Section 10 Low pressure compressed air systems

10.1.1 The requirements of this Section are applicable to low pressure (LP) compressed air systems intended for essential pneumatic control and instrumentation purposes. The documentation required by Pt 5, Ch 13, 1.3 Plans and particulars 1.3.1 is to provide information to demonstrate compliance with Pt 5, Ch 14, 10.1 General 10.1.2.

10.1.2 Low pressure compressed air systems are to produce and distribute cooled compressed air throughout the ship to supply all pneumatic control and instrumentation systems where the air pressure requirements are typically 0,3 to 1 MPa. LP compressed air systems may include air compressors, oil/water separators, filters, dryers, distribution lines and air receivers.

10.1.3 The design of LP compressed air systems is to be capable of providing a continuous flow of air to meet the demands of all essential services under all ambient conditions. This demand may include the use of intermittently used equipment that is part of the ship's equipment, such as power tools for machinery maintenance, testing equipment and line cleaning. Compressed air systems used for diesel engine or gas turbine starting are to comply with the requirements of Pt 5, Ch 2, 13 Air compressors and Pt 5, Ch 4, 6 Starting arrangements as applicable.

10.1.4 User equipment requirements for the quality of compressed air in terms of dewpoint (dryness), oil content and solid particle count are to be recognised in the selection and configuration of compressors, equipment, filters and dryers which are included in the system.

10.1.5 Configuration arrangements of LP compressed air systems may consist of:

1. Dedicated LP air compressors and LP air receivers with a distribution system for LP users; or

2. Supply from the starting air system to dedicated air pressure reducing valves/cross-over stations feeding into a distribution system for LP users.

10.2.1 Where LP air is not derived from the starting air system, at least two LP air compressors are to be provided. The output of any one compressor is to match the total demand of all essential users. The system is to be arranged for auto-start of the compressors and means are to be provided to indicate if any compressor is operating longer and more frequently than the manufacturer’s recommended operating periods.

10.2.2 If only one LP air compressor is to be provided, a cross connection to the starting air system is to be made via a reducing valve/cross-connection station.

10.2.3 Where LP air is derived only from the starting air system, at least two means of supplying air to the LP air system are to be provided. Each of the two means of supplying air is to have sufficient capability of supplying the total demand on the LP air system with one of the means out of action.

10.2.4 Where the starting air system is fitted with an auxiliary compressor it is to be capable of continuous running and to be capable of maintaining the stored capacity of starting compressed air in the air receivers as required by Pt 5, Ch 2, 13 Air compressors and Pt 5, Ch 4, 6 Starting arrangements whilst also supplying essential LP services.

10.2.5 Where the starting air system is designed to maintain sufficient compressed air for LP services and engine starting arrangements, an additional auxiliary compressor will not be required.

10.3.1 The LP air system and any associated air receivers are to be configured to provide sufficient stored energy to supply LP compressed air without the pressure in the system falling below a level that is insufficient for the operation of all essential users. See also Pt 6, Ch 1, 2.5 Control systems, general requirements 2.5.7.

10.3.2 All air receivers are to comply with the requirements of Pt 5, Ch 11 Other Pressure Vessels as applicable.

10.3.3 Stop valves on air receivers are to permit slow opening to avoid sudden pressure rises in the piping system.

10.4.1 Drain pots with drain valves are to be provided throughout the distribution system at all low points.

10.4.2 Pipelines that are situated on the low pressure side of reducing valves/stations and that are not designed to withstand the full pressure of the source supply, are to be provided with pressure gauges and with relief valves having sufficient capacity to protect the piping against excessive pressure.

10.4.3 In-line filters capable of being cleaned/changed without interrupting the flow of filtered air are to be fitted in the system.

10.5.1 Where valves, which are required by the Rules to be capable of being closed from outside a machinery space in the event of a fire, have pneumatic closing arrangements, a dedicated air receiver is to be fitted to supply compressed air to the valves. This air receiver is to be located outside the machinery space.

10.5.2 The air receiver is to be maintained fully charged from the main LP air system via a non-return valve located at the air receiver inlet which is to be locked in the open position.

10.5.3 In the case of passenger ships, a permanently attached hand-operated air compressor capable of charging the air receiver is to be provided in the space in which the air receiver is located.

10.5.4 The capacity of the air receiver is to be sufficient to operate all valves and any other essential supplies such as ventilation flaps without replenishment.

10.5.5 Where valves, which are required by the Rules to be capable of being operated in the event of a flooding, are pneumatically operated, the arrangements are to comply with Pt 5, Ch 14, 10.5 Pneumatic remote control valves 10.5.6.

10.5.6 A compressor is to be fitted to supply compressed air to the valves. This compressor is to be accessible and operable in the flooding condition. Where valves are required by the Rules to be operable from above the bulkhead deck, the compressor is to be located above the bulkhead deck. Consideration shall be given to alternative arrangements which are equivalent to those required by the Rules.

10.6.1 The control, alarm and monitoring systems are to comply with Pt 6, Ch 1 Control Engineering Systems.