Pneumatic Valve and Damper Actuators: A Design Comparison
Industrial valves, dampers and louvers are operated either electrically or pneumatically. This post compares the three major categories of pneumatic valve actuators, namely:- Rotary vane
- Scotch-yoke
- Rack & pinion
All three can be configured in either direct acting or spring return versions. Direct acting actuators use the air supply to move the actuator in both directions (open and close). Spring return actuators, as the name implies, uses springs to move the actuator back to its "resting" state. Converting from direct acting to spring return is done through simple modifications, typically just adding an external spring module, or removing the end caps from rack and pinion actuators and installing several coil springs.
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| Rotary Vane Actuator |
Rotary Vane Actuators
Vane actuators generally provide the most space savings when comparing size-to-torque with rack and pinion and scotch yoke. They have an outstanding reputation for long life because then contain only one moving part, as opposed to rack and pinion and scotch yoke actuators that have many. They tend to withstand dirty and corrosive atmospheres better than rack and pinion and scotch yoke actuators. Vane actuators also use externally mounted, helically wound "clock springs" for their spring return mechanism.
Scotch Yoke
Scotch-yoke actuators use a pneumatic piston mechanism to transfer movement to a linear push rod, that in turn engages a pivoting lever arm to provide rotation. They come in a wide variety of sizes, but are very often used on larger valves because they are capable of producing very high torque output. Spring return units have a large return spring module mounted on the opposite end of the piston mechanism working directly against the pressurized cylinder.
Rack and Pinion
A rack & pinion pneumatic actuator uses opposing pistons with integral gears to engage a pinion gear shaft to produce rotation. Rack & pinion actuators (sometimes referred to as a lunch box because of their shape) tend to be more compact than scotch yoke, have standardized mounting patterns, and produce output torques suitable for small to medium sized valves. They almost always include standard bolting and coupling patterns to directly attach a valve, solenoid, limit switch or positioner. Rack and pinion actuators use several smaller coil springs mounted internally and provide the torque to return the valve to its starting position.The practical difference between these three types of pneumatic actuators comes down to size, power, torque curve and ease of adding peripherals. For the best selection of valve actuator for any quarter turn valve application, you should seek the advice of a qualified valve automation specialist. By doing so your valve actuation package will be optimized for safety, longevity, and performance.
Scotch yoke mechanism image courtesy of Wikipedia.
Rack and pinion mechanism image courtesy of Wikipedia.
Updated Kinetrol Rotary Actuator Catalog - March 2018
Here is the March 2018 edition of the Kinetrol Rotary Actuator Catalog. You may view it in the embedded viewer below, or download it from this link.
Kinetrol Blueline Actuator Stands Up to Harsh Conditions in Cheese Factory
A very large mozzarella cheese producer in the USA had an actuator problem with their EFV’s (Enclosed Finishing Vats). The flow of the curds being blown into the EFV’s is controlled by star valves and pneumatic actuators. The actuators and valves serve (2) critical purposes: 1) The shut off of the star valve; and 2) controlling the air flow of the blower.The cheese plant had continuous service problems with their existing actuators. Some had to be replaced within one week of installation. Failure of the actuators caused the curd line to be plugged, and when replacement of the actuator was needed, it would result in a huge mess to be cleaned up off of the production floor. With a 24/7 production timetable, a solution needed to be found to keep the EFV’s up and running.
Kinetrol Blueline vane actuators were recommended because of their 4 million operation guarantee and the new proprietary coating that meets FDA specifications and is permitted for use in food service.
The Kinetrol Blueline actuators eliminated the maintenance issues completely and the Blueline coating has held up excellently after caustic wash-down, with no signs of degradation or fading.
https://kinetrolusa.com
972-447-9443
Words Used to Describe Kinetrol Actuators
The Most Reliable 1/4 Turn Pneumatic Actuator on the Market Today. Period.
For over 50 years Kinetrol has been providing trouble-free valve and damper actuators to the chemical, biofuel, food & beverage, metal, mineral, oil, gas, pharmaceutical, power generation, paper, textile, water, wastewater, and transportation industries.https://kinetrolusa.com
972-447-9443
The Advantages of Torsion Springs for Pneumatic Actuators
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| Kinetrol uses a torsion spring as the motive force for their actuator spring return. |
Torsion (clock) springs posses a natural tendency to expand, producing a cumulative torque that increases as the spring is wound tighter. Both ends of the torsion spring are attached to other, separate components. When one component rotates around the center point of the spring, the spring will increasingly try to return to the original state. When a torque is applied to a spiral torsion spring, an angular displacement is created between the first and second loading points. The coil then deflects (tightens), and the spring material is placed under stress, which in turn exerts a linear rotational "output" torque.
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| An internal view of the clock spring. You'll note similarities with the Kinetrol spring return unit. |
Practically speaking, spiral torsion springs allow for lower torque loss, lower torque stress, and much greater reliability for use in valve and damper actuation.
Advantages of the torsion spring:
- High torque delivery per unit of deflection
- Low cost
- Compact
- Reliable
- Adjustable
Epoxy Stove Enamel Finish: A Kinetrol Advantage
Epoxy stove enamel is a high quality stoving finish that provides excellent adhesion to a substrate. Epoxy stove enamel forms a very hard, abrasion resistant, chemical and solvent resistant coating that stands up to many extreme environmental conditions. Epoxy stove enamel finish provides high level chemical/corrosion resistant qualities, and is used often in applications such as machinery, industrial equipment, and heavy duty transport machinery.
Kinetrol actuators are engineered specifically for high-cycle, dirty, and corrosive applications. The combination of epoxy stove enamel finish and stainless steel external hardware provide Kinetrol actuators outstanding protection from dirt and harmful chemicals.
Kinetrol USA
https://kinetrolusa.com
972-447-9443
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