Overview
The accuracy of any pneumatic control system depends on how well the final valve follows the incoming signal. Line pressure changes, stem friction, differential pressure shifts and diaphragm hysteresis can all create positioning error if the actuator is left to respond without feedback correction. A positioner compares the control signal with the actual valve position and adjusts the pneumatic output to the actuator accordingly, helping the valve reach and hold the demanded position more consistently. That correction improves loop stability, repeatability and valve response, particularly on variable-load duties where pressure conditions and process demand do not stay constant. Smart positioners also add diagnostics, communication and commissioning visibility, making them useful where the valve package needs better feedback for maintenance and operating decisions rather than simple air-to-open movement alone. The broader Spirax Sarco offering also includes controllers, interface devices and sensors that help turn the valve package into a coordinated control system rather than a collection of isolated hardware items.
Related feedback and valve-package routes
Feedback hardware becomes useful only in the context of the final valve assembly. Continue into steam control valves when the positioner choice depends on the installed valve duty, and use pneumatic actuators when the immediate comparison is actuator format rather than signal hardware.
If the project is moving toward lower routine air use or electric drives, compare electric actuators.
EP5 Electro-pneumatic Positioner
The EP5 is a Spirax Sarco traditional electro-pneumatic valve positioner for applications that need stable valve positioning with a straightforward design. It accepts a 4-20 mA current signal or 0.2-1.0 bar pneumatic signal, fits single-acting linear pneumatic actuators and provides valve position feedback. It can be paired with SPIRA-TROL, STERI-TROL and similar control valve series.
Spirax Sarco EP500 Electro-pneumatic Positioner
The Spirax Sarco EP500 is a standard electro-pneumatic positioner for linear and rotary pneumatic control valves. It uses a 4-20 mA input signal with split-range capability, integral pressure gauges, central or offset mounting and a quick-fit electrical connection cap to deliver reliable position feedback correction without the communication and diagnostic features of the SP400 and SP500 smart positioners.
Spirax Sarco SP400 Positioner
The Spirax Sarco SP400 is a loop-powered electro-pneumatic valve positioner for linear and 90 degree rotary pneumatic valves. It uses a 4-20 mA input signal, non-contact valve position feedback and automatic air output correction to help the valve reach and hold the demanded position.
Spirax Sarco SP500 Smart Positioner
The Spirax Sarco SP500 is an enhanced loop-powered electro-pneumatic smart positioner for linear and rotary pneumatic valves. Building on the SP400 platform, it adds optional HART communication, diagnostic data logging, retransmission capability and a 24V power board, while retaining the same 4-20 mA input, Hall effect non-contact feedback and piezo valve technology.
Spirax Sarco SP7-10, SP7-11 and SP7-12 Smart Positioners
Spirax Sarco SP7-10, SP7-11 and SP7-12 smart positioners control pneumatic linear or rotary actuators and support 4-20 mA, HART, PROFIBUS PA or Foundation Fieldbus communication routes.
Spirax Sarco SX80 Controller
The Spirax Sarco SX80 is a 1/16 DIN panel mount process controller offering universal input for RTD and thermocouple signals, universal output with VMD 3-point, 4-20 mA analog, relay and logic, PID auto-tuning, 3 setpoints and a built-in 18 VDC transmitter power supply.
EP6 Electro-pneumatic Positioner
A 4-20 mA electro-pneumatic positioner for NAMUR-compatible linear and rotary pneumatic valve actuators, with safe-area and approval-specific Ex configurations.
Continue your instrumentation selection
Accurate modulation depends on more than the actuator alone. Positioners, controllers and sensors determine how well the valve package interprets, follows and reports the control signal.
See the wider controls context
Return to the wider control systems range when the instrumentation choice is part of a broader control hardware or system architecture decision.
Match feedback to the actuator package
Use pneumatic actuator pages when the next step is choosing the air-powered actuator platform that the positioner or controller will manage.
Build the complete control valve assembly
Review control valves when you need to connect positioner choice with valve trim, duty conditions and the final valve assembly.