As a result of this, the spring force, position 9, is equalised and a transverse bore, position 10, with a
considerably larger bore than position 7, will open.
Because the bore is larger, oil collections at the oil return valve inlet can quickly be removed.
When the oil has been removed, the gas flow will rise, and the piston, position 7, will close the
transverse bore. The gas flow will be lowered to a minimum.
Through the sight glass, position 6, it is possible to watch the oil return. As a small amount of gas
will always pass through the nozzle, position 7, gas bubbles will be visible.
You can service the valve by closing the stop valves, position 3 and 4.
Figure 21: Sectional view of valve structure
Note:
The sectional view shows the valve structure. Some of the internal oil channels are not
visible.
Cold-start system
The unit is equipped with a special "cold-start" discharge valve. This valve ensures a rapid
development 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
Exposure to refrigerant fumes can cause injury or death.
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.
49
SAB 283-355 A-Frame OHU 6042 and OHU 7650 (including ATEX) Screw Compressor Unit
