Engineering manual - UniSAB III 1.10.8
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001930 en 2021.06
excess pressure is calculated as the difference between oil pressure before filter (P4) and the discharge
pressure (P2).
2.2.37
Oil pump low pressure shutdown
SGC compressors (SAB 120
→
→
151, SAB 193
→
→
355, SAB 193 H
→
→
355 H, SAB 157 HR and SAB 273 S)
This shutdown is issued if the oil pump excess pressure is less than a preset value, see Table 9. The
shutdown is only active when the oil pump is running, and it is delayed with a preset delay
Oil pump low
shutdown
, see Table 52.
For SAB 120
→
151, SAB 193
→
355, SAB 193 H
→
355 H, SAB 157 HR and SAB 273 S, the oil pump ex-
cess pressure is calculated as the difference between oil pressure before filter (P4) and the discharge
pressure (P2).
2.2.38
Liquid slugging alarm
This alarm protects against possible liquid in the compressor. The alarm is issued by a sudden decrease
in discharge temperature which is greater than default 5
°
K for a fixed 5-second period. The 5°K limit is
set in
Set point 1
for Discharge gas superheat.
For reciprocating compressors, the alarm will be suppressed for 20 seconds after compressor motor
start to avoid a false alarm in the start-up phase.
For reciprocating compressors, the alarm will also be suppressed for 60 seconds after a capacity step
has been engaged to avoid a false alarm. This is because the discharge temperature may drop due to
the increased capacity when a capacity step is engaged.
For screw compressors, the alarm will be suppressed for 20 seconds after compressor motor start to
avoid a false alarm in the start-up phase.
For SABflex, the alarm will be suppressed for 20 seconds after compressor motor start and during the
stop sequence to avoid a false alarm in the start-up and stop phases.
2.2.39
Liquid slugging shutdown
This shutdown protects against possible liquid in the compressor. The shutdown is issued by a sudden
decrease in discharge temperature which is greater than default 10
°
K for a fixed 5-second period. The
10°K limit is set in
Set point 2
for Discharge gas superheat.
For reciprocating compressors, the shutdown will be suppressed for 20 seconds after compressor motor
start to avoid a false shutdown in the start-up phase.
For reciprocating compressors, the shutdown will also be suppressed for 60 seconds after a capacity
step has been engaged to avoid a false shutdown. This is because the discharge temperature may drop
due to the increased capacity when a capacity step is engaged.
For screw compressors, the alarm will be suppressed for 20 seconds after compressor motor start to
avoid a false alarm in the start-up phase.
For SABflex, the shutdown will be suppressed for 20 seconds after compressor motor start and during
the stop sequence to avoid a false shutdown in the start-up and stop phases.
2.2.40
High balance pressure reduction alarm
This alarm is released if the calculated
balance pressure reduction
P
bal_press_red, rel
= P
disch, abs
– P
oil_press_
2, abs
is higher than the high alarm limit. See Table 9.
The high oil balance pressure reduction supervision function is operative when the compressor is
running.
2.2.41
High balance pressure reduction shutdown
This shutdown is released if the calculated
balance pressure reduction
P
bal_press_red, rel
= P
disch, abs
– P
oil_
press_2, abs
is higher than the high shutdown limit. See Table 9.
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