Page 144 - Introduction to Marine Engineering

130 Pumps and pumping systems

Expanded
bellows

A/tAAA/u1

Figure 6.18 Expansion bellows piece

absorb vibration (Figure 6.18). The fitting must be selected according to
the variation in system temperatures and installed to permit the
expansion and contraction required in the system.
Drains are provided in pipelines and usually have small cocks to open
or close them. It is essential that certain pipelines are drained regularly,
particularly in steam systems. When steam is admitted to a pipeline
containing a reasonable surface of water it will condense and a partial
vacuum occur: the water will then be drawn along the pipe until it meets
a bend or a closed valve. The impact of the moving water in the
pipework will create large forces known as 'water hammer', which can
result in damage to pipework and fittings.

Bilge and ballast systems

The bilge system and the ballast system each have particular functions to
perform, but are in many ways interconnected.

Bilge system
The bilge main is arranged to drain any watertight compartment other
than ballast, oil or water tanks and to discharge the contents overboard.
The number of pumps and their capacity depend upon the size, type
and service of the vessel. All bilge suctions must be fitted with suitable
strainers, which in the machinery space would be mud boxes positioned
at floorplate level for easy access. A vertical drop pipe would lead down
to the bilge.