Page 138 - Introduction to Marine Engineering

124 Pumps and pumping systems

shaft bearing bush together with the casing and impeller wear rings
should be examined for wear.

Ejectors

An ejector is a form of pump which has no moving parts. An ejector
arrangement is shown in Figure 5.7, Chapter 5. A high-pressure liquid
or a vapour such as steam discharges from a nozzle as a high-velocity jet
and entrains any gases or liquids surrounding the nozzle. The mixture
enters a converging-diverging diffuser tube where some of the kinetic
energy is converted into pressure energy. Ejectors can be arranged as
single or multi-stage units and have particular applications, for example
the air ejector in a closed feed system (see Chapter 5).

Piping systems

A ship's machinery space contains hundreds of metres of piping and
fittings. The various systems are arranged to carry many different
liquids at various temperatures and pressures. The influences of
operational and safety requirements, as well as legislation, result in
somewhat complicated arrangements of what are a few basic fittings.
Valves, strainers, branch pipes, etc., are examples of fittings which are
found in a pipe system.

Pipes
Machinery space pipework is made up of assorted straight lengths and
bends joined by flanges with an appropriate gasket or joint between, or
very small-bore piping may use compression couplings. The piping
material will be chosen to suit the liquid carried and the system
conditions. Some examples are given in Table 6,1,
Where piping is to be galvanised, the completed pipe with all joints
fully welded is to be hot dipped galvanised. The pipes are supported

Table 6.1 Pipework material
System Material
Waste steam Carbon steel to BS 3601
SW circulating Aluminium brass
Wash deck and firemain Carbon steel to BS3601 — galvanised
Bilge and ballast Carbon steel to BS3601 - galvanised
Control air Copper
Starting air Carbon steel to BS 3602