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What pressure are you actually filling your rifle to - a case for push-button bleed valves?

Discussion in 'Anything Airgun Related' started by cloverleaf, Mar 6, 2014.

  1. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    So, we all know the drill when filling out PCPs... attach fill line, crack open main valve until the gauge on the bottle reads the correct fill pressure, shut off main valve and bleed.

    Recently when filling I've noticed a significant amount of air loss from the rifle during the bleed process - I suspect this is because the one-way valve in the inlet on the gun requires a certain pressure differential across it to close properly and seal. By it's nature the bleed screw on the pump or bottle (particularly the MDE bottles it would appear) releases the air fairly slowly.

    If you watch the gauge on an HW100 when bleeding it's often easy to spot a fall of around 10bar cylinder pressure during the bleeding process; likewise if I fill an S400 up to 190bar, bleed then repressurise, the valve in the gun appears to open at around 180bar - indicating that the cylinder pressure has fallen by 10bar or more.

    With regged guns this issue is no more serious than a bit of wasted air; however for un-regged rifles it potentially threatens to skew the results of any energy curve testing or adjustment.

    Back to the HW100 example - the issue seems less pronounced if the bleed valve is opened rapidly; however it still occurs. I've noticed a few "push-button" type bleed valves being offered. While I'd never afforded these much thought in the past, if they dump the air more rapidly than a screw type perhaps their use might minimise any issues with cylinder pressure loss during bleeding...


    Any thoughs? ;)
     
  2. Akita177

    Akita177 The Absolute State of Britian podcast

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    I wonder how the volume of the whip used effects it?
     
  3. stevemandm

    stevemandm Honorary Member

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    never noticed this, or even given it thought. i would imagine that if you fill to the same reading (from the fill bottles gauge), and bleed the same way, the power curve of the rifle will be constantly the same as from the previous fill
     
  4. Accuspell

    Accuspell Pro Poster

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    Open the bleed screw on the valve faster!

    I am not confident about the accuracy of ANY gauge on a rifle. It will give a rough indication of whether it is full, half full or empty and that is about it. Trying to read an actual pressure on a clock the size of a penny with a needle the thickness of a matchstick is never going to be accurate - the needle thickness is about 10 bar on that scale!
     
  5. walker

    walker Busy Member

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    very good point made by steve. i think its irrelevant tbh. ive never noticed a drop in pressure when i bleed the air off. you need to do it quickly.
     
  6. coney

    coney Engaging Member

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    I used to fill to180bar and noticed that I was losing approx 5% through the bleeder, so I now fill 190bar net180.
     
  7. craigfishin

    craigfishin Donator

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    I.like 200 i. My rifles but always fill to 205 to allow a little drop , i also wonder how much air we waste through bleeding especially those with long whips
     
  8. Ruddles

    Ruddles Engaging Member

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    The other thing to note is that when you fill the rifle, the air compresses and therefore warms up slightly. As it cools down, the pressure drops slightly. Gas laws.
     
  9. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    I'd suspect that more volume means slower pressure drop (more air having to pass through the bleed screw) and hence the problem is made worse.


    Yes, there's certainly an argument for consistency, which is fine if you only ever fill from the same source. I'd expect problems to potentially arise if you're less consistent or use differing fill sources. Of course inconsistency between gauges would also be another factor to consider if filling from multiple sources..


    Easier said than done in some cases ;)

    Totally agree about the gauges on guns, with the exception of that on the HW100 which is generally pretty good. Regardless of a gauge's accuracy, they should all be good enough to register a 10bar pressure drop during bleeding!


    I agree about opening the valve quickly; however as mentioned above sometimes it's not always that easy..


    Thanks - similar figures to what I've seen on a few guns :)


    Cool - could work out the wastage; can't be arsed though :p

    It's probably not a huge amount compared to what's going in the gun.


    Yup, this is why it's always a good idea to fill them slowly - prolongs seal life too :)


    I suspect this problem occurs to varying degrees depending on how easy the bleed valves are to operate. As an example of two extremes, the valve on my FX pump dumps the air extremely rapidly, while that on one of my club's bottles needs to be hung off to get any air out of it at all. I should probably compare the two when I get the opportunity..
     
  10. Steve K

    Steve K Posting Addict

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    Both my HW100's are filled to 210 BAR

    My MCT Daystates are filled to their stated pressure

    I have a CDT Air Wolf that's stated pressure is 200 BAR but i fill it to 160 BAR as that is when the rifle performs at it's optimum .

    Huntsman is filled just under it's stated 210 BAR as it also performs best from 200 BAR down

    Ranger is also filled under stated pressure for best performance

    AA 510 is filled to stated pressure

    Rapid filled just over stated pressure

    I suppose it's all relevant but, then you have temp fluctuation to consider ;)
     
  11. mattyts

    mattyts Donator

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    If your bothered about air wastage,buy yourself a microbore hose instead of a regular one.
     
  12. ratman60

    ratman60 Very Active

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    hello. on my S410 and vermy i fill from this guage only 180 and 160 respective not bottle, as my 2 other PCPs have no guage i can only go by bottle, unfortunatly there is allways air loss when filling a pcp but never thought about your comments mike but again another interesting thread. i will take note of replies
     

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