Valve position indicators are electrical switching devices that mount directly on a valve actuator, or indirectly on a transfer case. They are used in conjunction with a valve positioner.

Types of Valve Position Indicators

Valve position indicators are used with both rotary actuated valves and linear actuated valves and provide two basic switching options: non-contact and mechanical.

• Non-contact switches or proximity sensors use inductive or transistor-transistor logic (TTL) and include reed switches.
• Mechanical switchers are activated by energized arms connected to a moving stem or shaft. There is a mechanical linkage to the actuator.

Valve Position Indicator Specifications

Valve position indicators differ in terms of display, the number of indicated positions, the number of switches, and pole and throw specifications. Shaft diameter and operating temperature are additional considerations. Most suppliers specify shaft diameter in English units such as inches (in) or metric units such as centimeters (cm). Operating temperature is measured in either degrees Fahrenheit (°F) or degrees Celsius (°C).

Display

Some valve position indicators display information on a rotating dial or sliding scale. Other products feature a light emitting diode (LED) indicator. Valve position indicators with position transmitters are also available. These devices provide continuous, signal-based information about a valve’s open, closed, or intermediate positions.

Number of Indicated Positions

The number of indicated positions describes the degree to which the valve position indicator displays the valve's position.

• Two-way devices provide a basic on/off indicator.
• Three-way, four-way, 120°, and 180° indicators provide more control over the valve's indicatedposition.

Image Credit: Marwin Valve

• Continuous indication provides a full range of valve position.

Pole and Throw

There are several different pole and throw categories.

• Single pole, single throw (SPST) switches make or break the connection of a single conductor in a single branch circuit.
• Single pole, double throw (SPDT) switches have two terminals and make or break the connection of a single conductor with either of two other single conductors.
• Double pole, single throw (DPST) switches have four terminals and make or break the connection of two circuit conductors in a single branch circuit.
• Double pole, double throw (DPDT) switches have six terminals and make or break the connection to two separate circuits.

Valve Position Indicators Features

Electrical switch ratings, shaft/mounting options, and optional features are important considerations when selecting valve position indicators.

• Electrical switch ratings include the maximum AC current rating, the maximum DC current rating, the maximum AC voltage rating, and the maximum DC voltage rating.
• Mounts can be made available on either standard shafts or specialty shafts.
• Intrinsically safe (IS) is a protection technique for safe operation of electronic equipment in explosive atmospheres.
• Explosion proof products can survive harsh environments such as explosions.
• Chemical or corrosion resistant products can survive harsh environments such as exposure to chemical or corrosive materials.
• Networkable valve position indicators can be linked to a network and monitored by other devices.

• Backlit or illuminated position indicators can be used in dim or non-existent lighting.

• Field adjustable products can be taken out into the field.

Standards

Valve position indicators must follow certain standards to ensure proper design and functionality. Additional standards can be found the IHS standards store.

• BS EN 60534-6-1 - Industrial-Process Control Valves Part 6: Mounting Details for Attachment of Positioners to Control Valves Section 1: Positioner Mounting on Linear Actuators.
• BS 7461 - Specification for electrically-operated automatic gas shut-off valves fitted with throughput adjusters, proof of closure switches, closed position indicator switches or gas flow control.
• IEC 60534-6-2 - This part of IEC 60534 is intended to permit a variety of positioning devices, which respond to a rotary motion, to be mounted on the actuator of a control valve, either directly or by employing an intermediate mounting bracket. This standard is applicable where interchangeability between actuators and positioners is desired.

Image Credit: Dwyer | Assured Automation