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Easiest Hammer Valve

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Easiest Hammer Valve

Unread postAuthor: Lockednloaded » Sat Dec 25, 2010 4:29 pm

I was making a push-button pilot for an un-regged co2 gun when I came across a simpler option. I got fed up with it, so I ordered a brass push-button valve from mcmaster (6790T42). It handles unregged co2 perfectly, and can be opened just by pushing down on it with your thumb! Its perfect for a hammer valve, so I hooked it up directly to my co2 tank and all I need is a proper hammer mech. Its so simple and clean!

I would like some help with the actual hammer though :?
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Unread postAuthor: omniscient » Sat Dec 25, 2010 4:43 pm

If;
"It handles unregged co2 perfectly..."


Then why is it only rated at 300psi? :wink:

<a href="http://www.mcmaster.com/#6790t42/=aazvl5">(6790T42)</a>
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Unread postAuthor: Lockednloaded » Sat Dec 25, 2010 4:45 pm

it must have a huge safety margin. QEVs are rated to 150psi normally, but the are regularly used well above that
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Unread postAuthor: omniscient » Sat Dec 25, 2010 5:47 pm

Lockednloaded wrote:it must have a huge safety margin. QEVs are rated to 150psi normally, but the are regularly used well above that


CO2 is over 800psi @ 70*F and when flowing unregulated, can freeze a valve, when the valve is wide open... even momentarily.

I would highly recommend using a regulator to drop the pressure well below 300psi, as guessing on a safety margin of over 2-1/2 times is not wise.
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Unread postAuthor: Lockednloaded » Sat Dec 25, 2010 6:28 pm

I know the dangers of co2, and I know what types of forces I am dealing with, so I know I'm totally fine
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Unread postAuthor: saefroch » Sat Dec 25, 2010 7:01 pm

High-pressure push-button pilot? Here. Much like Tech's QDV, but it's springloaded so it'll shut again once it's vented. Can't find the thread with the video though...

I'd be concerned about your QEV's diaphragm... like omniscient says, the pressure drop will cause a big temperature drop, especially since you're starting from room temperature.
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Unread postAuthor: Lockednloaded » Sat Dec 25, 2010 7:53 pm

I didn't say anything about a QEV, I'm firing air gun pellets with this as the firing valve. This is a factory made valve, so I didn't have to modify anything, I'm not keen to use modified parts with un regulated co2
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Unread postAuthor: D_Hall » Sat Dec 25, 2010 7:55 pm

Lockednloaded wrote:I know the dangers of co2, and I know what types of forces I am dealing with, so I know I'm totally fine

I would tend to argue that the first part of that sentence contradicts the last part of that sentence.
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Unread postAuthor: JDP12 » Sat Dec 25, 2010 8:02 pm

I was thinking the same thing D_Hall... CO2 can have some bad results if not handled correctly. I've had it freeze valves open before.

Not saying you shouldn't use it, just saying that you should make sure you take the necessary precautions when handling it.
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Unread postAuthor: Lockednloaded » Sat Dec 25, 2010 8:14 pm

I am confident in this valve's integrity, I have personally dismantled it and I found no weak links. It's a machined brass body, so the very worst thing that could happen is the valve opening, which is high unlikely after what tests have shown. It held 2000psi over night, so I don't doubt it's strength
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Unread postAuthor: saefroch » Sat Dec 25, 2010 10:36 pm

Lockednloaded wrote:I didn't say anything about a QEV
Apologies, I thought this was for use in another project.

I suggest doing some tests with the CO2 first. The problem isn't the pressure... and if I'm patronizing here, please forgive me. The temperature issue with using a propellant gas like CO2 comes from the fact that it's at room temperature, and thus can cool valves, seals, and other connections. Using a gas compressed on-site and used soon after compressing doesn't have the same issues because the gas heats on compression, and is still pretty hot just before it's decompressed. The biggest worry I'd have is that I'd get a valve frozen open and the thrust produced tears the gun out of my hands, damaging said hands and various other objects. Even just doing some leak tests on my ball valves with some 1,000psi air, when I vent the compressed volume (keeping in mind that these are ball valves) by opening one of the valves partway, it kicks back so hard I've lost my grip on it before.

Some simple (and safe!) testing should resolve any concerns.
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Unread postAuthor: Lockednloaded » Sun Dec 26, 2010 12:17 pm

Safety is paramount for me, so what tests do you recommend? I left it over night and tried it in the morning with the co2 tank tilted in every direction.

again: does anyone know a good hammer design? I don't care if its bulky, I just need it to be fairly simple
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Unread postAuthor: saefroch » Sun Dec 26, 2010 1:48 pm

Do an initial dry-fire test where you're fully expecting all valves to freeze/get stuck open and dump the entire CO2 tank. Remotely trigger the valve (like with a length of rope), and have it attached to a very heavy object (bricks?) and backed against something that'll take the possible "recoil." (large rock/building)

What's wrong with BTB's design? If you put a significant flow restriction before the valve it'll behave like a hammer, right?
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Unread postAuthor: Lockednloaded » Sun Dec 26, 2010 1:54 pm

i dry fired it until the bottle was empty, I could open the valve by hitting it with my hand. there wasn't any recoil because its just releasing a small amount of gas
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Unread postAuthor: Gaderelguitarist » Sun Dec 26, 2010 2:03 pm

If you can easily depress the button at those pressures, why bother with a hammer mechanism?

Just create a trigger piece to actuate the valve. That's the most simple solution, and will make it easier to achieve semi and full auto firing depending on your loading setup.
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