Engineering manual - SAB 193-233-283 S A-frame (including ATEX)
008831 en 2020.10
41/168
Technical description
4.9 No pump oil system
The screw compressor unit is designed to be self-lubricating. Oil supplied to the compressor from
the oil separator is at system head pressure. In the compressor, oil from all lubricating points is
returned to a point in the compressor body where the pressure is lower than the compressor dis-
charge pressure. During normal compressor operation, the compressor unit essentially operates
as its own oil pump. All oil entering the compressor is moved by the compressor rotors out the
compressor outlet and back to the oil separator.
For normal high-stage operation an oil pump is not required.
4.10 Demand pump oil system
This system is designed to provide adequate compressor lubrication when the oil differential pres-
sure across the compressor suction and discharge side is low. It applies to high-stage and booster
applications.
On start-up, the control system calculates the differential pressure between the compressor dis-
charge and the main oil injection port. If this differential pressure is less than 2.5 bar [35 psi], the
demand pump will turn on and continue to run until obtaining a 3 bar [45 psi] differential
pressure.
Note: For alarm descriptions and shutdown or cut-out parameters, see separate control system
manual.
4.11 Flow security
To ensure compressor lubrication before start-up, an oil level transmitter (LIT) is placed in the oil
separator reservoir. The transmitter registers the oil level and is connected electrically to a tem-
perature sensor, which will only let the compressor start when both limits are fulfilled.
4.12 Compressor oil separation system
The compressor is an oil flooded screw compressor. The oil charged to the compressor for lubrica-
tion, sealing and cooling of the compressor block is mixed with the refrigerant gas and led to the
oil separator collectively.
Oil and gas are separated in the oil separator and the gas, which is almost free of oil, leaves the
compressor unit through the discharge connection. The system is described in detail below.
Note: Automatic oil return: Open service valves completely to keep coalescer end of separator
free of oil.
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