ROTORK /YCT  YT-1200  Series - YT-1200RD112L2

The YT-1200 pneumatic positioner controls a valve by receiving a pneumatic input signal to move an actuator to the correct position. It works on a feedback principle: when the input signal changes, the device moves the valve, and a feedback mechanism (e.g., a lever) senses the new position. The device compares the required position with the actual position and exhausts or pressurizes the actuator's chamber with air until the valve reaches the target position and the feedback matches the input signal.

Step-by-step working principle

1. Input signal reception: A pneumatic control signal (e.g., 3-15 psi) from a controller is received by the positioner.
2. Initial movement: An increase in the input signal causes a bellows to stretch, which moves a flapper away from a nozzle, widening the gap.
3. Exhausting air: This gap allows air to exhaust from the pilot chamber through the nozzle, which causes the spool to move to the right.
4. Actuator response: As the spool moves, it unblocks a seat, allowing compressed air to flow to the actuator's chamber (OUT1).
5. Valve movement: The increased pressure in the chamber moves the actuator's stem, which rotates the valve to the new position.
6. Feedback loop: The valve's rotation is transferred to a cam and a feedback lever, which pulls on a span spring.
7. Position alignment: The system continues to adjust the air supply until the force from the bellows and the force from the feedback spring are balanced.
8. Stable state: At this point, the flapper is moved back to its original position, the gap to the nozzle is reduced, and the air exhaustion stops. The actuator and valve are now holding the new position that corresponds to the input signal.

The working principle step-by-step

1. Input signal: The positioner receives a low-pressure input signal (typically 3–15 psi) from a controller. This pressure acts on a bellows inside the positioner.
2. Flapper and nozzle mechanism: The bellows' expansion or contraction, caused by the input pressure, moves a flapper. The flapper controls the gap at a nozzle, regulating the flow of a higher-pressure supply air.
3. Spool valve activation: The pressure change from the nozzle affects a spool valve, causing it to shift position. If the input signal increases, the gap at the nozzle widens, causing the spool to move and direct supply air to the actuator.
4. Actuator movement: The high-pressure air from the spool valve is sent to the pneumatic actuator, causing it to move and adjust the valve's position.
5. Position feedback: The movement of the valve stem is mechanically fed back to the positioner via a feedback shaft and a cam. This motion repositions the flapper.
6. Equilibrium: As the valve moves closer to the desired position, the feedback mechanism adjusts the flapper, which alters the pressure at the nozzle. The system reaches equilibrium when the force from the input signal bellows is balanced by the feedback mechanism, at which point the spool valve closes and the actuator stops moving.
7. Signal amplification: The positioner also acts as a signal amplifier or booster. It uses its own higher-pressure air supply to provide the necessary force to the actuator, allowing a low-pressure control signal to command a powerful output.

Key components

• Bellows: A pressure-sensitive element that expands and contracts in response to the input signal pressure.
  Flapper and nozzle: A mechanical assembly that converts the bellows' movement into a pneumatic pressure signal.
• Spool valve: A key component that, based on the nozzle pressure, directs supply air to the actuator or exhausts it.
• Actuator: The pneumatic device that physically moves the valve based on the positioner's air supply.
• Feedback mechanism: A cam and lever assembly that transfers the valve's position back to the flapper, completing the control loop.

 Full Datasheet

Positioner Transmitter Feature   YT-1200RD112L2

Basic Ordering Information