Valve positioners play an important part in industrial plants. The instruments ensure control valves are properly communicating with the controlling elements of the plant. If the valve or actuator isn't in the correct position as designated by the input signal, the valve positioner intervenes and corrects the position. Valve positioners are available in pneumatic, electro-pneumatic and digital models.

The conditions of an industrial plant can often be hard on instruments. Control valve positioners typically need to endure extreme temperatures, corrosive environments, high vibration and poor air quality. Valve positioners are approved for certain environmental conditions depending on the model and features. When purchasing a control valve positioner, consider the following:

1. Determine the environmental conditions of your plant and the amount of time and service you're willing to devote to your valve positioner.

2. Know that digital valve positioners often require less maintenance because they have the ability to diagnose themselves.

3. Ensure the valve positioner has non-metallic housing if it will be exposed to corrosive conditions.

Action Steps
The best contacts and resources to help you get it done

Buy valve positioners designed for hazardous environments

If you're planning to place the valve positioner in an area with extreme conditions, including high vibration and poor air quality, purchase a positioner designed to handle hazardous environments. Most control valve positioners are durable and corrosion resistant, but be sure the one you buy is approved for hazardous locations.

I recommend: Purchase the Model VI electro-pneumatic positioner from Valve Related Controls. The vibration-resistant control valve positioner is epoxy sealed to keep out dust and moisture, and is approved for use in hazardous locations. Browse a selection of anti-vibration and explosion proof valve positioners at Cole Industrial and Technical Supply.

Find digital valve positioners

A digital valve positioner offers you convenience and time saved with its ability to diagnose itself as well as its valve and actuator. The positioner monitors the valve travel position and actuator pressure, which allows you to service the instrument only when its truly necessary.

I recommend: Browse digital valve positioners at Emerson Process Management. The company's digital valve positioners are microprocessor-based current-to-pneumatic instruments. Boig and Hill offers Worcester Controls digital valve positioners available with automation services and repair. The Modular Valve Positioner by Hamilton Company is a self-contained bidirectional instrument available in a digital model.

Purchase control valve positioners that won't corrode

Because it's so critical industrial valve positioners function properly all the time, buy only instruments that won't be susceptible to corrosion. Most valve positioners manufacturers expect their instruments to be placed in corrosive environments, but don't assume every positioner is corrosion resistant.

I recommend: Buy valve positioners online from Dwyer Instruments. The company's instruments are corrosion resistant, compact and inexpensive. The standard units aren't approved for hazardous locations, but a hazardous location option is available on special orders. SVF Flow Controls houses valve positioners in non-metallic casing to provide protection against corrosion.

Tips & Tactics

Helpful advice for making the most of this Guide

• •  When ordering a valve positioner, consider your company's safety needs. Some valve positioners suppliers offer instruments with programmable shut-off features and additional function inputs that can be used to set a safety position or block the valve.