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What are the requirements of valves for pressure difference in refrigeration systems?

December 07,2023

Refrigeration systems are devices that use refrigerants to undergo phase changes at different temperatures and pressures, thereby achieving heat transfer. The main components of refrigeration systems include compressors, condensers, evaporators, throttling valves, etc., which are connected by pipes into a closed cycle. In refrigeration systems,  valves are important components that control the flow, pressure and direction of refrigerants. Their performance and selection directly affect the efficiency and safety of refrigeration systems. This article will introduce the requirements of valves for pressure difference in refrigeration systems, and how to choose suitable valves.

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Pressure difference is the pressure difference between the two ends of the valve, which is the driving force and an important indicator of the valve performance. The size and change of pressure difference will affect the opening, flow, noise, leakage, wear and tear of the valve, etc.

Therefore, valves have certain requirements for pressure difference in refrigeration systems, mainly as follows:

1. The nominal pressure of the valve should be greater than or equal to the maximum working pressure of the refrigeration system, to ensure the strength and sealing performance of the valve. Nominal pressure is the maximum pressure that the valve can withstand at a specified temperature, generally expressed by PN, in MPa. The maximum working pressure of the refrigeration system is the highest pressure of the refrigeration system under normal operation or abnormal conditions, generally expressed by Pmax, also in MPa. If the nominal pressure of the valve is lower than the maximum working pressure of the refrigeration system, the valve may burst, deform, leak and other failures, endangering the safety and stability of the refrigeration system.

2. The pressure difference range of the valve should be suitable for the pressure difference change of the refrigeration system, to ensure the regulation performance and reliability of the valve. Pressure difference range is the maximum and minimum pressure difference that the valve can work normally, generally expressed by ΔPmax and ΔPmin, also in MPa. The pressure difference change of the refrigeration system is the change of the pressure difference of the refrigeration system under different working conditions, generally determined by the properties of the refrigerant, the demand of the refrigeration capacity, the change of the ambient temperature and other factors. If the pressure difference range of the valve is not suitable for the pressure difference change of the refrigeration system, the valve may jam, jitter, lose control and other failures, affecting the effect and life of the refrigeration system.

3. The pressure difference loss of the valve should be as small as possible, to improve the efficiency and energy saving performance of the refrigeration system. Pressure difference loss is the pressure drop caused by the valve to the refrigerant flow, generally expressed by ΔPv, also in MPa. Pressure difference loss will cause the enthalpy drop of the refrigerant, thus reducing the refrigeration capacity and refrigeration efficiency of the refrigeration system. Therefore, the structure design, flow channel shape, opening control and other aspects of the valve should minimize the pressure difference loss, and the selection, installation, debugging, maintenance and other aspects of the valve should also pay attention to reduce the pressure difference loss.

According to the requirements of valves for pressure difference in refrigeration systems

The selection of suitable valves should follow the following principles:

1. According to the working medium, working pressure, working temperature, working flow and other parameters of the refrigeration system, determine the type, material, specification, connection mode and other basic parameters of the valve. The common types of valves in refrigeration systems are stop valve, ball valve, butterfly valve, Check Valve, safety valve, regulating valve, overflow valve, pressure regulating valve, etc., which have their own characteristics and application scope, and should be selected according to different working conditions and requirements. The material of the valve should be able to withstand the corrosion and temperature change of the refrigerant, the specification of the valve should match the diameter of the pipe, and the connection mode of the valve should adapt to the connection mode of the pipe.

2. According to the pressure difference change and pressure difference loss of the refrigeration system, determine the flow coefficient, opening characteristic, flow characteristic and other performance parameters of the valve. Flow coefficient is the flow of the valve under unit pressure difference, generally expressed by Cv, in m3/h. The larger the flow coefficient, the stronger the flow capacity of the valve, and the smaller the pressure difference loss. Opening characteristic is the relationship between the opening and the flow coefficient of the valve, generally there are linear, balanced and quick opening three types. Flow characteristic is the relationship between the opening and the flow of the valve, generally there are linear, balanced and equal percentage three types. The performance parameters of the valve should be selected according to the control requirements and flow changes of the refrigeration system.

3. According to the safety and reliability of the refrigeration system, determine the sealing performance, strength performance, durability performance and other safety parameters of the valve. Sealing performance is the leakage of the valve in the closed state, generally expressed by L, in m3/h. The better the sealing performance, the stronger the shut-off ability of the valve, and the higher the safety of the refrigeration system. Strength performance is the strength and stiffness of the valve under the specified pressure and temperature, generally expressed by σ, in MPa. The better the strength performance, the stronger the pressure resistance of the valve, and the higher the stability of the refrigeration system. Durability performance is the service life of the valve under the specified working conditions, generally expressed by N, in times. The better the durability performance, the stronger the wear resistance of the valve, and the higher the reliability of the refrigeration system.

In summary, the requirements of valves for pressure difference in refrigeration systems are multifaceted, including nominal pressure, pressure difference range, pressure difference loss, etc., which directly affect the efficiency and safety of refrigeration systems. Therefore, the selection of suitable valves should be based on the working parameters, performance parameters and safety parameters of the refrigeration system, to achieve the best matching and coordination.


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