Page 141 - Offshore Electrical Engineering Manual

128 CHAPTER 12 Process Drives and Starting Requirements

FIGURE 2.12.3
Typical electric shaft-driven fire water pump.
Courtesy SPP Offshore, a division of SPP Ltd.

lowered down the suction or ‘stilling’ tube. Alternatively, the stilling tube may be
sectionalised and the motor fixed in the lowest section of the tube. The tube is then
lowered down a platform riser and jointed section by section until the motor suction
is 10 or more metres below the sea surface at the height of the lowest expected tide.
For cooling purposes, the motor must be below the pump, and therefore, difficulty
is often experienced in avoiding damage to cables which have to pass between the
pump and the stilling tube in order to reach the motor terminals. Bites need to be
taken out of the pump retaining flanges to allow the cables past, and the cable overall
diameter must allow a loose fit through these to avoid damage. A photograph of this
type of pump set is shown in Fig. 2.12.4.

DIESEL–ELECTRIC FIRE PUMPS
Statutorily, every offshore installation has to be provided with at least two (depend-
ing on the capacity) serviceable fire pumps, each of which must be powered indepen-
dent of the other. A third pump must be provided to cater for unavailability during
servicing. Pumps must also be physically segregated and located geographically well
away from each other to minimise the risk of both pump systems being damaged by
the same fire or explosion. Further details on capacities of pumps etc. are obtainable
from the Department of Energy Guidance Notes on Offshore Firefighting Equipment
(see Appendix A).