Working Principle
1. Signal Input: The control system (DCS/PLC) outputs a 4~20mA electrical signal.
2. Positioner Conversion: The valve positioner converts the electrical signal into 0.02~0.10MPa air pressure.
3. Diaphragm Drive: Air pressure pushes the diaphragm, compresses the spring, and drives the push rod/valve stem/valve core to move.
4. Flow Regulation: The valve core displacement changes the gap with the valve seat, controlling the medium flow rate.
5. Force Balance: Air pressure thrust = spring reaction force + medium force, stabilizing the valve position.
Key Characteristics
1. Operating Mode (Safety Mode)
• Air-to-Open (FC): Opens with air pressure, closes without air pressure (preferred for fuels and hazardous media)
• Air-to-Close (FO): Closes with air pressure, opens without air pressure (preferred for cooling water and venting)
2. Flow Characteristics (Determined by Valve Core Shape)
• Linearity: Stroke is proportional to flow rate (stable load)
• Equal percentage: Small opening, slow adjustment; large opening, fast adjustment (most commonly used, suitable for temperature/pressure control)
• Fast opening: Small opening, rapidly maximizes flow (on/off control)
Applicable operating conditions
• Chemical industry: Reactors, distillation columns, pipeline flow/pressure regulation
• Petroleum industry: Crude oil transportation, oil-gas separation, heating furnaces
• Power industry: Boiler feedwater, desuperheating and pressure reduction, flue gas desulfurization
• Metallurgy: Hot blast stoves, water treatment, blast furnace gas
