Flooded type water cooled screw chiller (PCB Control) MCAC-CTSM-2012-11
80
For easier startup of compressor, the loading must be minimized. Therefore, SV1 is energized to
bypass oil to the low-pressure side directly. The slider does not move and keep the maximum
opening in suction end to bypass the refrigerant. After the completion of startup the compressor then
can increase loading gradually by de-energizing the SV1 solenoid valve. It is recommended to run
compressor at 25% loading for about 30 seconds before starting to increase loading.
Partial load: 50% Operation
With the same principle as stated in 25% loading, SV2 is engergized and others are de-energized to
achieve 50% loading.
Partial load：75% Operation
Receiving a feedback from system demanding for lower capacity, the SV3 is energized to allow oil to
flow back to the low-pressure side through the valve channel. The piston returns to the outlet of SV3
oil passage and the slide block moves to let part refrigerant flow back to the low-pressure side
through bypass opening. This action would reduce the discharge volume and make the compressor
operating at 75% loading
Full load: 100% operation
After the completion of startup, SV1, SV2 and SV3 are de-energized and oil flows straight to cylinder
and pushes piston forward, driving the slider to gradually reduce bypass opening. When the
opening is closed completely, the compressor is running at 100% loading.
Stepless control (25%~50%)
Solenoid valve activating table of stepless control
SV
Status
SV0
(NC)
SV1
(NC)
Startup OFF ON
Loading ON OFF
Unloading OFF ON
Holding OFF OFF
ON: energize, OFF: de-energize
The principle of linear capacity control system is same as four-step one, except that the control logic
of solenoid valve varies. The four-step capacity-control needs three NC (normal close) solenoid
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