3.3.22 SABflex
The SABflex compressor is a frequency regulated screw compressor without capacity slide but
with automatic Vi-control. A demand driven oil pump is optional.
Starting sequence
Once the compressor has received permission to start, Unisab III will send a start signal to
the frequency converter and to the cooling fan.
When the compressor starts up, the SSTV valve will close in order to reduce the internal suc-
tion pressure and quickly increase the oil pressure. When the timer Start unload has run out,
the Start-up limiter is activated and the timer Max. start-up time is started.
The SSTV valve is kept closed until the oil pressure is above the low alarm curve Y + a neutral
zone (NZ
oil,rel
) and the suction pressure is below high alarm limit for internal suction pressure
- a neutral zone (NZ
suct,int
).
Speed will remain at 1,000 rpm until the oil pressure is above the low alarm curve Y and the
internal suction pressure is below high alarm limit for internal suction pressure. If the timer
Max. start-up time runs out before the oil and suction pressure is inside the alarm limits, the
compressor is stopped with a shutdown.
After this forced start-up period, where oil and suction pressures are inside the alarm limits,
the compressor is now in normal operation. The SSTV limiters for High torque, high internal
suction pressure and low oil pressure will now be active too.
The default setting for the timer Start unload is 15 seconds and for Max. start-up time it is
600 seconds.
Alarm surveillance
During start-up the following alarms are delayed:
Low oil pressure 15 sec.
High filter diff. pressure 300 sec.
Low superheat 300 sec.
High superheat 300 sec.
Low/high oil temperature 300 sec.
The delayed alarms are described in section 6.5. Timers.
Running
After the starting sequence and during normal running operation the following SSTV limiters
will be active: high torque, low oil pressure and high internal suction pressure. See subsection
3.2.3. Special limiters for more information.
Stopping sequence
At normal stop (to avoid back-spin) the SSTV valve is closed for the time stated in the timer
SSTV delay before the compressor is stopped. The default setting is 40 seconds but it is ad-
justable between 0 and 60 seconds.
Note: The SSTV timer starts counting after the stop delay timer has run out. This means that
the compressor will not stop immediately even though the stop key is pressed or the instant
stop digital input is removed.
Compressor control and surveillance
Engineering manual - Unisab III 1.10
001930 en 2014.09
113/319
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