1.3 Bilge system: operation
The bilge system is used to remove small quantities of fluid that have leaked or condensed into a dry space. The system serves the machinery spaces, cargo holds, cofferdams, voids, stores, tunnels and pump rooms. Each space has its own piping but the pump is likely to be shared. 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.
The emergency bilge suction or bilge
injection valve is used to prevent flooding of the ship. It is a direct suction
from the machinery space bilge which is connected to the largest capacity pump
or pumps. An emergency bilge pump is required for passenger ships but may also
be fitted as an extra on cargo ships. It must be a completely independent unit
capable of operating even if submerged.
Bilge and ballast systems are interconnected
so that each can perform the other's function in an emergency, ie a ballast
pump could be used to pump out a flooded engine room. They are connected by
means of a crossover valve.
A centrifugal pump with a priming device is usually used, driven by an electric motor housed in an air bell. The power supply is arranged from the emergency generator. The various pumps and lines are interconnected to some extent so that each pump can act as an alternative or standby for another. The capacity of a bilge system is defined by the diameter of the bilge main and pump capacity for the volume of the enclosed space.
As an example, the pumping system in a passenger
ship must be able to drain water from any dry space when one or more of the
ship’s other compartments are flooded. However, the system is not required to
empty the flooded space. A flooded passenger ship is required to have at least
one bilge pump, with its own power supply, available for pumping. Bilge
suctions must have remotely operated suction valves. The minimum number of
pumps required is three or four, depending on the ship’s design.
Mud boxes and strum boxes (line filters) are
fitted at the ends and in bilge lines to stop debris being sucked into the
pipe.
The requirements for bilge systems on ships carrying dangerous goods are basically the same as for cargo ships. However, systems drawing fluids from gas-hazard spaces are kept segregated with their own pumps and pipes, where appropriate, from systems serving gas-safe spaces.