Hydraulically-driven pumps improve fire-fighting reliability

Paul Boughton

Safety is a critical consideration for all offshore production facilities, and the most important part of such safety systems is the firewater pumps with its associated equipment.

Firewater pumps are left in standby for 99percent of the time. If required they will provide seawater to the firewater main in shortest possible time without creating pressure surges.

Frank Mohn AS developed the idea of using hydraulically driven firewater pumps.
As firewater pumps requires quite high pressures 30 to 35 metre above seawater level, the concept of a split design was selected.

A submerged hydraulically driven pump is used to lift water to deck level feeding a direct diesel engine driven pump to increase the pressure to the required level.
Both pumps are powered by the same diesel engine.

Advantages include:


  • The submerged pump, being a single stage, gives a robust, low vibration unit.
  • By slowly rotating the submerged pump at stand-by, the submerged unit is given a good life. This is possible due the hydraulic system. A small electric driven circulation pump is installed in the hydraulic loop, providing a continuous flow of hydraulic oil to the submerged unit.


By flexibility, it is referred to the fact that driver unit can be located away from the submerged unit. This means that the diesel engine can be moved to a safer location as opposed to a direct driven unit, which always has to be close to the submerged pump.

Frank Mohn Flatøy AS is based in Frekhaug, Norway.www.framo.no


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