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QEV problem

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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QEV problem

Unread postAuthor: NoXi » Fri Oct 03, 2008 8:42 pm

Hey guys, i got my 1/4" qev and just finished making my .177 sniper. I hook up my tank to it, which is pressurized at around 170-200) and it starts to leak out from the barrel. All the fittings and such are in the right place, the barrel on the exhaust, the chamber on the "out" and the pilot valve (blowgun) on the in. Do you guys know why it leaks through the barrel? Thanks
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Unread postAuthor: Maniac » Fri Oct 03, 2008 9:19 pm

Check the seals on the pilot side there could be a leak that is causing it to constantly pilot.
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Unread postAuthor: NoXi » Fri Oct 03, 2008 10:16 pm

i just checked it and it doesnt seem like there is a bad seal. Maybe ill try it out more tomorrow once i get the air compressor out. But any more suggestions on what might be wrong?
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Unread postAuthor: jook13 » Fri Oct 03, 2008 10:36 pm

I am guessing that the chamber and barrel need to switched? I saw that you said the barrel is on the exhaust port, but maybe check by switching just to be sure? I have no other suggestions other than the valve is a dud or tampered with.

Does it start to leak after a certain pressure or as soon as you start to fill it?
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Unread postAuthor: i-will » Fri Oct 03, 2008 10:57 pm

my guess is that it is not sealing cuz it is not a perfect 90 degree cut or that the material used for the seal isn't doing it's job right. find something a little softer. a silicone seal worked for me. it didn't have to be perfect cuz the silicone can mold to the sealing edge with little effort. plumbing silicone is cheap and perfect. go buy a tube. 8)
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Unread postAuthor: jook13 » Fri Oct 03, 2008 11:01 pm

i-will: you know that a QEV is a valve that is commercially available and premade right? not a homemade piston valve.
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Unread postAuthor: NoXi » Fri Oct 03, 2008 11:01 pm

Well, i air it up to 120-200 psi, but the thing is, my configuration is kind of different then others since my compressor is in the garage. I am using a old c02 tank as my chamber and i fill my c02 tank and then i screw it into an asa instead of filling it through the "in" slot since my compressor is in the garage and cant be used until tomorrow. I think that may be the problem.

I also GGDT'd it and for some reason, it says it is only shooting at 196 fps. The barrel is a 1/4" brakeline that is 29" long and the chamber, like i said, is a 20 oz c02 tank. Is the chamber way to big for the barrel? I want to try and make it shoot at least 600 fps or so. Thanks.
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Unread postAuthor: i-will » Fri Oct 03, 2008 11:13 pm

qev and piston valve is the same thing. look it up.

the kind they use in paintball guns are just smaller versions of the ones used in a spuddy.

if it's a store bought then u gotta buy a new rubber seal (piston). they're very cheap. even online.

if it's homemade then i stand by my first comment.

anything else to say, jook13?
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Unread postAuthor: jook13 » Fri Oct 03, 2008 11:19 pm

but the thing is, my configuration is kind of different then others since my compressor is in the garage. I am using a old c02 tank as my chamber and i fill my c02 tank and then i screw it into an asa instead of filling it through the "in" slot
you lost me... sorry. you are basically saying you fill up a tank so that it is portable? what do you mean by "asa"?

I believe that some QEV's need to be filled up through the "in" slot and some allow you to fill up through the "in" or "chamber" slot. Maybe take that info and experiment a little? if I was way off base with my interpretation then sorry.
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Unread postAuthor: blind909 » Fri Oct 03, 2008 11:23 pm

Could you get up a pic, that would really help and your pilot valve is supposed to be in the exhaust side, and your barrel in the in.
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Unread postAuthor: NoXi » Fri Oct 03, 2008 11:27 pm

jook13 wrote:
but the thing is, my configuration is kind of different then others since my compressor is in the garage. I am using a old c02 tank as my chamber and i fill my c02 tank and then i screw it into an asa instead of filling it through the "in" slot
you lost me... sorry. you are basically saying you fill up a tank so that it is portable? what do you mean by "asa"?

I believe that some QEV's need to be filled up through the "in" slot and some allow you to fill up through the "in" or "chamber" slot. Maybe take that info and experiment a little? if I was way off base with my interpretation then sorry.


Yea i think thats the problem.

blind909 wrote:Could you get up a pic, that would really help and your pilot valve is supposed to be in the exhaust side, and your barrel in the in.


Yea sure ill post it soon.
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Unread postAuthor: jook13 » Fri Oct 03, 2008 11:29 pm

qev and piston valve is the same thing. look it up.

the kind they use in paintball guns are just smaller versions of the ones used in a spuddy.

if it's a store bought then u gotta buy a new rubber seal (piston). they're very cheap. even online.

if it's homemade then i stand by my first comment.

anything else to say, jook13?


its true, kinda. a qev is basically a piston valve but it is machined and premade. I would imagine that a commercially available valve wouldnt have "my guess is that it is not sealing cuz it is not a perfect 90 degree cut or that the material used for the seal isn't doing it's job right
". and if it did the valve is faulty. I personally wouldnt try to fix a valve that I bought if this was the case, I would try to get a refund or a new properly working valve.

But this is besides the point. it sounds kinda like he is filling his spuddy gunny from the wrong place.
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Unread postAuthor: NoXi » Fri Oct 03, 2008 11:35 pm

ImageImage

The silver thing with the gauge on it is called an ASA. It is a term for paintballers which is the thing that you plus your air tank too.

It looks pretty weird right now. The barrel is not connected as you can see.

Here is another pic.

ImageImage


I also GGDT'd it and for some reason, it says it is only shooting at 196 fps. The barrel is a 1/4" brakeline that is 29" long and the chamber, like i said, is a 20 oz c02 tank. Is the chamber way to big for the barrel? I want to try and make it shoot at least 600 fps or so. Thanks.
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Unread postAuthor: i-will » Fri Oct 03, 2008 11:54 pm

i agree with jook13.

i'd return it and exchange it for another.

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Unread postAuthor: mark.f » Sat Oct 04, 2008 12:42 pm

You're filling from the wrong side of the Q.E.V. You should fill from the pilot side.

Also, how do you shut off gas flow from the ASA adapter? You have to be able to shut off gas-flow from it to be able to pilot the valve.
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