Description
Foxboro 43AP-FA42N/PB-AA
Technical Specifications
- Product Type: Pneumatic Valve Positioner.
- Input Signal: Standard pneumatic range (e.g., 3-15 psi or 6-30 psi).
- Supply Pressure: Compatible with standard instrument air supplies.
- Action: Selectable direct or reverse acting.
Functional Features
- High Accuracy: Eliminates hysteresis and stiction in the valve assembly for precise flow control.
- Fast Response: High-capacity air relay for rapid valve stroking and improved loop dynamics.
- Vibration Resistance: Rugged design maintains calibration and performance in high-vibration environments.
- Flow Characterization: Can be configured with cams or electronic linearization to match specific valve characteristics.
Application Scenarios
Used in critical control loops across refining, chemical processing, and marine/offshore platforms where precise flow modulation is essential for product quality and safety.
Performance Parameters
- Linearity: Typically ±0.5% of span or better.
- Air Consumption: Low standby consumption with high dynamic capacity for fast response.
- Response Time: Millisecond-level response to input signal changes.
Material Composition
Housing is typically cast aluminum or stainless steel. Internal components include precision-machined brass, stainless steel, and synthetic elastomer diaphragms and seals compatible with clean, dry instrument air.
Structural Characteristics
A compact, rugged device mounted directly on the valve actuator. Features a nozzle-and-flapper or spool-valve pilot stage, a high-capacity relay, and a feedback linkage assembly. Includes local adjustment screws and a pressure gauge port.
Working Principle
The positioner compares the pneumatic input signal with the actual valve stem or shaft position via a feedback linkage. Any discrepancy creates a force imbalance that modulates the supply and exhaust ports, driving the actuator until the valve position exactly matches the input signal.
Installation Requirements
Mount securely to the valve actuator. Connect the air supply through a filter-regulator. Connect the output to the actuator. Adjust the feedback linkage for proper travel and linearity according to the manufacturer’s instructions.
Usage Precautions
- Always use clean, dry, oil-free instrument air to prevent internal fouling.
- Do not exceed the maximum supply pressure rating.
- Perform regular stroke checks and leak tests to maintain optimal performance.
