A positive displacement sludge pump should never be operated with the ___________ closed.

Operating a positive displacement sludge pump with the discharge valve closed can lead to serious problems for the pump and the system. Positive displacement pumps work by moving a specific volume of fluid with each cycle; this means they are designed to push a set amount of sludge or liquid through the discharge line. When the discharge valve is closed, the pump will continue to attempt to displace its volume, which creates excessive pressure in the system. This can result in damage to the pump, including potential rupture of pipes or the pump casing, and can also lead to safety hazards due to the build-up of pressure.

In contrast, operating with the inlet valve closed is dangerous because it can lead to cavitation, while a closed drain or control valve does not critically affect the pump's operation in the same way as a closed discharge valve does. Understanding these operational principles is essential in maintaining the integrity of wastewater treatment processes and ensuring safety in plant operations.