The compressor is of the crosshead design. Figure
10-26 shows cross-sectional views of the LPAC. The
frame extension houses the crossheads and crosshead
guides and is open to the atmosphere. It separates the
cylinders, which are not oil lubricated, from the
crankcase. Oil wiper assemblies (seals) are located in
the frame extension to scrape lubricating oil off the
piston rods when the compressor is in operation. Oil
deflector plates are attached to the piston rods to prevent
any oil that creeps through the scrapers from entering
the cylinders. Oil that is scraped from the piston rods
drains back to the sump. Air leak along the piston rods
is prevented by full floating packing assemblies bolted
to the underside of the cylinder blocks.
During operation, ambient air is drawn into the
first-stage cylinders through the inlet filter silencers and
inlet valves during the downstroke. When the piston
reaches the bottom of its stroke, the inlet valve closes
and traps the air in the cylinder. When the piston moves
upward, the trapped air is compressed and forced out of
the first-stage cylinders, through the first-stage cooler
and the first-stage moisture separator. When the
second-stage piston starts its downstroke, the air is
drawn into the second-stage cylinder. Then, it is further
Figure 10-26.—LPAC, cross-sectional views (reciprocating type.)
10-28
