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Q.E.V

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: jon_89 » Tue Dec 25, 2007 7:56 pm

I am going to get a quick exhaust valve but I cant find one online. Where can I get one for cheap? I have looked on mcmaster but cant find them. One more question can they handle more than the pressure they are rated for? I ask because the ones I have seen online say 145 psi max but I see people taking them to 150 psi and above. Thanks
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Unread postAuthor: VH_man » Tue Dec 25, 2007 8:35 pm

page 941..... Right angle valves near the bottom of the page.
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Unread postAuthor: jon_89 » Tue Dec 25, 2007 8:42 pm

Can i take it above 125 psi though? My plan is to use a .25 inch barrel do i want a valve the size of the barrel or the size of the chamber?
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Unread postAuthor: DYI » Tue Dec 25, 2007 8:48 pm

Can i take it above 125 psi though? My plan is to use a .25 inch barrel do i want a valve the size of the barrel or the size of the chamber?


GGDT should answer that question. Also, I don't think you told us what size your chamber was.
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Unread postAuthor: Hotwired » Tue Dec 25, 2007 8:50 pm

All pneumatic components have a pressure rating. the one stamped on them has a safety factor plus operating considerations.

e.g. a QEV might say 150psi but the diaphragm/piston will hold up to 300

...and we also know a basic metal blowgun has 30psi on it but is very definitely not going to fail even at 300psi, that one is for ensuring conventional users dont use excessive force to blow material about.

Unless you write to the manufacturers asking them the pressure it fails at and having your own safety margin your only reference is if other people have the exact same type and the pressure they use it at.

Someone has to test it personally to destruction to know but you can be sure that 125psi is not just below its failing pressure.
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Unread postAuthor: unisonmind » Tue Dec 25, 2007 8:56 pm

.....
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Last edited by unisonmind on Wed Dec 26, 2007 6:52 pm, edited 3 times in total.
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Unread postAuthor: POLAND_SPUD » Tue Dec 25, 2007 9:14 pm

what about 400 psi... would 'normal' QEV work at this pressure? or is it just too much?
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Unread postAuthor: cwazy1 » Tue Dec 25, 2007 11:47 pm

lol no, thats just really pushing it. i'd only take to around 200, 250MAX
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Unread postAuthor: jackssmirkingrevenge » Wed Dec 26, 2007 3:15 am

jon_89 wrote:do i want a valve the size of the barrel or the size of the chamber?


No matter how big your valve is, the ultimate flow restriction is always the barrel, so for your barrel anything above 1/2" is a waste.
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Unread postAuthor: pizlo » Wed Dec 26, 2007 10:29 am

so jack, if my barrel is 1/4 will I get a performance difference by using a 1/2 valve, instead of a 1/4 valve?
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Unread postAuthor: Hotwired » Wed Dec 26, 2007 10:45 am

Yes.

A 1/4" barrel can only allow so much flow but a 1/2" valve will allow that maximum flow to be reached faster than using a 1/4" valve.

The laws of diminishing returns applies though so using a 1" valve instead of a 1/2" valve for a 1/4" barrel isn't going to have a worthwhile effect.
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Unread postAuthor: jackssmirkingrevenge » Wed Dec 26, 2007 10:50 am

As Hotwired said above, in spite of being the same nominal diameter, a 1/4" QEV vill not have the same flow as 1/4" tubing, but a 1/2" valve should exceed it comfortably.
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Unread postAuthor: Infernal Maveric » Wed Dec 26, 2007 3:13 pm

You can use QEVs at 400 PSI w/o trouble. I have taken many QEVs up to, and past the 400PSI mark and they work great.

The ones I have been using ar Detrol QEVs. 12mm in/out/exh portings.

As mentioned, for a 1/4" barrel, a 1/2" would be best, as it allows maximin flow through, and out of the QEV. It may restrict flow slightly, but it will give you good potential for use in future cannons.
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Unread postAuthor: origin unknown » Wed Dec 26, 2007 3:22 pm

Get them from fastenal under "exhaust valves".
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Last edited by origin unknown on Fri Dec 28, 2007 4:30 pm, edited 1 time in total.
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Unread postAuthor: jon_89 » Wed Dec 26, 2007 3:34 pm

Were do you get the detrol valves from?
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