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qev and pop off problem

Built a BB Machine Gun? 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 and pop off problem

Unread postAuthor: Herwer » Sun Sep 01, 2019 8:23 am

Hi , i was planning to make airsoft full auto gun , with qev and adjustable pop off valve. The problem is when i fill the gun with air pop off dont pilot qev and all air goes thru pop off valve and it sounds like ss-shhhhhh. I think pop off cant pilot qev beacuse the air is still going from blowgun. I mounted on blowgun ball valve for smaller flow. I dont want to fill it from the chamber side so please help me.
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https://imagizer.imageshack.com/img922/7328/N7TloC.jpg
https://imagizer.imageshack.com/img921/4525/cJ5BdC.jpg
https://imagizer.imageshack.com/img923/2043/Oe9BWU.jpg
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Re: qev and pop off problem

Unread postAuthor: keks2033 » Mon Sep 02, 2019 2:41 pm

Air goes too fast through the gun to pump the wheels. Due to the large flow of pop-off, the valve cannot close. After the gun and in front of the pop-off valve, put a partition with a very small hole, with a diameter of 1-0.5 mm, not more, this will help.
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Re: qev and pop off problem

Unread postAuthor: jackssmirkingrevenge » Tue Sep 03, 2019 1:53 am

Herwer wrote:I dont want to fill it from the chamber side so please help me.


Why not? It would be much more efficient...

Otherwise you're going to need to balance flow from the air feed that is just enough to put sufficient air to actuate the pop-off, but not too much that the air coming from the feed refills the pilot chamber so fast that the pressure doesn't drop enough to actuate the QEV.
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Re: qev and pop off problem

Unread postAuthor: Herwer » Tue Sep 03, 2019 5:14 am

keks2033 wrote:Air goes too fast through the gun to pump the wheels. Due to the large flow of pop-off, the valve cannot close. After the gun and in front of the pop-off valve, put a partition with a very small hole, with a diameter of 1-0.5 mm, not more, this will help.

I dont get it. partition where? can you tell me more
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Re: qev and pop off problem

Unread postAuthor: Herwer » Tue Sep 03, 2019 5:20 am

jackssmirkingrevenge wrote:
Herwer wrote:I dont want to fill it from the chamber side so please help me.


Why not? It would be much more efficient...

Otherwise you're going to need to balance flow from the air feed that is just enough to put sufficient air to actuate the pop-off, but not too much that the air coming from the feed refills the pilot chamber so fast that the pressure doesn't drop enough to actuate the QEV.

Maybe if I puncture 1mm hole into piston and add spring to qev, this desing will work? i dont want to make chamber filled qev beacuse this is my last qev and i need this for other project. And I'd to make homemade qev that will be using hot glue piston or epoxy putty piston , so i cant make the hole
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Re: qev and pop off problem

Unread postAuthor: jackssmirkingrevenge » Thu Sep 05, 2019 5:05 am

Image

The issue is the volume indicated, this expansion alone might be sufficient to fire the mechanism because of the pressure drop in the pilot volume.
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hectmarr wrote:You have to make many weapons, because this field is long and short life
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Re: qev and pop off problem

Unread postAuthor: Herwer » Thu Sep 05, 2019 11:46 am

jackssmirkingrevenge wrote:Image

The issue is the volume indicated, this expansion alone might be sufficient to fire the mechanism because of the pressure drop in the pilot volume.
Sorry , but i am not really good in english , so it wont work for this? or i dont get it?
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Re: qev and pop off problem

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Re: qev and pop off problem

Unread postAuthor: Herwer » Sat Sep 07, 2019 1:55 pm

how about this? he have big pilot volume, he is filling from pilot side and this is working for him with standart pop off. Maybe if i will add more pilot volume and change my adjustable pop off to standart it will work. He said that adjustable pop offs arent working with this desing. pneumatic-cannons/topic22037-15.html
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Re: qev and pop off problem

Unread postAuthor: keks2033 » Mon Sep 09, 2019 12:42 pm

there is too much extra volume in the gun. Pop of the valve does not have time to lower everything, so that the piston valve would work. Try to fill the whole empty space with cold welding or epoxy glue. For air, make a channel 3-4 mm in diameter, this is enough.
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Re: qev and pop off problem

Unread postAuthor: keks2033 » Mon Sep 09, 2019 12:50 pm



I did it once. Maybe it will help you.
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Re: qev and pop off problem

Unread postAuthor: Herwer » Thu Sep 19, 2019 12:54 pm

I saw this airsoft-pellet-guns/topic16151.html , and i tried to make it , tapped hop up chamber to 1/8 and attached it to blowgun , and it dont works its just jam , air is going thru the barrel and bbs are retreating to magazine from air stream (something like that), it shot 1time and that it not full auto , the bbs from magazine are just like being pushed back to magazine, what is the problem?

https://imagizer.imageshack.com/img924/6734/O9fO0j.jpg
https://imagizer.imageshack.com/img923/7034/N4Vzt3.jpg
https://imagizer.imageshack.com/img924/2885/51VaCW.jpg
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Last edited by Herwer on Sat Sep 21, 2019 12:08 pm, edited 1 time in total.

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Re: qev and pop off problem

Unread postAuthor: jrrdw » Fri Sep 20, 2019 5:38 am

I this picture
https://imagizer.imageshack.com/img924/6734/O9fO0j.jpg it looks like there is a piece of thread tape or a mar on the piston that could be the cause of the jamming. This is a piston QEV correct? My eye's aren't failing me???
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Re: qev and pop off problem

Unread postAuthor: Herwer » Fri Sep 20, 2019 2:31 pm

Ym, that is not qev, it's a hop up unit that is attached to blowgun. I hooked up magazine and it didn't shoot full auto, only 1 sometimes 2, it is like jamming, maybe flow is not enough?
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