SpudFiles

Here's my design for a piston type valve with a minimum of modification. I've got it built and it works, although not below 30 P.S.I. This could probably be remedied by improving the seal between the rear coupling and the 2 in. pipe.
!!!NOTE!!!
I built this thing around a wye which normally is only used for drain pipe and is not rated. You could replace the wye with a T if you cannot find a pressure rated wye.

The main reason i like this valve is that I don't need to mess with any rubber seals, the pvc bushing/coupling hold air perfectly. I also think it looks sweet.

Please note that the rear 1.25 in. coupling has been wrapped with aluminum tape to ensure a minimum loss of pressure.

If you DO have access toa lathe, go ahead and add some O-rings to the rear 1.25 in. coupling. This will ensure that only the air in the exhaust cavity is lost due to triggering the valve and no unneeded air leaks around the coupling from the main pressure chamber.

Here's some images of the parts & firing sequence.







Assembly should be apparent except for a few slightly modified fittings.

Some bushings need to be shaved so that the pipe can be passed through.



Also you should modify the the 1.25 in. coupling, and the 1.25 in. - 0.5 in. bushing to make sure that they slide together easily.



This valve works great for me. The only problem is that it wastes a lot of air to trigger the valve. I don't mind because I have a sweet little air compressor.
One might also ask why the hell I built all this to bump up the valve size from one inch to 1.25 inchs. I really don't know, but it looks pretty so lets just leave it at that. It should also be scaleable to larger sizes, but keep in mind that a 3 inch piston charged to 50 psi will be sucked back with 353 LBS and you'll need to implement some sort of buffer in the rear of the exhaust pipe. Even with this 2 inch pipe there's 157 LBS pulling it back.

Dang pheonix. That would prbably make a cool looking valve. I was designing a wye piston around a 4in wye, but It never turned out because I couldn't find any pressure rated wyes over 2 in I just might try building this. The only thing I would find wrong with it would be getting the 1.25 by .5 bushing to seal well on he barrel.

Actually it sealy perfectly. That's because it seals against the side of the coupling which come slightly tapered to ensure a good fit. I don't know if will hold air for days on end, but it works for me.

I really like the idea. I don't know about it sealing perfectly, maybe an addition of o-rings even if it doesn't leak may help improve over all performance?

The front part seals REALLY well so well in fact it takes about 10 lbs. of force to jam it back manually with a stick. I suppose o-rings might help a bit, however wwith the gun charged to say... 50PSI you've got 61= (50 * (((1.25/2)^2)PI)) LBS. of force sealling that thing shut. 61 LBS! All O-rings in te bushing part would do is make the gun need 61 lbs w o-rings compared to 71 lbs w/o o-rings to trigger the valve. Seriously an unmodified coupler and bushing seal pretty much airtight. IF there is any loss it would be negligible.

Where O-rings would help is in the rear 1.25 in coupling. All i have to make up the space is a few wraps of aluminum tape. The front bushing needs a considerable amount of force to "un-wedge" it. In the valve i've got there's enough space that losses in the exhaust are pretty big. However I have no access to a lathe, and the point is to eliminate O-rings to seal anything.

add pix man i cant see no pix