SpudFiles

So, I was persuaded by this forum to evolve from the modded Orbit sprinkler valve to a QEV. So far, things aren't working.

I got this valve here: http://www.amazon.com/Legris-Nickel-Pla ... _p_imgnr_4



It was only $8 when I got it, with free shipping, but I can't figure out how to get it to work.

It has a nice label on the side with ports labeled "P," "A," and "R." I assumed that P (on the right in the pic) was the pilot and hooked my blowgun to that. Then I hooked my pressure reservoir to A (the top) and the barrel to R (the left). In this config, the valve never seals and air just leaks down the barrel. I tried every other conceivable switch of the hookups and I just can't get the valve to seal at all. If I blow or apply vacuum in the "P" port, I can hear the diaphragm flipping, but it still doesn't want to work.

Is it defective? Am I hooking this up wrong?

Add a chamber to port A - otherwise it won't seal.

R - barrel, A - chamber and P - pilot is correct.

In this config, the valve never seals and air just leaks down the barrel.

The diaphragm is also a one-way valve - you have to fill from the pilot side, not the chamber side, otherwise what you described above will happen.

Damn I assumed he knew it has to be filled from pilot side. Though after rereading it isn't clear whether he's aware of that.

If you want to fill from the chamber side, a pinhole in the edge of the QEV diaphragm will do the trick.

Thanks, Jack. That explains my problem. I had stupidly assumed it would function in approximately the same manner as the modded Orbit Watermaster valve. I do have a chamber on the A side, but I was also filling from the A side. My intended use for this was to build an under-barrel M203 style paintball grenade launcher and power it with a take-off from the gun's air supply line. Filling from the pilot side is problematic for that design because doing this would require a slide-check valve to pilot instead of a blowgun trigger.

If I use the blowgun trigger here, I would end up venting the gun's air supply to the atmosphere which would waste enormous amounts of my limited air supply each time I fire it. The slide-check in-line valve would work, but would be far too bulky and long to incorporate into the design, which needs to sit in a limited space in the front of the foregrip on the gun. Also, the slide-check doesn't look at all like a trigger.

Also, I have no space with this design for any additional reservoir, as the gun's air supply line and expansion chamber will be acting as the air reservoir.

Any ideas on a way around this?

I am intrigued by the pinhole idea. Would that allow the valve to function in the way I wished it was?

For reference, here is a pic of the M203 type launcher I am trying to roughly replicate.


I am using 2" PVC pipe, with the QEV intended to sit right behind the barrel.

Humancarpentry wrote:I am intrigued by the pinhole idea. Would that allow the valve to function in the way I wished it was?

Yes, never tried it personally but many on the forum have done it. A light spring (really doesn't need to be substantial) behind the diaphragm in the pilot area helps with resealing but is not strictly necessary. Remember, you only need a small hole and depending on the material of the diaphragm, you might need to heat the pin first.

Sweet. Thanks Jack. Will try it.

OK, finally got around to this. Here's a pic of the QEV valve disassembled. Where exactly should I make the pinhole?

Sweet. Thanks, Jack. Will probably put this first one into my MKII version of my paintball mine...