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HELP with Legris 1/4" 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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HELP with Legris 1/4" QEV

Unread postAuthor: Humancarpentry » Sun Mar 23, 2014 7:05 pm

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-Plated-Brass-Exhaust-Female/dp/B00ANVTNP4/ref=pd_rhf_ee_p_imgnr_4

Image

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?
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Re: HELP with Legris 1/4" QEV

Unread postAuthor: POLAND_SPUD » Mon Mar 24, 2014 2:45 am

Add a chamber to port A - otherwise it won't seal.
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Re: HELP with Legris 1/4" QEV

Unread postAuthor: jackssmirkingrevenge » Mon Mar 24, 2014 6:37 am

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.
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Re: HELP with Legris 1/4" QEV

Unread postAuthor: POLAND_SPUD » Mon Mar 24, 2014 9:40 am

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.
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Re: HELP with Legris 1/4" QEV

Unread postAuthor: jackssmirkingrevenge » Mon Mar 24, 2014 9:58 am

If you want to fill from the chamber side, a pinhole in the edge of the QEV diaphragm will do the trick.
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Re: HELP with Legris 1/4" QEV

Unread postAuthor: Humancarpentry » Mon Mar 24, 2014 11:24 am

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.
Image

I am using 2" PVC pipe, with the QEV intended to sit right behind the barrel.
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Re: HELP with Legris 1/4" QEV

Unread postAuthor: jackssmirkingrevenge » Tue Mar 25, 2014 4:31 am

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.
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Re: HELP with Legris 1/4" QEV

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Re: HELP with Legris 1/4" QEV

Unread postAuthor: Humancarpentry » Wed Mar 26, 2014 12:20 am

Sweet. Thanks Jack. Will try it.
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Re: HELP with Legris 1/4" QEV

Unread postAuthor: Humancarpentry » Thu Apr 24, 2014 7:08 pm

OK, finally got around to this. Here's a pic of the QEV valve disassembled. Where exactly should I make the pinhole?
Legris QEV.jpg
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Re: HELP with Legris 1/4" QEV

Unread postAuthor: jackssmirkingrevenge » Fri Apr 25, 2014 5:50 am

here.jpg
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Re: HELP with Legris 1/4" QEV

Unread postAuthor: Humancarpentry » Fri Apr 25, 2014 11:13 pm

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