Pressure Protection
Pressure control used for security purposes, is physically the same as pressurestat used as the main control. High pressure cut-out as shown below, is one of the most common pressure-controlled safety devices used in the refrigeration cycle. He feels the pressure head (highside pressure) and is typically set to the completion of a cycle down to the pressure rises too high. Excessive highside pressure might arise as a result of dirty condenser coil, pump failure, or a contamination of the water with water-cooled condenser. Dirty condenser fan fault or blocked air flow can cause excessive pressure on the air cooled condenser.
As high-pressure safety control, low-pressure control is the same device used as the primary control. Its capillary connects directly into a loop so that the system is shutting down below a predetermined minimum safe working pressure. It protects cycle from damage caused by such factors as the refrigerant loss, excessive compression, evaporator freeze-up, and air inlet in the refrigeration cycle through the lowside of the leak.
Where it is desirable to call the service mechanics attention to excessive pressure problem, fusible plug or membrane, is sometimes used.
Although these devices, as a rule, not considered as a security measure, they really protect the system from excessive pressure.
Fusible plug installation, shown here has a soft metal rod with a low melting point. In the case of very strong pressure, or fire, the temperature of molten core. This allows the gas to escape before hazardous pressure inside the loop. Rupture installation achieves the same goal in another way. Its thin metallic disk breaks above the maximum desired pressure, to avoid dangerous high blood pressure...
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Refrigeration 
