High Pressure - Low Volume Chamber?

[BeaverRat]

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

[velocity3x]

.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.

[dewey-1]

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

[Lockednloaded]

What's your pilot valve? you should still be getting fairly decent performance

[BeaverRat]

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.

[Lockednloaded]

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?

[BeaverRat]

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?

[Lockednloaded]

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

[BeaverRat]

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

[Technician1002]

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.

[BeaverRat]

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).

[Gun Freak]

(WTF??!!)

[Lockednloaded]

You Lucky SOB!
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

[Gun Freak]

Hell, set up a cascading qev series to pilot that one of yours, it should have no problems

[BeaverRat]

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