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Attempting to visually disect a 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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Attempting to visually disect a valve

Unread postAuthor: Rokmonkey » Mon Mar 10, 2008 9:48 pm

Okay, I have been staring at these videos and pictures for quite some time and I just can't figure out how he did it. I'm assuming it's a metal chamber, pressurized up in the hundreds of PSI. I thought the valve was a QEV but Im just not sure. Any second opinions on this?


Most of you have probably seen this before, just couldn't find a topic 'bout it.

http://milsimlabs.com/rapid%20mortar.htm
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 10, 2008 10:01 pm

Your assumntions appear to be correct - you can do this with a QEV, assuming you have a high pressure air/co2 source, or a high flow and volume low pressure source. If you open the pilot then close it again rapidly, the valve will reseal, allowing for multiple shots.
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Unread postAuthor: Rokmonkey » Mon Mar 10, 2008 10:04 pm

So what's he pulling then? From far away looks like a Quick Disconnect but don't see how that'd work.

And are QEV's pressure rated to say 250-400 PSI?
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Unread postAuthor: CS » Mon Mar 10, 2008 10:14 pm

Old Post wrote:Rokmonkey, most likely a pop-off safety valve. Normally they aren't manually controlled, but you can unseal them by pulling on their ring. The pop-off safety valve being connected to the QEV pilot.

However he could have a valve that operates in a similar manner to that of a pop-off valve, who knows.

250-400 PSI, I'd bet thats a pretty good ball park figure, however you'd want to check a specific valves rating before purchasing it.


"Pop-off safety valve" - Excuse me there called "Pop-Safety Valves"

While it could be a pop-safety valve, it wouldn't be your standard air compressor one that goes off at ~125PSI. (Because I'm assuming that this cannon operates at a much higher pressure) The type of the valve isn't overly critical, just so long as it can be quickly opened-and-closed. Something similar to a shop blowgun would work, given it can handle the pressure.

Just checked the 3/4" QEV over at McMaster, and there saying it's only good up to 125PSI. I got one myself and the body itself is made of metal, and looks fairly strong. Maybe there is problems with the diaphram becoming damaged at higher pressures - you know its only rubber.

EDIT: What was I thinking...?
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Unread postAuthor: MrCrowley » Mon Mar 10, 2008 11:07 pm

What were you thinking, I saw your post before the edit and wondered if your partial absence had somehow defected your knowledge. :)

There are reports of QEV's going higher then 200psi I believe. I know the British have taken theirs far higher.
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Unread postAuthor: Rokmonkey » Mon Mar 10, 2008 11:22 pm

Soo this means that they are good to 200?

Wanted to get a QEV at some point anyway, really only as good as sprinkler valves, pressure wise anyway?
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Unread postAuthor: MrCrowley » Tue Mar 11, 2008 12:00 am

Good to 200psi? Not sure, can they widthstand it, yes. The first thing that will fail is probably a leak in the diaphragm or piston, before the whole diaphragm/piston will be destroyed. But I doubt that will happen at 200psi.

Don't buy a QEV on my account that they are good to 200psi, but they should be able to widthstand it.
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Unread postAuthor: Rokmonkey » Tue Mar 11, 2008 12:10 am

So shouldn't we be able to rule out a QEV in this situation, he's using a metal chamber, and the guys I know who use metal chambers on airsoft/paintball mortars usually bring them to 400 PSI with a ball valve, and that ain't a ball valve. Think it might be a special order then?
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Unread postAuthor: CS » Tue Mar 11, 2008 12:32 am

Ah, fun! As you've proably noticed these "golden" numbers are hard to come by, especially in spudding.

200PSI? MrCrowley's guess is just as good as mine - probably. We often assume were safe when we are with in reasonable proximity of a pressure rating, however 200 lies a bit out of mentioned proximity.

To further stir the pot... High pressure isn't your only problem. You have to worry about your compressed gas freezing gun components, and filling the gun too fast. Filling too fast can unseat the diaphram. I've experienced the problem with a sprinkler valve, which also uses a diaphram.

What you might want to do is email the guy over at "MilSim Labs". Tell him your a intrested customer (which your not, but who's keeping track?) and your wondering about a few details. Ask him what the gun runs at, and ask if there is anything special about the QEV valve. Make some attempt to convince him your not just suckering off infromation, and you are indeed a intrested customer. His email is: gun_fighters@hotmail.com

Good Luck!

[EDIT]

Rokmonkey, chances are it is infact just a regular old QEV, but that is why I am intrested to what pressure he runs the gun at. While not likely, he could have swamp the diaphram/piston with one of his own - something your not going to detect from the pictures.
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Unread postAuthor: Rokmonkey » Tue Mar 11, 2008 1:44 am

Well, Ill just have to do that, I'll let you know what I found out.
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Unread postAuthor: grumpy » Tue Mar 11, 2008 4:07 am

there was already a thread on this a couple of months ago. anyway, what he is using is a qev and a slide check valve to fire it. you can get slide check valves from most any paintball website and mc masters has them upto 1/2".
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Unread postAuthor: Rokmonkey » Tue Mar 11, 2008 10:35 am

Oh, cool thanks.
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Unread postAuthor: EGOed » Tue Mar 11, 2008 11:49 am

Most paintball fields dont allow PVC air chambers on their fields for insurance purposes.....This may be the reason his chamber is steel , not because of high pressure applications.....My mortars are all steel chamber also because they are much more durable than PVC and the Pulse Valve that I use is only rated for 125psi also.
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Unread postAuthor: socoj2 » Tue Mar 11, 2008 1:24 pm

I dont see how he is keeping the pressure on the INlet side to keep the popet sealed..
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Unread postAuthor: jackssmirkingrevenge » Tue Mar 11, 2008 1:26 pm

EGOed wrote:not because of high pressure applications


To get so many shots out of a tiny chamber, there has to be a pretty high pressure in that tube.
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