RXB PLUS ROTARY SCREW COMPRESSOR UNITS S70-101 IOM
Page 33
OPERATION
DUAL-PORT LIQUID INJECTION
The dual-port liquid injection system is designed to obtain
the most efficient compressor performance at high and low
compression ratios by permitting injection of liquid refriger-
ant into one of two ports on the compressor.
The dual-port system contains all the components of the
single-port system with the addition of a double-acting sole-
noid valve SV9 and operates as outlined.
Solenoid valve SV7 is energized by the microprocessor when
the temperature element (TE3), installed in the oil piping
after the oil filter, exceeds the LICO setpoint. Liquid refriger-
ant is then passed through the temperature control valve
TCV1 to the double-acting solenoid valve SV9. Depending
on the compressor’s operating volume ratio Vi, the micropro-
cessor will select the flow of the liquid refrigerant to either
compressor port 3 or port 4.
When the compressor operates at 3.5 or 2.2, Vi compressor
port 3 (low Vi) supplies the liquid cooling. At 5.0 Vi, port 4
(high Vi) supplies the liquid cooling.
The temperature control valve TCV1 is equalized to a con-
stant back pressure by the differential pressure control valve
PDCV.
Both the differential pressure control valve PDCV and the
double-acting solenoid valve SV9 use discharge gas to
maintain downstream pressure. The gas downstream of both
valves is bled off to the compressor suction to ensure steady
and constant operation of the valves.
LIQUID INJECTION
ADJUSTMENT PROCEDURE
1. Close vent valve (V4).
2. Open service valve (V5) until approximately 80 PSIG is
registered at the Pressure Indicator (PI).
3. Open vent valve (V4) until 75 PSIG is registered at the
Pressure Indicator (PI).
4. Monitor the oil temperature of the compressor. If the oil
temperature rises above 130
O
F (R-717) or 150
O
F (R-22),
open vent valve (V4) a very small amount. This will reduce
pressure on the equalizer and allow more refrigerant to flow
to the compressor. If the oil temperature drops below 110
O
F
(R-717) or 130
O
F (R-22), close vent valve (V4) a very small
amount. This will increase pressure on the equalizer. The
ideal condition is to maintain an oil temperature as stable
as possible. An incorrectly tuned liquid injection system will
cause extreme swings in the discharge temperature and
the oil temperature.
The vent valve (V4) MUST be open
at least 1/4 turn during normal op-
eration. A higher initial pressure
(step 2) may be required.
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