What should be the state of the valves before starting a positive displacement pump?

Before starting a positive displacement pump, both the inlet and outlet valves should be open. This is crucial because positive displacement pumps work by trapping a fixed amount of fluid and then forcing it into the discharge pipe. If the inlet valve is closed, the pump may not be able to draw in fluid, which can cause it to run dry and potentially damage the pump. Similarly, if the outlet valve is closed, the pump could create excessive pressure, which may lead to system failures or even damage the pump itself.

Keeping both valves open allows the pump to operate effectively, ensuring proper flow and preventing damage. This setup optimizes performance and helps to maintain the longevity of the pumping system.