Emerson Vilter VSS - Section 2 • Theory of Operation; Refrigerant Flow; Oil Life and Oil Flow

2 – 1
VSS/VSM/VSH/VSSH • Installation, Operation and Maintenance Manual • Emerson • 35391SD
Section 2 • Theory of Operation
The refrigeration and oil systems work in unison, but
each one will be explained separately. Reference Figure
2-1 for refrigerant and oil ow descriptions. This is a typi-
cal refrigeration system with thermosyphon oil cooling.
Refrigerant Flow
The refrigeration compression process begins as refrig-
erant vapor enters the suction inlet (12). The refrigerant
vapor ows through a suction stop/check valve (11),
then through a strainer (10) to the compressor (9). The
refrigerant is then pressurized through the compressor
and discharged as high pressure refrigerant vapor into
the oil separator (1). In the oil separator, the oil is then
separated from the discharged refrigerant by impinge-
ment separation. The high pressure refrigerant ows out
to the condenser for cooling while the oil is pumped or
siphoned back to the compressor.
Moreover, suction stop/check valve (11) and discharge
check valve (2) are provided between the oil separator
to prevent refrigerant vapor or liquid from owing back
to the compressor during shutdown periods.
Oil Life and Oil Flow
Oil in the refrigeration system serves three primary pur-
poses. They are compressor lubrication, sealing clear-
ances between moving parts, and heat removal result-
ing from heat of compression and friction. Initially, oil
ow is driven by a mechanical gear pump (3). Once the
system reaches design conditions, the oil pump is shut
off and oil ow is maintained by differential pressure.
As the oil is separated from the refrigerant in the oil
separator (1), it is pumped or siphoned through an oil
cooler (5), then through an oil lter (4) and back to the
injection port (6) of the compressor (9). For additional
Figure 2-1. Refrigeration Compressor Unit P&ID
(Thermosyphon Oil Cooling with Single Oil Filter Shown)
LG
001
LG
002
FG
001
PI
003
DRAIN
TW
BLEED
MW
BLEED
TW
D100
OIL CHARGE
BLEED
CAPACITY
TW
750W
TW
250#
C100
V100
VOLUME
SUCTION
STOP VALVE
DISCHARGE STOP VALVE
D101
P100
TW
750W
TW
750W
DRAIN
DISCHARGE CHECK VALVE
PI
002
PI
001
TE
001
TE
004
QE
003
TE
005
PI
004
BLEED
PT
004
PT
003
PT
002
D102
D103
TW
TE
002
QE
001
QE
002
OIL SEPARATOR
COALESCING OIL RETURN LINE
HIGH PRESSURE
R717 VAPOR OUTLET
R717 VAPOR
TO ATMOSPHERE
LOW PRESSURE
R717 VAPOR INLET
PT
001
COMPRESSOR
MOTOR
FILTER
MOTOR AND
OIL PUMP
T
E100
R717 LIQUID
INLET
R717 LIQUID/VAPOR
OUTLET
100
PSID
SUCTION
CHECK VALVE
OPTIONAL
(STANDARD FOR BOOSTER &
SWING COMPRESSORS ONLY)
11 10
9
1
2
3
5
4
6
7
12
8