There are generally three types of lubrication systems in reciprocating compressors. They are for high-pressure, low-pressure, and oil-free air compressors.

High-pressure air compressor cylinders (except for nonlubricated compressors) are generally lubricated by an adjustable mechanical force-feed lubricator. This unit is driven from a reciprocating or rotary part of the compressor. Oil is fed from the cylinder lubricator by separate lines to each cylinder. A check valve at the end of each feedline keeps the compressed air from forcing the oil back into the lubricator. Each feedline has a sight-glass oil flow indicator. Lubrication begins automatically as the compressor starts up. Figure 14-7 shows the lubrication connections for the cylinders. The type and grade of oil used in

Figure 14-7.-High-pressure air compressor showing the lubrication system.

compressors is specified in the applicable NAVSEA technical manual. The correct type is vital to the operation and reliability of the compressor.

The running gear is lubricated by an oil pump that is attached to the compressor and driven from the compressor shaft. This pump is usually a gear type. It moves oil from the reservoir (oil sump) in the compressor base and delivers it through a filter to an oil cooler (if installed). From the cooler, the oil is distributed to the top of each main bearing, to the spray nozzles for the reduction gears, and to the outboard bearings. The crankshaft is drilled so that oil fed to the main bearings is picked up at the main bearing journals and carried to the crank journals. The connecting rods contain passages that conduct lubricating oil from the crank bearings up to the piston pin bushings. As oil is forced out from the various bearings, it drips back into the oil sump (in the base of the compressor) and is recirculated. Oil from the outboard bearings is carried back to the sump by drain lines.

A low-pressure air compressor lubrication system is shown in figure 14-8. This system is similar to that of the running gear lubrication system for the high-pressure air compressor. Nonlubricated reciprocating compressors have lubricated running gear (shaft and bearings) but no lubrication for the pistons and valves. This design produces oil-free air.