Solenoid Valve Fundamentals: Principle, Classification, and Applications

    Working Principle: A solenoid valve contains a sealed chamber with multiple ports connected to different fluid lines. A movable plunger sits between two electromagnetic coils. When one coil is energized, it attracts the plunger, opening or closing specific ports. The inlet is normally open, allowing fluid (oil, air, etc.) to flow into selected discharge lines. Fluid pressure then drives a piston in a cylinder, which moves a rod to actuate mechanical devices. Thus, controlling the solenoid current controls mechanical motion.

Classification
By medium/application: hydraulic, pneumatic, steam, gas, oil, fire-protection, refrigeration, corrosion-resistant, high-temp, high-pressure, zero-differential, cryogenic, vacuum, etc.
By internal structure: pilot-operated, direct-acting, compound, self-latching, pulse, bistable, bidirectional, etc.
By body material: cast iron, brass, cast steel, full stainless steel (304/316), non-metallic (ABS, PTFE).
By pressure rating: vacuum (-0.1~0 MPa), low (0~0.8 MPa), medium (1.0~2.5 MPa), high (4.0~6.4 MPa), ultra-high (10~21 MPa).
By temperature: ambient (5~80°C), medium (100~150°C), high (150~220°C), ultra-high (250~450°C), low (-40~0°C), cryogenic (-196°C).
By voltage: AC (220V, 380V, 110V, 24V); DC (24V, 12V, 6V, 220V). Standard: AC220V / DC24V.
By protection: explosion-proof, waterproof, outdoor-rated.

Applications & Characteristics
    Solenoid valves are digital (on/off) actuators, typically used for small-bore pipes (≤DN50).
    1. Switching: Fast on/off action via coil.
    2. Performance: Low flow coefficient (Cv) and small allowable pressure drop. More vulnerable to voltage spikes than motorized valves. Most reset on power loss; motorized valves require extra hardware for this.
    3. Use Cases: Ideal for special requirements like zero leakage or exotic media—though often more expensive.

Selection Principle
    Follow four priorities: Safety > Reliability > Suitability > Economy. Remember: though the valve cost is tiny in a full automation system, a wrong choice can cause massive downstream damage.

Key Advantages
    (1) Zero external leakage; internal leakage easily controlled → safe.
    (2) Simple system integration, PC-compatible, low cost.
    (3) Fast response, low power, compact size.
    (4) Limited precision and medium compatibility.
    (5) Highly versatile across industries.

(Source: Mechanical Expert Network)