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Sprinkler vs. QEV

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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Sprinkler vs. QEV

Unread postAuthor: skyjive » Thu Aug 21, 2008 11:56 pm

I'm working on a .5" copper gun that I plan to run of CO2 at about 120 psi. I have at my disposal a modded sprinkler (1") from BCARMS and a 3/4" QEV from mcmaster. My options are essentially
1) Use the sprinkler, which would work fine
2) Use the QEV with the sprinkler as a pilot valve

Would the QEV have significantly better flow/ opening time when piloted by the sprinkler as opposed to simply using the sprinkler as the primary valve?
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Unread postAuthor: jackssmirkingrevenge » Thu Aug 21, 2008 11:59 pm

For a half inch calibre, I'd go with the QEV and a blowgun pilot.
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Unread postAuthor: brogdenlaxmiddie » Fri Aug 22, 2008 12:02 am

I very much agree with JSR, no need to have super piloting in a small launcher like that.
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Unread postAuthor: skyjive » Fri Aug 22, 2008 12:13 am

Yeah that's what I thought at first, but the gun was pathetically underpowered at 200 psi with a QEV/blowgun and I think it wasn't piloting fast enough. So I don't want to take any chances with the pilot setup being inadequate. I of course realize its overkill, but as long as I have the sprinkler I might as well use it, right? I mean, there's not a point at which increasing pilot valve size actually hurts, there's just a point at which it doesn't really help either.
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Unread postAuthor: jackssmirkingrevenge » Fri Aug 22, 2008 12:22 am

skyjive wrote:the gun was pathetically underpowered at 200 psi with a QEV/blowgun and I think it wasn't piloting fast enough.


What's your chamber size and barrel length? Could it be that your expectations of power were unrealistic?
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Unread postAuthor: skyjive » Fri Aug 22, 2008 12:34 am

200 psi, chamber size ~30 in3 barrel length 68". As a baseline test I compared it to a PVC gun at 60 psi with 55 in3 and the same barrel caliber and length and it was far weaker, so I concluded there must be a valve problem.
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Unread postAuthor: frankrede » Fri Aug 22, 2008 1:15 am

That makes no sense, A working QEV will outpower a sprinkler easily.
You obviously were having some problems in your setup.
Did you have your air input running while you tried to pilot it?
Lets see a pic of your QEV
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Unread postAuthor: Pilgrimman » Fri Aug 22, 2008 2:49 am

It could be that, but I notice with my cannons that a bigger chamber always helps. Of course, that may just be an increase in PERCEIVED power from the extra noise... Bottom line, it makes no sense that a QEV is underperforming :?
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Unread postAuthor: psycix » Fri Aug 22, 2008 8:33 am

A QEV is always more powerful then a sprinkler of the same size.
Do not use a 1" sprinkler to pilot a QEV, it will give excessive pilot volume.
If you want optimal results for your QEV, use another QEV to pilot it ;)
Pilot valves are more about opening time then flow.
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Unread postAuthor: jonnyboy » Fri Aug 22, 2008 9:15 am

A qev is better. By the way if your running co2 with a copper gun why not pump up the pressure?
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Unread postAuthor: skyjive » Fri Aug 22, 2008 11:50 am

@ jonnyboy: Since the QE apparently wasn't working, I took the target pressure down to 120 so I could use a sprinkler valve

So I guess I should give a QEV/blowgun setup another shot, its possible that my pilot volume was too large since I had to have some 3/4" fittings on the pilot side of the valve in order to plumb in the quick change adapter for the 12g cartridges. Is it possible to fill a QEV setup from the chamber side instead? This would reduce pilot volume by allowing only the blowgun on the pilot side of the QEV.
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Unread postAuthor: POLAND_SPUD » Fri Aug 22, 2008 12:04 pm

3/4" is a lot for a blowgun...

wait a second.... have you diconected the CO2 source (or closed it's flow) before piloting ??
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Unread postAuthor: skyjive » Fri Aug 22, 2008 2:31 pm

The gun fills off 12g cartridges, the whole cartridge is dumped into th chamber so there should not be any pressure higher than chamber pressure coming from the cartridge once its finished dumping into the chamber. So I don't think that's the problem, although I do leave it attached and don't unscrew it before firing.

If 3/4" is too much for a blowgun to pilot efficiently (which I suspect is true), then what kind of pilot valve would be more appropriate?
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Unread postAuthor: brogdenlaxmiddie » Fri Aug 22, 2008 2:43 pm

1/2" ball valve
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Unread postAuthor: ramses » Fri Aug 22, 2008 2:59 pm

You can't fill from the chamber with a qev. Image

Keep in mind that unless there is a valve closed between the pilot volume and the co2 cartridge, the CO2 cartridge becomes part of the pilot volume.

You could see if Modding the blowgun helps.
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