Originally Posted by jgourlie
Everyone is using 30psi. That is good to know. I set my compressor to 40 to blow out the lines. Time to turn it down a bit. Good tip
What's the problem with 40 psig? The system is rated for at least 150 psig and is protected at 150 psig by the water heater pressure relief valve. You won't hurt the system with any pressure up to 150 psig, you'll just blow water all over if you leave a faucet open or when you open it. If you're comfortable with 40 psig, use it. If you like 30 psig and it clears your lines, use it.
Consider the argument that you need a pressure regulator on the incoming city water line or you'll have leaks. Why? You can get high pressure on the system anyway. If you use hot water and the water heater then heats water with no faucets open, the expansion of the water will cause the pressure to rise. If there's not enough air in the water heater to absorb this expansion, the pressure can cause the relief valve to weep until the pressure drops. I have that happen often and it's never caused a problem with the plumbing. It can make it hard to open the toilet water valve, but I just reach over and open the hot water on the sink for a second.