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Air cylinder refills and temperature.

Discussion in 'Anything Airgun Related' started by Bemused, Apr 19, 2014.

  1. Bemused

    Bemused Engaging Member

    Likes Received:
    I had my 3 litre cylinder filleed for the first time a few days ago. I was surprised at the temperature of the cylinder once it had been filled. I guess it would have been around 50ºC but thought nothing more of the matter.
    The next day James kindly showed me how to refill the Airwolf and we topped it up from 190B to 200B.
    Yesterday I refilled from 120B to 200B and today from 73B to 200B (I deliberately went low on pressure to see how the shots fell off).

    What surprised me to day was that I only just managed to fill to 200B.

    Then got to thinking back to the original fill temperature and seem to recall that every 1ºC temperature change results in 0.6B pressure change.

    Armed with this memory recall, and assuming I remembered my sums correctly the dive shop cocked up and under filled my cylinder.

    Any thoughts?
  2. mattyts

    mattyts Donator

    Likes Received:
    Yeah,happens pretty often,as the cylinder cools,pressure drops...if it's going to be a huge problem,ask your dive center to fill it up,wait a while then top it up :)
  3. jesim1

    jesim1 Kit bitch to the Stars

    Likes Received:
    Wigan/St Helens
    Hi Tony

    Your almost on the mark, and your theory is more real life than fiction.

    As an air gun user you are only interested in the top 150 bar of the cylinder, say from 150 to 300bar, so any less pressure you get is a big impact to your start of 300bar. e.g. If the dive shop only fills it to 250 after cooling then you have lost a third of your usable air pressure - and a third of your fills! A good dive shop will overfill a 232bar cylinder to say 250bar and let it cool to 220/230, but most 300bar cylinders are still only filled to 280/300 at best, because the compressor has to work very hard the higher the pressure, so they are reluctant to fill to say 320 and let it drop back to 300. The solution is luckily fairly simple - speak nicely to your compressor operator and explain why it's important for you to have as high a pressure as possible. Some dive shops fill cylinders in a water bath to help keep them cool on filling, but any shop can fill it to 300 if they have the gear, let it stand for half and hour while it drops to say 280, and then top it back up to 300 again.

    On the plus side your Airwolf has one of the largest cylinders around, so you get over 200 shots on a fill from 100bar, (2 or 3 times what other guns give) but the fill still takes a lot from a relatively small cylinder of 3L, especially if it's low in the first place. Your options are try to get whoever fills your cylinder to fill to the max, cool it, and fill again. Or you could get a larger capacity cylinder - say a 9L carbon fibre, which would triple your available useable volume while retaining about the same weight. (the pros and cons of these are another thread!)

    I could go mental and start reeling off calculations as I'm a qualified compressor operator - did I mention I used to dive - a lot!, but for the purpose here just take the advice as about right for the purpose it's intended for without an equation to prove it.

    Hope this helps.

  4. trumpetier

    trumpetier Pro Poster

    Likes Received:
    I drop my bottle at my local dive shop and normally pick it up a few days later whem im passing, what they do is fill the 300 bar bottle,leave to cool over night then top up the next day. Using this method i get around 20 fills of my s400 carbine.
  5. Snipertez

    Snipertez Donator

    Likes Received:
    Devon near Exeter
    Hi chaps, in my local dive shop it doesn't help if l'm floating about waiting and they then feel rushed to get the fill done. I now give them at least 20mins to sort it and make sure l get my moneys worth. Nothing wrong with asking for a full fill, that is what your paying for.

    20 - 40 bar short on a fill could equate to 150 - 200 shots :confused: and even more noticable with a smaller bottle.
  6. Clubshot

    Clubshot Clubshot

    Likes Received:
    North London. England
    Fill depends on Pump they use - Most Shop ones cut out around 305 Bar - Yes they will cool down

    But some have older pumps that do not always reach 300 Bar

    My Dive Shop fill my bottle off Storeage Tanks - slower and cooler with No Heat Loss

    Number of Fills also depends on what Gun you are Filling or topping up - a Large 500 cc bottle will take more air than the average Tube
    On most PCP's

    As most charge the same to fill 300 Bar - I fill my 12 Litres and Decant into my runabout 3 Litre bottle


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