The bilge system and the ballast system each have particular functions to perform but are in many ways interconnected.
Bilge system
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. 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.
Must read ➤ Types Of Piping
Ballast systems
The ballast system is arranged to ensure that water can be drawn from any tank or the sea and discharged to any other tank or the sea as required to trim the vessel. Combined or separate mains for suction and discharge may be provided. Where a tank or cargo space can be used for ballast or dry cargo then either a ballast or bilge connection will be required.
Read also ➤Pump Definition
The system must therefore be arranged so that only the appropriate pipeline is in service; the other must be securely blanked or closed off. Where tanks are arranged for either oil or ballast a change-over chest must be Fitted in the pipeline so that only the ballast main or the oil transfer main is connected to the tank.
Domestic water systems
Domestic water systems usually comprise a freshwater system for washing and drinking and a saltwater system for sanitary purposes (Figure 6.20). Both use a basically similar arrangement of an automatic pump supplying the liquid to a tank which is pressurised by compressed air. The compressed air provides the head or pressure to supply the water when required.
The pump is started automatically by a pressure switch which operates as the water level falls to a predetermined level. The freshwater system has, in addition, a calorifier or heater which is heated, usually with steam. Fresh water supplied for drinking and culinary purposes must meet purity standards specified by the Department of Transport.
Water produced from most evaporators/distillers will not meet these standards and must be treated to ensure it is biologically pure and neutral or slightly alkaline. A treatment plant suitable for a general cargo ship. The water is sterilised by an excess dose of chlorine provided as hypochlorite tablets.
It is then dechlorinated in a bed of activated carbon to remove the excess chlorine. Any colour, taste and odour which was present in the water will also be removed by the carbon. Excess chlorine is originally applied to ensure that complete sterilisation occurs.
Post a Comment