The development of electromagnetic valves has a long and evolving history. Currently, solenoid valves at home and abroad are classified into three main types based on their working principles: direct-acting, step-by-step pilot, and pilot-operated. Additionally, they can be further divided into six subcategories depending on the valve structure and material differences: 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.
The direct-acting solenoid valve operates by using electromagnetic force generated when power is applied. This force lifts the closing member off 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, thereby closing the valve. This type of valve is suitable for use in vacuum, negative pressure, or zero-pressure environments. However, it generally has a limited flow path, typically not exceeding 25mm in diameter.
The direct-acting and pilot-type solenoid valve combines both direct action and pilot operation. When there is no pressure difference between the inlet and outlet, applying power causes the electromagnetic force to lift both the pilot valve and the main valve’s closing member, opening the valve. Once a pressure difference is established, the pilot valve opens, increasing the pressure in the lower chamber of the main valve, which then allows the pressure to push the main valve open. When power is removed, the pilot valve closes, and the spring force or media pressure pushes the closing member down, closing the valve. This type is capable of operating under zero pressure, vacuum, or high-pressure conditions but requires more power and must be installed horizontally.
The pilot solenoid valve works by using electromagnetic force to open a small pilot hole, causing the pressure in the upper chamber to drop rapidly. This creates a pressure differential across the closing member, allowing the fluid pressure to push it upward and open the valve. When power is off, the spring closes the pilot hole, and the inlet pressure flows through a bypass, creating a low-pressure differential that forces the valve to close. These valves can handle higher fluid pressures and are often customizable for different applications, though they require proper pressure conditions to function effectively.
In summary, each type of solenoid valve has its own unique mechanism, advantages, and limitations, making them suitable for different industrial and commercial applications. Understanding these differences helps in selecting the right valve for specific operational needs.
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