Emerson 3000 Motorized Ball Valve-Digital Scroll Compressors, Manual Flushing, Control

Water-Cooled Models—Self-Contained Compressor

Figure 22 Metrex Valve adjustment

Adjusting collar nut

Table 12 Refrigerant control settings psi (kPa)

Low Pressure	Low Pressure	High Pressure
Cut Out	Cut In	Cut Out
20 (137.9)	65 (448.2)	400 (2758)

Manual Flushing

The valve may be flushed by rotating the socket head screw clockwise. This screw must be in the OUT position (counterclockwise) for normal valve operation.

4.4Motorized Ball Valve—Digital Scroll Compressors

On digital scroll units, discharge pressure is controlled by a motorized ball valve. During unloaded operation, the pressure changes during each digital cycle could cause excessive repositions with a pressure-operated water regulating valve. The control algorithm for the motorized ball valve uses an intelligent sampling rate and adjustable pressure thresholds to reduce valve repositions. The valve assembly consists of the brass valve, linkage and actuator.

4.4.1Control

The valve actuator operates on 24VAC power and is controlled by a 2-10VDC proportional control sig- nal. The valve will move from fully open to fully closed in 60 seconds. At 2VDC, the valve is closed; at 10VDC, the valve is fully open. There is a 20-second delay to position the motorized ball valve before starting the compressor.

Control Method

The control utilizes an upper and lower pressure threshold with a 35psi (241kPa) deadband to reduce valve movement. If the liquid pressure is between the upper and lower threshold, the valve remains at the current position. If the liquid pressure exceeds the upper threshold the valve opens, and if the pressure falls below the lower threshold the valve closes. There are multiple adjustment bands to ease discharge pressure back into control range.

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