Foxboro SRP981 Pure Pneumatic Valve Positioner | All-mechanical Split-range Controller

1. Product Overview

The Foxboro SRP981 is a fully mechanical pure pneumatic valve positioner, representing the most basic and reliable pneumatic control solution in the Foxboro valve controller lineup. Completely different from electric analog SRI series and digital HART SRD series positioners, this model adopts zero-electrical structural design, receiving only standard pneumatic control signals without any electronic components, circuit boards or digital modules. It is dedicated to closed-loop stroke positioning control of pneumatic actuators, eliminating electrical failure risks and adapting to extreme industrial environments where electronic equipment cannot operate.

Capable of compensating valve friction and medium load interference, the SRP981 delivers fast and stable pneumatic positioning output. It supports up to 4-fold split-range control and fully independent mechanical calibration of zero, span, gain and damping parameters. With simple structure, ultra-low failure rate and intrinsic explosion-proof safety characteristics, it is widely applied in traditional pneumatic control systems, fully meeting long-term maintenance-free operation requirements of process valves in high-risk and ultra-harsh industrial scenarios.

2. Core Technical Parameters

• Product Type: Full-mechanical pure pneumatic valve positioner (zero electrical structure)

• Applicable Actuator: Single-acting / double-acting linear and rotary pneumatic actuators

• Input Control Signal: Standard pneumatic signal 0.2–1.0 bar (3–15 psi)

• Supply Air Pressure: 1.4–6.0bar industrial standard clean air source

• Split-range Capacity: Supports maximum 4-fold multi-stage split-range proportional control

• Calibration Mode: Full mechanical independent adjustment of zero, span, gain and damping

• Positioning Accuracy: ±0.5% FS high steady-state positioning precision

• Response Time: ≤200ms fast pneumatic response speed

• Hysteresis Performance: <0.3% stroke range ultra-low hysteresis

• Linearity Error: <0.4% stroke range high linearity control

• Pneumatic Interface: Standard G1/8 or 1/4 NPT air inlet and outlet ports

• Mounting Standard: Compliant with NAMUR IEC 534 and VDI/VDE 3845 standards

• Safety Characteristic: Full pneumatic structure, inherent non-spark explosion-proof performance

• Working Temperature: -40°C ~ +85°C ultra-wide industrial temperature range

3. Core Product Features

Distinguished from electrically driven analog and intelligent positioners, the SRP981 features all-mechanical safety design, ultra-high environmental adaptability and superior split-range control capability, irreplaceable in pure pneumatic control systems:

• Zero-electrical Inherent Explosion-proof Safety Adopting 100% pure pneumatic mechanical structure without any electronic parts, wires or circuit components, the positioner produces no electric sparks or electronic faults. It achieves inherent explosion-proof effect without additional explosion-proof certification, perfectly adapting to ultra-high-risk flammable, explosive, high-temperature and humid industrial environments where electrical equipment is restricted.

• Independent Multi-dimensional Mechanical Tuning Equipped with independent adjusting screws for zero point, span, amplification gain and damping parameters. Field technicians can complete full-stroke precision calibration purely through mechanical adjustment, freely matching different valve friction coefficients, actuator stiffness and process load characteristics to ensure stable and linear valve action.

• Industry-leading 4-fold Split-range Control Supporting up to 4-segment split-range linkage control, one standard pneumatic signal can drive four valves to act in segments. It effectively improves the continuity and precision of multi-valve combined regulation, far exceeding the 3-fold split-range limit of conventional analog positioners, ideal for complex segmented process control scenarios.

• Fast Response & Strong Disturbance Suppression Optimized pneumatic transmission structure achieves 200ms ultra-fast response speed, with ultra-low hysteresis and high linearity. It can quickly compensate valve stem friction and medium pressure interference, eliminate valve jitter and dead zone, and improve the dynamic regulation accuracy of process control loops.

• Ultra-high Stability & Maintenance-free Operation The all-mechanical structure avoids chip aging, circuit failure and digital program crash risks. With few wearing parts and strong vibration and temperature resistance, it supports long-term 24/7 unattended operation, greatly reducing on-site calibration and maintenance frequency and lowering overall equipment operation costs.

• Wide Compatibility & Easy Installation Universal mounting structure matches all standard linear and rotary pneumatic actuators. Standard pneumatic interface is compatible with traditional pneumatic control instruments and air supply systems, enabling direct replacement and upgrade of old pneumatic positioners without modifying on-site piping layout.

4. Industrial Application Scenarios

Foxboro SRP981 is exclusively applicable to pure pneumatic control system scenarios and high-risk areas prohibiting electrical equipment. It is mainly used for valve positioning control in petrochemical oil and gas ultra-high-risk explosive areas, segmented split-range linkage regulation of thermal power plant auxiliary pneumatic valve groups, stable control of process valves in chemical high-temperature and high-humidity workshops, and maintenance replacement of old traditional pneumatic positioning systems. It is the most reliable and safest all-mechanical pneumatic valve control solution for special industrial harsh working conditions.