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Question on Semi-Auto

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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Question on Semi-Auto

Unread postAuthor: moonmaster » Tue Aug 25, 2009 3:32 pm

Would Mcmaster part #62475K22 work along with a QEV and air source for semi auto?

Or would a shuttle valve and ball valve work better?
I plan on using a blow forward breach, and I really want some semi auto goodness.
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Unread postAuthor: Willdebeers » Tue Aug 25, 2009 4:06 pm

You would need a pop-off valve to complete the cycle. Yes it would work, and you should check out phycix's tests on it.
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Unread postAuthor: moonmaster » Tue Aug 25, 2009 4:13 pm

I know about QEV and popoff full autos, but I'm looking for semi auto.
If you're describing something else I'm a moron.
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Unread postAuthor: Hubb » Tue Aug 25, 2009 4:16 pm

I would think that (with a continuous air source) any sort of valve could function semi auto.
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Unread postAuthor: Willdebeers » Tue Aug 25, 2009 4:19 pm

Oh, woops. :wink: Yeah, any valve can be semi auto with a continuous air supply. Why don't you have a QEV with a blowgun to have the trigger effect + semi auto?
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Unread postAuthor: moonmaster » Tue Aug 25, 2009 4:23 pm

Wouldn't that vent some air from my main chamber into the atmosphere? .......Unless I'm missing something....
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Unread postAuthor: Hubb » Tue Aug 25, 2009 4:33 pm

The only air that's going to be vented is that from the pilot area of the valve.
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Unread postAuthor: moonmaster » Tue Aug 25, 2009 4:37 pm

I meant that I plan on having a large onboard chamber that I use to fill the firing chamber through the QEV. If I put a blowgun on the pilot side of the QEV, won't that release air from the large onboard chamber without a second valve?
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Unread postAuthor: PVC Arsenal 17 » Tue Aug 25, 2009 4:46 pm

Yes, this valve would work. I own it. However it's a normally closed valve, which means you will have to hold the button down to fill the gun, and release it to fire. This is probably the opposite of what you want.

Look for a normally open valve such as the Clippard MJVO-3.

You can also use Slide check valves (sleeve valves). I recommend McMaster part# 4622K51

There is also the Pneumadyne A11-31-44 (which is in fact the opposite of #62475K22, I own both)
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Unread postAuthor: moonmaster » Tue Aug 25, 2009 4:58 pm

Okay, thanks for all the help everybody.
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Unread postAuthor: Willdebeers » Tue Aug 25, 2009 6:03 pm

Pvc, what? How would cutting off the air supply trigger the valve? There is no drop in pressure... I mean doing it like you have a tee, with a QEV/seconday chamber on one side, the blowgun on the bottom and the primary chamber on the other, filling the QEV. You would only press on the blowgun momenterily, so that the QEVis triggered but not all pressure is lost.
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Unread postAuthor: POLAND_SPUD » Tue Aug 25, 2009 6:23 pm

@willdebeers
these things are called spool valves.... the part he uses on his gun is a 3 way valve - so it has 3 ports and it has two positions...
port no1 is where you attach an air hose leading to your tank/compressor, port no2 is connected to the pilot side of a qev and port no3 is used for venting....

normally air can pass from port 1 to port 2 while port 3 is closed off (so it's filling the gun)....
but when you press the trigger/button/lever port 1 is closed off while air can pass from port 2 to port 3 (so it's venting the pilot volume)

there are many different kinds of spool valves... 3 and 5 way valves are the most popular but there are 4 way valves as well... and they can have more 'positions' too..
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Unread postAuthor: PVC Arsenal 17 » Tue Aug 25, 2009 7:58 pm

^correct.

For further explanation, look at this diagram of a slide check (sleeve valve). They work the same way, pretty much.

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Unread postAuthor: THUNDERLORD » Tue Aug 25, 2009 8:25 pm

For semi-auto involving a Blow-forward bolt, maybe you could pilot the QEV with a semi auto air-pistol.
Just insert a dummy co2 and run a pipe or hose into that install in the handle of co2 pistol, other end to pilot side of QEV.

The co2 cartridge powered airsofts with moving slide have lighter trigger pull and the full/semi/burst such as a Droizd (or paintball version) would be very interesting to test out.

A nail gun would provide a handle and nice trigger for semi, or an air hammer(chisel) for full auto (1000+ pilots per minute)
But for those a regulator would be necessary in between pilot line and tool air feed.

Currently working on similar design myself (only no QEV...homemade Piston design). 8)

EDIT: for full auto, a spring plunger in the chamber can press a rod depressing the trigger (pilot) automatically when proper pressure is reached (based on spring tension) or a pop-off pilot could be opened, either way there will be two triggers though.
EDIT2: (dang tired right now) Yes, the pilot will dump into atmosphere, but it will be worthwhile to test shooting pilot air either directly in front on Blow-forward bolt, or in between bolt and piston/QEV. :roll:
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Unread postAuthor: POLAND_SPUD » Wed Aug 26, 2009 8:07 am

co2 powered airsoft guns normally use a hammer valve... with a hammer valve you don't block off air supply so obviously some of it is wasted...

spool valves are the best for piloting QEVs... even paint ball guns use them so they are really ideal

most paint ball guns operate almost exactly on the same principle as the one used by PVC Arsenal 17 on TFS-semi,by btrettel on FANG and on my semi auto

on the surface it seems that all these guns are different but in fact they operate almost exactly like paintball guns... just have alook and compare
(the most important part is the spool valve that alternates between two positions... in one of them the small chamber is filled and the (sort of) air cylinder loads ammo... when the spool vlave is in hte other position it triggers the main valve and the air cylinder retracts - that's essentially the principle used on all these guns and the key part on all of them is a spool valve)

I wasn't aware of it at the time I built mine, which suggests that this is really one of the simplest and logical way to build a a semi auto/full auto mechanism
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