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Piston 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.
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Piston Valve Question

Unread postAuthor: Hubb » Tue Sep 18, 2007 11:50 am

All the piston valves I've seen are piloted from the rear. Is it possible to have a piston valve (or diaphragm valve) piloted from other than the rear? Example in the pic.

It seems like it would work but I was wondering if I misses something because I've never seen it done.
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Unread postAuthor: Tom » Tue Sep 18, 2007 12:13 pm

I think there's no problem with the place of the pilot exhaust but, the piston would hit the tube if you don't use a spring.
GR.Tom
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Unread postAuthor: spud yeti » Tue Sep 18, 2007 12:32 pm

The design would work, but you have to cosider:

a) The pilot pipe has to be flush with the inside, or far enough back to allow enough piston travel. I do not encourage the latter option though.

b) Once the piston has traveled past the pilot, obviously it cant pilot any further as it is sealed off by the piston. Solution would be to have the pilot far enough back that the piston travels enough before going past the pilot.

Otherwise the design is fine, but you have to weigh up the pros and cons. (i.e aesthetics vs. functionality) but this can also have a happy medium :wink:
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really good quote/phrase here
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Unread postAuthor: dongfang » Tue Sep 18, 2007 12:52 pm

Hi,

A side pilot would have the advantage that if the gun recoils out of your hands and lands on the end, probably nothing will get damaged.

You could also exploit the resealing and recompression behind the piston as a damper! I would still recommend a rubber bumper as a supplement .. you know, these days you have to use rubber, for safety ;)

Regards
Soren
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Unread postAuthor: Hubb » Tue Sep 18, 2007 1:05 pm

If built, the tee would be tapped, allowing the pilot hole to be flush and, of course, it would be designed to allow that 1/4 barrel diameter travel. I also considered the fact that the remaining air in the pilot area could act as a bumper and even assist in reseting the piston back against the barrel.

The main reason I was concerned with this is because I am wanting to construct a rifle type launcher where the stock comes off the end of the tee, making everything flush. This, in turn, would allow me to move the pilot hole as far back as needed and still keep it looking flush.
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Unread postAuthor: dongfang » Tue Sep 18, 2007 4:25 pm

Hi,

BTW, I just tried to tap a plastic fitting. The result was not very convincing - it´s like the taps cut off too much plastic (but are OK for steel).

I would press and glue in a bushing in your case, or try tap a scrap fitting first.

Regards
Soren
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