Classification, Characteristics, and Working Principle of Solenoid Valves

    Solenoid Valve Selection Guidelines

    Applicability

    ● Fluid must match the valve’s specified medium.
    ● Fluid temperature must be below the valve’s rated max.
    ● Max viscosity: typically ≤20 cSt; specify if higher.
    ● For ΔP < 0.04 MPa, use direct-acting valves (e.g., 2W, ZQDF). For ΔP > 0.04 MPa, use pilot-operated valves. Max system pressure must not exceed valve rating. Most solenoid valves are unidirectional—install a check valve if backpressure exists.
    ● Install a filter upstream if fluid is contaminated.
    ● Match orifice and pipe sizes. Provide bypass for maintenance. Specify slow-closing models if water hammer occurs.
    ● Account for ambient temperature effects.
    ● Select power supply based on load; AC inrush VA must be considered.

    Reliability

    ● Choose normally closed (NC) for short-on/long-off; normally open (NO) for opposite duty.
    ● Life cycle data is often from type tests; select reputable manufacturers due to lack of unified standards.
    ● For high-frequency, fast-response applications, use direct-acting or fast-series valves.

    Safety

    ● Standard valves are not waterproof; request IP-rated versions if needed.
    ● Valve pressure rating must exceed max system pressure.
    ● Use all-stainless for corrosive fluids; PTFE (e.g., SLF) for strong acids/bases.
    ● Use certified explosion-proof models in hazardous areas.

    Economy

    ● Among valves meeting applicability, reliability, and safety criteria, choose the most cost-effective.

    Operating Principles

    Direct-Acting Solenoid Valve

    Available in NC and NO types. In NC valves, de-energized = closed. When energized, electromagnetic force pulls the plunger against spring force, opening the orifice. De-energizing resets the valve via spring. Simple, reliable, works at zero differential pressure. Typical for orifices < DN6.

    Step-Direct (Semi-Direct) Solenoid Valve

    Combines direct and pilot action. Energizing opens a small pilot orifice, venting pressure from the main diaphragm/chamber top. System pressure then lifts the main seal. Reliable even at zero ΔP. Examples: ZQDF, 2W.

    Pilot-Operated Solenoid Valve

    Consists of a pilot valve and main valve. In NC type, de-energized = closed. Energizing opens the pilot, reducing pressure above the main diaphragm. Inlet pressure then pushes the diaphragm up, opening the main flow path. Requires minimum ΔP to operate. Used for larger orifices (e.g., DF > DN15, ZCZ).

(Source: Mechanical Experts Network)