Page 125 - Introduction to Marine Engineering

Chapter 6

Pumps and pumping systems

At any one time in a ship's machinery space there will be a considerable
variety of liquids on the move. The lengths of pipework will cover many
kilometres, the systems are often interconnecting and most pumps are in
pairs. The engineer must be familiar with each system from one end to
the other, knowing the location and use of every single valve. The
various systems perform functions such as cooling, heating, cleaning and
lubricating of the various items of machinery. Each system can be
considered comprised of pumps, piping, valves and fittings, which will now
be examined in turn.

A pump is a machine used to raise liquids from a low point to a high
point. Alternatively it may simply provide the liquid with an increase in
energy enabling it to flow or build up a pressure. The pumping action
can be achieved in various ways according to the type of pump
employed. The arrangement of pipework, the liquid to be pumped and
its purpose will result in certain system requirements or characteristics
that must be met by the pump.
A pumping system on a ship will consist of suction piping, a pump and
discharge piping (Figure 6.1). The system is arranged to provide a
positive pressure or head at some point and discharge the liquid. The
pump provides the energy to develop the head and overcome any losses
in the system. Losses are mainly due to friction within the pipes and the
difference between the initial and final liquid levels. The total system
losses, HTOTAL are found as follows:
HTOTAL — H FRSUCT + H FRDIS + HDISTANK + HSUCTTANK

where H FRSUCT = friction head loss in suction piping
HFRDIS = friction head loss in discharge piping
HDISTANK — height of discharge tank level above pump

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