Login    Register
User Information
Username:
Password:
We are a free and open
community, all are welcome.
Click here to Register
Sponsored
Who is online

In total there are 84 users online :: 4 registered, 0 hidden and 80 guests


Most users ever online was 155 on Mon Aug 15, 2016 1:40 am

Registered users: Bing [Bot], Google Adsense [Bot], MSNbot Media, Yahoo [Bot] based on users active over the past 5 minutes

The Team
Administrators
Global Moderators
global_moderators.png CS

Release valve question

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.
Sponsored 
  • Author
    Message

Release valve question

Unread postAuthor: c9d » Sun Dec 13, 2009 11:21 pm

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
  • 0


c9d
Specialist
Specialist
 
Posts: 44
Joined: Sun Nov 04, 2007 12:56 am
Reputation: 0

Unread postAuthor: jackssmirkingrevenge » Sun Dec 13, 2009 11:22 pm

Assuming your piston is made to tight tolerances, prefereably o-ringed, then yes.
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: c9d » Sun Dec 13, 2009 11:28 pm

Why would it have to be O ringed if I might ask?
  • 0


c9d
Specialist
Specialist
 
Posts: 44
Joined: Sun Nov 04, 2007 12:56 am
Reputation: 0

Unread postAuthor: jackssmirkingrevenge » Sun Dec 13, 2009 11:40 pm

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.
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: c9d » Sun Dec 13, 2009 11:52 pm

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?
  • 0


c9d
Specialist
Specialist
 
Posts: 44
Joined: Sun Nov 04, 2007 12:56 am
Reputation: 0

Unread postAuthor: Technician1002 » Mon Dec 14, 2009 12:58 am

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.
  • 0

User avatar
Technician1002
Chief of Staff
Chief of Staff
 
Posts: 5190
Joined: Sat Apr 04, 2009 11:10 am
Reputation: 14

Unread postAuthor: c9d » Mon Dec 14, 2009 1:06 am

How long did it take for your pilot and pressure chamber to equalize with only one hole?
  • 0


c9d
Specialist
Specialist
 
Posts: 44
Joined: Sun Nov 04, 2007 12:56 am
Reputation: 0

Sponsored

Sponsor
 


Unread postAuthor: jackssmirkingrevenge » Mon Dec 14, 2009 1:20 am

You could also have a floating o-ring, no need for equalisation holes.
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: Technician1002 » Mon Dec 14, 2009 1:39 am

c9d wrote: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.
  • 0

User avatar
Technician1002
Chief of Staff
Chief of Staff
 
Posts: 5190
Joined: Sat Apr 04, 2009 11:10 am
Reputation: 14

Unread postAuthor: Gippeto » Mon Dec 14, 2009 2:15 am

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.
  • 0

"It could be that the purpose of your life is to serve as a warning to others" – unknown

Liberalism is a mental disorder, reality is it's cure.
User avatar
Gippeto
Donating Member
Donating Member
 
Posts: 2393
Joined: Sat Jan 19, 2008 10:14 am
Location: The Great White North...Canada eh!
Reputation: 11

Unread postAuthor: c9d » Mon Dec 14, 2009 2:32 am

@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.
  • 0


c9d
Specialist
Specialist
 
Posts: 44
Joined: Sun Nov 04, 2007 12:56 am
Reputation: 0

Return to Pneumatic Cannon Discussion

Who is online

Registered users: Bing [Bot], Google Adsense [Bot], MSNbot Media, Yahoo [Bot]

Reputation System ©'