High Efficiency Valve for PVC Airguns

[Forum Admin]

With copper costing so much, I decided to build another PVC airgun. To keep things safe and utilize a free nebulizer, I'm keeping the pressure at 45 psi. I removed the compressor from the nebulizer, found it had 1/4 npt threads, and added a gauge and quick disconnect to it.

Since the pressure is so low, the valve is going to have to be very efficient. I decided to go with a balanced spool valve. The spool is made from 3/4" nylon rod. I machined the o ring grooves with my table saw blade set low and rotating the nylon rod. Instead of using a t fitting, I used a cross, which doubles the air flow. Here's the video:

<a href="http://www.youtube.com/v/dAossoHCu8E" target="_blank" class="new_win">http://www.youtube.com/v/dAossoHCu8E</a>

[Pellethuntr]

That's awesome Admin.. How well will that spool valve hold up at say max pvc pressure of 150 psi??

[Forum Admin]

With a proper trigger system and bumper, it should handle 150 psi quite well. I just shot a empty 12 gauge shell out of it, using that stub as a barrel. It flew about 50 yards and hit a tree.  This valve seems very efficient, I'm seeing good things in its future.

[Lord Joshy]

Nice...

[Pellethuntr]

With a proper trigger system and bumper, it should handle 150 psi quite well. I just shot a empty 12 gauge shell out of it, using that stub as a barrel. It flew about 50 yards and hit a tree.  This valve seems very efficient, I'm seeing good things in its future.

Thats great! I just got a fire extinguisher that I want to use for a reservoir on a gun using this valve.. Where did you get the nylon rod??

[Forum Admin]

i got it from fastenal. They had it as a in stock item so i didnt have to pay any shipping lol

[Pellethuntr]

I don't think we have a fastenal close by.. Any ideas where I else I could get it without having it shipped.. I have never seen at like a Lowes or Home Depot

[Forum Admin]

try a close grained wood dowel. You could also cast one with epoxy.

[Pellethuntr]

try a close grained wood dowel. You could also cast one with epoxy.

I had thought about using a hard wood dowel.. I will have to do it.. How deep were your o-ring cuts??

[Forum Admin]

I dont remember, to be honest. I had to give it a bit of squeeze to make the .75 od o rings expand to .802. I've got a good trigger and valve reset system in place now. It also absorbs the shock of the piston with a spring and rubber bumper. I just need a barrel, loading system, and sights to finish it. I attached some new pics at the bottom of this post for all to see.

[Forum Admin]

I put a old barrel on to test it out and made some darts for it. The darts are made from a 20 gauge shotgun wad with a sheet rock screw hot glued on it. They fly straight and penetrate nicely. Here's a pic of the gun and a dart on the scale weighing in at 62 grains. I'll chronograph it in a couple days when I get off work.

[Forum Admin]

With a 16" barrel made from 1/2" pvc and 6" of dead space (which will be fixed when I put the loading system on), it will shoot a 64 grain dart 169 fps on a 45 psi. The same dart shoots 350 fps on a 120 psi fill. Fairly good results, and I think it can achieve better with a bit of tuning.

[Forum Admin]

I got rid of the dead space, swapped out the original spring for a lighter one, and added a muzzle brake. With a 16" effective barrel length, the a 64 grain dart shoots 222 fps on 45 psi. That brings the energy from 4 to 7 fpe, a very good increase. I havent tested it on 120 psi yet, but the results should be just as good if not better.

Another benefit of the lighter spring is a much better trigger pull. This and the muzzle brake should improve accuracy as well. I'll be posting a detailed construction video on this one soon, provided my kids will quit fussing in the background 

In the meantime, here's a video of the airgun shooting before I modded it:

<a href="http://www.youtube.com/v/ExLX1lArJ7E" target="_blank" class="new_win">http://www.youtube.com/v/ExLX1lArJ7E</a>

[Pellethuntr]

Cool, interested to see how your trigger works 

[Forum Admin]

I still havent been able to shoot a good video. Between running the store, being sick, and rowdy kids in the background, it just hasnt been meant to be. lol Anyhow, I did drill holes all over the piston to lighten it, making it open even faster. To test, I shot a 278 grain .58 caliber lead ball on a 100 psi fill. It shot at 196 fps, making 24 fpe. I'm pretty impressed with that, since the air chamber is so small and the barrel is only 16" long. This airgun might just need a larger air chamber and longer barrel to put out some serious energy. The most I've gotten out of a PVC airgun before is 104 fpe with a heavily modified sprinkler valve, overkill air chamber, and 36" barrel. That was with 200 psi, really pushing the limits of PVC.