What is the importance of a positioner in a control valve?

By "Apollo" Valves
June 13, 2018

Valve positioners are gadgets that are used in control valves to guide them into the perfect position by increasing or lowering the air load pressure on a valve’s actuator. In simple terms, these devices ensure that a valve is in the correct operating position depending on the signal from the process instrument controller.

Valve positioners are a convenient solution for streamlining a fluid system. They are used to manage valves in processes where fast and accurate control is required without hysteresis. In fluid systems, changes are often made, and this results in fluctuations. Control valves need to adapt to these alterations almost immediately to keep the system in balance. A positioner helps the valve to adjust to the correct position without error, thus avoiding variations that can be costly when compounded.

It is imperative to understand that positioners work in conjunction with valve actuators. Actuators are the devices/mechanisms that open and close valves – read more about them here.

Advantages of a positioner in a control valve

1. Increases control system accuracy

Valve positioners allow for better and finer control of a fluid system through the use of signals. This precise control helps to offset the variation in an actuator’s spring rate range, which can be plus or minus 8 percent.

2. Creates faster response speed

Positioners enable control valves to respond faster to any changes in the process. This allows for faster loading and helps prevent the adverse effects of many dynamic variations.

3. Helps minimize friction

Valve positioners help in decreasing the resistance effects of valve system packing and the resulting hysteresis. They are particularly vital for materials such as graphite, which is high-temperature packing material.

4. Controls higher/varying differential pressures across a control valve

If high or unstable differential pressures in the control valve make the valve’s position shift, a positioner can be used to aid in automatically regulating the air pressure in the actuator in accordance to the control signal.

5. Counters reactions resulting from flow changes

In cases such as when there is a high-pressure drop in the system and a fluid induces adverse reactions, positioners help to compensate for the resulting internal discrepancies.

6. Allows for split ranging

One controller can be used for two valves without trouble.

7. Allows distance between the controller and control valve

Valve positioners help in removing the effects of having a significant gap between a control valve and the controller.

8. Allows a wide range of flow variation

With the positioning devices, the fluid system can operate at below 10 percent travel in normal conditions.

9. Offers increased flexibility

They allow the use of piston actuators with immense apparatus air supply pressures.

Valve positioners come in three different types: analog I/P, pneumatic, and smart or digital positioners. Consider installing any of these types in your system to enjoy all of the above benefits, but take the time to research the pros and cons of each to find which one is the best fit for your system. Either way, all positioners will help in improving your system’s efficiency, reduce downtime, and save you time and money.

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