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    HERO-Rack and Pinion

    Pneumatic Rack and Pinion Actuators

    Bettis Rack and Pinion Pneumatic Actuators offer reliable torque to automate valves for a wide range of industrial applications from big to small, hot to cold, general to severe.

    PROD_AS_Bettis_RPE-Series_01

    What is a Rack & Pinion actuator?

    • Rack and pinion actuators are mechanical devices used to automatically open and close valves or dampers, usually for industrial applications.
    • “Rack and pinion” is a generic term for a pair of gears which convert linear motion into rotational motion. A linear gear bar called “the rack” engages teeth on a circular gear called "the pinion". Linear force exerted on the rack will cause a rotational motion of the pinion.
    • For valve automation, a common actuator design uses two piston-type racks moving in opposite directions to ensure balanced forces on the pinion. Typically, pneumatic air pressure is used to power the actuator. By applying pressure to the piston racks, the pinion can be turned to the desired position. The pinion bottom connects to the valve stem to open and close the valve as the pinion turns.

    How It Works

    Common Rack and Pinion Applications

    Rack and Pinion actuators are for automation and operation of quarter-turn valves like Butterfly, Ball and Plug valves as used in process industries like chemical, pharmaceutical, water processing, oil & gas, etc.

    The actuators are available in two constructions: Spring Return and Double Acting. Mechanical Spring Return is for fail-safe applications and can be assembled for “Fail-Close” or “Fail-Open” safety function.

    Double Acting actuators can be used for a “Fail-In-Last-Position” safety function.

    Advanced Rack and Pinion Applications

    Rack and Pinion actuators are available for a wide range of advanced applications. Most well know are the temperature related trim kits that allow High Temperature or Low Temperature operation.

    Other applications are related to manipulating the stroke differently (Full Stroke Adjustment), special coating requirements, special operating media, or fast operating speeds.

    For many of these advanced applications, dedicated control accessories are available.

    Valve Mounting

    Rack and Pinion actuators have standardized interface flanges/interfaces for valves, solenoids and control accessories.

    Valve interfaces generally comply to the ISO 5211 standard. This torque-based standard has become the industry standard and many valves are available that allow direct mounting, eliminating cost for bracket and coupling. For valves that do not allow direct mounting, many standardized brackets are available to reduce cost to a minimum.

    Between the actuator and the valve, a Declutchable Manual Override Gear Box can be mounted that allows manual operation of the automated valve package in case of emergencies or when maintenance of the actuator is required.

    Typical Rack and Pinion Controls

    Solenoid and control accessory interfaces comply to the VDI/VDE 3845 (NAMUR) standard and European actuator standard EN15714-3. The solenoid interface allows either piped or direct-mounted solenoids and allows various pneumatic interface sizes based on actuator volume to accommodate cycle speed requirements.

    The control accessory interface, on top of the actuator, allows the mounting of switch boxes or analog position transmitters. These devices are mounted to the actuator's pinion, which is mounted direct or indirect to the valve’s stem and allows position feedback of the automated valve package to the control room. Switch boxes in general sense the fully open and closed end positions where the analog position transmitters indicate the actual position throughout the stroke by means of a 4-20mA or 0-10V signal. For modulating applications, valve positioners are available to mount directly to the actuator top.


    Integrated Control Development

    Many suppliers offer various control components per the VDI/VDE 3845 (NAMUR) standard. However, the many different components must be ordered, stocked, handled, mounted, etc.

    Many customers look now for a more integrated valve operating system that reduces the variety of components and the number of potential malfunction points. Some switch box suppliers now provide semi-integrated solutions where the switchbox is equipped with a solenoid. One of the latest developments is integrating the control and the position feedback in one control module which fits on the full range of actuator sizes.

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