Engineering manual - UniSAB III 1.10.8
150/346
001930 en 2021.06
Compressor control and surveillance
3.7
Compressor control - adjusting slide speed
(screw compressors with hydraulic slides)
3.7.1
Capacity slide
The capacity slide is moved by adding or removing oil from the slide piston cylinder. The movement is
controlled by UniSAB III which activates the solenoid valves in the oil lines and moves the slide in the de-
sired direction. If this movement happens too fast, the system will become very unstable and cause un-
necessary wear and tear of the slide. To prevent this, adjustable throttle valves have been built into the
oil lines on most compressor types (Not SAB 80). By changing the opening degree of the throttle valves,
the slide movement can be adjusted to a suitable speed. The slide speed is checked with the compres-
sor in
Manual
mode, at normal oil temperature and by activating
and
used for capacity regulation.
With the slide in minimum position (< 5%) and with a constant pressure on
(capacity up), it takes
about 60 seconds for the slide to move to 100% and with a constant pressure on
(capacity down) ap-
proximately 60 seconds to move down to 0%.
If this is not the case, adjust the throttle valves. If the compressor is not equipped with throttle valves (e.
g. SAB 80) or if it is not possible to adjust the slide speed to approximately 60 seconds, do the following:
Measure the actual time it takes to move the slide from minimum to maximum position and then insert
that time in the menu
Control values/Capacity/CapacityControl/
Run time = xx.x sec.
For SAB 120, 151, 193, 233, 283 and 355 UniSAB III is preset to individual capacity slide movement
speed, i.e. the
Run Time
setting found in
Control values/Capacity/Capacity./Control/ Run Time
is com-
pressor type dependent. To get the
Run Time
setting for this compressor type see subsection
points for regulators, note 2
.
3.7.2
Volume ratio slide
The volume ratio slide is moved by adding or removing oil for the slide piston cylinder. The movement is
controlled by UniSAB III which activates the solenoid valves in the oil lines and moves the slide in the de-
sired direction. If this movement happens too fast, the system will become very unstable and cause un-
necessary wear and tear of the slide.
To prevent this, adjustable throttle valves have been built into the oil lines. By changing the opening de-
gree of the throttle valves, the slide movement can be adjusted to a suitable speed. The speed is
checked with the compressor in
Manual
mode and at a normal oil temperature. Bring the capacity slide
to 20-30% position. Select picture
Control values/Capacity/Vi slide pos./Control
and change the value
Set point 1 = 0.0%
to -10% by pressing
. This will move the slide to minimum position.
Return to
Vi slide pos./Values
to check the slide movement. When the slide has reached minimum,
change
Set point
to 110%. The slide will now move to maximum position. Check the speed of the move-
ment from 0% to 100% in the picture
Vi slide pos./Values
.
The movement from 0% to 100% must be adjusted on the throttle valves to last approximately 60 sec.
The same applies to the movement from 100% to 0%.
Use
Set point 1
with either -10% or 110% to move the slide back and forth until the speed is correct.
If it is not possible to adjust the speed to approximately 60 seconds or if the compressor is not equipped
with throttle valves, do the following: Measure the actual time it takes to move the slide from minimum to
maximum position and insert that time in the menu
Control values/Capacity/Volume slide position/Con-
trol/ Run time = xx.x sec
.
For SAB 193, 233, 283 and 355 UniSAB III is preset to individual Vi slide movement speed, i.e. the
Run
Time
setting in
Control values/Capacity/Vi slide position/Control/ Run time
is compressor type
dependent.
To get the
Run time
setting for this compressor type, see subsection
3.1.9 Set points for regulators, Note
2.
F2
F3
F2
F3
Summary of Contents for SABROE Unisab III Control
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