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LUBRICATION CYCLE
Summary
The oil pump, oil filter, and oil cooler make up a package located
partially in the transmission casing of the compressor-motor as-
sembly. The oil is pumped into a filter assembly to remove foreign
particles and is then forced into an oil cooler heat exchanger where
the oil is cooled to proper operational temperatures. After the oil
cooler, part of the flow is directed to the gears and the high speed
shaft bearings; the remaining flow is directed to the motor shaft
bearings. Oil drains into the transmission oil sump to complete the
cycle (Fig. 8 and 9).
Details
Oil is charged into the lubrication system through a hand valve.
Two sight glasses in the oil reservoir permit oil level observation.
Normal oil level is between the middle of the upper sight glass and
the top of the lower sight glass when the compressor is shut down.
The oil level should be visible in at least one of the 2 sight glasses
during operation. Oil sump temperature is displayed on the HMI
default screen. During compressor operation, the oil sump tem-
perature ranges between 125 and 165F (52 and 74C).
The oil pump suction is fed from the oil reservoir. An oil pres-
sure relief valve maintains differential pressure in the system at
the pump discharge. A range of 18 to 40 psid (124 to 172 kPad)
is normal. This differential pressure can be read directly from the
default HMI screen. The oil pump discharges oil to the oil filter
assembly. This filter can be closed to permit removal of the filter
without draining the entire oil system. The oil is then piped to
the oil cooler heat exchanger. The oil cooler uses refrigerant
from the condenser as the coolant. The refrigerant cools the oil
to a temperature between 120 and 140F (49 and 60C).
As the oil leaves the oil cooler, it passes the oil pressure transducer
and the sensor for the refrigerant expansion valve on the oil cooler.
The oil is then divided. Part of the oil flows to the thrust bearing,
forward pinion bearing, and gear spray. The rest of the oil lubri-
cates the motor shaft bearings and the rear pinion bearing. The oil
temperature is measured in the bearing housing as it leaves the
bearings. The oil then drains into the oil reservoir at the base of the
compressor. The control measures the temperature of the oil in the
sump and maintains the temperature during shutdown. This tem-
perature is read on the HMI default screen. See the Controls Oper-
ation and Troubleshooting Manual for details.
During the chiller start-up, the oil pump is energized and provides
40 seconds of lubrication to the bearings after pressure is verified
before starting the compressor. During shutdown, the oil pump
runs for 60 seconds to ensure lubrication as the compressor coasts
to a stop.
Ramp loading can be adjusted to help to slow the rate of guide
vane opening to minimize oil foaming at start-up. If the guide
vanes open quickly, the sudden drop in suction pressure can
cause any refrigerant in the oil to flash. The resulting oil foam
cannot be pumped efficiently; therefore, oil pressure falls off and
lubrication is poor. If oil pressure falls below 15 psid (103 kPad)
differential, the controls will shut down the compressor.
The oil pump is a gerotor-style pump with external filters. A
gerotor pump has two rotors, one inside the other; their center
points are offset with respect to each other. This type of pump
provides a smooth continuous flow. It is also quieter than other
designs. See Fig. 10 and 11.
Bearings
The 19XR compressor assemblies include a combination of radial
and thrust bearings. The low speed shaft assembly is supported by
two journal bearings. For 19XR3-E the bearings are located be-
tween the motor rotor and the bull gear — overhung rotor design.
The 19XR6-7 is fully supported with bearings located on each end
of the low speed shaft. The bearing closer to the bull gear includes
a smaller babbitted thrust face, designed to handle axial forces.
For 19XR Frame 3, C, E, 6 and 7 compressors the high speed shaft
assembly utilize rolling element bearings (radial and thrust).
Machines employing rolling element bearings can be expected to
have higher oil pressure and thrust bearing temperatures than
those compressors using journal bearing design.
Oil Reclaim System
The oil reclaim system returns oil lost from the compressor hous-
ing back to the oil reservoir by recovering the oil from 2 areas on
the chiller. The guide vane housing is the primary area of recovery.
Oil is also recovered by skimming it from the operating refrigerant
level in the cooler vessel.
PRIMARY OIL RECOVERY MODE
Oil is normally recovered through the guide vane housing on the
chiller. This is possible because oil is normally entrained with re-
frigerant in the chiller. As the compressor pulls the refrigerant up
from the cooler into the guide vane housing to be compressed, the
oil normally drops out at this point and falls to the bottom of the
guide vane housing where it accumulates. Using discharge gas
pressure to power an eductor, the oil is drawn from the housing
and is discharged into the oil reservoir.
SECONDARY OIL RECOVERY METHOD
The secondary method of oil recovery is significant under light
load conditions, when the refrigerant going up to the compressor
suction does not have enough velocity to bring oil along. Under
these conditions, oil collects in a greater concentration at the top
level of the refrigerant in the cooler. Using discharge gas to power
eductors, this oil and refrigerant mixture is skimmed from the side
of the cooler and is then drawn up to the guide vane housing.
There is a filter in this line. Because the guide vane housing pres-
sure is much lower than the cooler pressure, the refrigerant boils
off, leaving the oil behind to be collected by the primary oil recov-
ery method.
13
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