Air Receiver (Starting / Service Air)

Main designs

• Starting air receivers (starting air bottles), designed for the high pressure used for engine starting, typically 25 to 30 bar
• Control air receivers, which buffer the supply to automation and instrumentation
• Service air receivers for workshop, tools and general consumers at lower pressure
• Horizontal and vertical designs, chosen to fit the available space and the way the condensate is drained
• Receivers from small volumes up to very large vessels, in welded steel, with a cylindrical shell and domed ends

Main components

• Shell with domed ends and welded nozzles for the connections
• Inlet from the compressor with a non-return valve, and an outlet to the consumers with a stop valve
• Safety valve set to protect the vessel, and a pressure gauge for the operator
• Drain at the lowest point for condensate and oil, manual or automatic
• Manhole or inspection opening, so the inside can be examined during survey
• Name plate with design pressure, test pressure, volume and approval references

Selection and sizing

• Design pressure with a margin above the compressor's cut-out pressure and the maximum working pressure
• Volume and number of receivers, set by the requirement for consecutive engine starts, see the class rules for the engine type
• Arrangement of the receivers so that the starting air supply remains available if one receiver is out of service
• Connection to the main compressors and to an emergency compressor, with isolation valves
• Orientation, support and connection size, so the receiver fits the machinery space and the piping layout
• Internal corrosion protection and the drainage arrangement for water and oil

Regulations and class

Class rules require that the starting air system can start the main engine a stated number of times without recharging, with rules for the number and capacity of the receivers and the time in which the compressors must refill them. The pressure vessel itself is built to a recognised design code and approved by the classification society, which also carries out the periodic internal inspections, pressure tests and thickness measurements. Safety valves and pressure gauges are tested at intervals, and pipework for starting air has to meet separate rules on non-return valves and protection against explosions in the line.

Typical faults

• Internal corrosion from condensate that has not been drained, especially at the bottom of horizontal receivers
• Oil carry-over from the compressor into the receiver, which creates a risk of fire or explosion in the starting air line
• Faulty or stuck drain valves, which allow water to build up or air to escape
• Leaking safety valves or non-return valves, with a loss of pressure between starts
• Pressure loss from small leaks at flanges, valves or the manhole seal
• Out-of-date survey or test dates, found at class survey or port state control

What to look for in a supplier

• A type-approval certificate or design approval that matches the exact vessel, pressure and volume
• Documentation of the design code, the material and the weld tests, supplied with the vessel
• Safety valves, drain valves and gauges that are approved for the pressure and the medium
• Internal coating and surface protection, with information on repair if the coating is damaged
• Delivery with the connections, supports and name plate as required by the survey society

Drain every receiver at least once per watch and note when and how much water came out. A sudden increase in drained oil or water often means a compressor problem, and it is cheaper to find out before the next start.