Engineering manual - SAB 355 Screw compressor unit (including ATEX)
004100 en 2020.10
51/156
Technical description
Oil cooling systems should maintain oil temperature within the following ranges for R717 and
HCFC/HFC:
Liquid injection
oil cooling
External*
oil cooling
55-77°C
[130-170°F]
49-71°C
[120-160°F]
* : Refrigerant cooled (Thermosyphon) oil cooling (TSOC) or water-cooled oil cooling (WCOC.)
Table 5: Oil cooling
Single-port liquid injection. The single-port liquid injection system is designed to permit liquid
refrigerant injection into one port on the compressor at any given moment and operates as
outlined.
Solenoid valve, YY5, is energised by the microprocessor when the temperature sensor, installed
in the compressor discharge, exceeds the LIOC (Liquid Injection Oil Cooling) set point. High-pres-
sure liquid refrigerant is then supplied to the temperature control valve (TCV). See Fig. 28 and
Fig. 29.
Dual-port liquid injection
The dual-port liquid injection system is designed to obtain the most efficient compressor perform-
ance at high and low compression ratios by permitting injection of liquid refrigerant into one of
two ports optimally located on the compressor. This minimises the performance penalty incurred
with liquid injection oil cooling.
The dual-port system contains all the components of the single-port system with the addition of a
double-acting solenoid valve, YY9, and it operates as outlined.
The solenoid valve, YY5, is energised by the microprocessor when the temperature sensor, in-
stalled in the oil manifold, exceeds the LIOC set point. Liquid refrigerant is then passed through
the temperature control valve (TCV) to the double-acting solenoid valve, YY9. Depending on the
compressor’s operating volume ratio (V
i
), the microprocessor will select the flow of the liquid re-
frigerant to either compressor port SL-1 or SL-2, whichever is more efficient.
When the compressor operates below 3.5 V
i
, the compressor port, SL-1, supplies the liquid cool-
ing. When the (V
i
) rises above 3.5 V
i
, port SL-2 supplies the liquid cooling.
Liquid injection adjustment. For discharge temperature set point and PID regulator parame-
ters, refer to the operating manual for the control system. The discharge temperature set point is
set to the required oil temperature, see Table 5: Oil cooling in subsection 4.1.16
Fig. 28: P&I diagram, liquid injection with single port
C
ompressor Low Vi
Liquid refrigerant
from receiver
Solenoid valve
Strainer
Liquid line
Sight glass
Motorised
expansion
valve
Tubing line
5
170
165
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