Doing some resin casting and bought a 10 liter (2.6 gallon) pressure pot - wondering how big the compressor chamber must be. Any other tips would be great too!
2 Answers
Resin under pressure isn't something that I have tried yet, so @Lee-MeadowhawkDesigns (or anyone else) please correct me if I am wrong here...
Any size compressor chamber can get the pressure pot to the desired air pressure, as long as the compressor it is attached to can provide enough pressure to get the chamber to the required pre-equalized pressure. I'm imagining a setup that looks like this...
The compressor(A) pushes air into the chamber(B) which is attached to the pressure-pot(D) with an initially closed valve(C) in between the chamber and the pot.
With the valve closed, the compresser brings the pressure in the chamber up to a pressure which is just enough higher than the target pressure, that when the valve opens and equalizes the pressure between the chamber and the pot, the resulting shared pressure is the target pressure (60psi in this case). The effect of using a chamber and a valve in this way is that the pressure in the pot instantly reaches the target pressure in the moment that the valve is opened.
The challenge is then to calculate the higher-than-target pressure which needs to be in the chamber prior to the opening of the valve. The equation for figuring out that chamber pressure is...
((chamber-pressure times chamber-volume) + (pot-pressure times pot-volume)) divided by (chamber-volume plus pot-volume) equals (target-pressure)
Assuming that the pot-pressure will start at approximately 1 atmosphere (14psi) prior to equalization, the chamber pressures needed for each of the chamber volumes which @Lee-MeadowhawkDesigns suggested are...
So 75 psi for the 8 gallon chamber and 66 psi for the 21 gallon chamber.
Does that seem about right?
DANGER WARNING : Sudden pressure changes such as what would happen when the valve opens in the above setup can be very violent. If your pressure pot is not properly closed and sealed tightly, the incoming air can evacuate your resin through any cracks at damaging speed. Install enough hose between the valve(C) and the pot(D) that you are nowhere near the pot when the valve opens.
I have a 2.5 gal pot and use my 21 gal 125 psi compressor. It works with no problem at all. For a smaller and less pricey solution, I would go with at least an 8 gal 125 psi compressor, as it looks like it can provide the pressure for the pot. From the specs I see one like that would give you 5.5 CFM @ 40 PSI. My 2.5 gal pot requires 4.0 CFM @ 40 psi. You'll probably want to run at 30-35 psi, so you'll be good no matter what.
Depending on where you live, I can say that the 21 gal is worth the money if you're buying from Harbor Freight, as it is only somewhat more than the 8 gal and that 21 gal will keep the thing from running all the time. That's how I ended up with the big one.
