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New Piston Valve..

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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New Piston Valve..

Unread postAuthor: Infernal2 » Sun Mar 04, 2007 1:03 am

Hey guys I'm taking a break from building the Man Ray (All cast aluminum piston gun) and am making a few new valve design with my new lathe. I'm curious as to what you think a better design would be? Currently the valve is 2" T with 1 1/2" porting in and out. The threads have been turned down to fit flush and I'm using a modified coupler to hold the inside outflow pipe in place.

The valve is barrel sealing (just like it more, don't ask) but I'm wondering what you think would be better for the actual piston? Here are my options....

1) A one part piston that sits beyond the stop ring of the T.

or...

2) A two part piston that sits outside and inside of the T's stop ring.

Both of these are filled from behind, have o-rings, and are hollow. To clarify what I mean by one and two parts is the two part would look similar to Joel's Supah and the one part would simply have a longer spring and only look like the smaller front part of Joel's Supah.

Hopefully I haven't confused anyone. BTW, both will be powered by a 3/4" QEV and ball valve with a quick connect.
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Unread postAuthor: TwitchTheAussie » Sun Mar 04, 2007 4:13 am

Got any pics man? Im completely hopeless with valves other than pre-modded ones.
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Unread postAuthor: mark.f » Sun Mar 04, 2007 8:51 am

I suggest either a two part piston that sits behind the stop, (in the socket), and over it, because if you had a piston only over the stop, you would have very little room to work with before the piston started to go over the socket of the bottom port of the tee, creating sealing problems if you are using O-rings. Another thing is the way everybody else just about builds their piston valves. They place a length of 2" pipe into the back of the tee and then solvent weld a female adapter onto that, and then use a threaded bushing or tapped plug to attach their pilot. This give you plenty of room to work with and a single, continuous diameter all the way up to the end of the socket. This allows you to use longer pistons which let you still place the sealing port smack dab in the middle of the tee. I made my first valve this way.
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Unread postAuthor: Infernal2 » Sun Mar 04, 2007 9:27 am

Well, I'm actually using bar stock to accomplish this but decided to make them hollow to reduce weight. I'm just boring them out first and then adding end plates made of the same material. The only issue I have is that it seems a bit wasteful considering the piston's travel. Considering a one part will always be within the stop area of the T, why make it two parts. Its rather easy to ensure that one part will never move out of this area, even accounting for piston blow back. Of course, then again, a two part could probably be more efficient in that you wouldn't have to add a stopping mechanism onto the spring, just use a stronger spring.

Also, I'm curious if you think it would be worth it to machine fittings for the input/output rather than using stock parts and modifying them. It rather easy to cut the threads but it seems wasteful of the already expensive bar stock.
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