Why are centrifugal pump suction lines installed with a positive grade from the well to the pump inlet?

Centrifugal pump suction lines are designed with a positive grade from the well to the pump inlet primarily to facilitate better air elimination when priming. When a suction line is installed with a slight upward slope, it helps to ensure that any air trapped within the line can rise to the highest point and be vented out before the pump starts operating. This is crucial because the presence of air in the suction line can lead to cavitation, reduced efficiency, and potential damage to the pump.

Effective air elimination is particularly important during the priming process, as centrifugal pumps rely on a full column of liquid to operate correctly. If air pockets are present, they can disrupt this column and result in inadequate flow or pump failure. Therefore, maintaining a positive grade is an effective way to minimize air entrapment and ensure smooth operation of the pump system.