Rack and Pinion Style Pneumatic Valve Actuator

One example of a pneumatic rack and pinion valve actuator
Courtesy Rotork

Three primary kinds of valve actuators are commonly used: pneumatic, hydraulic, and electric.
Pneumatic actuators can be further categorized as scotch yoke design, vane design, and the subject of this post - rack and pinion actuators.

Rack and pinion actuators convert linear movement of a driving mechanism to provide a rotational movement designed to open and close quarter-turn valves such as ball, butterfly, or plug valves and also for operating industrial or commercial dampers. The rotational movement of a rack and pinion actuator is accomplished via linear motion and two gears. A circular gear, known as a “pinion” engages the teeth of one or two linear gears, referred to as the “rack”. Pneumatic actuators use pistons that are attached to the rack. As air or spring power is applied the to pistons, the rack changes position. This linear movement is transferred to the rotary pinion gear (in both directions) providing bi-directional rotation to open and close the connected valve.

Rack and pinion gear
Courtesy Wikipedia

The actuator pistons can be pressurized with air, gas, or oil to provide the linear the movement that drives the pinion gear. To rotate the pinion gear in the opposite direction, the air, gas, or oil must be redirected to the other side of the pistons, or use coil springs as the energy source for rotation. Rack and pinion actuators using springs are referred to as "spring-return actuators". Actuators that rely on opposite side pressurization of the rack are referred to as "direct acting".

Most actuators are designed for 100-degree travel with clockwise and counterclockwise travel adjustment for open and closed positions. World standard ISO mounting pad are commonly available to provide ease and flexibility in direct valve installation. NAMUR mounting dimensions on actuator pneumatic port connections and on actuator accessory holes and drive shaft are also common design features to make adding pilot valves and accessories more convenient.

Pneumatic rack and pinion actuators are compact and effective. They are reliable, durable and provide good service life. There are many brands of rack and pinion actuators on the market, all with subtle differences in piston seals, shaft seals, spring design and body designs. Some variants are specially designed for very specific operational environments or circumstances.

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Large Control Valves for Higher Pressures and Bubble-tight Shutoff

High performance
rotary control valve
(courtesy of Valtek)

High performance control valves, providing a bubble-tight seal along with a wide range of sizes and pressure classifications are used in many industrial applications. Examples are:

• Fire protection
• Gas service
• Condenser cooling
• Gas scrubbing
• Mine dewatering
• Pipeline service,
• Cooling water

This type of control valve should achieve bi-directional, bubble-tight shutoff while maintaining low breakout torque - at both high and low pressure drops.

Often, these valves are available in carbon steel, 316 stainless steel and other alloys and is available in ANSI Classes 150 through 2500, sizes 2 through 30-inch. 

Rotary disc, high performance control valves offer a double offset designed into the disc that lifts the disc out of the seat immediately upon actuation. This avoids wear on the seat and disc, reducing leakage and parts replacement. It also improves throttling by eliminating friction.

For more information, review the tech manual below:

Valtek Valdisk Control Valves from CTi Controltech

The Eccentric Plug Rotary Control Valve (also known as the Rotary Globe)

Eccentric Plug Rotary Control
or Rotary Globe Valve
(courtesy of Cashco)

Available in either a flanged or flangeless body style, the rotary globe control valve design provides excellent service life in a wide range of applications. This rotary globe design provides front access to the valve body, allowing use of various low-noise inserts, abrasion sleeve or alternate front- end seal retainers, making it one of the most user friendly control valves when it comes to maintenance.

The rotary globe control valve is a universal control valve that can be used in most control valve applications, with particularly excellent performance on steam. Where conventional ball or globe control valves have problems with body or trim wear, the design and typical options for rotary globe control valves provides longer life. The ease and flexibility of installing characterized inserts provides noise control for gases, and cavitation and flashing control for liquids. Also because of its design, it inherently can withstand temporary distortions due to “thermal shock” without compromising continued control of the process.

A very versatile control valve that provides easy maintenance and serviceability, saving time and money for plant operations.