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1. Dual-Pressure Control
A central "neutral" position is maintained by applying equal air pressure to both sides of the piston, creating balanced force equilibrium. This requires:
- Two 3-way solenoid valves (one for each actuator port)
- Precision pressure regulation (±0.1 bar)
2. Mechanical Positioning
Internal hard stops physically limit travel at predefined angles (e.g., 30°/60° for quarter-turn valves)
Adjustable cam systems allow field customization of intermediate stops
3. Spring-Centered Mechanism
Dual opposing springs automatically return the actuator to center when de-energized
Spring force must exceed process forces (e.g., flow-induced torque)
4. Closed-Loop Systems
Position sensors (potentiometers/MRIs) provide real-time feedback to PLCs
Proportional valves enable infinite positioning between limits
Key Considerations:
- Air consumption doubles versus 2-position models
- Requires moisture-free air to prevent midpoint drift
- Not suitable for high-vibration environments without locking mechanisms
Typical Applications:
- Mixing valve control
- Process bypass configurations
- Safety shutdown sequencing
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