I. Working principle
5/2 solenoid valve, as a key component in industrial automation control, the core of which lies in the movement of the spool through the electromagnetic force control valve, so as to accurately regulate the flow path of the fluid (gas or liquid). With its compact structure and powerful function, it is widely used in pneumatic control system.
The solenoid valve is composed 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 low-pressure system through the “S” port, and the “R” port is closed.
• Energized state: When the solenoid is energized, it generates a strong magnetic force to attract 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 low pressure system through the “R” port, and the “S” port is closed. This switching of on-off state realizes the precise control of fluid flow.
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 water-glycol solution, it is necessary to select leak-proof and corrosion-resistant seals. If it involves acid-base 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, low-temperature environments (such as frozen warehouse logistics automation) require solenoid valves to have strong low-temperature tolerance to prevent the sealing material from hardening and brittle cracking. High-temperature operations (such as steel smelting workshops) require high-temperature resistant coils and thermally stable valve bodies to ensure stable component performance.
• Pressure adaptation: Select according to the system pressure level. Low-pressure systems (such as pneumatic valve control of small household water purification equipment) use products with a pressure resistance of 0.1-0.5MPa. Industrial high-pressure 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.
2. Matching control features
• Electronic control mode: Single electronic control relies on solenoid force switching and spring reset. It has a simple circuit and low cost. It is suitable for simple start-stop control, such as simple packaging machine sealing cylinder control. The dual electric control can realize the two-way solenoid locking of the valve core and maintain the state when the power is turned off. It has significant advantages in multi-step 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: High-speed automated production lines (such as high-speed electronic component placement equipment) require solenoid valves to change direction quickly and move several times per second. Direct-acting valves with fast response are suitable for this purpose. If the frequency of movement is low, the advantages of pilot-operated valves with large flow rates are prominent, reducing energy consumption and equipment costs.
3. Pipeline connection coordination
• Diameter specification: Select according to the inner diameter of the pipe to ensure smooth flow of fluid and avoid throttling. 3 – 6mm O.D. for small flow fine chemical addition lines. Large ventilation and gas supply 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 connection (G thread, NPT thread, etc.) are easy to install, for small and medium pipe diameters. Flange connection is suitable for large-diameter, high-pressure pipelines to ensure a stable seal, and is common in chemical industry and municipal water supply and drainage. Ferrule connection is convenient for on-site commissioning and maintenance, and is widely used in hydraulic precision pipelines.
4. Environmental adaptability trade-off
• Protection level: Wet and dusty workshops (such as cement building materials production) require IP65 and above protection, which is waterproof and dustproof. Outdoor open-air equipment (e.g. smart irrigation solenoid valves) should be UV resistant and waterproof to IP67 or even IP68. In situations where there are flammable and explosive gases, choose explosion-proof 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, anti-vibration buffer, and internal components that prevent loosening to ensure long-term and reliable operation.
5. Electrical parameters
• Rated voltage: Select according to the on-site power supply. AC220V is highly versatile and widely used in industrial plants. DC24V is a safe low voltage and is preferred in battery-powered mobile devices with risk of human contact. Special environments (such as ocean-going ships) require AC110V, DC12V, etc. Selecting the wrong voltage may cause the equipment to malfunction or be damaged.
• Power consumption limitation: Battery-powered remote monitoring valve control system, energy-efficiency sensitive production line, low-power solenoid valve can extend battery life and reduce costs, which can be achieved by optimizing coil design and control circuit. When selecting, compare the power consumption parameters of different products.
