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Check Valve interrupter confusion

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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Check Valve interrupter confusion

Unread postAuthor: Solar » Thu Nov 19, 2009 5:11 am

If I wanted to hold back a supply of air until the source reached a set psi (say 100) I could use a simple safety relief type setup, and vent the air into a pipe fitting. But once the valve cracks, and pressure builds up downstream, the valve needs to stay open until the source drops below 100psi again. Unfortunately, back pressure would close this type of valve as soon as enough pressure is built up downstream, helped by the spring pressure that held the initial pressure back.

This I think operates similar to a check valve that has a high cracking pressure, which is opposite check valve operating design since most check valves tout <1psi cracking pressure.

My feeder system needs a dwell to give the longer rounds time to get into the breech. It operates too fast for it's own good with the exhaust valve at the base of the piston. By delaying the piston from getting fed air, I figured a pressure based delay would be the best way to insure timing.

Any thoughts on this? I have not had any luck with finding any off the shelf parts for this pneumatic logic.
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Unread postAuthor: psycix » Thu Nov 19, 2009 6:46 am

I think the following diagram does the thing you want.
It only lets air through if the pressure exceeds a certain pressure (adjustable with spring force), independent of the current output pressure.

With a bit of imagination you could build this into a T-piece.


However, if you can you should use a flow restriction to make the delay. Simply use a needle valve to limit the flow of air going in, its cheap and easy.
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Unread postAuthor: Solar » Thu Nov 19, 2009 7:42 am

ok. Off to the side porting eliminates any back pressure on the surface of the seal. I guess I could use a diverter valve to lose any trapped pressure once the valve closes back up.
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Unread postAuthor: btrettel » Thu Nov 19, 2009 11:14 am

Have you considered a needle valve? It doesn't do exactly what you describe but it would slow the flow to the piston.
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 19, 2009 12:14 pm

This valve is based on a similar system to what psycix illustrated, wouldn't that do the job?
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Unread postAuthor: Solar » Thu Nov 19, 2009 3:12 pm

Flow control won't work, I need to completely stop air from getting to the piston so it dwells for a brief instant. I think psycix and JSR's valves will do the trick.
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Unread postAuthor: POLAND_SPUD » Thu Nov 19, 2009 3:54 pm

I need to completely stop air from getting to the piston so it dwells for a brief instant
if all you need is an adjustable delay then you might try the design mentioned in my last thread here -> http://www.spudfiles.com/forums/viewtop ... tml#268107
it's not exactly what you are looking for but one of its part does what you need


there are off the shelf parts that do that... in fact, they are quite commonly used in pneumatics

you can find them in clippard catalogue -> http://www.clippard.eu/fileadmin/user_u ... _72dpi.pdf
(Delay Valves, pp. 263-265)

but as I said eariler they are quite common so other manufacturers have them as well... clicky (this might be more straight forward / easier to understand)
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Last edited by POLAND_SPUD on Thu Nov 19, 2009 5:28 pm, edited 2 times in total.
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Unread postAuthor: jrrdw » Thu Nov 19, 2009 5:04 pm

A few different options given. I'm interested in seeing how it turns out.
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Unread postAuthor: psycix » Fri Nov 20, 2009 6:27 am

The difference with "my valve" and JSR's valve, is that when his valve closes and the pressure on the output drops, it seals on the porting and the effective surface area reduces.
Which is why "my design" doesn't feature a sealing face.
Though it could be useful to have it pulse open quickly. It would require only one o-ring, but on the other side JSR's valve only works properly if the output side drops to zero pressure. The keep-open pressure is way lower then the pop-open pressure.

See for yourself what suits your needs the best way, and don't forget to keep us updated. :)
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Unread postAuthor: POLAND_SPUD » Mon Nov 30, 2009 7:02 pm

I am just curious... have you found the part you need ??

I've just got a delay valve (I want to build an oscillating circuit with it) and I think it's exactly what you need...

ohh and if you are looking for a more compact valve you might want to buy clippard's PV-1P (clippard catalogue p. 165)
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