Figure 3-17.Compressor assembly.
female rotor is driven aerodynamically by the
male. There is no physical contact between the
two rotors or between the rotors and case. Inter-
rotor contact is prevented by the rotors riding on
a film of refrigeration oil. Both rotors are
suspended by three pairs of ball bearings, one set
on the discharge end and two pairs on the inlet
end. Bearing lubrication is supplied by the
refrigeration oil. Suitable carbon and labyrinth
seals are incorporated to provide control of the
flow of lubricating oil. Thin ridges are machined
on the ends and flutes of the rotors to seal the
mechanism against excessive rotor leakage.
The compressor operates on the principle that
if a given volume of gas is trapped and the area
in which it is contained gradually decreases, the
pressure and temperature of the gas will increase.
The counterrotating rotors are fed a gas charge
from the inlet port. This charge fills the void
formed by the rotors. As they rotate, the charge is
trapped and forced forward through the housing.
The action of the rotors is to decrease the interlobe
area in which the charge is contained as they
revolve. This increases the pressure and tempera-
ture of the refrigerant. As the outlet port is
reached, the charge will be contained in the small-
est area during its travel through the compressor.
Therefore, it is at its highest temperature and pres-
sure and is discharged into the system.
The variable compressor speed is provided by
the governor-controlled, hydraulically driven
motor, which responds to electronic impulses
from the Freon circuit to increase or decrease
speed as demanded by the cooling load.
The electrical wiring of the speed-sensing sys-
tem is such that when the equipment cooling sys-
tem is shut down, the servomotor will be driven to
low speed. This relieves starting loads and also
precludes the possibility of an overspeed during
The compressed Freon gas is discharged from
the compressor and immediately passes through
a check valve, which prevents the high-pressure
discharge from motorizing the compressor in
reverse at system shutdown.
The compressor section requires lubrication;
therefore, an oil is mixed with the Freon during
system servicing. This oil is also discharged from
the compressor outlet and is reclaimed by the oil
OIL SEPARATOR. The oil separator is
located downstream of the compressor and check
valve. It operates on a centrifugal principle; that
is, the oil mist refrigerant enters the inlet port of
the separator at a tangent to the wall of the
cylindrical housing. This imparts a swirling or
centrifugal action to the mixture. The centrifugal
force has a greater effect on the heavier oil vapors,
causing them to collect on the walls and the
conical screen. The oil drips from the screen and
collects at the bottom of the oil separator.
Oil flows from the bottom of the separator
through an oil flow indicator and filter and is
injected into the compressor at the shaft seal
cavity. The refrigerant vapor rises through the
tubular baffle and leaves the separator. A circular
sight gauge is provided on the separator to check
the level of system oil during operation. Normal
oil level is a half full sight gauge.
OIL FLOW INDICATOR. The oil flow
indicator in the oil return line is basically a metal
cage with a sight window. It is used to observe
the amount of oil returning to the compressor and
to prevent compressor failure when no flow is
OIL FILTER. Oil returning to the com-
pressor passes through a filter, which ensures a