Emerson Liebert iCOM - Manual (Page 22)

Operation
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3.2 Motorized Ball Valve in Digital Scroll Units
On digital scroll units, discharge pressure is controlled by a motorized ball valve. During unloaded
operation, pressure changes during each digital cycle could cause a pressure-controlled water regulat-
ing valve to open and close an excessive number of times.
The motorized ball valve is designed to maintain a consistent peak discharge pressure on Water/Gly-
col Cooled Digital Compressor Systems.
The control algorithm for the motorized ball valve uses an intelligent sampling rate and adjustable
pressure thresholds to reduce the number of times the valve opens and closes. The valve assembly
consists of the brass valve, linkage and actuator.
Each compressor has one motorized ball valve that is driven by the analog output of the Liebert iCOM
control board based on pressure. If there is a call for cooling, the compressor start is delayed by a 30-
second timer. During this delay, the motorized ball valve is set to 50% open. The compressor will start
after the 30-second timer elapses.
Motorized Ball Valve Manual Mode: (Service/Service) Manual operation can be selected to allow
service personnel to control the motorized ball valve from the Liebert iCOM control only when the
system is in manual mode.
When Auto BV Control is selected, the motorized ball valve functions as it would be during normal
system operation.
When Manual BV Control is selected, the user must be careful in setting the analog output because
the ball valves will remain in the position set in the Service menu until the control is switched back to
Auto or until a technician changes the valves to another manual position (the motorized ball valve in
manual mode can be set in 1% increments from fully closed to fully open). Low- or high-discharge
pressure may occur during this mode, depending on environmental conditions and the position of the
motorized ball valve.
The motorized ball valve is driven by a 2-10VDC proportional control signal: the valve is closed at
2VDC, 50% open at 6VDC and fully open at 10 VDC.
3.2.1 MBV Operation After Compressor is Turned Off
Once a compressor has stopped, the MBV control will continue to change the MBV position to main-
tain system pressures for a maximum time of 10 minutes by following the auto control algorythm.
When the 10-minute delay has expired or the discharge pressure is below its minimum threshold the
motorized ball valve will close until the next compressor activation.
3.2.2 Service Offset—Changing System Pressure Settings
The MBV control is set to maintain a system pressure specific to the particular type of cooling unit. A
properly trained and qualified technician can increase or decrease the pressure through the Ball
Valve Setpoint Offset found in the Service/Options Setup menu. The range is 0 to 50 PSI; the default
is 30 PSI.
NOTE
Compressor operation will be delayed 30 seconds to allow the motorized ball valve to position
itself for initial startup.
NOTE
Adjusting this parameter will increase or decrease the operating compressor discharge
pressure by changing the targeted range of control. The discharge pressure is the peak pressure
of the digital cycle.