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If W is negative a pump is required; if it is positive a turbine could be installed to extract
energy from the system. PIPING AND INSTRUMENTATION 207
The head required from the pump D P f / g P/ g z 5.5a
The power is given by:
Power D W ð m / , for a pump 5.6a
and D W ð m ð , for a turbine 5.6b
where m D mass flow-rate, kg/s,
D efficiency = power out/power in.
The efficiency will depend on the type of pump used and the operating conditions. For
preliminary design calculations, the efficiency of centrifugal pumps can be determined
using Figure. 5.9.
75
70
65
200
Efficiency, % 60 100 Capacity, m 3 /h
125
55 75
50
50
25
45
10 20 30 40 50 60 70 80 90
Head, m
Figure 5.9. Centrifugal pump efficiency
Example 5.2
A tanker carrying toluene is unloaded, using the ship’s pumps, to an on-shore storage
tank. The pipeline is 225 mm internal diameter and 900 m long. Miscellaneous losses due
to fittings, valves, etc., amount to 600 equivalent pipe diameters. The maximum liquid
level in the storage tank is 30 m above the lowest level in the ship’s tanks. The ship’s
