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Check valve concept

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 concept

Unread postAuthor: jmeyer1022 » Mon Mar 30, 2009 6:14 pm

Not sure if this would work but here it is.

Image
*1 1/4 coupling with O-ring Groove, plug on each side
*Blue: Bolt
*Red: steel washer
Green: rubber
The circle at the back is a safety pop off valve
I figure the piston will slide forward and pressure will build behind, Once it reaches the pop-off limit it will allow pressure into the chamber through the piston with a small equalization hole on the side of it. Once the pressure is equal on both sides of the safety pop off it will close back up. Will this work out? If not, is it because once the pressure equals the valve will just stay open? I'm sure it's been done before if it does work just thought I'd shoot it out there.
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Unread postAuthor: Gippeto » Mon Mar 30, 2009 6:27 pm

Considering that in order to make the o-ring/s seal, the tolerances will have to be tight, why bother with the check valve at all?

With tolerances that close, air loss during piloting will be minimal anyway. Or, if you're stuck on having an o-ring, would you consider a floating o-ring as a check valve?

Much simpler, seeing as you'll be making the grooves anyway.

Or am I missing a "special" goal that you're hoping to achieve?
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Unread postAuthor: jmeyer1022 » Mon Mar 30, 2009 7:47 pm

No, special goal but my piston is so tight with the o-ring that air doesn't get around it only behind it. So I figure with the safety pop off valve threaded into the inside side of the plug it'll act as a check valve. With the safety pop off valve if it works the way I hope it will work the air will fill until the pressure is equal on both sides keeping the pilot air tight from the chamber increasing performance. I've searched google and the forums for floating o-rings and I'm finding very little that go into detail.
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Unread postAuthor: Gippeto » Mon Mar 30, 2009 7:55 pm

Think about the o-ring groove.

Now picture a hole drilled straight into the side of the piston, where the hole is half in the o-ring groove, and half "outside" of the groove, on the chamber side. This hole should extend slightly deeper than the o-ring groove.

Air pressure will take the path of least resistance. It will first, expand in the pilot area, and force the piston against the end of the barrel.

Then, when the piston can no longer move, the air will "push" on the o-ring. forcing it to move slightly into the hole you drilled.

This allows air to bypass the o-ring, going underneath it, into the hole, and fill the chamber.

Under piloting conditions, the o-ring is forced to the pilot side of the groove, effecting a seal.

Make sense?
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Unread postAuthor: jmeyer1022 » Mon Mar 30, 2009 8:09 pm

Any chance you have a pic of this? I think I have a good image in my head, but it's not a clear one sadly. :( Any help would be awesome, and thanks for the help you've provided thus far.
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Unread postAuthor: Gippeto » Mon Mar 30, 2009 8:41 pm

REAL bad paint drawing coming up...run while you still can! :lol:

The white circle shows where to drill the hole.
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Unread postAuthor: jmeyer1022 » Mon Mar 30, 2009 10:34 pm

I'll give your concept a try tomorrow, how big should that hole be? like half way into my O-ring groove and halfway out like 1/8th size or smaller?
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Unread postAuthor: mark.f » Mon Mar 30, 2009 11:03 pm

Well, you can try the floating o-ring or build a small check valve for your piston.

The point is that the check valve doesn't have to be perfect, just good enough to flow well one way, and VEEEeeeeeerrrryyyy slow the other way.

Think about it. If you have a perfect sealing piston, and perfect sealing check valve, then not only can you pilot the gun with a small pilot like a blowgun or schrader valve, but it'll also actuate off something like a leak.
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Unread postAuthor: Gippeto » Tue Mar 31, 2009 12:30 am

I used a 1/8" drill bit for the piston on the copper guns.

I only needed one hole, and will recommend you start with only one as well.

If the chamber doesn't fill as fast as you would like, enlarge the o-ring groove so that the o-ring fits looser before you drill additional holes.
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Unread postAuthor: jmeyer1022 » Tue Mar 31, 2009 7:54 pm

Image

That's what mine looks, did I go to big? I haven't tested it yet any input before I test it out.
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Unread postAuthor: Gippeto » Tue Mar 31, 2009 9:27 pm

You went too big. :cry:

The hole is only supposed to go half way into the o-ring groove. This allows it to form a seal when the piston is being piloted.

With the hole going all the way through the o-ring groove, you no longer have any "check valve" effect.

But all is not lost.

If it was sealing as tight as you mentioned, you're probably okay still. You made an equalization port is all.

Your chamber should fill now, and flow back into the pilot area will still be VERY minimal. :D


After thought;

Is that the sealing face shown in the picture?

If yes, it may "wheeze/whistle" a little when you pilot it (or it may not).

How deep did you drill that hole?
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Unread postAuthor: jmeyer1022 » Tue Mar 31, 2009 9:30 pm

The hole goes through the coupling wall only on one side, and it only goes halfway into the o-ring groove the pic distorts it for some reason. and the sealing face is on the opposite side.
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Unread postAuthor: Gippeto » Tue Mar 31, 2009 10:59 pm

Alrighty then. :)
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