AODD pumps are popular when self-priming is required. Creating a low-pressure zone—less than the atmospheric pressure of 14.7 psi—inside the fluid bowls is how the AODD pump draws fluid. If air pressure supplied to the pump is too high, the pump will change over too quickly and there will not be enough time for the fluid to be drawn into the pump.
To solve this priming issue in a matter of seconds, slow down the pump by using the air regulator to decrease the air pressure entering the air valve. Once the pump speed has been reduced and the fluid has had enough time to enter the pump, increase the air pressure and operate the pump at a faster speed.
Credit by Michael Sandlin
https://www.pumpsandsystems.com/pumps/october-2016-5-minute-fix-troubleshoot-diaphragm-pump