A centrifugal pump may fail to deliver water when first started if the __________.

Correct Answer: Option D — pump is not primed

Centrifugal pumps are not inherently self-priming. They require the casing and suction piping to be completely filled with liquid before starting. If the pump is not primed, the impeller will rotate in a gas-filled space, failing to create the necessary pressure differential to draw liquid into the pump casing.