Provided By - Pacogoatboy

OK, I'm not sure whether this is a regular old piston valve or what it is, but here is the design. I don't have any nice drafting software, and I am pretty awful using Paint, so these diagrams are kind of ugly. Rest assured that all of the things that should line up do, and that the pipes are all needed to make it fit together. The reason for the 4" PVC on the right side is that the actual fitting is much shorter in length and height than shown. There is almost no room for a 3" coupler to be welded into place inside the fitting itself, so it must be attached to an external 4" pipe. I started out using a 4"x3" bushing, with the backstop ground down. I intended to cement 2 3"x2" bushings back to back inside of it. Unfortunately, this made the street elbow sit in a position that was not centered in the upper part of the T. The walls of the upper part of the T slope somewhat, but they are straight from the top of the street elbow up, so I don't anticipate any problems with the gasket becoming unaligned. I forgot to include the guide bolt in my diagram. It will connect the spring, the gasket, and the steel disk. It also ought to help guide the gasket as it rises and falls. I am considering adding a small length of pipe pointing downward from the blowgun and a bit of gasket on top of the steel disk. This might help seal the valve in an open position while it is firing. There is room for the gasket to travel nearly 4" vertically inside of the fittings. Please, let me know what you think. Also, if this design is similar to any others that you can think of, please let me know. I'd like to look at theirs to compare and possibly improve this design.

A Rough Sketch of my Spud gun Valve (Version 1.1)
(under construction at this moment)



Valve Considerations

This is a diagram of the actuation of the valve (a close-up of the top section of the T fitting). At the moment there is a large volume of air that must be vented for the valve to open. I would like to reduce this volume, and I only see two ways of doing so.



The first possibility is to fill in the excess air space with some solid filler. Any suggestions would be welcome. There would be less air to vent, but the gasket would still have more than enough travel to properly feed a 2" exit pipe. The air must still travel from the bottom of the T fitting and reverse direction into the exit pipe.



The section option involves extending the exit pipe to the top of the T fitting, easily done by welding a short length of 2" PVC into the 90 degree elbow. This would reduce the volume of air that needs to be exhausted to fire, as well. It would create a longer path for the air to take in escaping the gun. The air would have to flow upward, then reverse direction and travel back down the exit pipe before leaving the gun, as in option 1 (or any other option that does not change the design of the gun radically. Would this create more drag, and thus a slower exhaust or not? I am inclined to prefer the first option, but I like the cost and ease of this option. (Nearly free and quite easy.)



A picture of the valve, closed and primed
(dark blue = high pressure)
(light blue = low pressure)



A picture of the valve, opened and firing



Provided By - Pacogoatboy