The compressor's crankshaft (figure 2, item 1) is turned by an electric motor, via a V-belt drive. As the crankshaft
turns, the pistons move up and down. During the downstroke of the low-pressure piston (figure 2, item 2), air is
drawn through an intake valve in the head of the compressor into the low-pressure cylinder (figure 2, item 3).
During the upstroke of the piston, this air is compressed.
The air that was compressed by the low-pressure piston (figure 2, item 2) is then released through a discharge
valve in the head of the compressor to a finned tube intercooler where the heat resulting from compression is
allowed to dissipate. The cooler compressed air is then drawn into the high-pressure cylinder by the downstroke
of the high-pressure piston (figure 2, item 4). On the upstroke of the high-pressure piston, the air is further
compressed before being discharged through a discharge valve in the compressor head. At this point, the
compressed air enters the vessel's compressed air piping system enroute to the starting air receivers.
Figure 2. Air Compressor
The air compressor is pressure lubricated. The moving parts within the crankcase (figure 2, item 5) are supplied
with lubrication by a positive displacement, gerotor type oil pump (figure 2, item 6). Oil is drawn up from the
bottom of the crankcase to the oil pump through an oil sump strainer screen (figure 2, item 7). The oil is then
forced under pressure through the oil filter (figure 2, item 8). After being filtered, the oil travels under pressure
through drilled journals in the crankshaft (figure 2, item 1) and connecting rods (figure 2, item 9) to lubricate
crankshaft bearings, wrist pin bearings, and the cylinder walls.