How To: Build an All-Metal Piston Valve Air Gun

Build an All-Metal Piston Valve Air Gun

How to Build an All-Metal Piston Valve Air Gun

For those who enjoy launching projectiles at high speeds, this article details how you can build an all-metal piston valve air gun. This device also works as a high-powered water gun.

How to Build an All-Metal Piston Valve Air Gun

Parts List

  1. (1x) empty propane tank
  2. (1x) 1/2" metal piping, 3 ft.
  3. (1x) 1/2" hose-to-thread 3/4" adapter
  4. (1x) 3/8" tee
  5. (1x) 3/4" tee
  6. (1x) 3/4" to 1/2" bell
  7. (1x) 3/4" male thread connector
  8. (3x) 3/8" male thread connectors
  9. (1x) 1/2" male thread to 3/8" female thread connector
  10. (1x) 3/8" to 1/2" bell
  11. (1x) 1/2" male thread connector
  12. (1x) 1/2" ball valve
  13. (1x) 3/8" female pull-latch connector
  14. (1x) 3/8" spring
  15. (1x) 3/8" piston

How to Build an All-Metal Piston Valve Air Gun

Tools List

  1. Hot glue gun
  2. Vice
  3. Various wrenches
  4. WD-40
  5. Teflon tape
  6. Rubber tape
  7. Air compressor with 3/8" male connector

Step 1 Propane Tank Prep

MAKE SURE IT'S EMPTY!! Place the tank in the benchtop vice and drill through the top valve (using a 3/8" bit). Empty the metal shavings out of the tank.

How to Build an All-Metal Piston Valve Air Gun

Step 2 Piston Prep

Spray some WD-40 into 3/4" male thread connector (#7). Place the connector on a hard, metal surface. Then carefully inject the hot glue into the connector until full. Let cool, the pop out the hardened glue. Cut a groove in the side of the hot glue piston, lengthwise, so that air can pass by.

Note: I used a different method of creating the piston, however this way works just as well.

Step 3 Assembly

Wrap the teflon tape around all threads. Then insert the metal tube (#2) into the hose-to-thread adapter (#3), making sure it goes all the way through and about 3/4" sticks out. Wrap with rubber tape as seen in this photo:

How to Build an All-Metal Piston Valve Air Gun

Now attach the ball valve (#12) to the 1/2" male thread connector (#11), then the male thread connector (#11) to the 1/2" bell (#10), then the bell to one 3/8" male thread connector (#8.1). See the following image for reference.

How to Build an All-Metal Piston Valve Air Gun

Now, attach the 3/8" female pull-latch connector (#13) to one 3/8" male thread connector (#8.2), then that connector (#8.2) to a 3/8" tee (#4), and finally the tee (#4) to the last  3/8" male connector (#8.3). See below image.

How to Build an All-Metal Piston Valve Air Gun

Attach the 3/4" male thread connector (#7) to the 3/4" to 1/2" bell (#6), then that bell (#6) to the 1/2" male thread to 3/8" female thread connector (#9). Insert the spring (#14) and piston (#15) into the 3/4" male thread connector (#7). See the following image.

How to Build an All-Metal Piston Valve Air Gun

Now, attached the 3/4" tee (#5) to the 3/4" male thread connector (#7), as below.

How to Build an All-Metal Piston Valve Air Gun

Attach the 3/4" tee (#5) to the 1/2" hose-to-thread 3/4" adapter (#3), as below.

How to Build an All-Metal Piston Valve Air Gun

Now, attach the 1/2" male thread to 3/8" female thread connector (#9) to the 3/8" male thread connector (#8.3), as below.

How to Build an All-Metal Piston Valve Air Gun

Attach the 3/8" male thread connector (#8.1) to the tee portion of the 3/8" tee (#4), as below.

How to Build an All-Metal Piston Valve Air Gun

Now it's time for the propane tank. Attach the tank (#1) to the tee portion of the 3/4" tee (#5).

How to Build an All-Metal Piston Valve Air Gun

Step 4 Usage Instructions

To use, connect the air compressor to the female pull-latch connector (#13). Pressurize the tank, then release the ball valve to fire.

Step 5 Finished Product!

Here's what the final piston valve air gun will look like:

How to Build an All-Metal Piston Valve Air Gun

Theory: The way this device works is quite simple. The tank is pressurized from the back, pressing the piston onto the metal tube and preventing the air from escaping. To fire, simply release the ball valve. This causes a pressure difference in front of the piston, and behind. The resulting effect is the piston is thrown backward, and all air escapes through the end of the tube, launching any projectile inserted at high speeds.

Tips

  • Don't overtighten the threads, it's damaging.
  • Add a little more teflon tape to the propane tank thread, it helps reduce air loss.
  • Enjoy!

Warnings

  • DO NOT FIRE AT LIVING BEINGS! This device can cause serious injury or death!
  • Do not unscrew the propane tank while pressurized.
  • I am not responsible for any damage you cause with this device!

11 Comments

This is great! I want to see it in action!

Here's a rather low quality video of a shot. https://www.youtube.com/watch?v=Q4frdvH2Kk0
I'll post a better video once i fix my camera :)

Looks like it should pack a pretty good punch. I've built a number of piston cannons over the years, they're a blast. By the size of that tank you could probably get more power if you increased the length of the barrel. I would guess it could be about twice as long as it is now before the projectile would begin slowing down. Of course, that would be less convenient to carry around.

yeah, i originally had the barrel quite long, but cut it a third down because of portability. it still shoots metal bearings through computer towers though, so im happy :)

Any videos of this in action?

http://fearoflightning.blogspot.com/2012/01/piston-valve-airgun.html :)

" tank is pressurized from the back, pressing the piston onto the metal tube and preventing the air from escaping. To fire, simply release the ball valve" enjoy :)

Very good article, support

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