These are also used to reduce the pressure from the high to the low sides and to meter the refrigerant flow. Two forms are available:
(i) High-side float valve. When vapour condenses in the shell of the condenser the liquid level therein tends to rise. The float in the valve rises and the latter opens, liquid flows through the port, some flashing to gas as its pressure reduces with a fall in temperature. The high-side float valve works rather like a steam trap and liquid is fed into the evaporator at the same rate as gas is pumped out of it by the compressor. Most of the charge in the system resides in the evaporator and its quantity is critical: too much will cause liquid to flow from the flooded evaporator into the suction line and too little will starve the evaporator and give insufficient cooling capacity. Usually used with single evaporators, condensers and compressors, distribution difficulties may arise if used with multiple evaporators.
(ii) Low-side float valve. This is similar in function to the high-side valve but it opens when the level in the evaporator falls, admitting liquid after it has expanded through the valve port with a drop in pressure and temperature. Figure 12.2 illustrates a low-side float valve applied to a submerged evaporator.
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