air compressor · compression system

Sauer WP 4060

The Sauer WP4060 is a marine air compressor, a machine that compresses air to high pressure for use aboard ship, most importantly to provide the starting air that turns large diesel engines over to start them. Large low-speed and many medium-speed marine engines are started not by an electric motor but by admitting high-pressure compressed air into the cylinders, so a supply of air stored in receivers at high pressure is essential, and the air compressor is the machine that charges those receivers. A compressor of this class is typically a multi-stage reciprocating machine: air is compressed in successive cylinders of decreasing size, with cooling between the stages, so that it can be raised to the high pressure (commonly around thirty bar for engine starting air) without excessive temperature. Compressing air heats it, so intercoolers between stages and an aftercooler remove heat, improve efficiency and remove moisture, while relief valves protect each stage and drains remove condensed water and oil. The compressor draws through a suction filter and delivers through a non-return valve to the air receivers. On board, starting-air compressors are usually installed in pairs or more to give redundancy, and they run automatically to keep the air receivers charged to pressure, cutting in and out as air is used for starting and manoeuvring the main and auxiliary engines and for other services such as control air and the ship's whistle. Reliability is important, because without starting air the engines cannot be started, and the compressors, receivers and associated pipework form part of the classed and surveyed machinery of the ship. Maintenance covers the valves, piston rings, cooling and the safety devices, and the correct functioning of drains and relief valves is watched closely. The Sauer WP4060 typifies the high-pressure marine air compressor that quietly performs the essential task of keeping a ship's engines ready to start.