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Great Stuff under pressure?

Posted: Mon Dec 20, 2010 12:03 pm
by Vincenzo
I want to insert a piece of pipe in a fitting in the pilot of my 2" piston valve, and fill around it with Great Stuff. I am just not sure if it will be able to withstand the pressure? I will be using a max of 120 psi.

Posted: Mon Dec 20, 2010 12:54 pm
by Hotwired
Helps if you tell us what it is.

I've checked and the most likely product seems to be insulation foam in a can...

No.

That isn't going to hold 120psi. A proper reducer/bushing is needed. You don't want to make the back of a 2" valve out of something you can poke your finger through.

Posted: Mon Dec 20, 2010 12:55 pm
by jackssmirkingrevenge
Hotwired wrote:That isn't going to hold 120psi. A proper reducer/bushing is needed. You don't want to make the back of a 2" valve out of something you can poke your finger through.
Unless he's just using it to fill dead volume and not as a stressed structural component, in which case it should be reasonably adequate at those pressures.

Posted: Mon Dec 20, 2010 1:08 pm
by ramses
Even to fill dead volume, it could be compressed. Any closed cells in the foam may fatigue and rupture. Then the foam would store air, but only absorb/release it slowly. Something like this I use caulk in my hybrid to fill dead volume, and it seems to work fine.

Posted: Mon Dec 20, 2010 1:49 pm
by Vincenzo
On second thought, how about plaster of paris? There won't be any force on it and I'd coat the top of it with something else... Should I take a pic to show you guys what I'm trying to do?

Re: Great Stuff under pressure?

Posted: Mon Dec 20, 2010 2:59 pm
by Selador
Vincenzo wrote:I want to insert a piece of pipe in a fitting in the pilot of my 2" piston valve, and fill around it with Great Stuff. I am just not sure if it will be able to withstand the pressure? I will be using a max of 120 psi.
Use the foam in the way that you wish.

But then cut away some of it, and fill the void left, with epoxy.
Vincenzo wrote:On second thought, how about plaster of paris? There won't be any force on it and I'd coat the top of it with something else... Should I take a pic to show you guys what I'm trying to do?
The foam is going to make for a lighter weight piston.

Yes, take the picture.

Posted: Mon Dec 20, 2010 3:04 pm
by saefroch
I wouldn't recommend using great stuff on a spudgun, as it is quite a flimsy material. As a general rule for myself, I say if it's ghetto, it's a bad idea. It does however make for a pretty good target. Picture would help with suggestions of alternate materials.

Posted: Mon Dec 20, 2010 5:40 pm
by Fnord
If in doubt, bondo.

Image

It's cheap and fairly tough.