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Water-Cooled Models—Self-Contained Compressor
39
Figure 22 Metrex Valve adjustment
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.
4.4 Motorized 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.
4.4.1 Control
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.
Table 12 Refrigerant control settings psi (kPa)
Low Pressure
Cut Out
Low Pressure
Cut In
High Pressure
Cut Out
20 (137.9) 65 (448.2) 400 (2758)
Adjusting collar nut