Powerful, But Easy to Build Quick exhaust valves, or QEVs, are great main valves for homemade airguns. They use standard pipe fittings, usually are constructed of metal, and can take a good deal of pressure. Here is one that I recently built:
Design I built this airgun to be easy and quick to construct, while being rugged and accurate. Not a beauty queen, but definitely performs up to the design standard I set. The heart of this airgun is a 1/2" QEV I purchased at my local Fastenal store. If you don't have access to one in your area, here's the one I got.
Like the sprinkler valves you've seen me use for airguns, a QEV is a pneumatically actuated valve. I use a shop compressor blowgun to pilot, or trigger, the QEV to fire the shot. A QEV can handle far more pressure than a sprinkler valve and is more sensitive, making them even more powerful. Let's take a close up look at the valve mechanism:
Building the Action The QEV I used is marked P, A, and R. P is the pilot, this is the side the trigger valve goes on. A is where the air chamber hooks up. R is where the air is released, so this is where the barrel goes. I'll start with the side labeled "p". I used a 1/2" to 1/4" bushing which connects to a 1/4" close nipple. This allows me to attach a 1/4" T fitting. The T fitting gives one connection for the trigger valve, and another for the fill valve. The trigger is a blowgun valve which has been cut to make it smaller. It attaches to the T with another close nipple.
Please note that there is no safety. It is also very important to make sure there are no air leaks, since a very small pressure differential will make this airgun fire on its own. To fill the airgun, I used a 1/4" to 1/8" bushing to attach a schrader valve. This is a valve that a bicycle pump attaches to. To get higher pressure, up to 400 psi, I use a shock pump. I found the schrader valve in the well section at my local Lowe's store.
The air chamber hooks up to the side labeled "A". It is made from a 1/2" threaded to 3/4" slip copper fitting. This attaches to a street elbow. The air tank is soldered to the street elbow and finished of with a cap. It is made from 3/4" type L copper pipe and is 12" long. The length of this air tank affects the power and air consumption of the airgun. Take a look at how I constructed a simple, yet effective stock, and how the air chamber looks in its entirety:
The Stock The stock is constructed from a scrap of 2x4 I found in my shop. To lighten the airgun a bit, I may go ahead and cut it in a L shape. I attached it to the air chamber with hot glue. Since I often try to recycle parts for other airguns, I decided to give this a try. So far it has held up well.
The Barrel The barrel I used is made from a 1/2" OD aluminum tube I bought from Lowe's. It is shrouded with a piece of 1/2" copper pipe. Check out this video at about 4:00 for more information on this barrel and sight construction:
Accuracy and Power So how does the airgun perform? Quite nicely, though I haven't chronographed it yet. I can shoot a 2" group offhand at 20 yards with it. It'll go right through 1/2" particle board at that range:
Fairly good performance for a smoothbore and cheap ammo. The ammo I used is 3/8" slingshot bearings, which have flats on two sides. The bearings are patched and loaded from the breech end. The airgun is pumped, then the barrel is replaced. The shot is now ready to be fired. Check out this video for some shooting footage:
Hunting Been wanting to nail a squirrel, but I got a sparrow instead. I used a 3.5" nail dart on this one: