In the case where the pump is below the source of supply, what is NOT required during priming?

In the context of pump operation, especially when dealing with priming, the goal is to fill the pump casing with liquid to create the necessary pressure for it to function effectively. When a pump is located below the source of supply, it is crucial to eliminate any air that may be trapped in the pump casing, as air can hinder the pump's ability to create suction and displace water.

Trapping air in the pump casing would be counterproductive because the presence of air would mean that the pump is not fully primed and can lead to issues like cavitation or loss of performance. Therefore, during the priming process, the pump must be free of air, which is typically achieved by opening an air vent valve to allow air to escape until water flows from the vents, indicating that it is fully primed. Closing the discharge valve is also a common procedure to focus the flow and ensure that water fills the pump casing rather than immediately being expelled through the discharge.

Thus, the option indicating that trapping air in the pump casing is not required during priming is indeed accurate, as the objective is to ensure the casing is filled with liquid rather than air for optimal operation.