Emerson VSG & VSSG Specifications Page 43

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Section 2 • Operational Descriptions
Single Screw Compressor PLC Operation Manual • Vilter/Emerson • 35391CM
Figure 2-16. Operational Diagram - VPLUS
VPLUS LIQUID INJECTION PUMP
Reference Figure 2-16
If installed, VPLUS liquid injection is a method of oil cool-
ing where liquid refrigerant is pumped through a nozzle
in the discharge housing of the compressor. A variable
speed pump regulates the amount of liquid pumped
into the compressor to control the amount of cooling.
A PID controller adjusts the speed of the VPLUS pump to
control compressor discharge temperature (tempera-
ture of the gas and oil mixture leaving the compressor).
When the discharge temperature exceeds the desired
temperature plus a deadband, the pump will increase
speed to add more cooling. When discharge tempera-
ture drops below the desired temperature minus a dead-
band, the pump will decrease speed.
When the compressor is stopped, the pump is
stopped.
When the compressor is running, the discharge
temperature rises above the “Start Pump At” set-
point and Separator Oil Temperature rises above
“Oil Separator Override Temp” in the “VPLUS Pump
Setpoints” screen, the pump will start at a settable
minimum speed.
• When the compressor is running and the discharge
temperature is above the deadband, the PID control-
ler will increase the pump speed.
• When the compressor is running and the discharge
temperature is below the deadband, the PID control-
ler will decrease the pump speed.
LIQUID
REFRIGERANT
S
TE
SUCTION
DISCHARGE
COMPRESSOR
VPLUS
TARGET
OUTPUT
TEMPERATURE
START
TEMPERATURE
MINIMUM PUMP
SPEED
DISCHARGE TEMPERATURE
PUMP SPEED
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