Section 9 Low pressure compressed air systems
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Naval Ships, January 2023 - Volume 2 Machinery and Engineering Systems - Part 7 Piping Systems - Chapter 5 Ship Type Piping Systems - Section 9 Low pressure compressed air systems

Section 9 Low pressure compressed air systems

Parent topic: Chapter 5 Ship Type Piping Systems

9.1 General

9.1.1 The requirements of this Section are additional to those contained in Vol 2, Pt 7, Ch 5, 2 Construction and installation of this Chapter.

9.1.2 Low pressure (LP) compressed air systems are to produce and distribute oil and moisture free cool compressed air throughout the ship to supply all systems and equipment where the air pressure requirements are 7 bar and below. The systems are to include air compressors, oil/water separators, filter/dryers, distribution lines and air receivers. For the purpose of maintenance and safety regulatory requirements, LP air systems may be defined as those where the air pressure requirements are 25–40 bar and below and this is to be defined in the System Design Description required by Vol 2, Pt 7, Ch 5, 1.3 Documentation required for design review 1.3.2.

9.1.3 The design of LP compressed air systems is to be capable of providing continuous flow for all demands of equipment and system consumers recognising continuous and intermittent users. This includes any portable equipment that may be part of the ship's equipment. Compressed air systems used for specific purposes such as for engine or gas turbine starting are also to comply with the requirements of this Section and Vol 2, Pt 7, Ch 3, 12 Air compressors and air starting arrangements and Vol 2, Pt 2, Ch 2, 6 Materials as applicable.

9.1.4 The quality (dryness, purity, etc) requirements of compressed air is to be recognised in the selection of compressors, equipment, filters and dryers to be included in the system(s).

9.1.5 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. Dedicated LP air compressors feeding directly into a distribution system for LP air users; or

  3. Supply from the HP air system to dedicated air pressure reducing valves/stations and air receivers feeding into a distribution system for LP users.

Where the arrangements are configured as described in Vol 2, Pt 7, Ch 5, 9.1 General 9.1.5 and Vol 2, Pt 7, Ch 5, 9.1 General 9.1.5.(b), arrangements are to be made for connections to the LP air system via reducing valves/stations from the HP compressed air system.

9.2 Compressors and reducing valves/stations

9.2.1 Where LP air is not derived from the HP air system, two or more LP air compressors are to be provided of sufficient capacity to supply the total design demand of the system with any one compressor out of action.

9.2.2 With the exception of the need to trunk in an air supply for CBRN design in Vol 2, Pt 7, Ch 5, 8.2 Compressors 8.2.5, the requirements of Vol 2, Pt 7, Ch 5, 8.2 Compressors 8.2.2 to Vol 2, Pt 7, Ch 5, 8.2 Compressors 8.2.7 are also to be complied with for LP air compressors.

9.2.3 Where the design of the LP compressed air system requires the use of dedicated LP air compressors feeding directly into a distribution system of LP air users, the compressors are to be capable of continuous running with arrangements for ensuring that compressor output matches demand.

9.2.4 Where LP air is derived only from a HP compressed air system, two or more reducing valves/stations are to be provided of sufficient capacity to supply the total demand of the LP air system with any one reducing valve/station out of action.

9.3 Air receivers

9.3.1 The LP air system and associated air receivers are to be configured to provide sufficient capacity to supply LP compressed air to users when the distribution line is isolated due to failure or damage.

9.3.2 The configuration of the LP air system and associated air receivers for each essential user of LP compressed air is to be arranged to provide, without replenishment, sufficient air to operate systems and equipment at an agreed capability level for an agreed period of time. In general, at least two air receivers of approximately equal capacity are to be provided for each essential user or group of users.

9.3.3 All air receivers are to be provided with mounting and fittings required by Vol 2, Pt 8, Ch 2, 9 Mountings and fittings.

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

9.4 Distribution system

9.4.1 The arrangement of LP compressed air pipes and isolation valves is to ensure continuous availability of supply in the event of the loss of any one compartment or zone. Isolating valves are to be fitted in each branch from the distribution system(s) to permit isolation of any damaged branches.

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

9.4.3 Reducing valves/stations for users of reduced pressure air are to be provided throughout the ship. 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. In-line filters are to be fitted at each reducing valve/station on the high pressure side.

9.4.4 A means is to be provided for connecting the LP compressed air system to a shore connection.

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