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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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Unread postAuthor: Lockednloaded » Sat Sep 04, 2010 11:43 am

Gun Freak wrote: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.


what numbers do you have to back this up? I've used both and a BV out performs as a pilot valve every time.
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Unread postAuthor: Gun Freak » Sat Sep 04, 2010 12:02 pm

No numbers, quoted from the Hubb Library. Just checked, however Hubb recently edited The Sprinkler Vavle file, which is where the tutorial for modifying the blowgun can be found... anywho, it wasn't there anymore. But if you have ever modified a blowgun you would know that it is possible to do it good enough to get better flow than a the ball valve equivalent.
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Unread postAuthor: Lockednloaded » Sat Sep 04, 2010 12:15 pm

they may have better opening time, but you cant drill a full 1/4" port in a blowgun. Even if you could, the flow is still restricted by the piston rod even if it is filed down.
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Unread postAuthor: POLAND_SPUD » Sat Sep 04, 2010 1:57 pm

It doesn't sound like 100 psi... there must be a leak
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Unread postAuthor: BeaverRat » Sat Sep 04, 2010 7:11 pm

Nope, it is 100 PSI, verified by an attached bike pump I dunked it underwater, and there are no leaks. When I actuate the blowgun, a small amount of air comes out the barrel and more comes out the blowgun. I even brought it up to 260 PSI, and still very little comes out the barrel, the majority comes out the blowgun.
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Unread postAuthor: MrCrowley » Sat Sep 04, 2010 7:16 pm

A lot of bike pump gauges are very bad and can be off by even 40PSI. I would put a gauge on the chamber, so you know the chamber pressure for sure and replace the blowgun with a ball valve.
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Unread postAuthor: Technician1002 » Sat Sep 04, 2010 7:23 pm

I hate to state the obvious. A piece of pipe tape or other obstruction has entered the valve and is producing the leak from the chamber to the pilot. This is preventing the valve from opening. Disassemble the valve and remove the contamination and try again. I'm surprised this has not been mentioned yet. There should be very little flow from the chamber to the blowgun trigger. Because there is, there is a problem. :roll:
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Unread postAuthor: POLAND_SPUD » Sat Sep 04, 2010 7:27 pm

I've never had this problem... never
Sometimes I even put stuff like sand into the barrel and a lot of other stuff.. yet nothign has ever happend

It is also possible that the piston has been inserted upside-down.. that would make sense becasue the thing really does not sound like 100 psi
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Unread postAuthor: BeaverRat » Sat Sep 04, 2010 8:39 pm

Nope, piston is correctly assembled. Even at 300 PSI, it sounds identicle, but a ton of air flows out the blowgun. I am going to return it and order this one instead:

http://www.fastenal.com/web/products/de ... 031&ucst=t

Can this QEV withstand 400-500 PSI?
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Unread postAuthor: MrCrowley » Sat Sep 04, 2010 8:44 pm

Have you looked for teflon tape or such in the valve like Tech101 said? Have you tried changing to blowgun to a ball valve? Can you take a picture of the diaphragm?
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Unread postAuthor: BeaverRat » Sat Sep 04, 2010 8:50 pm

Yep, no teflon tape in the diaphragm, and yep, no success with a 1/4th inch ball valve, same scenario. Most of the air just rushes out the pilot valve. This really puzzles me, a 1 inch sprinkler valve actuates perfectly from a blowgun and it has a larger diaphram than this QEV.
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Unread postAuthor: POLAND_SPUD » Sat Sep 04, 2010 9:14 pm

That one is even better that teh one you had. That's a european QEV

anyway there must be something wrong with your setup... you just have to find out what

Nope, it is 100 PSI, verified by an attached bike pump I dunked it underwater, and there are no leaks
Do that test again...
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Unread postAuthor: BeaverRat » Sat Sep 04, 2010 9:17 pm

Completed, no leaks.
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Unread postAuthor: Mr.Sandman » Sat Sep 04, 2010 10:27 pm

Try a ball valve, and let us know how it works, my hunch is that your problem lies with the blowgun. Contrary to what gun freak said, a blowgun will never offer the same flow and performance as a 1/4" ball valve.
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Unread postAuthor: Insomniac » Sat Sep 04, 2010 10:45 pm

Two posts ago he said he had no luck with a ball valve.... Read, people! :P
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