Positioner for a Control Valve: 6 Things You Should Know

WHAT IS THE PURPOSE OF A POSTIONER IN A CONTROL VALVE?

A positioner for a control valve is used to adjust a valve’s position based on a desired set point for a process variable, whether it be pressure, temperature, or flow.

HOW DOES A POSITIONER WORK?

Producers typically install valve positioners on the yolk or top casing of a pneumatic actuator for linear control valves. On rotary control valves, the valve positioner is installed?in line with the valve and actuator stems on top of the actuator or on the side of the actuator. Installation depends on?what type of actuator?one uses.?

Affixing the positioner to the actuators allows the positioner to measure the stem travel (linear valves) or degree of rotation (rotary valves). This also changes the position of the valve as required based on the input signal from the instrument controller.

When?the process variable differs from the desired set point, the instrument controller sends an electrical or pneumatic signal to the positioner. This varies its pneumatic output to the actuator to move the valve open or closed accordingly. This occurs until the process variable reaches the desired set point.

HOW MANY TYPES OF POSITIONERS ARE THERE??

There are 3 primary types of positioners:

• Pneumatic Valve Positioner
• Electro-Pneumatic (EP) Valve Positioner
• Digital Valve Positioner

WHAT IS A PNEUMATIC VALVE POSITIONER??

A Pneumatic Valve Positioner?receives a pneumatic signal (typically 3-15 or 6-30 psi)?from a controller. It then sends a corresponding?pneumatic signal to a pneumatic valve actuator.

WHAT IS AN EP?POSITIONER??

An Electro-Pneumatic Positioner, sometimes abbreviated "EP Positioner,"?receives an electric signal (typically 4-20mA or 0-10 VDC)?from a controller. It?then sends a corresponding pneumatic signal to a pneumatic valve actuator.?

EP Valve Positioners may also be referred to as “analog positioners.” This is because the electrical input to the positioner is an analog signal.

WHAT IS A DIGITAL VALVE POSITIONER?

A?Digital Valve Positioner?receives?an electric signal (typically 4-20mA, HART, PROFIBUS, or Foundation Fieldbus)?from a controller. It then sends a?corresponding pneumatic signal to a pneumatic valve actuator.

The electrical input to a digital positioner can be a digital signal, which allows more advanced capabilities for the user. Some refer to digital valve positioners as “smart positioners.”

The?Siemens PS2?is one example of?a digital valve?positioner. The PS2 can remotely monitor and control any pneumatic valve. We offer it with many different communication protocols to meet the needs of all end users.