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valve question

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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Unread postAuthor: boom_o_matic_2.0 » Mon May 25, 2009 9:42 am

I didnt wanna kick up a dead topic but I had a question about the schrader check valve...well I really dont understand what it means by sayin that they open up at about 100 psi with the spring. does that mean if the pressure on the outside of the schrader reaches above 100psi it will open and you dont even have to push the pin down in the valve core? I wanted something for my high pressure pump and this may be the answer I'm looking for in a check valve. and if it is what I"m thinking...would it exceed 100 psi in one pump if I built one like your how-to? cause if not I"d probably have to put some kind of pin at the bottom of the piston in the pump.
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Unread postAuthor: Ragnarok » Mon May 25, 2009 10:57 am

Gippeto wrote:If you ask Ragnarok nicely, I do believe he has a picture of something roughly similar, from HEAL.

That I do. This was while it was being made.
Obviously you cut off the excess threaded rod.

It'll be a bit heavy, but it'll handle the pressure just fine. Use an adequate bumper.

Which in my case, ended up being several layered rubber washers, and the springs on the back of the piston (which have now been replaced by something much sturdier - the original ones weren't exactly capable of combating the thousands of newtons of force on the other end of the piston.)
Either way, I soldered the olive that held the compression fitting at the back of the valve in place for double security - as it was not something you'd really want to break loose.
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Last edited by Ragnarok on Mon May 25, 2009 1:22 pm, edited 1 time in total.
Does that thing kinda look like a big cat to you?
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Unread postAuthor: Mike_Hunt0420 » Mon May 25, 2009 12:32 pm

thanks tons. you guys are always good for such helpful advice.
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Unread postAuthor: Gippeto » Mon May 25, 2009 8:53 pm

Boom o matic,

Yup, 70 psi of air pressure will open the schrader valve without anything touching the pin. Otherwise known as "cracking pressure".

The pump in the "how to" has over 100:1 compression ratio, it'll make enough pressure to open the schrader. Not problem.

The problem, is this;

Say you want to fill your spuddy to 300psi, you have to generate the 300psi, PLUS the cracking pressure of 70psi.

So, to get 300psi into your chamber, you have to do the same work as if you were making 370psi. Either take my word for it, or just try it and prove it to yourself, that extra 70psi is a fair bit of work.

A lower cracking pressure for the check valve in a pump is a good thing.

thanks tons


Just giving a little back. No worrys, and you're welcome. :)
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Unread postAuthor: boom_o_matic_2.0 » Mon May 25, 2009 8:58 pm

ok. so the hunt continues for a check valve. I could make one...but I really dont wanna. lol. I saw some up at tractor supply. I didnt check the cracking pressure on them though. maybe I can get one and adjust it...I dunno. just a thunk.
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Unread postAuthor: Technician1002 » Mon May 25, 2009 9:21 pm

boom_o_matic_2.0 wrote:ok. so the hunt continues for a check valve. I could make one...but I really dont wanna. lol. I saw some up at tractor supply. I didnt check the cracking pressure on them though. maybe I can get one and adjust it...I dunno. just a thunk.


It isn't really that hard to modify a tire valve. Cut off just enough length so it closes the valve, but with little spring pressure. This cuts the cracking pressure to just a few PSI. With needle nose plyers, just start unwinding some of the spring till the tension is low, then cut off the unwound section. Now you have a low tension spring.
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Unread postAuthor: Gaderelguitarist » Mon May 25, 2009 10:14 pm

@ Gippeto:
I'm impressed at how must pressure those fittings can endure! Thanks for putting up the link on that thread.

And was this thread hijacked?
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Unread postAuthor: boom_o_matic_2.0 » Tue May 26, 2009 11:31 am

yea it probably was. lol. sorry.
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