new to this and a little confused about valves

[mattyg]

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

[Biopyro]

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

[POLAND_SPUD]

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

[mattyg]

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.

[jackssmirkingrevenge]

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

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

[mattyg]

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??

[jackssmirkingrevenge]

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.

[mattyg]

well that sucks they were looking good

damn it they looked so promising

[Ragnarok]

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.

[POLAND_SPUD]

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

[jackssmirkingrevenge]

Yep, brian suggested something similar in the original thread.

[mattyg]

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.

[jackssmirkingrevenge]

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

[mattyg]

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

[T_Money]

i used this and added a spring: