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QEV+Slide valve without constant air supply

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets.
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QEV+Slide valve without constant air supply

Unread postAuthor: martinpeim16 » Mon Oct 14, 2013 4:24 am


I am building my second airgun, my first been a simple QEV+blowgun. I am trying to obtain multiple shots in semi-auto from my second gun using a QEV+Slide Valve configuration. I already looked at the other threads about this and know about GGDT and my chamber dimensions and barrel, but what i want to ask is if by using a FE 1Kg 200psi chamber i will be able to have enough air to charge the chamber multiple times with the slide valve and thus have multiple shots. Most ppl use this with a constant supply, but i am attempting a PCP type gun.

PS: Im not looking for the number of shots i will be able to get with 200psi, i know i need to provide a lot more detail, just wanna know if its possible and if its good enough to try.

My third gun will be hammer type, I wanna explore all types of configurations :wink:

Thanks for the input guys :)
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Re: QEV+Slide valve without constant air supply

Unread postAuthor: jackssmirkingrevenge » Mon Oct 14, 2013 5:32 am

You can do the maths.

I'm not going to go into thermodynamics so this is a simplification:

Say your FE is 1500 cc at 200 psi, and your firing chamber is 50cc.

First loading, considering boyle's law (where P1V1=P2V2), we know the original pressure and volume of the FE, and the new volume of FE + firing chamber.

Therefore 200 psi x 1500cc = P2 x 1550 cc

P2 = 300000/1550 = 193 psi

This will be the pressure at which you will fire your first shot.

For the second shot we do the same,

193 psi x 1500 cc = P2 x 1550 cc

P2 = 187 psi

This is the pressure of the second shot.

... and so on

A solution for more consistent shots would be to say regulate the pressure supply to 100 psi, which will give you a significant number of equal shots before power starts to wane.
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