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QEV in GGDT

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 in GGDT

Unread postAuthor: skyjive » Sun Dec 28, 2008 7:19 pm

First of all, does anyone have the GGDT specs for a McMaster 3/4" QEV? I couldn't find any, so I took one apart to measure my own, and so far I have:

Seat Diameter: 1.25 in
Dead Volume: 1.178 in^3
Piston Diameter: 1.75 in
Piston Mass: 8.3 grams
Pilot Volume: .98 in^3

What does "vent diameter" refer to, and how do I find the flow coefficient? Also, if anyone has numbers to check against mine that would be great.
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Unread postAuthor: btrettel » Sun Dec 28, 2008 7:32 pm

This thread suggests the Cv coefficient for McMaster-Carr's 3/4 inch valve is about 6: http://www.spudfiles.com/forums/dual-qe ... 12691.html
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Unread postAuthor: peeeto » Wed Jan 21, 2009 11:14 am

yes, using a Cv of ~6 worked well in predicting the velocity over a range of pressures for my tests.

please keep in mind that the 3/4" QEV was piloted by a smaller 1/4" QEV (as described in the post mentioned above), and that seemed to make a big difference in the way the 3/4" fired.

i didn't do any testing to estimate the Cv of the 3/4" QEV without using the smaller 1/4" QEV as a pilot, but do remember that, when using just a blowgun to pilot the 3/4" QEV, that the velocities were reduced, and the audible report of the GG was not nearly as "snappy", loud, or as satisfying as when the sucker is opened up fast...

hope this helps
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Unread postAuthor: john bunsenburner » Wed Jan 21, 2009 11:46 am

I hope you dont mind the little hijack of this thread but: What exactly is the valve coefficiency of a hammer valve and what is its seet diameter(is it just the ID of the pipe used or somehting else?)
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Unread postAuthor: peeeto » Thu Jan 22, 2009 12:56 pm

john, you might want to start a new thread when discussing a new topic - many people will pass by this thread title if they have read it before or aren't interested in the title, in which case, most forum members won't see your question...

unfortunately, i don't have experience with hammer valves. what manufacturer/model are you asking about? do you have a link to a spec. sheet, or even pictures? or is it a custom valve? ...just information to consider posting along with your new forum topic...

cheers,
peeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeto
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Unread postAuthor: torquey » Thu Jan 14, 2010 9:47 pm

OK, sorry to necropost here, but if the info in this thread is run against the hall site's specs for a 1" Orbit, the QEV simulates at 75% the fps the 1" does.

I thought 3/4 QEVs were supposed to outperform 1" modded sprinkler valves??
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Unread postAuthor: twizi » Thu Jan 14, 2010 10:09 pm

yes it does have better preformance
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Unread postAuthor: MrCrowley » Thu Jan 14, 2010 10:17 pm

twizi wrote:yes it does have better preformance

That's not the point... :roll:

He is saying that everyone says 3/4" QEV's out-perform 1" sprinkler valves, but using the parameters given for the 1" orbit sprinkler valve and the 3/4" McMaster QEV, the QEV only has 75% of the velocity of the sprinkler valve cannon.

You can't just agree that QEV's have better performance, next time think before you post or I will just delete it.

Back on topic, that is pretty interesting. I'll have to run in through GGDT and have a look for myself, probably a number of factors to think about. I wonder who ever said 3/4" QEVs are better in the first place...I've never compared the two myself before.
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Unread postAuthor: daberno123 » Fri Jan 15, 2010 6:53 pm

Everyone assumes a 3/4" QEV will outperform a 1" sprinkler valve based on the assumption that the QEV has a much better flow path than the sprinkler valve.

That being said, I'd like to see someone take some screen shots and post them so everyone can see.
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