Emerson Vilter Vission 20/20 Operation And Service Manual page 196

Section 24 • Twin Screw Control
Operation
Once the twin screw is configured, its operation is
very similar to the single screw's, and all options that
are available for single screw configuration are also
available for twin screw. The only operational differ-
ence is the manual mode of operation. Twin screw
compressors can experience leaky slide seals that can
cause the capacity slide to drift after it has been po-
sitioned by the controller. To counteract the capacity
slide drift problem, the twin screw manual mode op-
eration has an added anti-drift feature that automati-
cally maintains the position of the hydraulic actuator.
Slide Calibration - Capacity Slide Valve
Potentiometer
This section provides critical information and control
parameters related to the capacity slide actuator. The
"% cap" display shows the actual percentage value of
the capacity slide without any conditioning that might
24 – 2
Figure 24-2. Slide Calibration - Fixed VI
Vission 20/20 • Operation and Service Manual • Emerson • 35391SC 2.7
be applied to the other capacity position displays. In ad-
dition, this section displays the value of the actuator's
signals in millivolts in the "input Value" display box, see
Figure 24-2.
"-" Button:
• When the operator presses and holds this button, the
output associated with the capacity slide decrease
solenoid is energized and the oil pump is energized.
The oil pump is needed to force oil into the capacity
slide chamber to move the capacity slide.
"+" Button:
• When the operator presses and holds this button, the
output associated with the capacity slide increase
solenoid is energized and the oil pump is energized.
The oil pump is needed to force oil into the capacity
slide chamber to move the capacity slide.