Compressor for 5 gal pressure pot for casting

by David Abrams
(Chicago, IL)

Central Pneumatic air compressor and a CA Technologies pressure pot

Central Pneumatic air compressor and a CA Technologies pressure pot

I recently bought a 5 gal. CA Technologies pressure pot for molding/casting. Originally it's for paint, but I'm just using it to get 60 psi of pressure with a mold inside of it. The pot can go to 90 psi, so I'm well within my safe zone.

I also bought a Central Pneumatic air compressor that's 3 gal and can output 100 psi. I was told that the size didn't matter for what I was doing, as long as it could supply the recommended psi.

However... I let the compressor get to 90 psi, then hook it up to the pot, and instantly I loose pressure down to about 40 psi, and that's as much as I can get to the pot.

I have the regulator knob up all the way on the compressor and turning the regulator knob on my pot does nothing at this point.

Do I need a bigger compressor to facilitate this pot? Should it be a 5 gal compressor to match the gal amount?

I'm new to this so I appreciate any help you can give me. Thanks!

Comments for Compressor for 5 gal pressure pot for casting

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Jan 05, 2019

by: Bill

I am not sure how a closed vessel, 5 gallons in size, "used 4 scfm"? A closed vessel doesn't "use" air, it fills with air.

As to this... "Ultimately, I need it to pressurize quickly", that is the crux.

As I noted, your original compressor was reputed to develop 100 PSI output, yes? That means that it should fill any air reservoir with that 100 PSI, assuming that the compressor doesn't fail when filling a larger tank, or that it works!

Your 5 gallon pressure pot will hold about .66 cubic feet of air. That should not have been insurmountable even for that little air compressor you bought.

I surmise that your original compressor is not working properly. It should have been able to fill the pot with 100 PSI in time.

Again, that's the crux. Time.

The pot is only .66 cubic feet. If you want it filled virtually instantly, sure, buy the largest compressor you can afford.

Given that you will get about 3-4 CFM of compressed air at 90 PSI for each HP of motor size, you should be able to fill the pot comfortably within 60 seconds with the 1.5 HP machine.

Assuming I've got all the information straight.

Good luck.

Jan 05, 2019
Reply: Compressor for 5 gal pressure pot
by: David Abrams

No air leaks, the pot holds pressure, but the compressor itself, I'm afraid, isn't powerful enough to deliver 60 psi to the 5 gal pot.

The basic concept of what I'm doing it just filling the pot with air up to 60 psi, then unhooking the hose and letting a mold/cast sit in it while pressurized, until it cures, so there's no bubbles in it.

So far I'm just testing it so I can set the pot at 60 psi and have been unable to achieve that level of pressure.

I did some reading and already went out and got an 8 gal compressor with a rating of 150 psi / 4.1 scfm / 1.5 hp. I think this should be enough to deliver that kind of pressure to this pot, we'll see.

But for the sake of understanding this issue, I passed up a cheaper 6 gal compressor rated at 2.5 scfm.

Do you think that one would have been sufficient?

I saw a 2.5 gal pot that said it used 4 scfm, so I figured I needed the larger compressor for my 5 gal.

Ultimately, I need it to pressurize quickly because I'll be working with urethane that has a short pot life and I'll need to get it mixed, poured, and into the pressure pot within 5 min before it starts to set. So I can't have a compressor that takes a long time to get this pot up to 60 psi.

Jan 05, 2019
Compressor for 5 gal pressure pot
by: Bill

Not having used a pressure pot for casting, when it is operation, does the incoming air from the compressor leak out of the pot somehow?

If not, then the original info was correct, though it may take some time for the compressor to build the pressure necessary in the pot, the pot would simply be an additional tank, and when the overall pressure was reached, the compressor should shut off and both tanks should remain pressurized.

Unless... the pressure pot bleeds air all the time or the compressor has a leak somewhere.

Please advise.

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