Page 122 - Introduction to Marine Engineering

Feed systems 109

devaporiser is circulated by the feedwater before it enters the
de-aerator.
The de-aerator feedwater is very close to the steam temperature at the
same pressure and will, if subjected to any pressure drop, 'flash-off into
steam. This can result in 'gassing', i.e. vapour forming in the feed pump
suction. To avoid this problem, the de-aerator is mounted high up in the
machinery space to give a positive suction head to the feed pumps.
Alternatively a booster or extraction pump may be fitted at the
de-aerator outlet.

Feed pump

The feed pump raises the feedwater to a pressure high enough for it to
enter the boiler.
For auxiliary boilers, where small amounts of feedwater are pumped,
a steam-driven reciprocating positive displacement pump may be used.
This type of pump is described in Chapter 6. Another type of feed
pump often used on package boiler installations is known as an 'electro

Throat preoura connection
Nozzle box
Baffle plate wwsmbly
Mirth coupling
Wear down cover
Turbine »haft bolt
Turbine wheel
Ovmpeed
trip gear

Suction pmsure
conrwctlon

Exhaust connection
Knock-out knob
Figure 5.10 Turbo-feed pump