Release valve question

[c9d]

I was just wondering if this would be a good release valve for a 2" coaxial piston setup?

http://www.northerntool.com/webapp/wcs/ ... blow%2Bgun

[jackssmirkingrevenge]

Assuming your piston is made to tight tolerances, prefereably o-ringed, then yes.

[c9d]

Why would it have to be O ringed if I might ask?

[jackssmirkingrevenge]

The larger your piston diameter, the more amplified any small difference from the chamber inner diameter will be in terms of leakage into the pilot chamber. If air leaking into the pilot chamber exceeds the quantity of air that can leave the pilot valve, the piston will never fire.

Say you have a 4" chamber, inner diameter is 4.00 inches and piston diameter is 3.99, the area through which air can leak is 0.06275 square inches. Imagine your pilot valve has an opening of 0.25", this means that the available area to empty the pilot chamber is 0.04909 square inches, less than the air leaking around the piston so it will never work.

If you can make a piston with tight tolerances, a blowgun is fine, but if not I would look around for a larger pilot.

[c9d]

So assuming I o-ringed the piston, I would only use two or three 1/16" equalization holes? Or could I just have a smaller pilot valve area?

[Technician1002]

1 eq hole is plenty. That is all I used on the 2.5 inch Dragon cannon.
I was able to fire it fine with a 1/4 inch ball valve.

[c9d]

How long did it take for your pilot and pressure chamber to equalize with only one hole?

[jackssmirkingrevenge]

You could also have a floating o-ring, no need for equalisation holes.

[Technician1002]

How long did it take for your pilot and pressure chamber to equalize with only one hole?

I used a short shot in the quick connect on the pilot to close the valve and seal the barrel, then I filled directly in the chamber. It takes a very short time with a good compressor to fill it.
Instead of a blow gun, I used a ball valve with a quick connect for both fireing the cannon and closing the valve.

The o ring in the Dragon is in the cylinder wall, not on the piston.

[Gippeto]

No o-rings on the piston, no equalization holes...just careful construction.


http://www.spudfiles.com/forums/my-firs ... 12796.html

That being said, I DO like to use floating o-rings on pistons. The u-cup seal on the co-ax piston has also proven very effective and reliable.

[c9d]

@Jack
The thread you provided is interesting. I see how the floating o ring works and it is very similar to the ported piston head on my airsoft rifle.. only reversed. I really like Gipetto's piston with the U cup seal on it... I wonder how it worked out...

@Tech
was just trying to get an idea of the equalization time as I would like to limit the reload time to as low as 15 seconds. Thanks.