Engineering manual - SAB 355 Screw compressor unit (including ATEX)
004100 en 2020.10
39/156
Technical description
Easy to operate
UniSAB III has a systematic and easily accessible user interface which does not require any spe-
cial knowledge or education.
Operational data and status appear from the distinct display which features four lines with twenty
characters each. The user interface has arrow keys for menu selection, set key for parameter
changing and keys for selection of start/stop and resetting. Manual/automatic operation and
manual capacity regulation is performed with function keys.
Safety monitoring and control
UniSAB III provides safe monitoring by means of shutdown and alarm values/settings for all
measuring points. If a set value is exceeded, a red diode will flash slowly in alarm situations with-
out stopping the compressor and quickly in shutdown situations. A display text will show the
cause of the alarm or shutdown. In both alarm and shutdown situations separate relays are acti-
vated for connection of a remote lamp, bell or alarm panel.
It is easy to find all the set values and their alarm and shutdown values through the straightfor-
ward menu system.
Besides monitoring the compressor pressures and temperatures, UniSAB III also calculates the
suction pressure vapour overheating, monitors the capacity slide position and oil flow and calcu-
lates the oil filter differential pressure on screw compressors and SMC reciprocating compressors.
For correct fault diagnosis in case of compressor shutdown, UniSAB III immediately stores all
shutdown situations in its memory which can be displayed and analysed on the display at any
time.
Instrumentation
Depending on the compressor type, UniSAB III is equipped with a number of pressure and tem-
perature transducers as well as position transmitters on the compressor.
Screw compressors are fitted with four pressure transducers and three temperature transducers
as well as one or two slide position transmitters.
Furthermore, a thermistor input is available for motor protection.
Factory test
Every UniSAB III is tested during the production process and when it is mounted on the compres-
sor. A computer test is performed before the compressor leaves the factory.
For further information, see separate UniSAB III manual.
4.1.4 Compressor
The compressor is equipped with an external suction filter (23a), which is mounted on the com-
pressor suction port. The suction filter has a built-in non-return valve (21), preventing the com-
pressor from rotating backwards during an idle period. See section 4.1.6 Suction filter with built-
in non-return valve.
The filter prevents impurities in the gas from entering and damaging the compressor.
The suction stop valve (101) is mounted directly on the suction filter. The discharge gas is sent via
the discharge line to the oil separator (193). Gas on the discharge side of the compressor is mixed
with a relatively large amount of oil injected into the compressor for lubrication, cooling and tight-
ening. The oil and the gas must be separated before the discharge gas proceeds into the refriger-
ation plant.
The rotary screw compressor uses mating asymmetrical profile helical rotors to provide a continu-
ous flow of refrigerant vapour. Rotor lobe combination 4+6 male rotor drive is designed for both
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