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3/4 QEV Won't Actuate

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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3/4 QEV Won't Actuate

Unread postAuthor: BeaverRat » Thu Sep 02, 2010 11:46 pm

Hello, I recently finished a 3/4 inch Deltrol (mcmaster) QEV cannon with a 3/4th inch barrel, but it doesn't seem to work. I am filling and piloting from the pilot side of the valve. To pilot the QEV, I am using a blowgun. The problem is, at any pressure (I ran it mainly at 200 PSI), when I pull the blowgun trigger, the QEV doesn't actually actuate, the air from the chamber just blows out the blowgun.

Any ideas?

Thanks
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Unread postAuthor: hi » Thu Sep 02, 2010 11:50 pm

You may have it hooked up wrong. If not you might need a faster way you pilot it, but a blowgun should be plenty to open the valve.
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Unread postAuthor: BeaverRat » Fri Sep 03, 2010 12:11 am

Im almost positive I have it hooked up right... I have used QEV's before, but never had this problem. Here is how I have it hooked up.

Exhaust - barrel
Cylinder - chamber
In - pilot/fill valve
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Unread postAuthor: MrCrowley » Fri Sep 03, 2010 1:22 am

How much pilot volume do you have? You shouldn't have a problem using a blowgun (although a ball valve would be better) unless you have a big pilot volume. Have you tried using a ball valve or something to pilot it?
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Unread postAuthor: BeaverRat » Fri Sep 03, 2010 9:26 am

I have virtually no pilot volume: I have a 3/4 to 1/4 reducer, then a tee connected to the back. The schrader and blowgun connect on the tee.
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Unread postAuthor: POLAND_SPUD » Fri Sep 03, 2010 9:36 am

Pics help a lot, you know ?? Post it here then we might be able to work out what the problem is

I've never heard about a defective QEV so probably you already got the right answer...
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Unread postAuthor: BeaverRat » Fri Sep 03, 2010 5:41 pm

I will post pics and a video later today.

Thanks guys
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Unread postAuthor: jackssmirkingrevenge » Fri Sep 03, 2010 11:30 pm

Have you tried shifting the piston manually? Could it be jammed or torn?
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Unread postAuthor: BeaverRat » Sat Sep 04, 2010 12:58 am

Yep, I took it all apart, the piston is in perfect shape. I really don't understand how it couldn't work. When pushed against the barrel, the piston equilization hole is so small, a blowgun should be able to easily pilot it with the miniscule pilot volume I have. Instead, all the pressure just drains out of the blow gun.
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Unread postAuthor: MrCrowley » Sat Sep 04, 2010 1:07 am

How big is your chamber? Do you have a gauge on your chamber? I remember once with a sprinkler valve I had, I filled from the pilot side but it didn't fill the chamber. I know it seems obvious but may as well check to be sure.
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Unread postAuthor: POLAND_SPUD » Sat Sep 04, 2010 1:20 am

check if the blowgun is connected in the right way
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Unread postAuthor: BeaverRat » Sat Sep 04, 2010 1:32 am

How would the blowgun not be connected in the right way? I don't want to look like a fool, but it isn't rocket science putting together a QEV cannon.

McCrowly: I did think of that, but the shape of the piston seams to me like it would allow the pressure to push past the sides. I do not have a pressure gauge on the chamber, I rely on the pump.

Here is a video:

http://www.youtube.com/watch?v=eH-ieOkurl0
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Unread postAuthor: Gun Freak » Sat Sep 04, 2010 8:52 am

Try modding the blowgun or increasing size of the pilot valve.
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Unread postAuthor: Mr.Sandman » Sat Sep 04, 2010 10:01 am

Perhaps you should try a 1/4'" ball valve, It offeres much better flow than a blowgun.
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Unread postAuthor: Gun Freak » Sat Sep 04, 2010 11:24 am

A properly modded blowgun can achieve the same if not greater flow than a 1/4" ball valve while still offering the trigger-like feel that many desire from using a blowgun.
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