Working principle and selection method of 5/2 solenoid valve

I. Working principle

A 5/2 solenoid valve is a key component in industrial automation control. Its core principle lies in using electromagnetic force to control the movement of the spool, thereby accurately regulating the flow path of fluids (gases or liquids). With its compact structure and powerful functions, it is widely used in pneumatic control systems.

Directional control valve: A 5/2 solenoid valve belongs to the category of directional control valves, which are essential components in fluid power systems, responsible for controlling the flow direction of fluids. In the case of 5/2 solenoid valves, they are crucial for precisely directing the movement of actuators and controlling the sequential flow of compressed air.

The solenoid valve consists of an electromagnet, a valve body, a valve core, a spring, and a seal. There are five interfaces on the valve body, marked as P (pressure inlet), A (working outlet 1), B (working outlet 2), R (exhaust/return port), and S (drain port).

Normal state (no power): At this time, the electromagnet has no magnetic force, and the valve core is in a certain initial position under the action of the spring force. Usually, the “P” port is connected to the “A” port, the “B” port is connected to the external environment or lowpressure system through the “S” port, and the “R” port is closed.

Energized state: When the solenoid is energized, it generates a strong magnetic force that attracts the spool to move to another position. At this time, the “P” port is connected to the “B” port, while the “A” port is connected to the outside world or lowpressure system through the “R” port, and the “S” port is closed. This switching of the onoff state realizes the precise control of fluid flow.

Types of 5/2 solenoid valves: 5/2 solenoid valves can be divided into singlecoil and doublecoil types. The singlecoil type usually has a spring or pilot air return, so when it is deenergized, the valve returns to its initial state. The doublecoil type has no such return facility and requires the second coil to be energized to return the valve to the starting position. The doublecoil solenoid valve has the advantage of not requiring longterm poweron, and a shortpulse signal is sufficient, which can prolong the service life of the solenoid valve.

II. Selection method

1. Fluid adaptation

• Type considerations: For gas applications, ordinary sealing materials can handle conventional gas transmission such as compressed air. If it is a liquid, such as hydraulic oil or waterglycol solution, it is necessary to select leakproof and corrosionresistant seals. If it involves acidbase corrosive liquids, the valve body material must be upgraded to stainless steel or even special alloys to prevent corrosion damage.
• Temperature range: When the working environment temperature fluctuates greatly, lowtemperature environments (such as frozen warehouse logistics automation) require solenoid valves to have strong lowtemperature tolerance to prevent the sealing material from hardening and brittle cracking. Hightemperature operations (such as steel smelting workshops) require hightemperatureresistant coils and thermally stable valve bodies to ensure stable component performance.
• Pressure adaptation: Select according to the system pressure level. Lowpressure systems (such as pneumatic valve control of small household water purification equipment) use products with a pressure resistance of 0.10.5MPa. Industrial highpressure scenarios (such as hydraulic control of oil extraction) must use solenoid valves with a pressure resistance of several MPa or even higher. Overpressure operation is prone to leakage and valve core deformation failure.
• Fluid compatibility: Fluid compatibility is a crucial factor in the selection of solenoid valves. It refers to the ability of the valve’s materials, especially the sealing materials and the valve body material, to resist the corrosion, erosion, and chemical reactions of the fluid being transported. Different fluids have different characteristics, such as acidity, alkalinity, viscosity, and volatility, which can affect the performance and service life of the solenoid valve.

Special fluids and corresponding measures: In some special applications, such as in the chemical industry, there may be fluids with strong corrosiveness, high viscosity, or low volatility. For example, when dealing with strong acidbase fluids, in addition to using stainlesssteel or alloy valve bodies, specialpurpose seals made of fluorinerubber or other highperformance materials may be required. For highviscosity fluids, it may be necessary to choose a solenoid valve with a larger flow passage to avoid blockage.

2. Matching control features

• Electronic control mode: Singleelectronic control relies on solenoid force switching and spring reset. It has a simple circuit and low cost. It is suitable for simple startstop control, such as the control of the sealing cylinder of a simple packaging machine. Dualelectric control can realize the twoway solenoid locking of the valve core and maintain the state when the power is turned off. It has significant advantages in multistep process switching in automated production lines, frequent reversals, and the need to remember the position, such as the fixture switching of welding robots in automobile manufacturing.
• Response frequency: Highspeed automated production lines (such as highspeed electronic component placement equipment) require solenoid valves to change direction quickly and move several times per second. Directacting valves with fast response are suitable for this purpose. If the frequency of movement is low, the advantages of pilotoperated valves with large flow rates are prominent, reducing energy consumption and equipment costs.
• Actuation speed: Actuation speed refers to the time it takes for a solenoid valve to switch from one state to another. For highspeed automated production lines, a fastactuationspeed solenoid valve is required to ensure the accuracy and efficiency of the production process. The actuation speed is related to the type of solenoid valve (directacting or pilotoperated), the power of the electromagnet, and the structure of the valve.
• Impact of control mode on system stability: The choice of electronic control mode has a significant impact on the stability of the control system. In some complex industrial control systems, the dualelectriccontrol mode can improve the reliability and stability of the system because it can maintain the valve core position even when the power is off. However, in some simple systems, the singleelectroniccontrol mode is sufficient, which can reduce costs and simplify the control circuit.

3. Pipeline connection coordination

• Diameter specification: Select according to the inner diameter of the pipe to ensure smooth fluid flow and avoid throttling. For smallflow finechemical addition lines, the outer diameter is 36mm. Large ventilation and gassupply main ducts need to be 20mm or larger. Too large a diameter will increase costs and cause delayed responses, while too small a diameter will hinder flow.
• Interface: Threaded connections (Gthread, NPTthread, etc.) are easy to install and are suitable for smalland mediumdiameter pipes. Flange connections are suitable for largediameter, highpressure pipelines to ensure a stable seal and are common in the chemical industry and municipal water supply and drainage. Ferrule connections are convenient for onsite commissioning and maintenance and are widely used in hydraulic precision pipelines.
• Pipevalve connection: The connection between the pipe and the valve is an important part of the fluid system. A proper connection can ensure the tightness and stability of the system, as well as the smooth flow of the fluid. Different connection methods have their own characteristics and application scenarios, and the choice should be based on factors such as the diameter of the pipe, the pressure of the system, and the installation environment.
• Installation and maintenance of different connections: Different pipevalve connection methods have different requirements for installation and maintenance. For example, threaded connections are relatively easy to install, but attention should be paid to the tightness of the threads to prevent leakage. Flange connections require more installation space, but they are easy to disassemble and maintain. Ferrule connections are convenient for onsite adjustment, but the installation process requires certain skills to ensure the sealing effect.

4. Environmental adaptability tradeoff

• Protection level: Wet and dusty workshops (such as cement building materials production) require IP65 and above protection, which is waterproof and dustproof. Outdoor openair equipment (e.g., smart irrigation solenoid valves) should be UVresistant and waterproof to IP67 or even IP68. In situations where there are flammable and explosive gases, choose explosionproof types, which are divided into ExdⅡBT4, ExdⅡCT6, etc. according to the hazard level to ensure safety.
• Vibration and shock resistance: When installed on vibrating machinery (such as air control for mining crushers) and mobile equipment (such as hydraulic systems for construction machinery), the solenoid valve must have a reinforced structure, antivibration buffer, and internal components that prevent loosening to ensure longterm and reliable operation.
• Environmental protection level: The environmental protection level of a solenoid valve indicates its ability to resist the influence of the external environment. The IP (Ingress Protection) rating is a common standard for measuring the protection level of electrical equipment against solid particles and liquids. The higher the IP rating, the better the protection performance of the solenoid valve in harsh environments.
• Application examples in different environments: In addition to the common industrial environments mentioned above, there are some other special environments where solenoid valves need to have specific adaptability. For example, in foodprocessing plants, solenoid valves need to meet the requirements of foodgrade hygiene and be easy to clean. In medicalequipment applications, solenoid valves need to have high precision and reliability to ensure the accuracy of medical operations.

5. Electrical parameters

• Rated voltage: Select according to the onsite power supply. AC220V is highly versatile and widely used in industrial plants. DC24V is a safe low voltage and is preferred in batterypowered mobile devices with a risk of human contact. Special environments (such as oceangoing ships) require AC110V, DC12V, etc. Selecting the wrong voltage may cause the equipment to malfunction or be damaged.
• Power consumption limitation: In batterypowered remotemonitoring valvecontrol systems and energyefficiencysensitive production lines, lowpower solenoid valves can extend battery life and reduce costs, which can be achieved by optimizing coil design and control circuits. When selecting, compare the powerconsumption parameters of different products.
• Electrical safety: Electrical safety is an important consideration in the selection of solenoid valves. The rated voltage and power consumption of the solenoid valve should match the onsite power supply to avoid overvoltage, overcurrent, and other safety hazards. In addition, in some special environments, such as explosivegasfilled environments, explosionproof solenoid valves are required to ensure the safety of the entire system.
• Energysaving and efficiencyimprovement measures: In addition to optimizing the coil design and control circuit to reduce power consumption, some new technologies and materials can also be used to improve the energy efficiency of solenoid valves. For example, the use of highpermeability magnetic materials can improve the magnetic field strength of the electromagnet, thereby reducing the power required to actuate the valve core. At the same time, the optimization of the valve structure can also reduce the flow resistance of the fluid, improving the overall efficiency of the system.