Texas Wastewater Class A Practice Exam

The discharge from a centrifugal pump is indeed affected by the head against which it works. A decrease in head allows the pump to operate in a more favorable condition for flow, thus increasing the discharge. When the head is lower, the pressure available for moving the liquid through the pump and out into the system is greater. This is because the pump does not have to overcome as much resistance, enabling it to push more fluid through its outlet.

In contrast, increasing the head would require the pump to work harder against greater resistance, which may lead to a decrease in discharge. Similarly, increasing motor speed generally increases the head developed by the pump, which could also result in a reduced flow if the system is operating at a negative slope in performance due to increased resistance. Regarding fluid density, a decrease could affect pump performance differently, but primarily through viscosity and fluid dynamics; however, this does not directly correlate with an increase in discharge in the same way that head does.

Thus, decreasing the head allows for higher flow rates from the centrifugal pump, illustrating the direct relationship between head and discharge.