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Thread: HW100: maximum input pressure?

  1. #1
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    Default HW100: maximum input pressure?

    This one goes out to the Weihrauch HW100 experts. (In particular: Bludlust, I'm counting on you here. Don't let me down! )

    I'm making preparations to modify my FAC HW100. My shooting priorities have changed, and I want to build a 12 ft.lb carbine that I can use for HFT.

    To this end, I've recently bought two Walther/Hammerli AR20 maxi air tubes. These tubes have a safe working pressure of 300 Bar (more than 400 Bar test pressure). One of them will be modified to accept the air outlet valve from my HW100's existing air tube.

    What I need to know is this: what is the safe maximum input pressure that the HW100 action and regulator can accept?
    It's obvious that just because the air tube I'll be using can tolerate 300 Bar, it doesn't necessarily mean the HW100 components can!
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  2. #2
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    I would not mess with OEM stuff designed for a specific pressure.

    Russian roulette with that beautiful face of yours and your fingers!

    I can't see there being any real benefit to it, other than a few extra 12fpe shots from a fill, and then the ball ache of having to reconfigure (read guess) the regulator spring washers until you get it right.
    Last edited by Bludlust; 17-06-19 at 14:36.
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  3. #3
    Sharp Shooter
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    Quote Originally Posted by Nick V View Post
    What I need to know is this: what is the safe maximum input pressure that the HW100 action and regulator can accept?
    Manufacturers generally mark rifles with a maximum safe working pressure - does the HW100 have such markings on it?

    If it does, don't exceed it.
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  4. #4
    Marksman

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    Just my 2c:
    When the rifle was designed a safe Operating pressure was chosen. This was then multiplied by a Load Factor (1.2 for instance [ for the odd overfill or rifle left in the sun ect.] )The engineers will not make this figure public because they really don't want you to go over the Operating pressure. This load factor pressure is the multiplied by a Safety Factor (typically 1.5 for pressure vessels but not always). This is then the pressure they design for bearing in mind the fatigue life due to filling and emptying of the pressure vessel and all the other components involved.
    So what is the long and the short?
    Someone spent a few months even a year to design the Air Rifle taking material properties, load paths and maximum pressures into account to give you a well balanced rifle that is not over engineered but is still safe and usable. So please don't use a 300 bar Cylinder with a 200 bar gun it might work for a while under "ideal conditions" but the engineers didn't design for that in the end.
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  5. #5
    Sharp Shooter
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    I would not try being Myth Busters with Air Rifles.
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  6. #6
    Sharp Shooter

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    Hi Nick. The max operating pressure of the HW100 air tank is 200 bar. Depending on the pressure vessel code used for design, on top of this there will be a maximum temperature, safety margin, test pressure, creep allowance and corrosion allowance. None of these can be safely exploited by the operator. Remember that the fill valve, regulator and pressure gauge also see the tank pressure and would be designed for the 200 bar maximum. If a seal fails the high pressure could even penetrate further back. Assuming the 300bar fill pressure doesn't directly cause any damage due to higher forces on the parts; the regulator's operation can also be affected.

    Regulators are designed to control downstream pressure for a defined range of upstream pressures. Pressures outside this range upset the balance of forces on the controlling element which, on the HW100, is a piston with carefully chosen diameters on the inlet pin and piston face and an opening force supplied by a spring with adjustable preload (Bellevile washer stack on HW100).

    If you dramatically increase the tank max. pressure by 50% then the chances are the Belleville stack may not exert enough force on the actuating pin to open the inlet valve. You'll need to increase the preload on the Belleville washer stack or maybe even add washers .... and this will increase the downstream regulated pressure (and the power). Only way to bring it back into balance would be to make the piston size and regulator cylinder bore larger or maybe reduce the already tiny bore of the inlet valve. This brings new dangers because you must get custom parts made either way.

    HW100 FAC in .177 operates at about 23 ft.lb as standard. When you reduce power to 12 ft.lb the shot count goes up substantially even with the shorter cylinders used for the carbines. You can also carry a spare cylinder to swap out.

    For me the risks of running the rifle at higher fill pressure when the operating manual repeatedly says not to exceed 200bar is a risk I wouldn't take. It also introduces risks when you sell the modified rifle to someone else one day. Rather sell it and buy what you want.
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  7. #7
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    Always good to tap the brain pool!

    When contemplating a scheme like this, my default is to reach out for ideas and advice from people who know the rifle in question better than I do.
    I asked on the off-chance that someone might have done this - or something similar - before. In my experience, that's usually the case!

    Judging by the feedback, I'm aborting the idea.
    I was sceptical about the risk/benefit ratio of charging to 300 Bar anyway - the only reason I pursued the idea this far was because I know the air tube can accept it, and I knew it couldn't hurt to ask.
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  8. #8
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    So: with the 300 Bar charge idea laid to rest, what replacement internals would I need to de-tune the rifle from FAC to 12 ft.lb?
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  9. #9
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    Quote Originally Posted by Nick V View Post
    So: with the 300 Bar charge idea laid to rest, what replacement internals would I need to de-tune the rifle from FAC to 12 ft.lb?

    Nothing really.

    I got my FAC down to shooting 790 fps with 8.44 by simply playing with the hammer spring tension and a VERY marginal reg adjustment.

    NB... LOOSEN THE GRUB SCREW!!!!! before cranking anything on the hammer spring adjustment. I have yet to find a secondhand HW100 with an undamaged hammer adjuster.

    DON'T fiddle with the regulator unless you have a pressure gauge to screw in. I adjusted mine (using the factory Belville washer config) down to 110 bar. factory on the FAC (I stand to be corrected) was at around 115-120. You will easily get 50 shots from a carbine cylinder.

    Someone down in CT (I think it is JVL) knows more than me about HW 100 reg adjustment and building stumpies. Perhaps you should reach out to him for more accurate advice?
    Last edited by Bludlust; 19-06-19 at 08:33.
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  10. #10
    Prof. Jan Itor

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    @Jacowp is a wizard with HW100s
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  11. #11
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    Quote Originally Posted by Citizen K View Post
    @Jacowp is a wizard with HW100s

    THAT'S HIM! What the Janitorial Engineering Professional said!

    JacoWP is the ORIGINAL stumpie builder.
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  12. #12
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    Thanks gents!

    I'm having to ration my time carefully at the moment, in between 'work' work and building an HW98 HFT hybrid stock for my Ultra SE. But I'll reach out to Jaco and see what he says.
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  13. #13
    Sharp Shooter

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    There are quite a few articles on the www about adjusting power levels on the HW100. I would leave the reg alone and try to get the power down using only hammer spring pre-load.
    Also when reading ... the factory reg pressure settings vary a bit with power level and caliber.

    Also, from the factory the FAC rifles have 600mm barrels as standard. Shorter barrels are used on all lower power derivatives so consider changing the barrel first, then the hammer spring preload and then the reg only if necessary. And don't forget what Blud said about the grubscrew....
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  14. #14
    Sharp Shooter
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    I know JacoWP is a wizard with all Hw100 rifles. He builds the carbine versions at 12fpe to give 60 shots. So on your longer tube you wil get probably a gazilion
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