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QEV question

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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QEV question

Unread postAuthor: vng21092 » Mon Jan 19, 2015 12:32 pm

I know this might sound redundant. But how do you get a QEV to work semi-auto when filling from chamber? In my last build I put a ball valve between chamber and tank to control the flow and volume, but I know that if I left the ball valve open and took a shot, all the air would rush out (happened couple times =\), ALL of it. What stops all the air from rushing out the moment the piston draws back? A strong spring would just prevent the valve from opening, and a weak one will just leave it open as all the air rushes out. And if there is no separation between chamber and tank, what controls the volume of air flowing through?
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Re: QEV question

Unread postAuthor: bravootome » Mon Jan 19, 2015 1:00 pm

A 3 way valve as pilot.
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Re: QEV question

Unread postAuthor: vng21092 » Mon Jan 19, 2015 1:48 pm

fill from chamber though... basically like your old 6mm QEV, how did yours seal off the barrel after every shot

Image
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Re: QEV question

Unread postAuthor: bravootome » Mon Jan 19, 2015 2:53 pm

[quote="vng21092"]fill from chamber though... basically like your old 6mm QEV, how did yours seal off the barrel after every shot

There is a 2nd valve( homemade ) attached to the pilot (see the scatch ) that closes and allow the pressure to built up behind the piston ,, the piston is sucked on the barrel and seals it
The spring behind the piston has no contribution to the process , it is only there to help inflate the gun..

Look on wizz2285 youtube channel trough his older videos, he has a tutorial...
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Re: QEV question

Unread postAuthor: vng21092 » Mon Jan 19, 2015 3:58 pm

Image

This picture? From what I understand the spring pushes the piston against the barrel, and it also pushes the bolt, blocking off the pilot port allowing the pilot to fill, readying for the next shot. And from my understanding of how a QEV works, the pressure drop in the pilot causes the high pressure air from the chamber to push back the piston and come out the barrel.

Now what I DON'T understand is, after the first shot, how is your barrel resealing if the pressure in the chamber is still higher than that of the pilot? Wouldn't air keep flowing out until equalization? Whats stopping the air from continuously flowing out?
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Re: QEV question

Unread postAuthor: bravootome » Tue Jan 20, 2015 1:27 am

No, the spring behind the piston only helps when i inflate the gun from 1 atm pressure ( otherwise the piston would be pushed back )

When the 2nd valve closes( after first shoot) , the pressure behind the piston and from inside the pilot egualise and infront of the piston it is created a sort of vacum ( by air rushing trough the barrel) and the piston is sucked back sealing the barrel...
It A pretty interesting process and far more advanced and better than hammer valves, in my opinion...
have a look: https://www.youtube.com/watch?v=Hd3oltz-HmA
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Last edited by bravootome on Tue Jan 20, 2015 4:46 am, edited 1 time in total.
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Re: QEV question

Unread postAuthor: jrrdw » Tue Jan 20, 2015 3:18 am

That video is private! Youtube should do away with that crap..... :roll:
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Re: QEV question

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Re: QEV question

Unread postAuthor: bravootome » Tue Jan 20, 2015 3:59 am

jrrdw wrote:That video is private! Youtube should do away with that crap..... :roll:


I dont get it...my video is a crap....or what ? it is private for a reason ...
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Re: QEV question

Unread postAuthor: bravootome » Tue Jan 20, 2015 4:47 am

bravootome wrote:
jrrdw wrote:That video is private! Youtube should do away with that crap..... :roll:


I changed the link, it should work now.
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Re: QEV question

Unread postAuthor: vng21092 » Tue Jan 20, 2015 8:31 am

No, the spring behind the piston only helps when i inflate the gun from 1 atm pressure ( otherwise the piston would be pushed back )

Why would it be pushed back if there's a spring behind it? Also you're filling from the pilot so that should push the piston forward on its own. O_o

I'm sorry I just really don't understand this concept of the vacuum thing. I looked through wyz2285 videos, couldn't find anything. Thanks though, I'll try to figure it out.
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Re: QEV question

Unread postAuthor: bravootome » Tue Jan 20, 2015 8:45 am

I am not filling from pilot, but from chamber( that "thing" on the pilot is the 2nd valve) . anyhow, if you want to build it, it will work.
Here you see the valve that makes it semiauto.
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Re: QEV question

Unread postAuthor: vng21092 » Tue Jan 20, 2015 10:03 am

So when he pulls the blowgun trigger, pilot pressure drops but then it activates the valve at the exhaust end of the blow gun trapping the some of the pilot air inside. Why? He ends up releasing it after the shot anyway.
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Re: QEV question

Unread postAuthor: bravootome » Tue Jan 20, 2015 11:00 am

vng21092 wrote:So when he pulls the blowgun trigger, pilot pressure drops but then it activates the valve at the exhaust end of the blow gun trapping the some of the pilot air inside. Why? He ends up releasing it after the shot anyway.


cause that is what closes the main piston and allow multishoot. He wont b able to close the trigger in miliseconds everytime he take a shoot. That's what that valve does.......
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Re: QEV question

Unread postAuthor: vng21092 » Tue Jan 20, 2015 11:33 am

I seriously have no idea how that works... =[. How does the pilot closing help the main piston close? Between the piston pushing back after the first shot, where/how does equalization even occur? I just don't get it, sorry.
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Re: QEV question

Unread postAuthor: bravootome » Tue Jan 20, 2015 2:13 pm

vng21092 wrote:I seriously have no idea how that works... =[. How does the pilot closing help the main piston close? Between the piston pushing back after the first shot, where/how does equalization even occur? I just don't get it, sorry.


Try to imagine the whole process ...Perhaps i didnt mention there is a space between th piston and his "room" so air pass by ..
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