SAFETY CONTROL AND DEVICES :

Most of the safety cut outs are electric switches, actuated by bellows movement via amplifying leverage.

HIGH PRESSURE SAFETY CUT - OUT - This is used to protect against too high a discharge pressure, which will overload the compressor and may damage components. The control is usually set to cut - out and stop the compressor motor at a pressure of about 90% of the maximum working pressure of the system.

LOW PRESSURE SAFETY CUT - OUT - This is used to protect against too low a suction pressure, which usually indicates blockage or loss of refrigerant. The control is normally set to stop the compressor at a pressure corresponding to a saturation temparature 5°C below the lowest evaporating temparature. In some small plants, it is also used as a temparature control, stopping and starting the compressor to maintain the desired pressure and temparature.

OIL PRESSURE SAFETY CUT - OUT - This is used to protect against too low oil pressure in forced lubrication system. It is a differential control, using two bellows. One side responds to the low side pressure, and the other responds to the oil pressure. The oil pressure must always be greater than the low side pressure for the oil to flow. If the oil pressure falls below a minimum valve, the control stops the compressor.

THERMOSTAT - Thermostats are temparature controlled electric switches which are used for both safety and control functions. When fitted to compressor discharge lines, they are set to stop the compressor if the discharge temparature is too high.

PRESSURE RELIEF DEVICES - To prevent excessive pressure in cpmpressor and condenser of a refrigeration system, they are fitted with pressure relief devices. They are in the form of (a) spring loaded relief valves which are set to open at the maximum working pressure and close when the pressure drops to a safe level, (b) Bursting discs which comprise thin metal diaphragms designed to burst at a pressure equal to maximum working pressure and (c) Fusible plugs which contain a metal alloy which will melt when the temperature in the system corresponds to maximum working pressure.

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