Question

Statement (I): The specific speed (N_S) of a centrifugal pump is defined as the speed (in rpm) at which it works most efficiently.

Statement (II): The specific speed is a characteristic of pumps that can be used as a basis for comparing the performance of centrifugal pumps.

1. Both Statement (I) and Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I)
2. Both Statement (I) and Statement (II) are individually true but Statement (II) is not the correct explanation of Statement (I)
3. Statement (I) is true but Statement (II) is false
4. Statement (I) is false but Statement (II) is true

Answer 1

Correct Answer - Option 4 : Statement (I) is false but Statement (II) is true

Specific speed of a pump is defined as the speed of a geometrically similar pump which produces a unit power when working under a unit head. By geometrically similar means that pump is identical in shape, dimensions, blade angles and gate opening etc. It is denoted by the symbol Ns. It is given as:

\({N_s} = \frac{{N\sqrt Q }}{{{H^{3/4}}}}\)

Where

N is in rpm

Q is in m³/s

H is in m.

The specific speed is used in comparing the performance of different type of pumps such as reciprocating pumps, centrifugal pumps etc as every pump has different specific speed.