Section 2 • Theory Of Operation; Refrigerant Flow; Oil Life And Oil Flow - Emerson Vilter VSS Installation, Operation & Maintenance Manual

Section 2 • Theory of Operation
R717 VAPOR
TO ATMOSPHERE
1
DRAIN
PT PI
001
001
12
BLEED
SUCTION
STOP VALVE
LOW PRESSURE
R717 VAPOR INLET
(Thermosyphon Oil Cooling with Single Oil Filter Shown)
The refrigeration and oil systems work in unison, but
each one will be explained separately. Reference Figure
2-1 for refrigerant and oil flow 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 flows 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 flows out
to the condenser for cooling while the oil is pumped or
siphoned back to the compressor.
VSS/VSM/VSH/VSSH • Installation, Operation and Maintenance Manual • Emerson • 35391SD
250#
PI
PT
002
002
BLEED
V100
OIL SEPARATOR
LG
001
LG
002
TW
TW TW TW
750W 750W 750W
QE QE QE TE
001 002 003 005
11 10
TE
TW
004
SUCTION
CHECK VALVE
FG
001
TE
TW
001
OIL CHARGE
9
D100
MOTOR
C100
D102
COMPRESSOR
CAPACITY
Figure 2-1. Refrigeration Compressor Unit P&ID
2
DISCHARGE CHECK VALVE DISCHARGE STOP VALVE
100
PSID
OPTIONAL
MW
(STANDARD FOR BOOSTER &
SWING COMPRESSORS ONLY)
MOTOR AND
OIL PUMP
P100
4
8
PT
003
PI
BLEED
003
DRAIN
7
6
PT
004
D103
PI
VOLUME
BLEED
004
Moreover, suction stop/check valve (11) and discharge
check valve (2) are provided between the oil separator
to prevent refrigerant vapor or liquid from flowing 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
flow is driven by a mechanical gear pump (3). Once the
system reaches design conditions, the oil pump is shut
off and oil flow 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 filter (4) and back to the
injection port (6) of the compressor (9). For additional
HIGH PRESSURE
R717 VAPOR OUTLET
3
TE
002
TW
5
R717 LIQUID/VAPOR
E100
T
OUTLET
R717 LIQUID
INLET
2 – 1