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High Pressure - Low Volume Chamber?

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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High Pressure - Low Volume Chamber?

Unread postAuthor: BeaverRat » Tue Sep 21, 2010 6:22 pm

Hello,
Here is the setup of my newest cannon:

.80" X 18" chamber (about 9 inches cubed)
.80" X 30" barrel (about 15 inches cubed)
3/4" QEV

Anyway, at 400 PSI (from a fridge compressor) what kind of performace should I expect? I fired it, and it was not too immpressive...

Thanks
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Last edited by BeaverRat on Tue Sep 21, 2010 8:26 pm, edited 1 time in total.
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Re: High Pressure - Low Volume Chamber?

Unread postAuthor: velocity3x » Tue Sep 21, 2010 6:39 pm

BeaverRat wrote:.80" X 18" chamber (about 9 inches squared)
.80" X 30" barrel (about 15 inches squared)


That should read "Cubed".....not squared. As for performance, your chamber might be to small. I use a 1:1 ratio with 1kpsi.
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Re: High Pressure - Low Volume Chamber?

Unread postAuthor: dewey-1 » Tue Sep 21, 2010 6:50 pm

BeaverRat wrote:Hello,

.80" X 18" chamber (about 9 inches squared)

9 cubic inches

.80" X 30" barrel (about 15 inches squared)

15 cubic inches

3/4" QEV


edit; velocity posted faster
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Unread postAuthor: Lockednloaded » Tue Sep 21, 2010 7:11 pm

What's your pilot valve? you should still be getting fairly decent performance
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Unread postAuthor: BeaverRat » Tue Sep 21, 2010 8:28 pm

Well, the pilot valve is a blowgun... I can get better performance off my piston valved PVC cannon (same bore) at 100 PSI vs the metal QEV cannon at 450 PSI. The chamber of the PVC cannon is roughly 50 inches cubed and it has a 60 inch barrel.
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Unread postAuthor: Lockednloaded » Tue Sep 21, 2010 9:32 pm

A blowgun is usually not a sufficient pilot valve even a heavily modded one. Contrary to popular belief, a 1/4" BV is way better. Does the QEV seem at all out of the ordinary to you?
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Unread postAuthor: BeaverRat » Tue Sep 21, 2010 9:44 pm

If blowgun isn't a proper pilot valve, than why do we mod sprinkler valves (which have even bigger porting than my QEV) with blowguns to increase performance?
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Unread postAuthor: Lockednloaded » Tue Sep 21, 2010 10:02 pm

Have you ever put a larger pilot valve on a Sprinkler valve? It hugely increases performance. Blowguns are just used because of the trigger like feel
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Unread postAuthor: BeaverRat » Tue Sep 21, 2010 11:59 pm

I am thinking about using a 1/4th inch QEV actuated by a blowgun... That should work. Since I like the short 30 inch barrel, I will also increase the chamber volume to match a 1:1 C:B ratio (or should I increase the chamber avove a 1:1 ratio?).

Thanks
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Unread postAuthor: Technician1002 » Wed Sep 22, 2010 12:57 am

I found the orifice size and the edges in the flow path greatly affect performance in valves operating at the transonic flow rates. This is one reason pistons do so well. The QEV may have limitations due to the orifice size and the edges entering and exiting the valve.

I know this does not solve the problem, but may give some insight into the limits on performance.

A 3/4 inch QEV has step size transitions entering the piston chamber and exiting with a 90 degree bend in a high turbulence flow area. I think this limits performance.

Fixing the trigger might not fix the flow problem.

A small chamber may vent out the barrel faster than the pilot pressure can vent which may prevent the valve from fully opening and remaining open for the duration of the shot. This can be tested by using a larger chamber and seeing if the performance greatly improves by holding the pressure in the chamber higher longer to hold the valve open.
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Unread postAuthor: BeaverRat » Wed Sep 22, 2010 5:12 pm

Thanks, ill try a bigger chamber... Strange thing happened today: I recieved 10 3/4th inch QEV valves in the mail (I did not order them).
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Unread postAuthor: Gun Freak » Wed Sep 22, 2010 5:19 pm

POLAND_SPUD wrote::shock: (WTF??!!)
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Unread postAuthor: Lockednloaded » Wed Sep 22, 2010 5:40 pm

You Lucky SOB! :o
what company screwed up so bad?

And a 1/4" QEV should solve the piloting problem,

Oh and if your planning to get rid of some, I'm your man :lol:
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Unread postAuthor: Gun Freak » Wed Sep 22, 2010 5:58 pm

Hell, set up a cascading qev series to pilot that one of yours, it should have no problems :D
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Unread postAuthor: BeaverRat » Wed Sep 22, 2010 6:08 pm

Well, the 1/4th inch qev pilot solved the problem, it works perfect now. The question is, what to do with 10 qev's...
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