GWWI WEF Wastewater Treatment Fundamentals Practice Test

A positive displacement pump should not be operated against a closed valve because it delivers a fixed volume of fluid for each cycle of the pump. When these pumps are operating, they generate pressure as they attempt to move the fluid, and if there is no outlet (such as when a valve is closed), the pressure can increase significantly. This excessive pressure may cause damage to the pump and associated piping systems, potentially leading to mechanical failure or even ruptures.

In contrast, centrifugal pumps can handle closed valve conditions better in short durations, as they rely on fluid velocity to generate pressure and can recirculate within the pump itself when the outlet is blocked. Gear pumps and diaphragm pumps, while they have their own operational constraints, still differ from positive displacement pumps when it comes to pressure buildup and mechanical stresses faced against a closed valve. Understanding the operational principles of these different types of pumps is critical in choosing the right one for specific applications and avoiding unsafe operating conditions.