Hammer & QEV Valve Questions

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BeardlessDwarf
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Sun Aug 28, 2022 5:42 pm

Hello, people of Spudfiles! This is my first bolt-action airgun, and I've no idea what pressure it requires. The rifle will hopefully shoot a 0.357 caliber slug out to 300 yards out of a 21-inch barrel, powered by a paintball hpa tank. I'm hoping to get maybe 600-900 fps. If I could get calculations, or the math equations to figure it out myself, that would be great. Be warned though I may mess it up as I'm only 16 and really bad at math. I also need some help designing a valve at that high of pressure. I found a hammer valve tutorial by the "face off" youtube channel, but I don't know whether that would suffice. I was thinking maybe a Quick Exhaust Valve that is actuated by a hammer valve? Has anyone tried anything similar to that? Oh yeah, one more question. What does that quote that appears on every post mean? "Hectmarr wrote: You have to make many weapons, because this field is long and life short." I have no idea what the purpose of it is. Thanks my SpudMen.


face off hammer valve link:
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jackssmirkingrevenge
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Thu Sep 01, 2022 6:30 am

Welcome to the forum!

I suggest you download Gas Gun Design Tool as it's the best way to be able to calculate approximate performance figures and work out what parameters you need to tweak.
I was thinking maybe a Quick Exhaust Valve that is actuated by a hammer valve?
That's one possibility, it depends on what tools and materials you have available and what techniques you can master.
What does that quote that appears on every post mean?
That's my own forum signature and a reminder that tempus fugit in an effort to avoid procrastinating ;)
hectmarr wrote:You have to make many weapons, because this field is long and short life
BeardlessDwarf
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Mon Sep 05, 2022 2:15 pm

Thank you! I can make the hammer valve combined with the quick exhaust valve, I'm just not sure if it is worth it. Would it boost performance or nah?
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mrfoo
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Tue Sep 06, 2022 1:23 pm

With a standard hammer valve the hammer has to open *and hold open* the entire valve that's going to be used to flow the air you're using for propulsion. As pressure and bore size go up, you'll need more and more hammer force to open the valve. A QEV + hammer valve reduces the hammer force required to open the valve, and crucially the flow you're releasing isn't trying to re-close the valve as soon as it's opened, instead it's holding it open.. So yeah, it's basically better.

There are other ways to solve the problem, for example the counter balanced hammer valve.
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jackssmirkingrevenge
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Fri Sep 09, 2022 12:44 pm

As mrfoo said it's more a matter of practicality as you scale things up, at some point the hammer strength required becomes too much and a QEV is more feasible.

For example when Gippeto went hardcore with a 0.760 bore pneumatic at 1500 psi it made sense to take this approach.
hectmarr wrote:You have to make many weapons, because this field is long and short life
Dembouz921
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Sun Sep 11, 2022 10:40 am

If you want to make an easy and solid hammer valve, don't do the one in the face off video, use a threaded rod, an acorn nut and a steel washer, screw everything together with an o-ring or teflon tape and you will hace an airtight valve.

Now for the gun, making an hammer valve or qev gun is up to you, a qev gun might be simplier to build if you use a blowgun as a pilot valve and a ball valve setup to fill the qev chamber after each shot
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