Engineering manual - SAB 355 Screw compressor unit (including ATEX)
004100 en 2020.10
61/156
Technical description
cooler is mounted on the unit with the oil piping connected. Water connections and controls are
field installed.
Thermosyphon oil cooling: The optional thermosyphon cooler is a plate and shell design (Vah-
terus) or a plate type oil cooler (AlfaNova). It is designed for design pressure 28 bar on the shell
side and 28 bar on the plate side. The oil coolers are mounted on the unit with the oil piping con-
nected. Refrigerant connections and controls are field installed. The oil temperature is maintained
between 50°C [120°F] and 60°C [140°F].
4.1.28 Liquid injection oil cooling
High-stage compressor units may be supplied with single-port (low Vi) or dual-port (low Vi and
high Vi) liquid injection oil cooling. Single port will be furnished for low compression ratio opera-
tion and dual port for high compression ratio operation. Booster compressor units use single-port
liquid injection oil cooling due to the typically lower compression ratios.
The control system on high-stage units with dual-port liquid injection oil cooling automatically
switches the liquid refrigerant supply to the high port when the compressor is operating at higher
compression ratios (above 3.5 Vi) for best efficiency.
Where low compression ratios are anticipated, thermosyphon or water-cooled oil cooling should
be used.
It is imperative that an uninterrupted supply of high pressure liquid refrigerant is provided to
the injection system at all times. Two items are of extreme importance, the design of the re-
ceiver/liquid injection supply and the size of the liquid line.
It is recommended that the receiver is oversized sufficiently to retain a five minute supply of re-
frigerant for oil cooling. The evaporator supply must be secondary to this consideration. Two
methods of accomplishing this are shown below.
The dual dip tube method, Fig. 37, uses two dip tubes in the receiver. The liquid tube is below the
evaporator tube to ensure continued oil cooling when the receiver level is low.
Fig. 37: Dual dip tube method
The level control method, Fig. 38, utilises a float level control on the receiver to close a solenoid
valve feeding the evaporator when the liquid falls below the amount necessary for five minutes of
liquid injection oil cooling.
To evaporator
To compressor
oil c
ooling system
From condenser
Receiver
Locate to provide
5 min. liquid supply
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