Sizing a Marine Air Compressor for Starting and Service Air

Two numbers and one constraint

A marine air compressor is specified by the flow you need in m3/h, the working pressure in MPa, and whether cooling water is available where the unit has to sit. Everything else on the datasheet follows from those. Most starting air systems are built around 3.0MPa, which is 30bar, so that is the pressure most enquiries land on.

Working back from the receiver

Start with the air receiver volume and the charging time your classification society requires. Those two give the free air delivery the compressor has to produce at your working pressure. That is the number to send us. Quoting from a nameplate kW figure instead is how vessels end up with an oversized motor and a compressor that short cycles.

Reference models in the range

Published sample models include a double row air cooled piston compressor at 20.4 m3/h (0.34 m3/min) and 3.0MPa, 600 r/min on a 5.5kW motor at 210KG, and a 14.5 m3/h (0.24 m3/min) unit at 3.0MPa running 1200 r/min on a 4kW motor at 160KG, with 18.5 and 22 m3/h variants at 1500 and 1800 r/min. Anything between or beyond those points is built to order.

Air cooled or water cooled

Air cooling removes the seawater connection entirely, which takes out a hull penetration, a fouling problem and a maintenance item. It suits small and medium duty. Water cooling is used where the heat load or the ambient temperature in the machinery space is high enough that air cooling cannot keep up.

The emergency compressor is a different machine

Class requires an independent means of starting the main engine when the main receivers are empty. An emergency compressor is judged on whether it starts and delivers after weeks standing idle, not on duty cycle efficiency, and it is often installed outside the main machinery space, which makes noise a real constraint. Specify it separately from the service compressor.

Getting it accepted on arrival

Every compressor is tested before it leaves the factory, and the test video and test report can be supplied before shipment. We issue written installation advice for the connection to your receivers and pipework, and the marine type certificate from CCS, BV, LR or RINA is applied for against the society you name on the order.