Drives Most compressors are directly coupled to their power source - usually the electric motor. Some are belt driven, another attempt to get quieter operation. Belt drives were particularly common on the continent of Europe. As mentioned above, some diesel locomotives drive the compressor pump directly through a mechanical link with the diesel engine, so there is no separate electric motor. Cooling Compressing air makes it hot, so at least one set of cooling pipes will be provided.
Some compressors have two sets.
Of course, the cooling produces condensation, which collects as water in the air pipes and, combined with oil from the compressor lubrication, forms a sludge which can quickly clog up sensitive brake valves. To overcome this problem, air systems are nowadays always provided with air dryers. Drying The air dryer consists of a pair of cylinders containing desiccant, which extracts the water and allows dry air to pass into the main reservoir. Water collected is automatically dumped once in each pumping cycle - the noise of the burst of water being discharged can often be heard at the end of the compressor's pumping cycle. The governor is designed to detect the point at which the compressed air level in the system has fallen to the lowest permitted level.