SpudFiles

could sombody please explain how a qev works? i looked in the wiki but i still dont get what the second port is for

If you understand how a barrel sealing piston valve works then thats how a QEV works.

Air is pumped in from one arm of the T shape and charges a resevoir coming off the middle port.

The resevoir air is dumped through the other arm of the T when pressure from the inlet port drops (say a blowgun is used to vent it).

The QEV's may have the barrel seal made of a rubber diaphragm or a lightweight plastic shape, both respond very quickly.

Heres a diagram from the wiki:



The bore it shows is ridiculously small though and I've not seen any QEV with that much solid metal in it.

A QEV is basically a small, machine-made piston valve used for venting pressure from high-pressure gas cylinders and pistons (usually in heavy duty manufacturing machinery) at very high speed. It works exactly like a normal piston valve. If you're unfamiliar with the concept, read up here:
http://www.advancedspuds.com/valve2.htm
http://www.spudfiles.com/forums/viewtopic.php?t=299&
QEV's are perfect for piloting piston valves, or for use as the main valve in a small (marble-shooter size) pneumatic gun. They open very fast, and dump air very efficiently for their size.

There are three ports. One goes to the pressure chamber, one goes to the barrel (or to the atmosphere if you're using the QEV as a pilot for a piston valve). Intake and exhaust, if you will. Pretty simple. The other port is for the pilot, which fires the valve.

Check out this gun by Hotwired, using a QEV. One of the cleanest guns I've ever seen, btw. http://www.spudfiles.com/forums/viewtopic.php?t=6013& . One port of the QEV goes to the chamber, one goes to the barrel, and one goes to the blowgun (pilot) which fires the gun.

Hope that helps.

Peace,
Pete Zaria.

does the schaeder(sp?) have to be on the same arm as the pilot? or can i fill ir from the chamber?
and if port 2 in the diagram is my barel, how will it hold pressure?

Chamber filling is less reliable than pilot side filling because of how the seal is made, It might work but its not designed to. The pilot port has to be pressurised first to seal the barrel off then air is forced into the chamber.

1 = pilot port
2 = chamber port
3 = barrel/exhaust port

3 is sealed off until 1 loses pressure from it being vented and the air from the chamber at 2 rushes out through 3.

what is port 3 all weirdly shaped?
think i could find one at home depot?

The shape is exaggerated in that diagram. Look at pictures of a real one. If the exhaust port is tapered, it's just to improve flow out the exhaust.

Very very little chance of finding one of these at a hardware store. Call plumbing shops and places that sell equipment for machine shops and/or hydraulic stuff.

I don't mean to nag or flame, but uh, two people (Hotwired and myself) just took a collective 15 or 20 minutes to give you links/diagrams etc... and you didnt even say "thx."

Peace,
Pete Zaria.

sorry man, forgot my manners for a sec.

Np

Heres a more realistic diagram with less of the freaky bits in it:

http://www.iit.bas.bg/PneumoDemo/airoff.gif

If you have access to an irrigation/farm store, that would be the best place to see/get one. They can even SHOW and explain to you how it works. They probably have some torn apart or have replacement parts for them. You can also see other types of valves and replacement diaphragms there. Look for suppliers of Zimmatic, Valley or Reinke parts.

I found a wholesale outfit and spent nearly an hour there with a salesman showing me all types of different valves and things. I went there and was honest- let em know I was building an awesome spudgun and wanted to learn as much as I could about the properties and uses of their valve systems. Most guys will be happy to spend a few minutes with you, as long as they aren't busy with other things. (I went during the winter)

would a bike pump be good enough to seal this thing? im going for 1/2 inch.
also: can you just skrew in threaded pipe?

a bike pump will seal a 1/2" easily I'm using a foot pump on a 3/4" QEV

whered you get it? im currently looking for a place to get one

Hey people I want to ask do I have to pump every time I will shot or? I mean If I put an air compressed bottle on the cord npt ball valve that goes in the P could I shoot more times or?
Thx
here is a link of a cord npt ball vale
http://image.dhgate.com/0x0s/f2-albu-g2 ... -rp-rb.jpg