Common Pressure Valves and Protection Devices of Refrigeration Units

1、The function of evaporative pressure regulating valve

Evaporative pressure regulating valve is generally used in a refrigeration compressor which is responsible for both high temperature cold storage and low temperature cold storage.  Evaporative pressure regulating valve is generally installed on the evaporator outlet pipe of high and low temperature cold storage to maintain the stability of evaporative pressure in evaporator of different temperature and working pressure in the system. Evaporative pressure regulating valve is divided into direct action type and control type.

2、The function of condensing pressure regulating valve

Condensing pressure regulator When the cooling system is running, the condensing pressure must be within the normal range.  If the condensing pressure is too high, it will cause the damage of refrigeration equipment and the increase of power consumption. If the condensation pressure is too low, it will cause the refrigerant liquefaction process and the expansion valve work, so that the refrigeration system can not work normally, resulting in a significant decrease in refrigeration capacity.

The condensation pressure of water-cooled condenser is adjusted by adjusting the flow rate of cooling water.  According to the working principle of different condensing pressure regulating valve is divided into temperature control of water control valve and pressure control of water control valve.  

Most of the condensing pressure regulating valves used in small and medium-sized cold storage refrigeration systems are pressure controlled water regulating valves.  Pressure control of the water control valve is directly with condensation pressure as a control signal to control the valve opening, its working principle and temperature control of the water control valve is the same.  In the structure of the pressure control water control valve also has a direct action type.  

3、The function of safety valve

In order to prevent the pipeline burst caused by the high pressure exceeding the limit value in the small and medium-sized cold storage refrigeration system, safety valve should be set on the pipeline of the refrigeration system.  In this way, when the high pressure in the system exceeds the limit, the relief valve automatically starts to discharge the refrigerant to the low pressure system or to the atmosphere.  

It is mainly composed of valve body, spool adjusting spring, adjusting screw and so on.  The inlet end of the safety valve is connected with the high pressure system, and the outlet end is connected with the low pressure system. The working principle of the safety valve is that when the high pressure in the system exceeds the safety limit value, the high pressure gas automatically opens the spool from the outlet into the low pressure system.  Normally, the opening pressure of the safety valve is limited to 2.0 ~ 2.1MPa for R22 refrigeration system.  

4、The function of fusible plugs

Fusible plugs are often used to ensure the safety of high pressure liquid storage (liquid reservoir) in small and medium sized cold storage systems where freon is used as refrigerant. The fusible alloy is cast in the fusible plug. The melting temperature of the fusible alloy is very low, generally below 75℃. The melting temperature of fusible alloys varies with the composition. Fusible plugs with different melting temperature and composition of fusible alloys can be selected according to the pressure to be controlled in the system when fusible alloys are used in refrigeration system.  

When the refrigeration system is working, if the pressure in the reservoir increases suddenly, the temperature of the refrigerant will also increase.  When the temperature rises to the melting temperature of the fusible alloy, the fusible alloy immediately melts, forming a void, and the refrigerant in the reservoir is released into the atmosphere, thus protecting the safety of the human body and equipment.  After the fusible plug is melted, it is necessary to recast the fusible alloy and continue to use it after leak detection. Generally, replacement is adopted in the maintenance process.  

5、The function of check valve

Check valve is also known as non-return valve, single flow valve, or cut-off valve, its role is to ensure that the medium in the pipeline directional flow without backflow. Check valves are installed on the exhaust pipe of the refrigeration compressor and the outlet pipe of the liquid pump. When installing check valves, note that the direction marked on the valve body should be consistent with the allowed flow of refrigerant.