Lubrication Cycle; Summary; Details; Bearings - Carrier AquaEdge 19XR Start-Up, Operation And Maintenance Instructions Manual

LUBRICATION CYCLE

Summary

The oil pump, oil filter, and oil cooler make up a package locat-
ed partially in the transmission casing of the compressor-motor
assembly. The oil is pumped into a filter assembly to remove
foreign particles and is then forced into an oil cooler heat ex-
changer where the oil is cooled to proper operational tempera-
tures. 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 trans-
mission 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 observa-
tion. 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 oper-
ation, the oil sump temperature ranges between 125 and 165F
(52 and 74C).
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 140F (49 and 60C).
As the oil leaves the oil cooler, it passes the oil pressure trans-
ducer 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 lubricates the motor shaft bearings and the rear pinion
bearing. The oil temperature is measured in the bearing hous-
ing as it leaves the bearings. The oil then drains into the oil res-
ervoir at the base of the compressor. The control measures the
temperature of the oil in the sump and maintains the tempera-
ture during shutdown. This temperature is read on the HMI de-
fault screen. See the Controls Operation and Troubleshooting
Manual for details.
During the chiller start-up, the oil pump is energized and pro-
vides 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 com-
pressor 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 ra-
dial and thrust bearings. The low speed shaft assembly is sup-
ported by two journal bearings. For 19XR2-E the bearings are
located between the motor rotor and the bull gear — overhung
rotor design. The 19XR6-7 is fully supported with bearings lo-
cated 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 Frame 2 19XR compressors the high speed shaft assembly
is supported by two journal bearings located at the
transmission end and mid-span, behind the labyrinth seal. The
transmission side of the midspan bearing also contains a tilting
shoe type thrust bearing which opposes the main axial forces
tending to pull the impeller towards the suction end. The
impeller side face of the midspan bearing includes a babbitted
thrust face, designed to handle counter-thrust forces.
For 19XR Frame 3, 4, 5, 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
housing 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 op-
erating 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 refrigerant in the chiller. As the compressor pulls the re-
frigerant 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 compres-
sor 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 pressure is much lower than the cooler
pressure, the refrigerant boils off, leaving the oil behind to be
collected by the primary oil recovery method.
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