Types of Valve Positioners

• Pneumatic devices send and receive pneumatic signals. They are intrinsically safe and can provide a large amount of force to close a valve.
• Electric valve positioners send and receive electrical signals. There are three electric actuation types: single-phase and three-phase alternating current (AC), and direct current (DC) voltage.
• Electro-pneumatic valve positioners convert current control signals to equivalent pneumatic signals.
• Digital or “smart” devices use a microprocessor to position the valve actuator and monitor and record data. They are very accurate, use less air than analogue positioners, and allow for online digital diagnostics.

Performance Specifications

• Pneumatic input signal range and maximum supply pressure are measured in pounds per square inch (psi).
• Split ranges commonly include 4 – 10 mA and 12 – 20 mA. Two-way, three-way, and four-way splits are available.
• There are three types of output actions: direct, reversible, and field reversible.

Features

Intrinsically safe (IS) valve positioners do not produce sparks or other thermal effects that would ignite a specified gas mixture. Devices that are made from stainless steel are used in corrosive or high temperature environments. The valve positioner should also come with a valve position indicator that suits the intended application.

Applications

Valve positioners differ in terms of applications, features, and approvals. Some products are designed for automotive, aerospace, marine, medical, or military applications. Other products are suitable for food processing or pharmaceutical applications. General-purpose devices are commonly available.