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Piston Valves Explained & How to Make

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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Piston Valves Explained & How to Make

Unread postAuthor: Butch902 » Mon Jan 03, 2011 9:21 am

Piston Valves Explained & How to Make

I have been looking on Spudfiles for a little time now and I never really understood how piston valves worked or how to build one. So if your having trouble understanding piston valves or you want to build one view these's link's. I found it very helpful


Barrel Sealing Piston Valve - Part 1
http://www.youtube.com/watch?v=75O71AHTIr4

Barrel Sealing Piston Valve - Part 2
http://www.youtube.com/watch?v=kMaK33Cn ... re=related

Barrel Sealing Piston Valve - Part 3
http://www.youtube.com/watch?v=Qo0SKiXI ... re=related

Thanks VerbotenDingleberry for making these's video's
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Unread postAuthor: Technician1002 » Mon Jan 03, 2011 1:14 pm

He covers the ratio of area of the 2 inch seal on the barrel and the 3 inch piston in the pilot, but he did not elaborate on what the pilot pressure has to drop to to cause it to start to open and when it opens, how much the pressure in the pilot rises again. The design simply relies on a very large fast pilot valve to ensure the pilot pressure drops rapidly and vent the compression from the piston moving into the pilot volume.

There is more info on the ratio of the barrel seal area vs the piston diameter in the Wiki along with some other valve configurations besides Barrel Sealer.

The Wiki has a page dedicated to piston valves and other pages covering many other types of valves. Start here for lots of info on the various valves.
http://www.spudfiles.com/spud_wiki/index.php?title=Category:Valves

His mention of the valve being open when it moves back 1/4 the diameter is correct for a Coaxial valve where air can enter from all 360 degrees of the side, not just one side for a valve in a T. If you build a valve in a T you will want to allow for more opening area due to 3 of 4 sides of the valve are blocked by the wall of the T.

The video is a great example of a very high pilot leakage valve working by brute force opening of the pilot with a high flow sprinkler valve. Other valve designs with small eq ports between the chamber and pilot area (better seal such as an o ring) can perform very well with a smaller trigger valve.
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