Load Balance or Staging Valves are, essentially, hot gas bypass valves. They may be piped directly from the discharge of each compressor to the suction of that compressor or from the discharge of each compressor to the upper portion of the evaporator. On single compressor units, this connection may be piped directly from the condenser to the evaporator. In all cases, there will be an electronic expansion valve or a solenoid valve to control flow through this line.
This valve is used to ¨unload¨ the compressor while it is being brought up to operating speed. It is also used to reduce the pressure ratio of the operating compressor (ratio between discharge pressure and suction pressure), when an additional compressor is going to be brought on-line.
Under certain circumstances, under low load conditions, the valve may also be used as a hot gas by-pass.
In the more tropical climates where the author works, the Load Balance Valve/ Staging Valve, is only used during compressor ramp up and during the process of starting an additional compressor when one or more compressors are already operating.
Verification of proper operation of the valve can be accomplished by monitoring temperature of the Load Balance Valve/ Staging Valve near where the line connects to the suction of the compressor or to the evaporator. During the process of bring the compressor up to speed (ramp up), the temperature of the line will increase as the valve is opened and ot gas from the discharge/ condenser connection feeds back through the suction line/ Evaporator connection.
During compressor ramp up, as the compressor passes through the area of 10,000 to 15,000 rpm and the Discharge check valve begins to open, there will be a ¨clacking¨ noise from the discharge check valve as the compressor develops enough pressure differential (between the suction and the discharge) to overcome the spring tension holding the discharge check valve closed. In proper operation, the Load Balance Valve/ Staging Valve being open allows the compressor to pass through this phase rapidly.
If the Load Balance Valve/ Staging Valve is not working properly, there is risk that during this period when the discharge check valve is being opened during compressor ramp, the compressor pressure differential will not increase as fast as it should, the period during which the discharge check valve is transitioning from closed to open will be extended and the compressor can experience a Front Radial Bearing Displacement Fault.
Repeated instances of the compressor experiencing this Front Radial Bearing Displacement Fault can result in Front Radial Bearing failure.