How would you troubleshoot a double diaphragm pump that is reciprocating but no liquid is being pumped?

To troubleshoot a double diaphragm pump that is reciprocating but not pumping liquid, checking the check balls seating is fundamental, as these components are critical to the pump's ability to maintain adequate flow direction and pressure. The check balls prevent backflow, allowing the liquid to be drawn into the pump chamber during the suction stroke and then expelled during the discharge stroke.

If the check balls are not seating properly due to wear, debris, or other obstructions, they can fail to create the necessary seals, leading to inadequate or no liquid being moved through the pump. Ensuring that these check balls are functioning correctly will directly address the issue of liquid not being pumped despite the pump's motion. This troubleshooting approach is essential before considering other components in the system, such as the diaphragm or actuator valve, as those failures would typically present differently than what is described in the question.