SpudFiles

hey all Im new here and have what is probably a very noob question.
I have been designing a semi auto based on a video I found on you tube
by wyz
the design integrates a blow forward bolt into a sleeved barrel and uses a qev to discharge air= down the barrel
now I dont want to use a slide valve as I want a trigger system that is more realistic.
i was considering using a blow gun but then the air has no where to vent
ive also heard if I put a little pin sized hole in the outer edge of the QEVs piston that it will allow it to vent and i would be able to use a blower.. My only concern with that is Would that reduce the posible rate of fire???
and if it does reduce the rate of fire what alternatives are there.



Edit: just found this on ebay but its only rated to around 110 psi alot lower than i want to go
http://www.ebay.com.au/itm/1-4-PT-Air-I ... 904&_uhb=1

Hi mattyg, I'm having a little trouble working out what you're asking. You want to know what kind of valve is best to trigger a QEV for semi-auto use?

Perhaps you could post the video you're basing your design on? Also I recommend writing your posts in a program like microsoft word as it does all the grammar stuff and makes it easier to read posts

You want something like this >>

It's called a 3 way valve
You want one that's normally open not normally closed (though some are universal)

You can either buy one with manually operated (with a lever/button) or one actuated by a solenoid and use a push button switch

here is the vid I was following
[youtube][/youtube]

I was thinking a 3 way valve but I though normally open and normally closed didn't particularly matter with a 3 way valve as you can just switch which port you use for exhaust and charge????
Maybe I don't understand how they work properly!
I was looking at the valve that i posted the ebay link for as a possibility but it will only handle around 110psi and I wish to go much higher than that.

http://www.spudfiles.com/pneumatic-cann ... ev#p365630

An explanation of how the whole 3-way valve setup works which you might find useful.

Yep thats exactly how I thought it worked.

jackssmirkingrevenge you put up a link to this valve
http://www.ebay.com/itm/1-8-PT-Female-T ... 484fbd5fbb

This is a lot more compact than the valve I was looking at and has a slightly higher pressure rating 1MPA (145psi)
but this still seems fairly low for what I am planning.
has anyone attempted to run higher pressures though these valves??

mattyg wrote:This is a lot more compact than the valve I was looking at and has a slightly higher pressure rating 1MPA (145psi)
but this still seems fairly low for what I am planning.
has anyone attempted to run higher pressures though these valves??

They're upside down :-/ start here and read on.

well that sucks they were looking good

damn it they looked so promising

It is possible to find "normally closed" valves though, that just ain't one.

If it doesn't actually clearly say so in the product text, an understanding of pneumatic symbols (ISO 1219-1 is the most common standard) will probably get you through.

technically it's it possible to use a normally closed valve too. You just have to build a simple trigger system that keeps it pressed when the trigger is in normal position. Damn it hard to explain it using words so here's a diagram

The added advantage is that NC valves are easier to get and you can make a more comfortable trigger

Yep, brian suggested something similar in the original thread.

Yep I saw that I was of the same thought as you though. If possible I would rather use off the shelf item.
but this is not my biggest concern.
My biggest concern remains the relatively low pressure rating of these valves.

What pressure do you intend to fire at? These are probably good for at least 300 or so psi.

I was intending on running around 300 psi
if I run the valve at those levels will it loose reliability or shorten its lifespan?
I am willing to pay more for a higher rated valve i just cant find any

i used this and added a spring: