Why is a vacuum test performed on a pump?

A vacuum test is performed on a pump primarily to ensure there are no air leaks in the system. This test is crucial because if air is allowed to enter the pump, it can significantly affect the pump's performance and its ability to create suction. The presence of air can lead to cavitation, which can damage the pump and reduce its effectiveness in moving water.

By conducting a vacuum test, operators can verify that the pump is airtight, which is essential for maintaining proper operation and ensuring that the pump can efficiently draw water from the source. This test involves creating a vacuum within the system and monitoring it for any changes, which might indicate a leak.

The other options, while relevant to pump operation, do not specifically relate to the purpose of a vacuum test. Checking efficiency, measuring fluid viscosity, or determining discharge pressure involves different testing methods and parameters, rather than assessing the integrity of the pump's ability to maintain suction without air intrusion.