To prevent a loss in prime, positive displacement pumps should be started with what condition?

For positive displacement pumps to operate effectively and to prevent losing prime, it is essential that the pump is started with a specific condition. Running a positive displacement pump with the discharge valve open ensures that the pumped fluid can flow freely from the pump. This condition is crucial because if the discharge valve is closed or restricted, the pump may build up pressure internally, potentially leading to damage or a malfunction.

Maintaining an open discharge path allows the pump to create the necessary pressure to move the fluid through the system and helps maintain a consistent prime, which is vital for the pump’s operation. Positive displacement pumps rely on moving a fixed volume of fluid with each cycle, and having an open discharge allows this process to occur without interruption.

In contrast, opening the suction valve or closing the intake valve could lead to air entering the system, thereby losing prime. The presence of water in the pump is necessary, but simply having water isn’t sufficient unless downstream conditions allow for that water to be displaced effectively.