Emerson iCOM user manual Motorized Ball Valve in Digital Scroll Units

Operation

3.2Motorized 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.

NOTE

Compressor operation will be delayed 30 seconds to allow the motorized ball valve to position itself for initial startup.

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.

3.2.1MBV 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.

3.2.2Service 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

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.

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