What is the term for the pressure against which a pump must operate?

The correct term for the pressure against which a pump must operate is "Head." In hydraulic systems, "head" refers to the height of fluid that a pump has to lift to move water from one location to another. It is a critical factor in determining the efficiency and effectiveness of a pump, as it directly relates to the amount of energy needed to overcome gravitational forces and friction losses in piping. The head can be measured in feet or meters and reflects both the elevation gain and the pressure required to overcome resistance in the system, which may include static lift, dynamic lift, and pressure losses due to friction.

Understanding the concept of head is essential for selecting the appropriate pump for a specific application, as it helps determine the right size and power of the pump needed to achieve the desired flow rates under varying conditions.