The development of electromagnetic valves has a long and rich history. Today, solenoid valves at home and abroad are generally classified into three main types based on their working principles: direct-acting, step-by-step pilot, and pilot-operated. In addition, depending on the valve structure and material differences, they can be further divided into six subcategories: direct-acting diaphragm type, step-by-step gate type, pilot diaphragm type, direct-acting piston type, step-by-step piston type, and pilot piston type.
A direct-acting solenoid valve operates by using electromagnetic force generated when power is applied. This force lifts the closing member from the valve seat, allowing the valve to open. When the power is turned off, the electromagnetic force disappears, and a spring pushes the closing member back onto the valve seat, thus closing the valve. These valves are suitable for use in vacuum, negative pressure, or zero-pressure environments. However, they typically have a maximum flow path of around 25mm.
The distribution-type solenoid valve combines the direct-acting and pilot principles. When there is no pressure difference between the inlet and outlet, the electromagnetic force directly lifts both the pilot valve and the main valve’s closing member, allowing the valve to open. Once a pressure difference is achieved, the solenoid pilot valve opens, causing the pressure in the lower chamber of the main valve to rise. This pressure difference then pushes the main valve open. When power is removed, the pilot valve’s spring force or the media pressure pushes the closure down, closing the valve. These valves can operate under zero pressure, vacuum, or high-pressure conditions, but they require more power and must be installed horizontally.
A pilot solenoid valve works by opening a small pilot hole when powered, which causes a rapid drop in pressure in the upper chamber. This creates a pressure difference around the closing member, allowing fluid pressure to push it upward and open the valve. When power is off, the pilot hole is closed by the spring force, and the inlet pressure flows through a bypass hole, creating a low-pressure area that pushes the closing member downward, thus closing the valve. These valves are capable of handling high fluid pressure ranges and can be customized for different installation requirements, though they must meet certain pressure conditions to function properly.
In summary, each type of solenoid valve has its own unique operating principle, structural design, and application scenarios, making them suitable for various industrial and commercial uses. Understanding these differences helps in selecting the right valve for specific applications.
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