possible way eliminate 3 way valve

[Sticky_Tape]

I think I have a way to eliminate the need for a three way valve in one of those semi auto dart guns. Placeing a pop off just before the pilot valve. The idea is simple really a pop off needs say 150 psia (consider atmosphere 0psi inlet 150 and outlet atmosphere 0psi) so if the gun isn't filled yet and you turn on the airsource reged to 160psi the gun fills up to 160 but when the gun fires the pressure in the gun has to drop about 150 psi before the pop off pops again and fills the gun getting it ready for the next shot. hope you understand it's hard to exsplain.

[Hotwired]

You'd be hard pressed to find a new concept around here.

Pop-off valves have been theorised and also made into working designs for fully automatic action and yes if the refill rate is that slow it could also be semi.

Also developed somewhat in more recent designs with replacements for the basic pop-off.

[jonnyboy]

I believe jsr and some other people with marble guns have done similar. I think the first person to do it made his own and called it a snap valve.

EDIT found the link.
[url]http://www.spudfiles.com/forums/deathra ... 12290.html[/url=snap valve]

[Sticky_Tape]

The pop off isn't the pilot it is the fill. It's just an idea to get rid of the hard to get three way valve

[Hotwired]

Whoops, my bad.

Fatally flawed I'm afraid. Yes, to start with it will be 160psig going in and 0psig in the chamber...

...but the spring and surface area in that pop-off is set to resist a difference of 150psi...

10psig in the chamber and 160psig from source and the pop-off will shut again.

[Sticky_Tape]

Markfh11q mad a full auto this is just an idea to get rid of the three way valve I remeber someone saying that pop offs closed at a fraction of the opening pressure?

[Hotwired]

When a pop-off vents to the open air it is effectively venting to 0psig. By venting into a small closed chamber the resistance to it being open will build up and it will shut again much sooner.

10psi causing it to shut is an exaggeration but it is a poor mans regulator and whatever your chamber pressure the cannon pressure will be notably lower.

That said if you wanted it to do that...

[Sticky_Tape]

Regulated to 300psi?

[Hotwired]

I grabbed a datasheet from one of my bookmarked pneumatic suppliers:

http://www.airlines-pneumatics.co.uk/we ... de6000.pdf

Of note is where it says this model vents at 10% overpressure and reseats at 10% below set pressure.

So even having one set for 300psi means you need 330psi to get it to dump into the chamber.

Then once the chamber has achieved 60psig the valve will reseat.

Or whatever combination of source pressure dropping/chamber pressurising gets there first.

[POLAND_SPUD]

unfortunatelly there is no way to replace a 3 way valve with something else... not without lowering efficiency...
however you could add a pop-offf valve to pneumatically powered spool valve to achieve full auto

spool valves are not that difficult to get... check e-bay there should be hundreds of them...
http://www.spudfiles.com/forums/solenoi ... 16722.html I got this one for 26PLN (that's roughly 14 $) without shipping and I got a 24V and 230 V solenoids for free..

the real problem is to find a manually actuated one... you can use either a spool valve or a hand slide valve... hand slide valves are not that expensive and are easier to get

use google and compare the prices.. sometimes you can find some good offers...

I don't know if it's against the rules or not but I found one company - www.MICRO.com.ar that has some good offers... their stuff is about 40% cheaper than comparable products... (well at least this is true where I live)
It seems that it has something to do with the fact that it's an argentinian company