What action should be taken when a pump is under excessive strain from high head?

When a pump is under excessive strain from high head, it is crucial to take measures to prevent damage and ensure the longevity of the pump. Restricting the discharge is a valid action to alleviate the strain the pump is experiencing. By reducing the discharge flow, the pump can operate within a more manageable range, which helps to decrease the pressure and workload on the pump. This adjustment can prevent overheating or mechanical failure that might occur if the pump continues to operate under excessive strain.

The other options may exacerbate the situation—allowing the pump to run at full capacity could lead to further mechanical stress, while reducing inlet pressure may not adequately address the root cause of the high head issue. Increasing the speed of the motor would also typically increase the flow and pressure, potentially worsening the strain on the pump. Thus, restricting the discharge provides a direct and effective method for mitigating the excessive strain on the pump.