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QEV, 3 way valve, slide valve help

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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QEV, 3 way valve, slide valve help

Unread postAuthor: 1nxtmonster » Fri Feb 07, 2014 5:38 pm

So..... i'm pretty close to finishing my qev airsoft gun. But the slide valve isn't really working well as a trigger b/c of friction, consistency, etc. So what kind of manual 3 way valve would work well as a pilot for a qev that could be filled through, then when you trigger it it blocks off from the supply and pilots the qev? (Like a slide valve)

Thx
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Last edited by 1nxtmonster on Sat Feb 08, 2014 2:09 pm, edited 1 time in total.

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Re: QEV, 3 way valve, slide valve help

Unread postAuthor: jackssmirkingrevenge » Sat Feb 08, 2014 9:08 am

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Re: QEV, 3 way valve, slide valve help

Unread postAuthor: 1nxtmonster » Sat Feb 08, 2014 10:51 am

I wasn't able to find in that thread if those 3 ways were normally open or closed. Do you remember?
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Re: QEV, 3 way valve, slide valve help

Unread postAuthor: jackssmirkingrevenge » Sat Feb 08, 2014 11:19 am

Normally open, but Brian suggested a good way to fix this:

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Re: QEV, 3 way valve, slide valve help

Unread postAuthor: 1nxtmonster » Sat Feb 08, 2014 11:58 am

Ahhh...how bout this: http://www.ebay.com/itm/MEAD-MV-50-NEW- ... 35c017e55b

Due to size constraints, i'm not sure if it can fit in the gunstock. So I was doing some thinking, and came up with a shut-off valve:

Screen Shot 2014-02-08 at 11.58.18 AM.png
Screen Shot 2014-02-08 at 11.58.18 AM.png (28.63 KiB) Viewed 1915 times
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Re: QEV, 3 way valve, slide valve help

Unread postAuthor: jackssmirkingrevenge » Sun Feb 09, 2014 9:46 am

How does the "shut off valve" work exactly?
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Re: QEV, 3 way valve, slide valve help

Unread postAuthor: 1nxtmonster » Sun Feb 09, 2014 2:36 pm

What it was supposed to do, was work like a slide valve in the fact that it should shut off the air source while piloting. I built one, and it kind of works, but not really any better than just putting a flow restrictor in place behind the pilot.

If I make a cast epoxy qev piston, and spring behind it, could I chamber fill and pilot from behind with like a blowgun or something simmer?
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Re: QEV, 3 way valve, slide valve help

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Re: QEV, 3 way valve, slide valve help

Unread postAuthor: jackssmirkingrevenge » Sun Feb 09, 2014 4:50 pm

1nxtmonster wrote:If I make a cast epoxy qev piston, and spring behind it, could I chamber fill and pilot from behind with like a blowgun or something simmer?


Pretty much what I did here using a schrader as a pilot.



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Re: QEV, 3 way valve, slide valve help

Unread postAuthor: 1nxtmonster » Sun Feb 09, 2014 8:59 pm

Yep, pretty much that. I'm making a pilot valve like this:

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Last edited by jrrdw on Mon Feb 10, 2014 8:44 am, edited 1 time in total.
Reason: Fixed video.

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Re: QEV, 3 way valve, slide valve help

Unread postAuthor: 1nxtmonster » Sun Feb 16, 2014 3:48 pm

Sorry for double post, but does anyone know a reason for a drastic power loss in a qev slide valve setup? Same pressure
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Last edited by 1nxtmonster on Mon Feb 17, 2014 3:58 pm, edited 1 time in total.

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Re: QEV, 3 way valve, slide valve help

Unread postAuthor: bravootome » Mon Feb 17, 2014 7:33 am

1nxtmonster wrote:Sorry for double post, but does anyone know a reason for a drastic power loss in a rev slide valve setup? Same pressure

is the sound more a fss than a boom ?
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Re: QEV, 3 way valve, slide valve help

Unread postAuthor: 1nxtmonster » Mon Feb 17, 2014 10:23 am

Yeah, instead of a nice loud "CRACK" its more like" sssshhpow"
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Re: QEV, 3 way valve, slide valve help

Unread postAuthor: jackssmirkingrevenge » Mon Feb 17, 2014 10:32 am

1nxtmonster wrote:Yeah, instead of a nice loud "CRACK" its more like" sssshhpow"


Have you opened your QEV to see what state your piston is in? Did you lube it with WD40 or something similarly bad for rubber?
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Re: QEV, 3 way valve, slide valve help

Unread postAuthor: 1nxtmonster » Mon Feb 17, 2014 3:07 pm

I opened the qev, and the piston is fine. I didn't lube it with anything bad, but some gunk had built up from lubing the slide valve. So i cleaned the qev out, cleaned the slide valve out, and removed a few cc's of dead space from my loading mech. In the process i broke something, so the epoxy is curing.

Well, the epoxy is cured enough that I took a few shots. Power is good, not sure if it was a problem with the qev, slide valve, or dead space in the loading mech.

**Edit** Under pressure, the slide valve doesn't want to move. The more pressure, the harder it is to move. I am using this slide valve:

41RHQmwGPBL._SL500_AA300_.jpg
41RHQmwGPBL._SL500_AA300_.jpg (10.19 KiB) Viewed 1610 times


Any ideas?
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Re: QEV, 3 way valve, slide valve help

Unread postAuthor: bladeul2006 » Sun Feb 23, 2014 2:46 am

thats how it works. look at my build pneumatic-cannon-database/topic25393.html
basically the same idea on my pilot, just machined by me. At 400 psi it's fairly hard to pull it back. I use to lube it with silicon oil for a easier pull
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