How do you check if a used regulator is good or bad without any fittings attach to it yet? (No solenoid, no metering valve, no brass/ stainless steel fittings, Nothing!).
This is particularly when someone buys a used regulator in e-b-a-y that has not been tested to be working or not. So, it can be returned within time period specified by the seller.
You at least need CO2 coming into the regulator to test it. Attach the regulator to the CO2 tank. Makes sure the working pressure is reading 0 psi. The tank pressure should read 800 psi. Then, close the CO2 tank valve. The tank pressure should still be reading 800 psi. If after couple of days and the pressure is still reading 800 psi, you have no leaks from the regulator to the CO2 tank.