Engineering manual - SAB 355 Screw compressor unit (including ATEX)
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004100 en 2020.10
Technical description
4.1.24 Oil level switch
Fig. 33: Oil level switch
An oil level switch is mounted on the oil separator. Under normal operation the switch must al-
ways be activated. If the oil level drops below minimum the switch will be deactivated and this will
be registered on the UniSAB III control system.
4.1.25 Cold-start system
The unit is equipped with a special "cold-start" discharge valve. This valve ensures a rapid devel-
opment of oil pressure at initial start-up in order to lubricate the compressor without requiring an
oil pump, even in cold ambient temperatures with all pressures equalised.
Warning!
Be extremely careful when dismantling the cold-start valve on the discharge side of the unit, as
condensed refrigerant often is trapped between the cold-start valve and the stop valve. A bleed
valve on the side of the check valve is used to vent the space between the check valve and the
stop valve.
Exposure to refrigerant fumes can cause injury or death.
Warning!
Inside the valve, there is a very heavy, tight spring. Provided the valve is intact, the spring
presents no danger when dismantling.
High-stage units
For high-stage units, the cold-start valve is equipped with a large spring which creates a 2.0 bar
[30 psi] pressure in the oil separator (above suction pressure) for lubrication of the compressor.
Once the compressor is running it will begin to force gas to the condenser at connection P2.
As the condenser heats up, the pressure will begin to rise as the compressor suction pulls down in
pressure. As soon as a differential pressure has developed between the condenser and suction
side, these pressures will act across a piston inside the cold-start valve to partially overcome the
spring force. When the differential pressure reaches and exceeds 2.0 bar [30 psi], the piston fully
overcomes the spring force and powers the valve fully open for a very low operating pressure
drop.
F
our red LEDs
Plast housing
M4 fixing screw
NW27
1/2 “ BSP
Tube AISI304
Dia. 15 mm
PROCAP -LS20
105 mm
77 mm
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