29
8.7 FLYWHEEL AND MOTOR PULLEY:
Normally compressor is driven by V belt arrangement
through flywheel and motor pulley. No. of V grooves for
belts depends upon compressor shaft power and
compressor speed.
NOTE: Flywheel, Motor Pulley & V Belts must be
protected by belt guards.
8.8 OIL SEPARATOR
Figure 29: Oil Separator
A refrigerating plant is fitted with one or more oil
separators to prevent the capacity of the system from being
reduced by oil which has been carried over with the
refrigerant. Particularly at very low temperatures, this
might also lead to blockage of the system owing to freezing
of the oil in the evaporator. The separator is fitted between
the compressor and the condenser. In two stage
compressors an additional separator may be installed
between the L.P. and H. P. cylinders, before the intercooler.
The oil separator consists of a closed cylinder fitted with a
refrigerant inlet and outlet, an oil drain stop valve, an
automatic oil return valve with float and a deflector plate.
The high pressure gas enters the separator and impinges on
the deflector plate demister, causing the heavier oil
droplets to be deposited on it. The gas diffuses outwards in
a radial direction, but it is prevented from rising directly by
a baffle plate. The remainder of the oil still present in the
gas is deposited upon the separator wall by the centrifugal
effect of the gas flow. The separated oil is collected at the
bottom of the separator where a float controlled return
valve is fitted. When the oil level exceeds a preset level, the
valve opens and the oil is returned under pressure to the
crankcase (pressure in separator exceeds crankcase
pressure), The valve automatically shuts off when the oil
level has fallen sufficiently. The hand operated oil drain is
also fitted in order to be able to drain the oil during the
running in period as the oil is heavily polluted and
therefore must not be returned to the crankcase.
8.9 INTERCOOLER:
Most two-stage compressors are fitted with an intercooler
between the L.P. delivery and the H.P. suction. While being
compressed the gas temperature rises to such a level that,
without intercooling, further compression in the second
stage raises the temperature to a dangerous degree. The
Intercooler reduces the temperature of the gas from the L.P.
cylinder, thus bringing the operating temperature within
reasonable limits. There are many types of intercoolers,
from simple units to complex systems, set up adjacent to,
the compressor.
In one type of inter stage gas cooler high pressure, liquid
refrigerant is injected in the hot L. P. discharge gas by
means of an adjustable injection valve. This adjustable
injection valve may be of either thermostatic or manual
type, having automatic or non-automatic settings
respectively. From the L. P. cylinder the hot compressed
gas enters the L. P. side of intercooler. As the pressure in the
liquid receiver in which the refrigerant collects after
condensation, exceeds the delivery pressure of the L.P.
Cylinder, a certain amount of liquid will be injected into
the L.P. delivery compartment. This amount depends on
the degree of opening of the injection valve. The injected
liquid evaporates, thus lowering the temperature of L.P.
delivery gas. Since the liquid injection valve is situated on
the L.P. side of intercooler, the passage of gas from L.P. to
H.P. ensures complete evaporation of liquid. The H.P.
suction is thus operating with compressed gas of
reasonably low temperature.
1. Inter stage gas cooler with whirl vessel
2. Injection unit.
3. Main injection connection
4. Thermostatic expansion valve
5. Solenoid valve
6. Hand operated stop valve
7. The bulb for expansion valve.
8. Injection line.
Figure 30
8.10 CRANKCASE HEATER:
The crankcase may be fitted with a built-in heater to
maintain the oil at working temperature while the
compressor is stopped. Generally these crankcase heaters
are only required for R-22 plants. This is because, while the
compressor is stopped, the crankcase oil may become
saturated with liquid refrigerant, the extent depending on
the pressure and temperature. If the compressor starts
under these conditions a sudden decrease in crankcase
pressure will cause dissolved liquid refrigerant to
evaporate. This will cause foaming of the oil, thus
impeding the proper functioning of the oil pump, and also
producing the possibility of an oil stroke. Heating of the oil
while the compressor is stopped, will, ensure that the
above conditions do not arise.
Recommended Crankcase Heaters For Various
Compressors
Sr. Compressors Heater Qty Part No.
No. Type rating per
watts. Compr.
l. KC 2, KC 3,
KC 4, KC 6,
KC 21, KC 31,
KC 42, KC 51 325 1 082.26.172.50
2. KC 9, KC 12,
KC 63, KC 72
KC 84, KC 93,
KC 102 525 1 082.26.173.50
TO CONDENSER OR
INTERCOOLER
DEFLECTOR COVER
FROM
COMPRESSOR
DEFLECTOR PLATE
TO CRANKCASE
FLOAT VALVE
OIL DRAIN STOP VALVE
‘S’ TYPE
(WITH BAFFLE PLATE)
FROM COMPRESSOR
TO CONDENSER
OR INTERCOOLER
DEMISTER PAD
TO CRANKCASE
FLOAT VALVE
OIL DRAIN STOP VALVE
‘D’ TYPE
(WITH DEMISTER PAD)
REFRIGERANT GAS
OIL
2
3
4
5
8
1
7
6
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