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16 . Schedule number of a pipe, which is a measure of its wall thickness, is given by
A. 1000 P'/S
B. 100 P'/S
C. 1000 S/P'
D. 10000 P'/S

17 . The net positive suction head (NPSH) of a centrifugal pump is defined as the sum of the velocity head and the pressure head at the
A. discharge.
B. suction.
C. suction minus vapor pressure of the liquid at suction temperature.
D. discharge minus vapor pressure of the liquid at the discharge temperature.

18 . With increasing flow rate, the hydraulic efficiency of a centrifugal pump
A. monotonically decreases.
B. decreases and then increases.
C. remains constant.
D. increases and then decreases.

19 . In case of hydraulically smooth pipe, the resistance to flow depends only on the Reynolds number, whereas for a hydraulically rough pipe, the resistance to flow is governed by the relative roughness.
A. relative roughness.
B. absolute roughness.
C. friction co-efficient for flows at equal Reynold number.
D. all (a), (b) & (c).

20 . Water hammer in a pipeline results from the
A. bursting of pipelines due to closure by a valve.
B. rapid pressure change due to a rapid change in the rate of flow.
C. pressure increase due to closure of a valve resulting in decrease in rate of flow.
D. none of these.