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Pop off valve and regulator

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Pop off valve and regulator

Unread postAuthor: Demon » Mon Apr 19, 2010 5:21 pm

I would like some information about pop off valve, are they simply spring retained pistons that liberate air at a certain set psi?
If yes, how can people vent piston cannons with that, i mean such a valve would simply limit the flow when the spring is pushed to the air liberating limit, i cannot see how they can reset and then wait for the air to refill? I mean, they really "pop-off"

And is a flow regulator easy to make ?
(links please)

This is for a full auto carbine project (the one that i posted, with no major differences but shooting full auto :twisted: )

The flow regulator is in an attempt to get a constant rpm and the pop off a constant fps output .
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 19, 2010 5:34 pm

Image

i mean such a valve would simply limit the flow when the spring is pushed to the air liberating limit, i cannot see how they can reset and then wait for the air to refill? I mean, they really "pop-off"


The spring has enough strength to keep the air pushing on the seat in until a certain pressure is reached. Once the pressure is too much, the piston, which has a wider diameter than the seat and therefore greater area, is exposed to the pressure, overwhelming the spring causing it to pop until pressure drops enough for it to reclose.

I had an extensive play with commercial pop-offshere ;)
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Unread postAuthor: Demon » Mon Apr 19, 2010 6:46 pm

Thank you a lot jackssmirkingrevenge (You dont mind if i have copy/pasted your name :D )

Even tough i understand the principle, i dont get how are the part assembled in the pop-off you posted :scratch:
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Unread postAuthor: iknowmy3tables » Mon Apr 19, 2010 6:48 pm

And is a flow regulator easy to make?

I don't think so, unless you mean a flow control valve which is so cheap you might as well buy it. This is probably your best bet but I don't know if anyone has tried it
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Unread postAuthor: POLAND_SPUD » Mon Apr 19, 2010 7:03 pm

I think he wants to set up it like this:
air source and tank -> flow control valve -> small chamebr -> pop-off as the main valve

by adjusting the pop-off you can adjust the RPS... I can't think of any reason why it won't work
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Unread postAuthor: c11man » Mon Apr 19, 2010 9:08 pm

or use a needle valve... it workes great for me
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Unread postAuthor: iknowmy3tables » Mon Apr 19, 2010 9:14 pm

yeah needle valves are ideal flow controllers, but a flow control valve is so cheap that I don't see any reason to make one, it's not really worth the work unless your just puting a clamp on a tube or making a non adjustable pin hole
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Last edited by iknowmy3tables on Tue Apr 20, 2010 8:02 am, edited 1 time in total.

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Unread postAuthor: jackssmirkingrevenge » Mon Apr 19, 2010 11:37 pm

Demon wrote:Even tough i understand the principle, i dont get how are the part assembled in the pop-off you posted :scratch:


Does it help if we use a bigger one as an example :)

It's exactly the same principle as my custom pop-offs like this one.

Image

[youtube]http://youtube.com/watch?v=w8e9Z5t1NDs[/youtube]
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Unread postAuthor: Demon » Tue Apr 20, 2010 10:55 am

Does it means that i can simply connect the pop-off to the barrel?

Is it as good or better then to use it to pilot a piston valve ? Its a lot simpler also.

I want to hit the 60-300 RPM range
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 20, 2010 11:07 am

Demon wrote:Does it means that i can simply connect the pop-off to the barrel?

Is it as good or better then to use it to pilot a piston valve ? Its a lot simpler also.


When I tried connecting a 1/4" pop-off to a 6mm barrel, power was very disappointing. It was only when I built my own with optimised parameters that things really took off:)

... so unless you're willing to build one from scratch, it's a much better idea to use a commercial pop-off to pilot a QEV or piston valve. Not as efficient with air as having a pop-off valve feeding directly into the barrel, but certainly as powerful as any QEV/piston launcher.

I want to hit the 60-300 RPM range


Very possible, just tweak the rate at which air is going into the pop-off.
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Unread postAuthor: Demon » Tue Apr 20, 2010 3:54 pm

I think he wants to set up it like this:
air source and tank -> flow control valve -> small chamebr -> pop-off as the main valve


Thats exactly what i want to do, but my concern is that the RPM will constantly decrease because of less psi/les flow in the small chamber

And i am pretty sure that my valve will be powerful enough, i will use a big surface difference ( 5mm to 15 mm ) .

So what i tought is :
main chamber --- air regulator (150 psi) --- trigger valve--- small hole --- firing chamber --- pop-off set to 125 psi
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Unread postAuthor: Demon » Wed Apr 21, 2010 6:05 am

Bumb because it sunk
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 21, 2010 6:19 am

Demon wrote:Thats exactly what i want to do, but my concern is that the RPM will constantly decrease because of less psi/les flow in the small chamber


It depends what you're feeding it from. This happened to me feeding from my compressor starting at 110 psi, by the time it gets to around 75-80 it would stop firing alltogether:

[youtube]http://youtube.com/watch?v=hXM-bPOtJGU[/youtube]

Still, by the time that happens, anything you're shooting at will be pretty much destroyed ;)
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Unread postAuthor: Demon » Wed Apr 21, 2010 6:45 am

It depends what you're feeding it from. This happened to me feeding from my compressor starting at 110 psi


I feed it from a 300 psi 7cubic inches cooper airtank
What i want is a constant rpm, so i will need a regulator (if i ever got to fire the first shot at 300 psi, it would make the rpm very fast until it got down to 125 psi.
So, will :

300 psi--- regulator set to 125psi --- small hole
regulate the flow?

For the trigger, i will make one that pilots the pop-off manually and in a full auto-mode, simpler and makes a better trigger .
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 21, 2010 7:47 am

That's a rather small tank, it's not going to give you many shots even if regged down. I think what you need is a much more efficient design, have you considered something like this:

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