Operating manual - SAB 120-151 A-frame (including ATEX)
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008668 en 2019.08
Operating instructions
Fig. 19: Control valve
Adjustment (capacity control)
Capacity slide valve movement for SAB 120 and 151 without adjustment, driven by the pressure
difference between suction and discharge sides of the compressor, will cause the capacity slide to
move fast towards higher capacity (up) and slow towards lower capacity (down). To avoid this
two one way regulating valves, 181 and 182, are built in as shown in Fig. 19. The regulating
valves separate the up and down slide speed.
The regulation valves are provided to adjust slide valve travel time, preventing excessive slide
valve “hunting”. The two valves should be adjusted to restrict oil flow to the compressor port so
that slide valve travel time from full load to full unload, or vice versa, is minimum 30 seconds.
See also the Engineering manual for Unisab for adjustment of the slide speed.
Note: A change in operating conditions, such as winter-to-summer operation, may require read-
justment of the slide valve travel time.
6.15 Volumizer II Vi control
The compressor is equipped with a special internal control that automatically adjusts the com-
pressor volume ratio to the most efficient of three available steps, (2.2, 3.5, or 5.0 volume ratio).
This gives the compressor the ability to operate at varying operating conditions while minimising
power consumption by avoiding over or undercompression.
Solenoid valves 3 and 4 control the Volumizer® II volume ratio control. Oil is internally ported to
apply hydraulic pressure to two stepping pistons in order to move the moveable slide stop to the
optimum position. The following chart shows the logic of solenoid operation to adjust the volume
ratio.
Vi YY3
YY4
2.2
Energised Energised
3.5
Deenergised Energised
5.0
Deenergised Deenergised
2
Control valve port labels
Energise “b” coil (YY2) to load
Energise “a” coil (YY1) to unload
182
181
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