Question

The specific speed of a pump is defined as the speed at which a geometrically similar pump would operate to deliver:

• A. Unit discharge at unit head
• B. Maximum efficiency
• C. Zero discharge at maximum head
• D. Infinite discharge at zero head

Hint:

Specific speed aids in classifying pumps and predicting their performance.

Answer 1

The Correct Option is A

Specific speed (Ns) is a dimensionless parameter that helps in the selection and comparison of pumps. It is defined as the speed at which a geometrically similar pump would operate to deliver a unit discharge (1 m³/s) against a unit head (1 m). It is given by: \[ Ns = N \sqrt{Q} / H^{3/4} \] where N is the rotational speed, Q is the discharge, and H is the head.

Answer 2

Definition Recall: Specific speed is defined by a fixed reference condition, worth memorizing directly rather than deriving.

It's the speed a geometrically similar pump would need to deliver ONE unit of discharge against ONE unit of head — i.e. unit discharge at unit head, matching option 1.

Maximum efficiency, zero discharge at max head, and infinite discharge at zero head are all pump performance-curve concepts, but none of them is the actual definition of specific speed.