To trace the development history of solenoid valves, both domestically and internationally, electromagnetic valves have been classified into three main types: direct-acting, step-byroughly guided, and pilot-operated. Based on structural differences and material variations, these categories can be further divided into six sub-types: straight-acting diaphragm type, step-by-step weighted type, pilot membrane type, direct-acting piston type, step-by-step direct-acting piston type, and pilot piston type.
**Direct-Acting Solenoid Valve:**
Principle: When power is applied, the electromagnetic coil generates a magnetic field that lifts the closing member off the valve seat, allowing the valve to open. When power is removed, the magnetic force disappears, and a spring pushes the closing member back onto the seat, closing the valve.
Features: This type can function properly under vacuum, negative pressure, or zero pressure conditions. However, it is typically limited to a maximum diameter of 25mm due to its design constraints.
**Distributed Direct-Acting Solenoid Valve:**
Principle: This valve combines the features of a direct-acting and a pilot-operated valve. In situations where 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 component, allowing the valve to open. Once the pressure difference reaches the required level, the electromagnetic force opens the pilot valve, increasing the pressure in the lower chamber while decreasing the pressure in the upper chamber. This pressure differential then pushes the main valve upward, opening it. When power is turned off, the pilot valve is closed by spring force or medium pressure, creating a high-pressure area above the closing member, which forces it downward to close the valve.
Features: It can operate effectively even in zero-pressure or vacuum environments, as well as at high pressures. However, it requires more power and is usually installed horizontally.
**Pilot Operated Solenoid Valve:**
Principle: When power is applied, the electromagnetic force opens the pilot port, causing a rapid drop in pressure in the upper chamber. This creates a pressure difference across the closing member, allowing fluid pressure to push it upward and open the valve. When power is removed, the spring closes the pilot port, and the inlet pressure flows into the upper chamber, creating a higher pressure above the closing member. This pressure differential forces the closing member down, closing the valve.
Features: These valves can handle higher fluid pressure ranges and offer flexible installation options (with some customizations). However, they require a minimum pressure differential to function correctly.
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