SpudFiles

When useing a pneumatic cannon, How much expantion is caused by the pressure?

Does this expantion cause slop in the piston?

Does anybody allow tolerances for this?

Maby Joel does, maby thats the differance between the supra and everybody elses!!!

I'm betting very little expansion happens, or else everybody's pistons would leak. Enless they had super thick O-rings, but then they wouldn't be able to get the piston in the gun in the first place.

Well, ok, here's my attept at figuring out how much the pipe will stretch...

For 4" sch 40 PVC pipe (3.998" ID, .237" wall)...

Ok, so at 100 psi there is a hoop stress of about 100psi*3.998"*1/2pi = 2650 psi.
This means that the pipe will enlongate 1 part in 420,000psi/2650psi = 1/159.
1 part in 159 times 3.998" mean the ID of the pipe will enlarge .025".

With a typical 3/16" thick O-ring (which is really the smallest I'd put on such a big piston), this means that the compression of the O-ring will be reduced ~7.5%.
O-rings in gas systems are typicaly compressed 5-10%.

boilingleadbath wrote:Well, ok, here's my attept at figuring out how much the pipe will stretch...

For 4" sch 40 PVC pipe (3.998" ID, .237" wall)...

Ok, so at 100 psi there is a hoop stress of about 100psi*3.998"*1/2pi = 2650 psi.
This means that the pipe will enlongate 1 part in 420,000psi/2650psi = 1/159.
1 part in 159 times 3.998" mean the ID of the pipe will enlarge .025".

With a typical 3/16" thick O-ring (which is really the smallest I'd put on such a big piston), this means that the compression of the O-ring will be reduced ~7.5%.
O-rings in gas systems are typicaly compressed 5-10%.

Daaaammmm

did some one say education???BLB stop making the rest of us look dumb!lol