I’ve always thought that there must be a more effective way to make a homemade air gun than by using a ball valve as a trigger. Well I’m putting an end to that. I’d like to introduce to you the PVAT- Piston Valve Air Tank. It is a completely homemade airtank that has many different applications and can be fired like any other actual gun air tank with its built in piston valve. Think of it as a homemade at2k tank. This writeup is for the rev.2 version of this design which fixed leaks experienced in rev.1. The pictures may not be all unique to rev.2 but you get the idea.
1” PVC coupler, end cap and 1” to 1/2” reducing bushing
4x 5/16” x 3/16” o-ring
5 1/2” 1/4” carriage bolt
4x 1/4” nuts
5/8L beveled faucet washer
Skinny strong spring (Ace #62 can work)
Vinyl tube of your choice
Fitting for said tubing
McMaster parts list, doesn't include faucet washer
48925K93 – 1” PVC 4880K53 – 1” PVC Endcap 4880K73 – 1” PVC Coupler 4880K314 – 1” x 1/2” Reducer 94115K008 – O-rings 92356A564 – 5 1/2” x ¼” Carriage Bolt 91845A029 – 1/4” Hex nuts 9657K222 – Spring 9117T113 – Vinyl Tubing 5372K511 – Vinyl tubing fitting
The bolt there is fully threaded and I can't find one that isn't so DON'T order that bolt. Just go to Lowes anyway it's easier. And get their hex bolts, they seem slightly thicker and make a better seal as I found out.
Saw for cutting PVC
Cut 3 5/8” of 1” PVC. Sand down the outside of the PVC and the inside of the fittings/plastic surfaces to be glued. Glue the bushing into the coupler then the coupler to the PVC. Make sure you shove it in all the way.
Find the exact center of the endcap and drill with a 1/4” bit.
Now take the faucet washer and drill the hole out to 1/4” so it fits on the bolt.
Take the piece of 1” PVC assembly we glued earlier and mark and drill a hole right where the end cap would end when it’s fully on. Make sure the hole is perpendicular to the PVC and is a size such that it is slightly smaller than your tubing fitting; mine was 3/16” so I drilled a 3/16” hole. Apparently 3/16” is nominal. (The coupler isn’t pictured)
Now take the fitting and make it look like this:
Then roughen up the smooth inside end and put some glue in the hole and stick the fitting in all the way. Then coat the joint with glue some more.
Take the endcap we drilled before and put an o-ring on the bolt. Then put the bolt through the hole. We are going to be gluing the o-ring to the end cap, so lube up the bolt, put some glue on the outside of the end cap, and push the bolt down and the o-ring so it’s glued on.
Now do the same thing with the inside of the end cap.
*After I tested this in rev.2 I decided I am going to put two o-rings on each side and reinforce them with epoxy putty in future versions.
Assemble the end cap/bolt (piston) like so:
It will seal against the coupler like so:
Put some glue on where the nut seals with the bolt so air can’t get through.
Now are you starting to get it? Heh.
Last step! Glue the endcap onto the PVC. Make sure it goes down all the way.
Congrats, you’re done. Attach a pump, fill the tank, and pull the pin to start shooting!
The finished product with a Hornet pump:
How it works:
When you pump, the tank fills with air. The rubber washer makes a seal with the bushing so no air gets out. When you pull on the bolt, the washer is pulled back, creating a path for the air to go into the barrel. When you let go, the spring causes the washer to re-seal so the cycle can be continued.
I only used one o-ring on each side, so after 5 pumps it started to leak. Everything else held up perfectly. I am able to get well over 100’ with 5 pumps. It holds pressure for a long time as well. Another thing to note is this can be made with any length carriage bolt and with any size PVC. Imagine a 3’ 3’’ tank like this! I also think you can use these to replace tanks in guns. Broken sm1.5k? You can replace it with this. Also you can integrate these anywhere and can be made very cheaply.
About the spring, the one I used for this version was one I found in my spring bin. However Ace #62, when cut in half, should also work. If some of you are concerned about difficulty, I would say you should definitely have experience making this. You have to cut/glue some things in pretty precise of a way that I wouldn’t recommend for beginners. However I would not say it is extremely difficult to make.
Sand the part of the bolt that will seal with the o-rings with fine sandpaper to smooth it down and lube all the surfaces that come in contact with each other. I didn’t use PVC cement because it doesn’t need it, and make sure you measure carefully before modding the design I used here.
I will probably be selling these so if you can't make one there is no need to worry.
Here is a video.
-EDIT- I have done some tests and after 15 mins it has not lost any noticeable pressure.
Edited by Lt. Stefan, 10 March 2010 - 09:42 PM.