Valve Position Indicators

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

Valve position indicators differ in terms of the number of indicated positions, the number of switches, and pole and throw specifications. Two-way devices provide a basic on/off indicator. Products with three-way, four-way, 120°, 180°, and continuous indications are also available. 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.    

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. Valve position indicators can mount on either standard shafts or specialty shafts. In terms of features, some devices are intrinsically safe (IS), explosion proof, and chemical or corrosion resistant. Others are networkable, backlit or illuminated, or field adjustable. 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).

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  MDC circular C-Loc® gate valves can be fitted with optional high precision, modular mechanical position indicators (MPI). This new MPI system consists of two single pole double throw micro switches...
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• Angle and Inline Valves Options Guide
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• Finding the right sensor for linear displacement
  Engineers need to know the technology and limitations behind the available sensors if they want to make the right choice. Howard A. Schaevitz Technologies Inc. Engineers continue to increase their use...
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