago and noticed that the new spring was 3 or 4 mm longer. Would this be due to being compressed for a few years in the firing pot or maybe the old springs were shorter anyway ?

Cheers
Mark
Good work - I hope you kept the original valve and that you don't fill your gun with a pump! Was at Air Arms a while ago and the amount of white valves in their bin made me sad - they replace them (all valves, not just the white ones) as a matter of course during a "service" and (for whatever reason) fail to recognise the inferiority of the newer black ones :(

Tbh If you have a rifle with a white valve, I think it definitely pays to hang onto / look after it. You raise an interesting point about the valve return springs; I can't see the loads they're under being sufficient to cause such shrinkage; similarly to the best of my knowledge they've been the same spec throughout the production run of the guns (although I might be wrong). Will have to chase some part numbers :)

Hoodster
30-03-2014, 12:43 PM
Very interesting read now I know why you told me not to swap my white valve stem.

cloverleaf
29-04-2014, 12:19 PM
At the beginning of this thread I probably mentioned that I first discovered this problem when replacing a leaking exhaust valve in one of my rifles.

It's now been 18 months since the valve was replaced (with a standard AA item) and the gun has been chronographed several times since - once just after the valve was fitted (03/08/2012), once around six months afterwards (26/04/2013) and then a further 12 months after that (22/04/2014).

All three shot strings are shown below - the gun has not been altered in any way since the initial setup. The Pellets used have been AA Field throughout; the fill pressure 190 bar for each test. The rifle has been stored with a cylinder pressure of somewhere within it's working range and has had no more than 500 shots through it (probably more like 250).

http://img.photobucket.com/albums/v96/theboymike/Shooting%20II/20140422VelocityTestingS410k054124Latest_2.jpg (http://smg.photobucket.com/user/theboymike/media/Shooting%20II/20140422VelocityTestingS410k054124Latest_2.jpg.htm l)

http://img.photobucket.com/albums/v96/theboymike/Shooting%20II/20140422EnergyTestingS410k054124Latest_2.jpg (http://smg.photobucket.com/user/theboymike/media/Shooting%20II/20140422EnergyTestingS410k054124Latest_2.jpg.html)


From the energy graph above it can be seen that the rifle was initially producing around 11.7ftlb average muzzle energy within its optimum fill pressure range. After six months this had fallen to around 11.5ftlb and after 18 months total it's now averaging a shade over 11ftlb. I don't suspect that the energy loss is strictly linear, but over the past 18 months the gun has lost around 0.25ftlb every six months.

This was completely expected; what has surprised me though is that the optimum fill pressure hasn't fallen significantly and is still around 180-190bar. I'll keep testing this rifle periodically until the people I've asked to make the replacement valve heads pull their fingers out and I can replace the crap that's in there now; which I hope might be within the next 6 months :p:rolleyes:

Tatts
29-04-2014, 12:46 PM
What great info that is :)

UrbanFox
29-04-2014, 16:53 PM
Nice one.:) :up:
Changed mine not too long back when I was tinkering. Must get a spare off Bondy, just in case.:)

atb
Bri

pava
26-05-2014, 17:54 PM
Firstly may I say thank you for posting this thread Cloverleaf. I found this thread by chance, not only is it brilliantly written, it is superbly illustrated too. I have a 2012 S510 in 177 that has slowly been losing power over the last 6 months or so. I have been toying with the idea of servicing and polishing the internals of my rifle for some time and this power loss anomaly has given me the perfect reason to do so.

Thanks to this post, I do have another possible cause for the power loss, other than a failing seal(s) that I suspected. Once again many thanks for an excellent and informative post.:D

Ichabod Armacost
26-05-2014, 18:05 PM
You's a clever old booger aint yer leafy.............You is also a credit to the forum, and no, I am not taking the pee!:up: Nice thread, great info for a lot of the members.:cool:

Akita177
26-05-2014, 21:39 PM
Could the S4xx and S5xx series of guns benifit from leaving them stored with a low pressure like 90-100bar?
As i would imagine leaving them store with 180/190bar could make this problem worse?

trumpetier
26-05-2014, 22:14 PM
Could the S4xx and S5xx series of guns benifit from leaving them stored with a low pressure like 90-100bar?
As i would imagine leaving them store with 180/190bar could make this problem worse?
mmmm....maybe...i normaly store my 400 at about 110 ish.....i fill it before i head off hunting and even if i dont use the 40 shots for hunting i always finish my session off plinking at inanimate targets, so the pressure is always down when i store it.....i no some people store them at full pressure...but not for me.

cloverleaf
27-05-2014, 12:04 PM
Thanks guys - I'm glad my "work" is appreciated and continues to be of interest / use to some on the forum :)

I'm less pleased however that it's been over two months since I submitted the revised exhaust valve drawings for manufacture and the slack tarts I chose to do it still haven't pulled their fingers out of their arses and made some prototypes.. Yes, they have more interesting (to them) and lucrative projects on the go, but are really starting to take the piss now (I wish they'd just refused to take the work on if they weren't interested). Will have to start looking at alternative suppliers, I suppose :rolleyes:



Could the S4xx and S5xx series of guns benifit from leaving them stored with a low pressure like 90-100bar?
As i would imagine leaving them store with 180/190bar could make this problem worse?
Seems like a logical conclusion, however I don't know if the relationship between load, deformation and time is linear (half the pressure might not mean half the deformation for any given timeframe) and keeping the pressure in the gun low would be a ballache bodge to get around a problem that could and should be cured by the use of properly-specced materials.

If you're happy with the hassle of manipulating storage pressure in order to extend the life of your valve to an extent be my guest; however I'd rather sort it properly with a decent exhaust valve that's actually fit for purpose :)

I have attempted to make Air Arms aware of the issue, but as always how much attention they'll pay to my whinging is debateable..

Jimbob 2705
10-06-2014, 23:59 PM
What a fantastic post Cloverleaf - as is most of your threads I should point out!

We have 6x S410's in .22, which in time have all gradually come down in power - but there is one worse than the rest.

I put it over the chronograph recently and get a reading of just 8ft/lb, what's interesting is that this rifle also has a terrible power curve like you mentioned!

So I decided to strip it down and give it a service - I replaced the seals, set the firing pot to 57mm, a new valve spring and also hammer spring....and as a result I only gained 0.5ft/lb - resulting in 8.5ft/lb!

The rifle does sound a lot better then it did, but I think that's because the firing pot was loose at first.

The obvious solution looks to be to replace then firing valve and see what happens - hopefully I will see the differences you have.

I should point out the rifles are all around 8 years old.

My concern is that replacing them doesn't seem to last long - as you mentioned in 6 months you lost 0.5ft/lb

The power of the rifles doesn't make that much difference to us, as they are only used indoors at 25 yards - so a lower power could benefit in more shots per fill - ideally around 10.5ft/lb would be ideal

The issue is the power curve though, which in the case of the one rifle is truly shocking!

'Many Thanks

James

cloverleaf
11-06-2014, 09:35 AM
Thanks James :D

Your issue definitely sounds like the valve is the problem; given the extremity of the situation I bet you'll find a very pronounced ring on the sealing face around the stem when you pull the valve out.

It's interesting that one of your rifles seems more affected than the others - my guess would be that it's either been overfilled at some point in its life, or the valve is just a bit softer than the rest. As already mentioned in this thread I've seen various degrees of severity of this problem over guns of various ages; the problem doesn't necessarily directly correlate with age (although it's obviously a factor) so I suspect there are other factors at play too.

I agree that the performance degradation of the current valve is disappointing; in contrast I've found the earlier guns (fitted with Nylon valves) to be far, far more consistently better-performing over time; showing no discernible change in performance over years of use..

As already mentioned I'm trying to get some replacement valve heads made (I do actually have a couple now but they don't fit the stem well) however this is being dogged by a couple of issues - a) I'm having a job correctly speccing the thread to get a good fit on the stem, and b) the company I'm trying to get to do the work (who took 3 months to get these ones done :rolleyes:) have bigger fish to fry and aren't particularly interested in my little job.

The plan was to try a few prototypes and get a batch CNC'd off the basis of their performance; I'm not going to chuck hundreds of quid at machine time until I know the design is sound, though. If only I had a lathe :(

Anyway, do let me know how you get on - I'm confident that a new valve will sort the issue :up:

Jimbob 2705
23-06-2014, 08:17 AM
I saw this when looking today Cloverleaf :

http://img.tapatalk.com/d/14/06/23/yra9usuq.jpg

http://www.bisley-uk.com/stockimages/documents/AASSFP_S400%20410%20510%20TDR%20MPRFT%20Firing%20P ot%20Diagram.pdf

I originally though that it was a solution to the problem, although in reality it just a top hat by the looks of things which helps the springs sit correctly! What a bummer!

The valves exactly the same unfortunately :(

cloverleaf
23-06-2014, 18:48 PM
Yup. Also they must have changed the pot design, since the new spring seats won't fit inside the old pots.. :(

Jimbob 2705
29-06-2014, 10:58 AM
Do you think the firing pot needs replacing on a 8 year old Cloverleaf? I'll be replacing the firing valve.

I guess if I want to fit a new firing valve spring I'll have to get the new style firing pot because as you mentioned the new springs won't fit...

cloverleaf
29-06-2014, 11:14 AM
To the best of my knowledge the springs are the same, the pots however must apparently be different to accomodate the spring seat. It's all starting to make sense now actually - if you strip an older rifle you'll see traces of brass dust on the exhaust valve and port assemblies - this is because the valve return spring oscillates against the pot during use; wearing off some of the material in the bore.

AA have obviously gone for a larger bore to prevent this contact; and hence a spring seat is now required to keep the spring concentric within the pot.

I certainly wouldn't bother replacing the pot unless you also want to fit the seat. The newer setup is doubtless a nicer solution than the old one from an engineering perspective, however I'd question what tangable difference in performance it would bring (other than removing the brass deposit problem). Perhap consistency might be improved slightly with no interference between the spring and pot?

I feel an experiment coming on :p

Hoodster
03-07-2014, 10:45 AM
I've just noticed T.R Rob is doing an aftermarket exhaust valve for the s400/500 series do you know of them ?
They look white so definitely a different material from the standard valve.

oddbob
28-08-2014, 11:48 AM
I came across this thread because my rifle was producing too much power and I needed to turn it down!

Hoodster, I've seen Terry's valve, if you watch his strip-down (of the rifle :eek:) you'll see that it has a longer stem than the standard item, I don't recall seeing the spring seat on the rifle he used in the video, so it may have been an older one. The valve stem on my rifle projects about 3mm above the face of the block, and I was interested to read cloverleaf's valve stem measurements - has my rifle already got the TRR valve fitted? Until I strip it down I won't know, in the mean time, I made up a nylon disk which sits on the hammer slide and stops the valve opening fully, it's reduced the power and noise.

Cloverleaf, your earlier experimentation with the spring damper, success with the hammer spring but failure on the valve spring - could this have anything to do with the internal size of the pot? Would it work on a later model pot, or perhaps be worth lining a later model pot with PTFE?

Would PTFE be suitable as a valve material? I can't understand why the stem is threaded - this would incur costs in production, surely if the valve seal is molded onto the stem then a crimped stem would be more cost effective, but then again, if Air Arms see the valve stem as a service item to be changed at each service (every six months by the look at your power curves) why would they not just sell a threaded seal to fit the stem?

cloverleaf
28-08-2014, 14:11 PM
I've just noticed T.R Rob is doing an aftermarket exhaust valve for the s400/500 series do you know of them ?
They look white so definitely a different material from the standard valve.
I wasn't aware of them.. tbh I'd generally steer clear of Mr. Robb's wares - firstly the valve is of non-standard stem length which will no doubt cause issues, secondly he appears to have a somewhat mixed reputation regarding his attitude and knowledge. For example, why does the valve have a longer stem? His website states:


Air Arms S300/S310/S410 Exhaust Valve made Slightly longer on the pin end and a fraction shorter on the spring holder end, for more opening time and control of lock time and power etc. Can be used in conjunction with our tuning kit.
Allows a lot more control of power curve and much more.
I can't see how altering the valve length can give greater control of any of the features he mentions; so I conclude that either one of us doesn't know what we're talking about (I hope it's not me :p), or all the spiel is just bullsh*t to cover for the fact that a longer stem allows more lift and hence more duration and muzzle energy.. which of course would take us over the limit - something that Mr. Robb's bits have been noted for in the past.



I came across this thread because my rifle was producing too much power and I needed to turn it down!

Hoodster, I've seen Terry's valve, if you watch his strip-down (of the rifle :eek:) you'll see that it has a longer stem than the standard item, I don't recall seeing the spring seat on the rifle he used in the video, so it may have been an older one. The valve stem on my rifle projects about 3mm above the face of the block, and I was interested to read cloverleaf's valve stem measurements - has my rifle already got the TRR valve fitted? Until I strip it down I won't know, in the mean time, I made up a nylon disk which sits on the hammer slide and stops the valve opening fully, it's reduced the power and noise.

Cloverleaf, your earlier experimentation with the spring damper, success with the hammer spring but failure on the valve spring - could this have anything to do with the internal size of the pot? Would it work on a later model pot, or perhaps be worth lining a later model pot with PTFE?

Would PTFE be suitable as a valve material? I can't understand why the stem is threaded - this would incur costs in production, surely if the valve seal is molded onto the stem then a crimped stem would be more cost effective, but then again, if Air Arms see the valve stem as a service item to be changed at each service (every six months by the look at your power curves) why would they not just sell a threaded seal to fit the stem?
I'm not sure about the valve - best bet would be to strip it and have a look. If the rifle's over the to it sounds like someone's been playing - I assume it was bought second hand?

By adding the Nylon disc to the striker rail you're effectively controlling the energy by limiting the valve lift, rather than by using transfer port restriction (as intended by the design). This approach is used by daystate on the Huntsman Classic etc, and has its own set of good and bad points compared to limiting energy on the port.

Tbh the spring damper didn't work out too well in the long term; losing it's effectiveness after having been fitted for a while. I think the problem with using a similar setup on the valve return spring was the flow rate of air past it was tearing it to pieces. IMO the best solution would probably be a well-fitting nearly-full-length spring guide; (AA are already halfway there with their newer setup) however I think valve return spring resonance is probably a pretty minimal issue to be concerning oneself with ;)

PTFE is definitely not a good choice for a valve material - it's key positive attributes are low friction, thermal and chemical stability - none of which would be of use in a valve application. In addition it's soft and prone to plastic deformation - so would only exacerbate the existing problems with the current valve.

As regards the threaded valve stem; firstly I suspect the early valve heads were also turned and screwed onto the stem - the setup only going to a molded head once production numbers justified the change in method of manufacture. Secondly, it's probably just as quick to cut a thread on a stem using the CNC tooling AA have at their disposal as it is to cut other features to facilitate good head attachment. Crimping would require another too and another operation - threading can be done in the lathe while the other features of the stem are being machined. Finally, I'm not complaining about the threading as it means we can reuse the stems!

As for replacing the head alone - while this appeals to me greatly as a cheapskate, hater of waste and enduring fan of sustainability; to AA it's faster and easier to replace the unit as a whole; plus the customer is footing the (admittedly fairly small) bill, so who cares..? :rolleyes:

Tron
28-08-2014, 15:01 PM
I have found after playing about with AA 400 series rifles that a longer firing valve is a good idea, as long as the rifle is set up properly use of such means you have a much better shot count and the sweet spot is much improved due to the valve opening up more as the cylinder pressure drops.

oddbob
28-08-2014, 15:20 PM
By adding the Nylon disc to the striker rail you're effectively controlling the energy by limiting the valve lift, rather than by using transfer port restriction (as intended by the design). This approach is used by daystate on the Huntsman Classic etc, and has its own set of good and bad points compared to limiting energy on the port.

PTFE is definitely not a good choice for a valve material - it's key positive attributes are low friction, thermal and chemical stability - none of which would be of use in a valve application. In addition it's soft and prone to plastic deformation - so would only exacerbate the existing problems with the current valve.



As for replacing the head alone - while this appeals to me greatly as a cheapskate, hater of waste and enduring fan of sustainability; to AA it's faster and easier to replace the unit as a whole; plus the customer is footing the (admittedly fairly small) bill, so who cares..? :rolleyes:

Re my rifle, I posted at length on another forum about the problems I'd had with it and how I'd solved it, I was shot down in flames for daring to talk about it. But basically yes, it was bought second hand (possibly even third or fifth hand, who knows?), and someone has certainly had a fiddle with it, I would tell you by pm but not openly on here what it was kicking out and how I tamed it, but the washer was the final solution - for now. I will certainly be setting the pot and checking that valve, I have a full service kit and a Robert Lane regulator to go on, though may just not bother with the regulator - I don't like the idea of drilling the cylinder, but that's for another thread on another day. Do you know what the standard valve length is by any chance? I'd probably be happy to leave the longer valve in, if that's what it is, and retain the washer, as it does take some noise out of the shot (try it), but would have to loose the washer if I fitted a standard valve. I did wonder if the washer would also add some preload to the hammer when the shot was taken, not sure what effect this would have on hammer bounce.

Yes, I was forgetting about the polytetrafluoroethylene's self forming properties :rolleyes: , while it would work where the ptfe form was constrained (by a cylinder end for example) when it hit (or in this case returned to) it's resting point. To use it in this rifle would require a rethink on both the valve and the valve seat shapes, a tapered arrangement like that on a mortise for example. Now I know T r Robb likes to use ptfe for his piston washers, but I'm not going to speculate on what he uses on his valve, with it's longer stem and spurious intentions.

And I share your view on the last point I've quoted ;) I happen to work for a large multi-national company which will do anything to save a penny on the production line, even if that penny saved costs another department 2p.........

oddbob
28-08-2014, 15:29 PM
I have found after playing about with AA 400 series rifles that a longer firing valve is a good idea, as long as the rifle is set up properly use of such means you have a much better shot count and the sweet spot is much improved due to the valve opening up more as the cylinder pressure drops.
I can see how that would work, but also how a slightly shorter valve opening could also work in the same way when correctly set up. I've watched Terry's video where he uses this valve, and he does emphasize the power being set to sub 12 ft/lbs. If my rifle is fitted with the longer valve, then at least I know it's possible to set it within the limits and that it has potential positive benefits.

mark112
28-08-2014, 17:34 PM
..... Do you know what the standard valve length is by any chance? .........Sorry for eavesdropping in on your thread but mine is something like this :-

102646

oddbob
28-08-2014, 17:44 PM
Sorry for eavesdropping in on your thread but mine is something like this :-



Eavesdropping is fine by me especially when you have something useful to add :), thanks for the info, will measure mine when I get it out, fnurr, fnurr.

Do you know if your's is a standard valve or one of T R Robb's valves?

Bemused
28-08-2014, 17:47 PM
This thread is a great read, many thanks to all who contributed.

Would the EV2 be similar? Its a MkI

oddbob
28-08-2014, 18:08 PM
This thread is a great read, many thanks to all who contributed.

Would the EV2 be similar? Its a MkI

Cloverleaf should do a book ;) but not based on that film of the same name, people might get confused.

mark112
28-08-2014, 18:15 PM
Eavesdropping is fine by me especially when you have something useful to add :), thanks for the info, will measure mine when I get it out, fnurr, fnurr.

Do you know if your's is a standard valve or one of T R Robb's valves?
Mine is a bog standard black one as opposed to the older white ones. For some reason my wife's eyes lit up when she heard that remark :)

oddbob
28-08-2014, 20:24 PM
Mine is a bog standard black one as opposed to the older white ones. For some reason my wife's eyes lit up when she heard that remark :)
Well I hope I don't feel inadequate when I get mine out and find it's an old white one :eek:

But thanks for clearing that up, after seeing the measurements cloverleaf posted of how far the tip of the stem changed according to the cylinder pressure I think mine is a bit longer but without knowing the length of the T R Robb or stripping my valve first it's an educated guess.

Cloverleafs measurements also showed just how much energy is in a pressurised air cylinder, a warning to all of us as if we needed it.

Jimbob 2705
08-09-2014, 13:08 PM
Well, I ran a chronograph string for one of the S410's we have, purely because it was leaking air, so I am going to strip it down to give it a full service, polish and I'll replace the Exhaust Valve.

This rifle hasn't seemed bad in the past, and it's not the one I have previously mentioned (which is running at 8.5ft/lb).

I'm actually quite impressed with the Chronograph String :

http://i1015.photobucket.com/albums/af273/Pictures2705/S410Chrono1_zps2fe660f6.jpg (http://s1015.photobucket.com/user/Pictures2705/media/S410Chrono1_zps2fe660f6.jpg.html)

Rifle was filled to 190Bar, and it is currently on 65/70 Bar - I never fill to 190 Bar, but decided too for the full chronograph string.

Highest power reading was 550fps with 16grain AA Fields, giving a power of 10.75ft/lb, so that is just about perfect for our needs (Indoors at 25 yards).

If you went from Shots 103 to Shot 188 they would all be within 12.5fps of each other, giving 85 consistent shots.

I'd roughly say it that'd be from a 130Bar fill, down to 80 Bar, which seems particularly low.

I'll run a new string once I've serviced the rifle, and see the changes.

As I said this rifle isn't particularly bad compared to another one we have, which I'll do a Chronograph String and Service for once I get time.

Many Thanks,

James

cloverleaf
08-09-2014, 22:46 PM
Good work James - ta for posting a full string :)

As you say the ideal fill pressure is very, very low and I'm confident that a new exhaust valve (and a good polish, as you say) will improve that massively.

I'm assuming the rifle is full length - the last one I did in .22 was giving over 100 shots at 11.7ftlb with AA fields from 190bar; with an extreme velocity spread of 1.5% or around 8ft/s. I think that was with a spacer on the striker spring and more restriction at the port to pull the ideal fill pressure up to 190bar.

A polish and valve should bring your energy and fill pressure up significantly - I'd guess on maybe 90+ shots within 1.5% velocity at mid to high 11's from a 170-180bar fill.

I'll be very interested to see another string / old and new compared once you've done the work :up:

Jimbob 2705
08-09-2014, 23:26 PM
Thanks for the reply Cloverleaf :)

Taking a chronograph string with my recently bought Chrono Connect software and USB lead (connected to a Chrony Chronograph) makes it a lot easier over a long string, as I can just put it straight into excel - perfect!!

Yes the rifle is a 'Classic' so full length.

I'm hoping to do the rifle tomorrow, so I'll have a string up by tomorrow night hopefully.

There is a questions I've been meaning to ask you actually - What would you say the best way to reduce the power would be?

Ideally I'd be looking at around 10.5ft/lb (basically where this one is). If I'm honest 10ft/lb would be enough, if it got me an even few more shots.

Out of interest, would you say if it was set up for a lower power, would it has a less of a power curve?

Reason for this is as it is only used up to 25 yards indoors, and I think that 1 ft/lb less (10.5 Vs 11.5) should give me an extra few shots which would be ideal.

Many Thanks

James

cloverleaf
08-09-2014, 23:37 PM
No problem - it's good to see someone else's results :)

The best way of reducing energy IMO is winding in the screw that shall not be named (PM me if you need clarification) - this will push up the ideal fill pressure while reducing peak energy. All being well with a new valve fitted energy should be somewhere near - perhaps a touch high if you polish the rail and valve. It's probably a good idea to let the rifle sit for a while with the new valve under pressure to get any immediate deformation out of the way before setting the energy (I sometimes leave them overnight before setting energy; or at least check again after a day or so and adjust as nec.).

If you reduced the energy on the port you will indeed get more shots / a flatter string (probably quite considerably so; disproportionately so compared to the energy reduction) - however IMO the lardarse .22 is already too slow at 12ftlb without making it slower :p

Will look forward to seeing how it pans out!

Jimbob 2705
11-09-2014, 13:53 PM
Yesterday I stripped the rifle down to give it its service.

I replaced every single seal/o-ring (even including the one in the barrel band), replaced the exhaust/firing valve, the firing valve spring (polished the ends), set the firing pot to 57mm, polished the hammer rail/rod, polished the inside and outside of the hammer, replaced the hammer spring which I polished and polished the loading bolt shaft - so basically I gave it the full works! ;)

Filled it up to 190 Bar, and left it over night...Good news - No leaks! :)
Interestingly it needed a quick blast of air to seal it, otherwise air would leak down the barrel - so I assume the firing valve needed seating properly as I had replaced it and the spring.

So today I gave it a Chronograph String...now I should point out that the 190 Bar I filled it up to was probably more likely 180-185 Bar due to it expanding from the heat from a low fill, I did top it up after 5 minutes but the cylinder was still slightly warm...


Anyway, onto the interesting part :

http://i1015.photobucket.com/albums/af273/Pictures2705/S410Chrono2_zps8961dab4.jpg (http://s1015.photobucket.com/user/Pictures2705/media/S410Chrono2_zps8961dab4.jpg.html)

Just look at the difference!! :eek: (And I should point out that the Chronograph never recorded one magazine, so you can expect 10 more consistent shots - Inbetween shots 100-110)

So this time we have a tiny, tiny, power curve...the good news is that you can use it from Shot 1, as the highest it got was only 16fps higher! Now in the real world you wouldn't even notice that, never mind at only 25 yards!

Now it will give 150 shots within 20fps of each other, well about 147 to be exact :D
They would all be within 18fps, if it wasn't for one slightly high one!

Another thing I should point out, is that it is now shooting on average at about 11.4ft/lb, with a highest of 11.68 - So I've gained a whole ft/lb! :up:

I'm going to drop the power down to 10.5ft/lb-11ft/lb...and I'm hoping I'll get somewhere in the region of 180 shots...not bad from a Cylinder type PCP (not one of these ugly bottle things:D)....


This just means I've got another 5 S410's to do this too.....:o;)

Jimbob 2705
11-09-2014, 14:09 PM
I should point out that the rifle gauge showed roughly 90 Bar by the end, so I'm guessing that it dropped off at almost bang on 100 Bar

cloverleaf
11-09-2014, 14:20 PM
Excellent work :D

Thanks for posting the graphs - it's great to see someone else's findings backing up my own :up:

Jimbob 2705
11-09-2014, 14:29 PM
Excellent work :D

Thanks for posting the graphs - it's great to see someone else's findings backing up my own :up:

Well I should say a Massive Thankyou to you, for finding out this in the first place!!!

I've serviced a fair few S4**'s, and it's good to know that this part needs replacing and is in fact the main culprit!

If you manage to some some new valves made, please, please get in touch - I'll take at least 6, probably 12 so I'd have a spare for each!

Or if you need some help with the design, testing, funding, etc - Just get in touch! :)

cloverleaf
11-09-2014, 15:22 PM
Ta - the valves are still on the back burner at the moment.. I did get one head made and it's currently running (generally well) in my S400.

The problem is that the blokes I asked to make the prototype weren't really interested and basically did half a job.. by the time I'd finished tidying the valve up I'd managed to mark the edge of the sealing face, so this had to be chamfered to get the valve to seal properly. Bottom line the valve wasn't made to / has been modified from the drawing so I have no way of knowing if the original design will work properly and I'm reluctant to order a batch of 50 or 100 CNC'd items.

The cost of getting a decent batch machined shouldn't be prohibitive; however it will be hard to swallow if the valves don't work and the whole thing becomes a total loss - because I couldn't properly test the design on account of the prototype being a bit of a lash up :rolleyes:

I agree that this is a problem that certainly needs looking at; the issue now is finding someone sufficiently trustworthy to manufacture the bits..

The whole thing is also somewhat of a balancing act regarding material spec and seat contact area. Too hard a material / too much seating area and the valve will leak; too soft a material / too little seating area and the valve will deform and cause the issues we're having with the current substandard offering.

Tbh this type of valve (soft head on a hard stem sealing against a hard seat) is a flawed design that invites head extrusion problems - a far better approach IMO is that used in the Theoben Rapid (and to an extent the later Daystate guns) where a single-piece metal valve seals against a softer (usually acetal) seat.

I'll keep the board posted of any progress - don't hold your breath though :p

Peter Norris
11-09-2014, 15:53 PM
Very well thought out and presented, thank you. We can only hope AA read it and carefully consider their selection of seal materials.....?

oddbob
12-09-2014, 09:02 AM
The problem is that the blokes I asked to make the prototype weren't really interested and basically did half a job.. by the time I'd finished tidying the valve up I'd managed to mark the edge of the sealing face, so this had to be chamfered to get the valve to seal properly. Bottom line the valve wasn't made to / has been modified from the drawing so I have no way of knowing if the original design will work properly and I'm reluctant to order a batch of 50 or 100 CNC'd items. :p

Have you thought of trying a bit of crowd funding, say a few of us share the costs, what would it come to? If a few were produced at cost only, to see how the design works, then the finalised design could be sold on evilbay for a reasonable amount.

cloverleaf
22-02-2015, 17:16 PM
Have you thought of trying a bit of crowd funding, say a few of us share the costs, what would it come to? If a few were produced at cost only, to see how the design works, then the finalised design could be sold on evilbay for a reasonable amount.
Thanks - tbh I hadn't considered this funding route, but then the numbers involved aren't really too scary. The big issue is being able to get a test valve made that's exactly to drawing, and hence truely representative of the design were it to be mass produced.

The test valve has been in my S400 for a good long time now (IIRC 6 months plus) so I might test that again soon to see if it's still behaving itself. If so I might look to getting a small batch made up :)

Chinnymonster81
22-02-2015, 18:16 PM
Have to wonder whether 3d printing is a possibility?

cloverleaf
22-02-2015, 18:18 PM
Given the surge in popularity of this production method it did also cross my mind; however your choice of materials is extremely limited, plus tolerances and surface finish would be inferior to a turned item.

There would be no particular advantage to 3D printing this item over turning it - 3D printing comes into it's own for complex shapes that would otherwise be difficult / time consuming to produce by other, conventional methods.

Ta for the thought, though :)

cloverleaf
04-10-2015, 19:29 PM
Curiousity got the better of me last week and I ran the parts-bin gun over the chrono.

When rebuilt last June the gun got a replacement, bespoke exhaust valve in white Acetal. The design was initially basically a simplified copy of the original, with a slight angled rebate inside to try and discourage any material shrouding the valve throat should the material around the valve seat face compress to any extent.

In order to work correctly the internal thread for the valve stem needs to run right to the end of its flat-bottomed hole. Despite asking the machinists to do this, the threads fell short and I had to chase out the end of the threads manually with a modified tap. No big deal, except that I had no sturdy way of holding the valve head (as there would have been when it was still attached to the parent bar in the lathe jaws) and I managed to slip and damage the edge of the sealing face.

The effect of this damage is a testament to the hardness of the material, as it refused to seal like this. In the end it went in a drill and had a rad put on the edge of the sealing face (maybe 0.25-0.5mm) to remove the damaged area; so the contact area at the seat is less than initially intended. Despite this I still had a little trouble getting the valve to seat - initially it leaked below about 120bar, but having got it pressurised to above this and having left it standing, it now seals perfectly.. so some plastic deformation appears to have taken place.

Sooo... here's the replacement valve next to an original black one - note that this was before the edge of the sealing face was modified:

http://img.photobucket.com/albums/v96/theboymike/Shooting%20III/SMALL_IMG_5918a.jpg (http://smg.photobucket.com/user/theboymike/media/Shooting%20III/SMALL_IMG_5918a.jpg.html)

http://img.photobucket.com/albums/v96/theboymike/Shooting%20III/SMALL_IMG_5926a.jpg (http://smg.photobucket.com/user/theboymike/media/Shooting%20III/SMALL_IMG_5926a.jpg.html)

http://img.photobucket.com/albums/v96/theboymike/Shooting%20III/SMALL_IMG_5924a.jpg (http://smg.photobucket.com/user/theboymike/media/Shooting%20III/SMALL_IMG_5924a.jpg.html)

http://img.photobucket.com/albums/v96/theboymike/Shooting%20III/SMALL_IMG_5923a.jpg (http://smg.photobucket.com/user/theboymike/media/Shooting%20III/SMALL_IMG_5923a.jpg.html)


Around 15 months ago when the valve was fitted the rifle was tested over its full operating pressure range with a number of different JSB pellets. In the interest of time and reduced wastage this was done using a 200mm long TDR cylinder, which has an internal volume of around 95cc compared to the Classic cylinder's volume of around 212cc.

Using 7.9gn Air Arms Express pellets the gun was giving around 42 good shots (those of within a spread of 1.5% of the max velocity) at a mean of 11.01ftlb with the TDR cylinder; equating to around 90 shots per charge with the Classic cylinder and de-pinger present.

When re-tested last week with the same pellets (type, not tin) the rifle gave between 77 and 81 good shots (the larger number allowing the inclusion of one low figure within each end of the curve) at an average of 11.08ftlb.

In the time between the two tests the rifle has been left pressurised (usually towards the upper end of the range) and had seen maybe 1-2 tins of pellets through it.

The above figures aren't nec. as bad as they might first seem, if we look at a graph of velocity versus cylinder pressure. Note that the earlier plot came from the test with the TDR cylinder so there are fewer data points and the plot looks less busy..

http://img.photobucket.com/albums/v96/theboymike/Shooting%20III/2015.09.30%20Velocity%20Testing%20S400c%20056630_1 .jpg (http://smg.photobucket.com/user/theboymike/media/Shooting%20III/2015.09.30%20Velocity%20Testing%20S400c%20056630_1 .jpg.html)


From the graph we can see that:

- The rifle actually produces a little more muzzle energy now than it did last year.
- The pressure at which velocity peaks is maybe 5-6bar lower for the more recent plot.
- The more recent plot show less velocity consistency - around 8ft/s shot to shot compared to around 5ft/s last year.

So actually not a bad result - the ideal cylinder pressure (along with ideal fill pressure) has only fallen by a few bar. The cause of the increased muzzle energy is a mystery, but is pretty minimal and could be down to variations in pellet weight and fit, as could the diminished consistency - although 8ft/s is still good for a .177 IME.

Alternatively it's possible that some bits have worn in, but they were pretty slick to start with :)

This performance is certainly better than that managed by my TDR (http://www.airgunforum.co.uk/forums/showthread.php/186420-Yet-another-addition-earlyish-Air-Arms-S410-TDR), which had a new (Standard) valve fitted around a year ago. Note that the graph shows velocity versus shot count but that refill pressure for both tests was broadly the same at around 100bar:

http://img.photobucket.com/albums/v96/theboymike/Shooting%20III/2015.09.17%20Velocity%20Testing%20S410TDR%20048456 .jpg (http://smg.photobucket.com/user/theboymike/media/Shooting%20III/2015.09.17%20Velocity%20Testing%20S410TDR%20048456 .jpg.html)

Overall, a promising result for the Acetal valve, IMO :)

(http://smg.photobucket.com/user/theboymike/media/Shooting%20III/2015.09.30%20Velocity%20Testing%20S400c%20056630_1 .jpg.html)

32:1
04-10-2015, 21:47 PM
Could the extra be the fact the material has crushed a touch giving the valve a fraction more lift when struck by hammer ?

32:1
04-10-2015, 21:59 PM
Opinions on these

http://www.trrobb.com/Air_Arms_S300S310S410_Exhaust_Valve_Slightly_longe r/p1449438_10264948.aspx

cloverleaf
04-10-2015, 22:10 PM
Thanks for the thought, although unfortunately it doesn't work like that :p

All effectively lengthening the valve stem will do is reduce striker stroke, reducing its impact and correspondingly lessening valve lift and duration. The only time a longer stem would yield more muzzle energy would be if you were hitting it that hard that the hammer was otherwise bottoming out on the exhaust valve body - and I suspect an S410 doing that under normal conditions would be very much on the naughty side of 12ftlb!

Akita177
05-10-2015, 00:18 AM
Could of the Acetal hardend/compressed a bit for lack of a better term before the softer head had a bit of slack that had to be taken up before the valve openend?
If the valve head has compressed a bit it may have less preload and this why the FPS gets higher and the pressure gets lower on the graph compare to old line.

bobbie1
05-10-2015, 01:22 AM
Very interesting read , would this apply to other guns with valves of similar material and shape ?

Patrick
05-10-2015, 10:04 AM
As everyone has said Cloverleaf,a very informative post and your to be congratulated on going to such efforts.If it is caused by over filling as suggested then let that be a warning to all AirArms owners not to over fill as well as the possible dangers in doing so.
No doubt you've cheered up any AirArms owners,myself included,who read this.:D

darklord
05-10-2015, 16:36 PM
It is well known else where this is a problem. Shame as its not as easy to repair now

singlespeed
05-10-2015, 17:45 PM
Cloverleaf.
I know earlier in the thread you suggested a solution to an extruded valve would be replacement with a new valve or machining the sealing face flat again. Instead of machining the face flat again, I wonder how easy/ difficult it would be to make a 0.2mm deep recess where the extruded part was? (0.2mm being the highest youve seen extruded).

You had the face of the acetal valve machined concaved, which as mentioned above by Akita177 probably means that deformation of the valve head has reduced spring tension slightly which increases power without the drawback of material shrouding the port for very low lift opening.

Deformation of the standard valve would also reduce spring tension which should increase power if it wasnt for the greater effect of the extruded material shrouding the port.

oedbachgen
05-10-2015, 18:11 PM
If you have your rifle regularly serviced by a gunsmith, wouldn't this stop this problem before it happens:confused:, just asking:o

32:1
05-10-2015, 18:57 PM
I pulled both my aa's down today to check valve seats, luckily they both looked good, both black versions and original, 510 is 6 years old and the 410 is 4 years old. I can see the edge of valve seat mark or lets say shadow.

So Id say they should be very reliable, I suppose AA could have bad batches of valves ?

singlespeed
24-10-2015, 17:27 PM
I agree about the valve - as much as I love the 400 series it's pretty basic and inefficient in some areas. IMO the throat is too large (in both diameter and length), as is the valve stem. In addition an angled valve seat might provide better flow at low lift (but would of course be more expensive to make). In contrast Daystate and FX seem to very nicely designed valves..
When I first saw inside the valve block of an S410, I was surprised to see square edges where the valve sits. Having spent a bit of time and looking at car cylinder heads, the valve seat area is an area where going from a basic single 45° seating face to three angle seats can give a decent increase in power. So going from square to single angle must surely be an improvement.

So, having a spare valve body with the original size transfer port, it was too tempting to try. Its only rough and ready cutting the seat angle using a slightly blunt 10mm drill (a new sharp bit would cut too well into soft aluminium, probably biting into the face) with tape around the flutes to save the surrounding threads and centralise the bit, gently hand turned to produce a countersink 0.75mm deep. The drill has an angle about 30deg so theres still room for improvement if i find a bit with a 60degree angle.

This will have reduced the area that the valve is left to sit on, but any deformation and extrusion caused should end up seating against the angled face of the port. So there shouldn't be any issue with partial valve lift and the extruded face masking airflow.

First test was it still holding air which was a good start. Ive increased my regulator prsssure from 80 up to 115, which should reduce power, so dont have any direct comparison. However that coupled with going from a 3.5mm transfer port down to the standard size the power actually went up.

I'll give it a few days to settle in, hopefully without losing pressure and also get the air bottle refilled again before running full string.

cloverleaf
25-10-2015, 13:30 PM
Could of the Acetal hardend/compressed a bit for lack of a better term before the softer head had a bit of slack that had to be taken up before the valve openend?
If the valve head has compressed a bit it may have less preload and this why the FPS gets higher and the pressure gets lower on the graph compare to old line.
I suppose it's possible that the seat area could have compressed without causing any more shrouding (due to the design of the valve); although this would also have the effect of (very slightly) shortening the striker stroke, which would reduce output. Still think the jury's out on this one :p



As everyone has said Cloverleaf,a very informative post and your to be congratulated on going to such efforts.If it is caused by over filling as suggested then let that be a warning to all AirArms owners not to over fill as well as the possible dangers in doing so.
No doubt you've cheered up any AirArms owners,myself included,who read this.:D
Thanks :)

Yes, while I certainly don't think that this problem is solely due to over-filling (as AA claim) it certainly can't help. I'd be interested to see how bad this problem is / if it exists at all in regged guns running lower output pressures (which would typically be between maybe 40 and 80% of what the valve in an unregged gun would see).



It is well known else where this is a problem. Shame as its not as easy to repair now
Indeed. Not so bad if you're handy with a lathe, though!



Cloverleaf.
I know earlier in the thread you suggested a solution to an extruded valve would be replacement with a new valve or machining the sealing face flat again. Instead of machining the face flat again, I wonder how easy/ difficult it would be to make a 0.2mm deep recess where the extruded part was? (0.2mm being the highest youve seen extruded).

You had the face of the acetal valve machined concaved, which as mentioned above by Akita177 probably means that deformation of the valve head has reduced spring tension slightly which increases power without the drawback of material shrouding the port for very low lift opening.

Deformation of the standard valve would also reduce spring tension which should increase power if it wasnt for the greater effect of the extruded material shrouding the port.
I'd thought similar - ultimately I think the feasibility of this approach comes down to how the material behaves and how likely it is to continue deforming. If it work hardens and is unlikely to deform further, this approach sounds like it might have legs :)



If you have your rifle regularly serviced by a gunsmith, wouldn't this stop this problem before it happens:confused:, just asking:o
Yes and no. The performance gradually degrades over time - so even if you had the valve replaced annually, you'd still see some fall in performance over this period.

Also, there's the cost element - assuming no AT and the replacement simply of the exhaust valve (and no additional seals), you're probably looking at around £40 for this job - every year. When a gun with a decent valve should do maybe 5yrs before requiring attention.

Given the choice between a gun that's going to cost nowt to run and be dead consistant over 5 (or more) years, or one that's going to be ever-changing and require £200's worth of work over the same period, I think we all know which we'd prefer to own :p



I pulled both my aa's down today to check valve seats, luckily they both looked good, both black versions and original, 510 is 6 years old and the 410 is 4 years old. I can see the edge of valve seat mark or lets say shadow.

So Id say they should be very reliable, I suppose AA could have bad batches of valves ?
It only takes a slight ridge to significantly alter performance - have you tried them over a chrono? It's the only way to be sure.

I'm sure the material does vary somewhat between batches; however I personally think this makes the difference between "crap" and "not-so-crap" rather than "crap" and "absolutely fine"..



When I first saw inside the valve block of an S410, I was surprised to see square edges where the valve sits. Having spent a bit of time and looking at car cylinder heads, the valve seat area is an area where going from a basic single 45° seating face to three angle seats can give a decent increase in power. So going from square to single angle must surely be an improvement.

So, having a spare valve body with the original size transfer port, it was too tempting to try. Its only rough and ready cutting the seat angle using a slightly blunt 10mm drill (a new sharp bit would cut too well into soft aluminium, probably biting into the face) with tape around the flutes to save the surrounding threads and centralise the bit, gently hand turned to produce a countersink 0.75mm deep. The drill has an angle about 30deg so theres still room for improvement if i find a bit with a 60degree angle.

This will have reduced the area that the valve is left to sit on, but any deformation and extrusion caused should end up seating against the angled face of the port. So there shouldn't be any issue with partial valve lift and the extruded face masking airflow.

First test was it still holding air which was a good start. Ive increased my regulator prsssure from 80 up to 115, which should reduce power, so dont have any direct comparison. However that coupled with going from a 3.5mm transfer port down to the standard size the power actually went up.

I'll give it a few days to settle in, hopefully without losing pressure and also get the air bottle refilled again before running full string.
Not that I want to be the one to p*ss on your campfire, however I think you've missed one fundamental difference with your cylinder head analogy. In an engine, the valve can often be the most restrictive part of the system, so flow gains here will improve mass air flow into the cylinder and hence allow the engine to make more power.

Conversely on a PCP the valve is rarely the most restrictive point in the system - this usually being the transfer port. So any flow "improvements" at the valve will make little or no difference since the port is the limiting factor.

I see where you're coming from with the angled port, however, while potentially limiting the effect of valve extrusion I suspect the smaller seating area will only serve to promote extrusion (as it will increase stress at the seat), while the larger area to which the atmospheric side of the valve is exposed will create a larger pressure differential over the valve when closed, making it harder to open; reducing muzzle energy and pushing down the ideal fill pressure (just as extrusion would).

Of course I'm happy to be proven wrong and will be interested to hear your findings, although ideally you need to approach it in a more scientific and pragmatic way (compare like-for-like and only change one variable at a time) to learn anything valid :)

singlespeed
25-10-2015, 17:01 PM
Not that I want to be the one to p*ss on your campfire, however I think you've missed one fundamental difference with your cylinder head analogy. In an engine, the valve can often be the most restrictive part of the system, so flow gains here will improve mass air flow into the cylinder and hence allow the engine to make more power.

Conversely on a PCP the valve is rarely the most restrictive point in the system - this usually being the transfer port. So any flow "improvements" at the valve will make little or no difference since the port is the limiting factor.

In car cylinder heads, the multi angle seats help at low valve lift values. In the PCP, at partial lift the valve is still going to be the restriction to flow. Being as the S410 only has a maximum valve lift of ~2mm, I figured that its nearly always close to the seat and the rapid flow rate must mean a 90°valve seat will be ineficient.


I see where you're coming from with the angled port, however, while potentially limiting the effect of valve extrusion I suspect the smaller seating area will only serve to promote extrusion (as it will increase stress at the seat), while the larger area to which the atmospheric side of the valve is exposed will create a larger pressure differential over the valve when closed, making it harder to open; reducing muzzle energy and pushing down the ideal fill pressure (just as extrusion would).

Of course I'm happy to be proven wrong and will be interested to hear your findings, although ideally you need to approach it in a more scientific and pragmatic way (compare like-for-like and only change one variable at a time) to learn anything valid :)
Yeah, ideally I would have done a back to back test in isolation but got a bit carried away. I was finding the 3.5mm transfer port and 80Bar pressure too noisy, so decided to retry the original valve body with standard port and a higher pressure.

I think you may be correct in thinking it would lower the ideal fill (operating) pressure, as I've just run a string. Only from 170Bar for now, as my bottle needs a topup.

.22 standard length classic S410 rifle
Lane regulator at 105Bar regulator pressure
Fully open standard diameter transfer port.
34gram hammer and short hammer spring shimmed to get 11.2FPE with AA fields.

Test string with RWS H point.
582 mag1
585
584
578
578
580
580
576
578
580

578 mag2
585
585
582
579
583
585
576
586
571

583 mag3
574
585
581
575
579
579
582
578
579

576 mag4
580
575
581
577
581
577
576
583
579

573 mag5
579
574
579
582
581
569
574
579
576

568 mag6
567
570
569
571
574
573
570
575
575

576 mag7
573
579
575
571 (120bar)
574
571
571
571
571

568 Mag8
570
576
568
571
566
578
574
569
572

569 Mag9
572
573
577
575
574
574
578
571
571

575 mag10
574
574
570
576
574
579 (100bar)
574
573
571

576 mag11
576
575
581
582
576
583
578
575
585

581 mag12
581
588
579
582
581 (90bar)
591
584
589
582

583 mag13
579
579
583
583
582
585
579
582
586

583 mag14
581 (80bar)
591
588
588
579
580
582
588
585

585 mag15
584
580
580
585
586
578
578
581
583

582 mag16
580
580
582
575
576
577
571
579
572 (60bar)

570 mag17
573
571
564
562
564
561
561
554
550

549 mag18
545
552
544
539
537
533
530
535
524 (40bar)

Thats not going to be the flattest of curves, but I think its safe to say its reasonably efficient, as I'm so glad my bottle didnt have 200bar in it :confused:
How the valve material bears up to sitting on less surface area will be the big question!

Edit for graph
http://i182.photobucket.com/albums/x124/singlespeed2007/Mobile%20Uploads/20151025_2235002_zpshlgquxcm.jpg
Theres definitely an increase in power after the regulator set pressure, so I'm thinking reduce the pressure from 105 to 95bar and restrict the transfer port as required

singlespeed
26-10-2015, 18:49 PM
After several strip downs and trying different reg pressures to try and remove the dip between 120 and 90Bar without much success, I removed the regulator inlet restrictor which had helped when the 3.5mm transfer port was on.

That and settling on 90bar regulator pressure removed the dip and restricting the transfer port brought the power to a usable level, but the dip was now replaced with erratic fluctuations and a high pitch squeak from the regulator or valve area :( maybe hammer bounce or the regulator spring having the same harmonic as something.

So, opened up the transfer port fully once more and screwed in the valve pot to reduce the power. Looks to be no spike/dip and the squeek has gone... well at least untill 120Bar which is all thats left in my bottle now.

32:1
26-10-2015, 20:11 PM
After several strip downs and trying different reg pressures to try and remove the dip between 120 and 90Bar without much success, I removed the regulator inlet restrictor which had helped when the 3.5mm transfer port was on.

That and settling on 90bar regulator pressure removed the dip and restricting the transfer port brought the power to a usable level, but the dip was now replaced with erratic fluctuations and a high pitch squeak from the regulator or valve area :( maybe hammer bounce or the regulator spring having the same harmonic as something.

So, opened up the transfer port fully once more and screwed in the valve pot to reduce the power. Looks to be no spike/dip and the squeek has gone... well at least untill 120Bar which is all thats left in my bottle now.

Well blow me down, Ive had that squeak from my lane reg at 140bar. What do you think it is and how did you cure it exactly, as after a dozen or so squeaky shots mine started leaking through vent hole

singlespeed
26-10-2015, 21:01 PM
Well blow me down, Ive had that squeak from my lane reg at 140bar. What do you think it is and how did you cure it exactly, as after a dozen or so squeaky shots mine started leaking through vent hole
Id noticed the squeak a few times yesterday but it was really evident when I tried a string today. Plotted straight onto a graph and I could see something was going wrong at shot 55 before hearing it starting to squeak about shot 68. http://i182.photobucket.com/albums/x124/singlespeed2007/Mobile%20Uploads/20151026_1933412_zpsexp01two.jpg

I didnt plot more graphs, just taking a few shots at 10bar intervals whilst filling. Different regulator pressures seemed to move the squeak up or down the pressure range and throttling the transfer port didnt make much difference. So, I settled on increasing the outlet valve tension and this seems to have worked at silencing it and tightening the fps spread :)

I'll be getting the bottle refilled tomorrow morning so I'll find out if the squeak is still anywhere :confused:

singlespeed
28-10-2015, 15:07 PM
Yesterday was a bit of a letdown. I managed to banish the squeak but shot count and more importantly, consistency suffered a lot :( one of the worst being.

http://i182.photobucket.com/albums/x124/singlespeed2007/Mobile%20Uploads/20151028_132632_zpsubxfxzsq.jpg

From earlier graphs, I figured 80bar was a bit too low and it turned out that way, leading to a steep drop off after the regulator cut.

Back at 90bar and the first few shots looked like it was going to be another erratic failure. But it steadied out and I'm reasonably happy with the outcome :)
http://i182.photobucket.com/albums/x124/singlespeed2007/Mobile%20Uploads/20151028_1345022_zpszqizkz7w.jpg

Theres a very small increase right at the end, but I think I'll leave that for now and see how it goes long term or, untill its time for a service.

cloverleaf
28-10-2015, 17:15 PM
Looks like you've certainly improved the setup compared to how it was initially!

A few thoughts..

- As you've observed, there is still a little spike at the end of the fill as the gun comes off reg - suggesting that the ideal reg pressure is a bit lower than the point at which it's set (I'd reckon on about 80 bar being where you want to be). If you reset the reg pressure to a slightly lower value the energy will probably be sailing a bit close to the wind (as it is currently when it spikes). You can alleviate this to an extent by tweaking the port adjuster in very slightly (I'd think a fraction of a turn - no more than 1/16).

- There is certainly some inconsistency between around 200 and 180bar, which is odd. In addition the mean velocity seems a bit low here. Have you checked the reg's output pressure over a range of input pressures? Many regs will vary their output as the input pressure changes. For example I set up a Theoben reg recently that varied between about 75bar output at 200bar input down to around 60bar output at 70bar input. What input pressure are you setting the reg up at? IME the best pressure is about in the middle of the operating pressure range; so in this case around 140bar. This sort of reg behaviour might also explain the gently rising velocity as cylinder pressure falls; although tbh I'm at a loss to explain the little dip at around 110bar. How large a pre-chamber are you running between the valve and the reg?

- There are a few low shots in the last plot (although a lot fewer than the preceding one!) and I think the consistency can be improved (my unregged S410k in .22 typically varies by no more than 3ft/s with these pellets). I think polishing the striker rail and valve stem would help here; although from the difference between plots it appears that the problem may be partially due to the reg too.

- I'm intrigued by the "4.5kg for 2mm movement of outlet valve" note - am I correct in assuming this is the load applied to the valve stem (when empty) to open the valve 2mm? Interestingly I've never really looked at it this way before..


Anyway, it definitely looks like you're heading in the right direction :)

singlespeed
28-10-2015, 18:54 PM
Great, thanks for the feedback :)
Ive answered within the quote below


Looks like you've certainly improved the setup compared to how it was initially!

A few thoughts..

- As you've observed, there is still a little spike at the end of the fill as the gun comes off reg - suggesting that the ideal reg pressure is a bit lower than the point at which it's set (I'd reckon on about 80 bar being where you want to be). If you reset the reg pressure to a slightly lower value the energy will probably be sailing a bit close to the wind (as it is currently when it spikes). You can alleviate this to an extent by tweaking the port adjuster in very slightly (I'd think a fraction of a turn - no more than 1/16).
Yeah, I was thinking of trying 5bar reduction in regulator pressure and seeing how that looked.

For a small reduction in power, whats your thoughts as per the merits or demerits of :-
screwing in the port adjuster screw.
screwing in the outlet valve port to increase outlet valve preload.
Reducing the length of spacer to reduce main spring tension. (Ive made up some spacers between 6mm and 8mm to go go between hammer and main spring)

- There is certainly some inconsistency between around 200 and 180bar, which is odd. In addition the mean velocity seems a bit low here. Have you checked the reg's output pressure over a range of input pressures? Many regs will vary their output as the input pressure changes. For example I set up a Theoben reg recently that varied between about 75bar output at 200bar input down to around 60bar output at 70bar input. What input pressure are you setting the reg up at? IME the best pressure is about in the middle of the operating pressure range; so in this case around 140bar. This sort of reg behaviour might also explain the gently rising velocity as cylinder pressure falls; although tbh I'm at a loss to explain the little dip at around 110bar. How large a pre-chamber are you running between the valve and the reg
I'm not sure of the volume for the regulated chamber. Just using the supplied standoff.

The reg was supplied at 105bar and is marked off in divisions which equate to 5bar. The stock gauge isnt accurate enough to validate wether I'm currently at 90bar or a few either way. Although, it may be good enough to show a drift in pressure over the fill range.

- There are a few low shots in the last plot (although a lot fewer than the preceding one!) and I think the consistency can be improved (my unregged S410k in .22 typically varies by no more than 3ft/s with these pellets). I think polishing the striker rail and valve stem would help here; although from the difference between plots it appears that the problem may be partially due to the reg too.
The inconsistncy and sqeaks that have been occuring could be the reg not seatting correctly or sticking. Maybe worth a look as its done about 3000 shots.

The striker rail and valve stem have already been polished and lightly oiled with sewing machine oil.
The face of the valve doesnt show any sign of ill effects from the reduced seating area.

- I'm intrigued by the "4.5kg for 2mm movement of outlet valve" note - am I correct in assuming this is the load applied to the valve stem (when empty) to open the valve 2mm? Interestingly I've never really looked at it this way before.
Yes, thats how Robert Lane recomends taking the initial setup. Scales and pressing the hammer against the striker to achieve (from memory) 4.25kg. But that could obviously be miles out depending on the main spring and reg pressure.


Anyway, it definitely looks like you're heading in the right direction :)

Akita177
29-10-2015, 00:25 AM
I would have thought 75-80bar was more the optimal for .22 though i may guess the transfer ports may need opening up/drilling and valve stem may need turning down for that section of air flow.

The Hammerli AR20 in 177 shoots pretty dam well down to 70bar-ish transfer port widht/lenght musy play a good part as i think the regs must be set to around 75bar.

32:1
29-10-2015, 08:02 AM
Re-sealed the reg and all seemed fine until that squeak started, bang on 140bar. Five or six shots squeaking and it started leaking again :rolleyes:

contacted Robert and waiting for his reply

Looks like this reg is set at 105b, is that ok for .177 ?
My valve spring pressure is way up compared to yours, 9.75lb

what do you think the squeak is, and how can I stop it as its causeing this reg to leak


Chris

http://www.airgunforum.co.uk/forums/attachment.php?attachmentid=126282&stc=1

32:1
29-10-2015, 09:08 AM
Forgot to say, I'm mega happy with regged rifle, its just the squeak causeing a leak that's raining on my parade, that is obviously if anyone has better setup info ;)

32:1
29-10-2015, 13:01 PM
Rob Lane replied with a tip, stripped and tweaked, refilled and tested.

Squeak gone from my 140b area, no issues until pressure was down to 105b where a squeak appeared just as it was going of reg Im guessing

90 great shots from 195 to 105 so Im happy

Chris
http://www.airgunforum.co.uk/forums/attachment.php?attachmentid=126286&stc=1