1. Centrifugal compressor with
3. Control center.
4. Chiller section.
2. Refrigerant colled motor.
5. Condenser section.
Figure 7-22.High-speed (36,000 rpm) single-stage centrifugal chiller.
pins. Hermetically sealed compressor units used in
Figure 7-23 shows a cross section of a typical open
type of eccentric shaft compressor with suction valves
in the valve plate of the head. Most belt-driven open
type of compressors under 3 horsepower use a splash
feed lubrication, but in larger size compressors, forced
feed systems having positive displacement oil pumps
are more common. The oil pump is usually driven
from the rear end of the main shaft. Oil from the
crankcase is forced under pressure through a hole in
the main shaft to the seal, main bearing, and rod
bearing, and through a hole in the rod up to the piston
window air conditioners are quite common in
commercial sizes (under 5 horsepower) and are even
made by some manufacturers in large tonnage sizes.
sometimes made in small sizes, but large tonnage units
are always of the semisealed type. The primary
difference between a fully sealed and a semisealed
motor compressor is that in semisealed types the valve
plates, and in some units the oil pump, can be removed
for repair or replacement. This type of construction is
helpful in larger sizes that are so bulky they would
cause considerable trouble and expense in shipping,
removing, and replacing the unit as a whole. Figure
7-24 shows a small semisealed compressor.
Sealed or semisealed units eliminate the belt drive
and crankshaft seal, both of which are among the chief
causes of service calls.
Sealed and semisealed
compressors are made either vertical or horizontal.
The vertical type (fig. 7-25) usually has a positive
displacement oil pump that forces oil under pressure of
10 to 30 psi to the main bearings, rod, or eccentric and
pins, although they are sometimes splash oiled.
Although oil pumps for forced feed lubrication are
also used on horizontal hermetic compressors, oil