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What's a self-venting piston valve?

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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What's a self-venting piston valve?

Unread postAuthor: kjjohn » Sat Oct 10, 2009 8:13 pm

Within the the next few months I am going to begin work on an advanced hybrid. I have already completed most of the design, but it requires a valve other than a burst disk for its operation. I know self-venting piston valves can be used, but I've never seen one. I already know how a normal piston valve works. Does anyone have a diagram or a good description of how a self-venting piston works?
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Unread postAuthor: Moonbogg » Sat Oct 10, 2009 9:07 pm

I'm not sure what you mean by self venting piston valve. But it sounds like what I used for the Striker. Check out the link in my sig and take a look at the design and pics of the piston to see if this is what you are talking about.
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Unread postAuthor: Technician1002 » Sat Oct 10, 2009 11:48 pm

I think he means a piston valved hybrid.

If it is what he means, it is built like a traditional barrel sealer air cannon, but there is no trigger valve on the pilot. The small (very tiny) EQ port ensures the pilot area is at the same pressure as the chamber. Because the pilot can't raise in pressure rapidly, when the hybrid mix is lit, the very rapid chamber pressure increase unseats the piston and it fires like a traditional air cannon. By selecting the ratio of the piston seat to piston diameter, the amount of pressure rise required to unseat the piston can be selected so the calculated "burst" pressure can be dialed in.

Search for piston valve hybrids. I haven't seen very many so the info on them is limited, but the theory exists.

It is mentioned in the wiki on this page;
http://www.spudfiles.com/spud_wiki/inde ... d_launcher

The valve is designed to open on the rapid rise in the chamber pressure.
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Unread postAuthor: Moonbogg » Sun Oct 11, 2009 7:42 pm

Ah, sounds like a great idea. I like the idea for choosing burst, or unseating pressure.
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