Finally, 4SPC completed (4" Sweet Piston Cannon)

[jrrdw]

Well jrrdw said for me to use a 3 inch one, which would go infront of the sealing face so the sealing face would get pushed through the porting.

But i dont know if that would work because my configuration is not exactly centered so then it may possibly not even seal.

I could, and might, use a 4" washer from mcmaster carr but i dont want it to interfere with the sides of the piston, so would i just go with a 3.75 inch washer?

When you said the piston needed to be flatened, you wern't kidding! After seeing the piston and reading it's not centered, you 1st need to get that center bolt centered, even if that means building another piston because your in danger of deforming the sealing face pushing on one side time after time will wear into it.

If you must use such a doom shaped piston you will need to support the back of the seal as well as the front.

Get your center bolt centered 1st!

A 4 inch washer behind and a 3.75 inch washer in front should make it seal nicely.

Flouresent blue stands out like crazy on black base coat.

[JDP12]

wow very nice job!! I like it

[SpudUke5]

Well the 3.75 inch washers came from Mcmaster and man were they thick!
I had no worry of these breaking. I will get a pic soon.

I at first had a problem of that this washer came of the piston and just sat in my piston area. So i unscrewed the plug and put on a homemade washer from sheet metal, which now prevents the support from coming off.

My current problem is leaking and the piston still...ugh. I know how to fix the leaking so thats noting.

The piston is fine, solid, and works good. When i actuate the piston, it doesnt move back, but rather the air pushes the sealing face forward partially into the barrel, but not ripping off the face. I just know that this is restricting flow. What causes this is the friction from my piston and the pipe. When i place in the piston, i have to hit it pretty good until it starts to slide easily. I did sand down the piston and the inside pipe, but it still seems to have friction, preventing it from sliding as easily, so im gonna lube it up more. If that doesnt work then im gonna sand.

So you guys got any ideas how to fix this?

[JDP12]

if you have access to a lathe, turn the piston down so its even

[SpudUke5]

Only if.....

[Velocity]

This is a very nice cannon...it turned out quite good. I kinda like how its a big cannon, yet still somewhat portable (while you might not think 4" fittings are portable, try going to 6"...it is so hard to lug those things around). The valve seems to have come out well. Great job on this build! I hope the advice that I gave you helped you out.

[SpudUke5]

Yea thx again Velocity.

I need to post that washer though, its thick, and i got four more!

Although there are still minor things to do and complete, the basic setup is ready so thats the most important part.

Just need to fix some leaks, with teflon and im going to glue my pilot setup because it leaks with the threaded pipe nipple.

Yea this thing is sluggish and its kind of hard to lug around. Man you should try putting on the barrel

I was going for a portable look as well, thats why its 4 inch parts and not too big like SWAT.

The piston is still a little hard to put in but now i found out another way to make a piston valve setup so its going to be easier to do without damaging my fittings anymore.

Just as i said before, you influenced me and helped me alot so i credit part of this build to you.

[SpudUke5]

Bump

I have finally done a damage shot, after all this time of fixing the valve, although i am not completely done yet. School just gets in the way too much.
(sigh)

But here is the pic!

YAY my first time working with the uploader!!

More to come

This shot was done at under 30 psi, probably 10-20, couldnt tell with my guage.

[bigbob12345]

Very cool damage
Charge it up to 100psi and take a video, im keen to see this beast at full power.

[covey12]

did not mean to post this sry

[SpudUke5]

O well its okay then cause i was gonna bring this up, but probably wounldnt have if you didnt do this.

Well i think im gonna take her apart because its hard to fix the leaks. There are leaks in the parts that i cemented and i dont know it happened. So i would have to take it apart to fix it and epoxy, in this case, wont help because ive tried and its tedious.

But this is somewhat last on my "to do list". I dont think ill be revamping this for a while, prob late summer hopefully.

[keep_it_real]

Two things:

To prevent leaks while you're cementing pvc, use more glue and try and give it a small turn while you push the fittings together. Also don't even think about pressurizing the connections until the glue is cured (even if it's only 20 psi). I've done both of these things and got leaks out of the deal.

To stop a leak just but globs of epoxy on the fitting. If you do this, it's better to glue around the whole fitting, not just where you're getting the leak. I've done this too and it will hold 100 psi fine.

[jrrdw]

Post pics of the inside parts needing work and I'm sure we can guide you through quick fixes.

[SpudUke5]

Sounds good, now all i gotta do is find some time and stop being lazy.

Ill get some as soon as i can.

EDIT: Although, i still might take this cannon apart not only because of leaking problems, but also because of the fact that its just to big and i would want to redesign the valve.

Or i can just cut down on the chamber and barrel size.