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Diaphragm Valve Spud Rifle

This particular spud gun uses a simple yet unique diaphragm valve that releases the pressurized air to propel the projectile.  This gun uses a 1/2" PVC pipe barrel which extends into the air chamber to where the diaphragm valve is located.   

The Diaphragm Valve Spud Air Rifle

This is the complete spud gun.  Note how the gun assembly, made of PVC, is mounted on top of the wood stock.  The stock is made with a pistol grip for a more comfortable feel.  The blowgun nozzle is glued to the pistol grip, which has been cut to the contours of the nozzle to make for a nicer fit.  The gun assembly and blowgun nozzle were glued in place on the stock with epoxy glue.

This is the rubberized PVC disc that makes up the diaphragm valve in the gun.  The barrel of the gun extends into the air chamber and goes to the back of the gun where the PVC disc is glued in place.  The disc is pressed against the breech of the barrel in its normal position, which helps seal the air chamber.

In order for this type of valve setup to work, the gun is divided into two air chambers - the main air chamber, where the barrel passes through and is in front of the PVC disc that closes the breech of the barrel, and the secondary air chamber, which is behind the PVC disc and holds the tire valve for pressurizing the gun, and the hose barb fitting that has a hose connected to it that leads to the blowgun nozzle.  When the gun is pumped up with a standard tire pump, pressurized air is inside the secondary air chamber, and then passes through a small hole in the PVC disc, and into the main air chamber.  When the gun is pumped up, both air chambers are under pressure and the PVC disc remains stationary.  When you squeeze the blowgun nozzle, you release the pressurized air in the secondary air chamber, which then causes the pressurized air in the main air chamber to push back against the PVC disc, which in turn opens the breech of the barrel and releases the pressurized air, propelling the projectile down the barrel. 

The diaphragm valve is a pretty common setup in the world of spud guns.  Its cheap, simple, and very effective.  Unlike some of the pricy valve setups, like modified sprinkler valves, and the complex valves, like piston valves, the diaphragm valve is easy to do, with very little in the way of mishaps.  Any spud gun made with a diaphragm valve tends to be more powerful than a simple ball valve spud gun since the valve opens and releases more air in a shorter amount of time. 
Plans for this model of spud gun are available through in Kindle format, just click on the picture above to take you to the listing in order to purchase.

When you want something built right, build it yourself.