Brief Analysis of Commonly Used Automatic Control Devices in the Refrigeration System

High/Low Pressure Controller:
It is used to control the suction end and the discharge end of the refrigeration compressor to prevent it from being damaged due to too low suction pressure and too high discharge pressure. When the pressure in the system is greater than the set point, the high-pressure controller will act; when it is lower than the set point, the low-pressure controller will act.
Solenoid Valve:
It controls the connection, disconnection or change of the flow direction of different media such as liquid or gas in the system.
Load Relief Solenoid Valve:
The solenoid valve automatically unloads and adjusts the refrigeration compressor according to the load of the evaporator, making the power of the compressor match the cooling capacity requirement of the evaporator and achieving the purpose of energy conservation.
Thermal Expansion Valve:
It is used to regulate the flow rate of the liquid refrigerant in the evaporator, and the supply amount is controlled by the superheat of the refrigerant. There are two types of thermal expansion valves: internal balance type and external balance type.
Flow Switch:
It is mainly used to measure and control the liquid flow rate flowing through the pipeline, such as water, ethylene glycol, etc.
Differential Pressure Controller:
It is a safety switch that can be used to protect the refrigeration compressor from being damaged due to too low lubricating oil pressure. If the oil pressure decreases, after a period of time, the controller will stop the compressor from working. It can also be used in the water system. By controlling the pressure difference between the inlet and outlet ends of the pipeline, the system can achieve a constant flow rate.
Temperature Controller:
It is an electrical switch that controls the temperature range and can be matched with the solenoid valve to control the temperature of the cold storage.
Anti-freeze Switch:
It is an electrical switch that controls the temperature range and can be matched with the solenoid valve to control the temperature of the cold storage. Its action point is determined according to the set value of the temperature controller and the sensed temperature.
Evaporating Pressure Regulating Valve:
It keeps the refrigeration unit at an appropriate evaporating pressure, which is beneficial for the compressor to operate under stable suction pressure conditions.
It can also be used as an indirect temperature controller to prevent the evaporator from freezing.
Hot Gas Bypass Valve:
It is used to regulate the refrigeration capacity of the compressor to match it with the load of the evaporator. The hot gas bypass valve can be installed on the bypass pipeline on the high-pressure side or the low-pressure side of the refrigeration system. Through the bypass pipeline, the hot gas on the high-pressure side is sent to the low-pressure side to replace part of the load, so that the suction pressure of the compressor is not lower than the limit value.
Liquid Injection Valve:
Generally installed at the discharge end of the compressor of the refrigeration unit, it is used to protect the refrigeration unit from being damaged or stopped due to too high discharge temperature or oil temperature.
Suction Pressure Regulation:
Installed on the suction pipe of the compressor, the suction pressure regulating valve is an automatic valve set between the outlet of the evaporator and the inlet of the compressor.
Differential Pressure Valve:
It maintains a constant pressure difference between the front and rear or the upper and lower ends of the refrigeration equipment.
Float Valve:
The float valve also belongs to the throttling mechanism, which has the functions of throttling and reducing pressure and keeping the liquid level in the container stable.
Condensing Pressure Regulating Valve:
Generally installed on the cooling water pipeline of the condenser (there are two types: air-cooled and water-cooled), it regulates the flow rate of the cooling water according to the change of the condensing pressure. When the discharge pressure of the compressor rises (that is, the condensing pressure rises), the valve will automatically open wider to allow more cooling water to enter the condenser and speed up the condensation speed of the refrigerant; conversely, when the discharge pressure drops, the valve will automatically close smaller to reduce the amount of cooling water entering the condenser, thus keeping the condensing pressure within a certain range.
Safety Valve:
When the pressure exceeds the set value, it will automatically open to release the excess pressure.
Pressure Gauge Valve:
It is a stop valve between the pressure gauge and the pressure vessel. When the pressure gauge needs to be replaced, this valve can be closed for replacement.
Check Valve:
It prevents the refrigerant from flowing backward and is also called a one-way valve. It is generally installed on the liquid supply or exhaust pipeline of the refrigeration compressor.
Four-way Valve:
It is a key component in the heat pump type air conditioner, playing the role of switching between cooling and heating in the refrigeration system.

By changing the directions of the compressor's exhaust pipe and return pipe entering the evaporator and the condenser, the purposes of cooling and heating can be achieved.
Electronic Expansion Valve:
The electronic expansion valve, the capillary tube, and the thermal expansion valve all belong to the throttling mechanism. The angular displacement generated by the stepping motor of the electronic expansion valve drives the rotation of the valve needle in the valve body, thus realizing the automatic adjustment of the flow area of the valve port and playing the role of automatically controlling the refrigerant flow rate of the system.
Sight Glass:
It is used to check the condition of the refrigerant in the liquid pipeline of the refrigeration unit;
The water content of the refrigerant;
The liquid flow condition in the oil return pipeline from the oil separator to the compressor.
The sight glass is equipped with an indicator, which indicates the water content in the refrigerant through color changes.
The indicator is dark blue when the water content in the refrigerant is very low and pink when the water content is very high. At this time, the dryer filter needs to be replaced.