Barrel-Sealing Piston Gun Problems

[spudkilla224]

I have done some research on barrel-sealing piston cannons, on how tight the piston should be, and how far back it should move, but i am confused on how to make my piston more stable in the back.

My piston is housed in a 2" Tee, and my piston itself it made from a 1.25" coupler with some tape wrapped around it ,the sealing face of the piston is a mouse pad. does this design sound like it would work? it just seems that the piston isn't big enough in diameter of the 2" Tee. And one other thing i have a question about is when i push the piston to see how the seal is against the barrel it looks fine, but it looks like there is some space behind the tape and the tee. the tape only is wrapped to the center of the 1.25" coupler and it ends at the tip of the barrel seal.

any help would be appreciated.

[mobile chernobyl]

the 1.25" fittings will allow too much wobble. do this:


about 5-6" of 3/8 thread all-thread rod.
Three 2" fender washers (Has 2" OD, ID slightly oversize - read on - available at lowes/depot)
Two large 3/8" washers (about 1.25" OD available at lowes/depot)
Two 2" OD by 3/8" ID Rubber washers from Home depot
Six 3/8 thread nyloc nuts.

This will be built like a shishkabob, the 5-6" allthread rod being the skewer, I'll explain it from sealing side to exhaust side:

Nyloc, large 3/8 washer, 2" rubber washer, 2" fender washer, nyloc nut
about 1.5"-2"
Nyloc, large 3/8 washer, 2" rubber washer, 2" fender washer, nyloc nut
about 1.5"
Nyloc, 2" fender washer, Nyloc

The only tricky part is with the 2" fender washers you will NEED to have the nylon end of the nyloc bolt facing the 2" fender washer. The nylon smaller part fits snug in the 2" fender washer centering it since it is slightly larger than the standard hole in a 3/8" washer.

There you go, an awsome, cheap, and super easy to make piston that seals pretty well both barrel and exhuast side. 2" fender washers fit with .049" (a little less than a sixteenth) clearance give or take .005" in 2" PVC (What you'll use on the one side of the Tee where the valve goes). There is very minimal wobble, and any that exists is permitable as it will straighten up when pressure is applied (I could get it to seat with just my lungs).

[psycix]

The piston outer diameter should approach the inner diameter of the pipe it slides in as much as possible. If its too loose, you can do 4 things:
-Find a bigger piston base
-Build a whole new piston out of other stuff (like the washer method or casted out of epoxy or hot glue)
-Wrap more duct tape (gives bad results, tape has to be perfectly smooth, one bump in it will screw it up. Tape might break down quickly)
-Use a sliding tube inside the tee, allowing smaller diameter pistons.

[Pilgrimman]

I have one question: (Maybe a dumb one) You know that the couplers only fit well in 2" PIPE not tees, right? If so, I see no problem with the design as you've described it.

[MrCrowley]

It wont work:

1) The tape is only at the front, this means the air can just go out near the back of the piston and if it does work it will jam because of the huge difference in diameter

2) The tape may cause it to jam even if you covered the whole piston as it doesn't look very smooth.

3) You said yourself even with the tape it's not a good fit.

Try a deodorant can or maybe plywood:
http://www.instructables.com/id/Golfbal ... That-Shoo/

[spudkilla224]

Thanks MrCrowley, i hav a question for you about your wood piston, how long is it in length? or how long should my piston for a 2" Tee?

[MrCrowley]

It must be around 3.5" long. The length doesn't matter so much. Just make it long enough so it can seal against the barrel but still be supported at the back, and try and take up as much pilot volume with the length.

[frankrede]

I'm tired of damn barrel sealers being a pain in the ass.
I can't have a piston last for anything hah
I'M BUYING A MAULER