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why the heck doesn't this thing work?

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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why the heck doesn't this thing work?

Unread postAuthor: pnematicrookie » Fri Feb 08, 2008 12:04 pm

after only gettin' to 40psi, you here air from the qev, and when i unhook the air compressor, the air quickly leaves the barrel part of the qev...i am begging for help...ive been tryna figure it out all last night and this morning :cry:
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Unread postAuthor: jackssmirkingrevenge » Fri Feb 08, 2008 12:06 pm

Is the QEV new? Take it apart and see if the internals are clean, you could have some dirt inside that is preventing it from sealing completely.

when i unhook the air compressor, the air quickly leaves the barrel part of the qev


Alternatively, is there a slight leak somewhere in the fittings at the exhaust side of your QEV?
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Last edited by jackssmirkingrevenge on Fri Feb 08, 2008 12:08 pm, edited 1 time in total.
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Unread postAuthor: goathunter » Fri Feb 08, 2008 12:08 pm

Is the flow correct on the QEV.Look at the little arrow on the side.Is it pointing away from the chamber?
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Unread postAuthor: jackssmirkingrevenge » Fri Feb 08, 2008 12:11 pm

goathunter wrote:Is the flow correct on the QEV.Look at the little arrow on the side.Is it pointing away from the chamber?


From what I know of that style of QEV it's mounted the right way in the pictures.
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Unread postAuthor: pnematicrookie » Fri Feb 08, 2008 12:30 pm

yeah the arrow is pointing towards the barrel, but there's no other leaks in the other fitting, i'll take the qev apart and check it out
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Unread postAuthor: POLAND_SPUD » Fri Feb 08, 2008 12:45 pm

JSR has made a typo, he ment that there may be a leak on the pilot side - not the exhaust side....

the best thing you can do is to put the whole gun under water to see where is it leaking...

I am 75% sure that it is caused by a leak on pilot side...
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Unread postAuthor: potatoflinger » Fri Feb 08, 2008 3:55 pm

Yeah, probably a leak on the pilot side, Did you use thread seal tape on the pilot side, because I can't see any coming out around the fittings? If you didn't use thread seal tape, there's your problem.
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Unread postAuthor: STHORNE » Fri Feb 08, 2008 7:31 pm

yeah, without thread seal tape on a pneumatic with threaded parts, your almost destined to fail.

if that doesn't work, try soldering
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Unread postAuthor: pnematicrookie » Fri Feb 08, 2008 10:42 pm

well i used teflon (i think thats spelled wrong) tape, but i really dont think thats the problem. do u think there's a possibility the orange sealing thingy in the qev was put in backwards? ....i know thats a little far'fetched but...im really frustrated, i bought 2 qevs and cant even use the damn things
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Unread postAuthor: MrCrowley » Fri Feb 08, 2008 10:55 pm

There's a thread on the UKSGC that was also linked to from JSR (IIRC) on this forum, that shows the internals of that type of QEV.

And you spelled teflon correctly.

You do close the ball valve before removing the air compressor right?

If you have no leaks, that's the only problem I can see.

You disconnect the compressor from the schrader while leaving the ball valve open. If it's closed, so the schrader valve is isolated, when the compressor is disconnected, the QEV should not pilot.

Maybe the ball valve is leaking?
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Unread postAuthor: jackssmirkingrevenge » Sat Feb 09, 2008 12:27 am

POLAND_SPUD wrote:JSR has made a typo, he ment that there may be a leak on the pilot side - not the exhaust side...


That's what I meant, but I figured he wouldn't understand if I said "pilot".

There's a thread on the UKSGC that was also linked to from JSR (IIRC) on this forum, that shows the internals of that type of QEV.


Inside a QEV ;)
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Unread postAuthor: POLAND_SPUD » Sat Feb 09, 2008 6:55 am

piston has to be oriented in this way but anyway i doubt it is casued by the piston..... It is most likely a leak on the pilot side... somethimes it just doesn't seal well.....

you should really pump the gun and put it underwater
to see where it leaks... it would help you and us a lot....

maybe you put the teflon tape in the incorect way or you have not screwed the fittings tightly or even the BV and the blowgun are leaking? the easiest way to find it out is to put the gun underwater - really (you can remove the barrel if you want to - it won't be needed for this )
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Unread postAuthor: pnematicrookie » Sat Feb 09, 2008 5:14 pm

alright thanx for the help guys, now let me stop asking to many questions before MrCrowley comes to my house and blast me with a super duper advanced hybrid cannon :cry: lol
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Unread postAuthor: MrCrowley » Sat Feb 09, 2008 5:17 pm

Only if you pay for the airline ticket to get there :wink:

So have you tried what I suggested?
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Unread postAuthor: pnematicrookie » Tue Feb 12, 2008 8:50 am

well guys i figured it out, jackssmirkingrevenge was right, it was all kinds of dust and crap on the orange thingy so i just wiped it off pretty good and it worked :) BUT it only goes to like 80psi, and i changes the chamber too, its bascially a 1 1/4 elbow to a 18in 1 1/4" tube...so shouldnt it have more volume?
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