SpudFiles

would an ordinary O-ring be capable of sealing pressure on a sliding rod (red) Yes, A double acting piston could be used instead, but they are not cheap ($42 each, mcmaster), and I will need 2 for my project(if I get around to building it). Max pressure would be 100psi of propane combustion byproducts.

EDIT: acutally, around 60psi of plain air. my bad

on a sidenote, what kind of dynamic friction should I expect from 3 oring seals, one 1" id tube, one in 5/8" id tube, and two sealing against a 1/4" rod, all with lube? I am not looking for measurements, just educated guesses.

thanks

well the rings (yes rings, i reckon 3 would be needed) would need to be reasonably snug... otherwise you will get leaks... so there will be friction... but you can always lube it up

I think you misunderstood the post; I Should have been more clear. Only one ring would be sealing the rod. The friction was a side note, a different question.

yes and i think that multiple o-rings would be needed and they would need to be a tight fit to themselves and the rod.

It should seal. What exactly are you making? Is the air supposed to push the piston?

I would be making a completely self contained semi-auto airsoft combustion. Air is supposed to push the piston, and be displaced by the piston(2 cylinders) It would be a lot simpler (2 O-rings on the main piston instead of 4), but I wanted it to fit into a m16 body.

depending on how much of a pain in the ass these seals turn out to be, as well as the amount of friction, I may cheat and use a solenoid to move a piston.

any idea of the amount of static friction?