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Pcps stand the test of time?

Discussion in 'Anything Airgun Related' started by tomsteebs, Feb 8, 2014.

  1. tomsteebs

    tomsteebs Donator

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    Was I'm my gunshop just now and the gunsmith they use has started to not work on pcp's cylinders or bottles. He says he ddoesnt want to because they don't get tested and they are surely at risk of the same problems as scuba tanks.

    Does this mean that we may start to see older pcps having dramatic explosions? :D

    Tom
     
  2. terry1001

    terry1001 Major Poster

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    No. It's a good idea to have a good look over your cylinder from time to time both inside and out. There should be no signs of corrosion or physical damage. The 2 1/2 year inspection carried out on bottles is a visual one only.
    As far as I know the cylinders on Air Arms rifles have a short length at each end, next to the threaded part, which is reduced thickness and therefore strength so that if there should be a failure it's more predictable. The volume of most rifle cylinders is quite small so pressure would drop very quickly although some of the large buddy bottles would take longer, and do more damage, if they were to burst. Steel diving bottles could cause tremendous damage if they were to explode as there is much more energy contained in the air in them.
    Small cylinders can withstand much higher pressures for the same wall thickness/material which is why the larger diameter bottles start to get quite heavy.
     
  3. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    Refusing to work on them sounds a bit unnecessary tbh, although I think his point carries some weight. IMO as long as a cylinder is kept in good condition and inspected for corrosion and damage, you should never have an issue.

    Despite the fact that pressure vessels on air rifles are extremely over-engineered for their application; I do wonder about the potential for a catastrophic failure given how some meat-heads neglect their gear. Of most concern would be internal corrosion resulting from the use of damp air to fill the guns; however in practice I've never really seen any significant internal corrosion in any rifle cylinder; and certainly none bad enough for me to fear for my safety / bin the cylinder ;)
     
  4. Accuspell

    Accuspell Pro Poster

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    There are moves afoot to have the air reservoirs of rifles subject to periodiic inspection - Daystate have similar concerns to your gunshop. The early modern PCPs used steel for the air tubes, and there is a fear of corrossion in them due to being filled by a hand pump with no air drying system on them. I actually saw one Olympic team member's Steyr pistol, she had filled it from a pump and within 6 months their was corrossin that at resulted in serious pitting in the cylinder - it hadn't ruined th epistol it just needed a new cylinder - and being filled with much drier air. Breathing air is subject to a moisture limit of 35 parts per million for 300 bar fills - a standard hand pump, in the UK, produces air with about 500 parts per million. A hand pump with an air drying pack on it about 80 parts per million. If you are going to use a hand pump, make sure it has a proper sir drying pack on it - NOT JUST A WATER TRAP.

    You hear about people worrying about rain on the outside of their rifle and then they go and fill it on a day like today from a hand pump- which is the same as pouring an eggcupful of water into the air cylinder......:confused:

    Actual explosions from PCP reservoirs are rare, but they have hgappened. A&M had a problam with one or two of their EARLY lightweight cylinders for the HW100 - they solved it by changing how the cylinders were made. Antonio Gentilini, the owner and founder of Gin B stocks was very seriously injured and was in intensive care for over a month from the blast from a PCP cylinder letting go.....so accidents are not unkonwn, but provided due care is taken they are safe.
     
  5. loki_79

    loki_79 Donator

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    Actually, although it feels like there is a lot of moisture about, it is not as bad as you think. The reason for all the rain and mist is that cold air is not very good at holding moisture. Looking at this chart, air at 30 degrees C can hold about 4.5 times more water than air at 5 degrees C, so 100% relative humidity today would have approximately the same moisture content as air at 22% relative humidity in the height of summer.
     
  6. Chinnymonster81

    Chinnymonster81 Busy Member

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    Hmm that will be interesting because the gunsmiths would all have to have the same inspection qualifications as a dive shop tester. Most likely it will just be an inspection and any sign of pitting means a change.
     
  7. Accuspell

    Accuspell Pro Poster

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    Only our houses are centrally heated, so you have moist WARM air - look at the RH for 20 degrees C (average UK house temp for central heating - many run their thermostats at 22*C - we have ours at 16 and all the neighbours say how cold our house is, but we don't get colds/flu!)
     
  8. Hunter 001

    Hunter 001 Donator

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    Do you know from what date A&M cylinders became more safe?
     
  9. Accuspell

    Accuspell Pro Poster

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    When they started machining them out of round bar, instead of using an outside company to make them from tube....it wasn't Ady's fault, the engineering firm changed the tube they used and didn't tell him. Now they are machined from round bar I believe.
     
  10. Hunter 001

    Hunter 001 Donator

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    thanks. My cylinder was made in 03/2013 and came with biannual free check, I hope it is safe one.
     
  11. loki_79

    loki_79 Donator

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    I was only pointing out that it is not intuitive, just because the air feels damp doesn't mean there is a lot of water in it, just that the relative humidity is high (relative humidity is the amount of water that is in the air, as a percentage of the maximum amount that there could be). Unless your house has a damp problem (or you are drying your washing indoors, etc), then the amount of water per unit volume in the air inside and outside your house will be about the same, as it is just the air from outside that has been warmed up by your central heating.
     
  12. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    Do you have any sources for those moisture content figures? Are they independent or did they come from an industry source? To me they seem highly suspect - I find it very, very hard to believe that sticking a canister of dessicant on the low pressure side of the pump (a'la the Hills Drypac) could achieve an 80% reduction in the moisture content of the water.

    Indeed, to me it seems that the primary purpose of additions such as the drypac is to separate punters from their money, rather than water from air :rolleyes: Of course I'm happy to be proven wrong with reliable data; and always happy to indulge in a bit of an experiment if possible / appropriate :up:

    I'm afraid the eggcup claim is utterly ridiculous and smacks of scaremongering tbh. I once used a Mk1 Hills pump (no moisture trap) to fill my S410k many times (20 or 30 at a rough guess) over a particularly humid summer. When it was later stripped I found several beads of water rolling around inside; amounting to maybe 0.5-1.0 cc in volume.

    Of course any water inside the cylinder is bad news and I wasn't particularly pleased as it had knackered my Nylon exhaust valve head. It had not however damaged the cylinder (just as with the outside, the inside surface of the cylinder had a thin film of oil protecting it) and 1cc over 30 fills is a little less than the "eggcup" analogy of 30-40cc of water from one fill :rolleyes:

    I'm not necessarily defending pumps, however my example was fairly exteme - an early pump (I think the sump on later ones may have been improved) and high humidity. In addition, no damage would have been caused had the exhaust valve not been susceptable to moisture.

    FWIW while it appears obvious that the air they supply is not as dry as that from an air cylinder, I have no problem filling from a pump, providing that the rifle does not have a Nylon valve and that the cylinder interior is easily accessible for inspection periodically, or if it's only occasionally used and the gun is otherwise filled from a bottle..
     

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