Compressor Control - Adjusting Slide Speed (Screw Compressors With Hydraulic Slides); Capacity Slide; Volume Ratio Slide - Johnson Controls SABROE UniSAB III Engineering Manual

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
With the slide in minimum position (< 5%) and with a constant pressure on
about 60 seconds for the slide to move to 100% and with a constant pressure on
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 3.1.9 Set
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 and F3
Engineering manual - UniSAB III 1.10.8
150/346
Compressor control and surveillance
used for capacity regulation.
F2
(capacity up), it takes
F3 (capacity down) ap-
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