Avoid Fretting and Backlash with Rotary Vane Actuators

Fretting and backlash
shorten actuator life and
negatively affects controllability
over time.

The American Society for Metals Handbook on Fatigue and Fracture defines fretting as: "A special wear process that occurs at the contact area between two materials under load and subject to minute relative motion by vibration or some other force."

In pneumatic valve actuators, fretting wear is caused by the repeated cyclical rubbing between gears in scotch yoke or rack and pinion actuators. Over a period of time, fretting will remove material from one or both surfaces. This extra material, or debris, is usually harder than its source material due to work hardening and oxidation. The resulting debris becomes an even more effective abrasive, increasing the rate of mechanical wear and continued fretting.

Backlash happens when gears change direction. It is caused by the gap between the trailing face of the driving tooth and the leading face of the tooth behind it. The gap must be closed before force can be transferred in the new direction, hence the phenomena of backlash. This is also sometimes referred to as "slop".

Both fretting and backlash significantly effect the service life of an pneumatic valve or damper actuator. Both are also detrimental to controllability when actuators are used to accurately manage the percent open status of a valve or damper.

Internal view of a rotary vane actuators.
Notice the vane is constructed from
a single piece of stock and
contains no gears.

An alternative actuator design is the rotary vane design that uses a single piece of machined steel for both the vane body and drive shafts. With this design, the shaft and vane are not affected by backlash, friction or wear. Vane actuator's incorporate a design with only a single moving part that provides very repeatable, smooth movement that will not decay over time.

For more information, visit http://www.KinetrolUSA.com or call 972-447-9443.

The Kinetrol Blueline Actuator for Food and Beverage Applications

The Role of Industrial Valve Actuators

Kinetrol pneumatic actuators installed on pipeline.
Valves are essential to industry. Valve automation refers to
the electric, pneumatic, or hydraulic systems deployed to
open, close or position the valve.

Valves are essential to industries which constitute the backbone of the modern world. The prevalence of valves in engineering, mechanics, and science demands that each individual valve performs to a certain standard. Just as the valve itself is a key component of a larger system, the valve actuator is as important to the valve as the valve is to the industry in which it functions. Actuators are powered mechanisms that position valves between open and closed states; the actuators are controllable either by manual control or as part of an automated control loop, where the actuator responds to a remote control signal. Depending on the valve and actuator combination, valves of different types can be closed, fully open, or somewhere in-between. Current actuation technology allows for remote indication of valve position, as well as other diagnostic and operational information. Regardless of its source of power, be it electric, hydraulic, pneumatic, or another, all actuators produce either linear or rotary motion under the command of a control source.

Thanks to actuators, multiple valves can be controlled in a process system in a coordinated fashion; imagine if, in a large industrial environment, engineers had to physically adjust every valve via a hand wheel or lever! While that manual arrangement may create jobs, it is, unfortunately, completely impractical from a logistical and economic perspective. Actuators enable automation to be applied to valve operation.

Pneumatic vane actuator
with spring return and positioner
on plastic body valve.

Pneumatic actuators utilize air pressure as the motive force which changes the position of a valve.
Pressurized-liquid reliant devices are known as hydraulic actuators. Electric actuators, either motor driven or solenoid operated, rely on electric power to drive the valve trim into position. With controllers constantly monitoring a process, evaluating inputs, changes in valve position can be remotely controlled to provide the needed response to maintain the desired process condition.

Manual operation and regulation of valves is becoming less prevalent as automation continues to gain traction throughout every industry. Valve actuators serve as the interface between the control intelligence and the physical movement of the valve. The timeliness and automation advantages of the valve actuators also serve as an immense help in risk mitigation, where, as long as the system is functioning correctly, critical calamities in either environmental conditions or to a facility can be pre-empted and quickly prevented. Generally speaking, manual actuators rely on hand operation of levers, gears, or wheels, but valves which are frequently changed (or which exist in remote areas) benefit from an automatic actuator with an external power source for a myriad of practical reasons, most pressingly being located in an area mostly impractical for manual operation or complicated by hazardous conditions.

Thanks to their versatility and stratified uses, actuators serve as industrial keystones to, arguably, one of the most important control elements of industries around the world. Just as industries are the backbones of societies, valves are key building blocks to industrial processes, with actuators as an invaluable device ensuring both safe and precise operation.

Rotary Vane Valve Actuators

Rotary vane actuator

A rotary vane actuator is simply a part of an automated valve assembly: its role is to change the position of the valve, converting the motive force of fluid pressure into torque and applying it to a valve stem.

Quarter turn valves are widely used in industrial process automation. Their application is primarily for operations requiring fully open or fully closed valve trim positions, although some do provide modulating service. A rotation of the valve stem through a 90 degree arc will reposition quarter turn valve trim between open and closed positions. A rotary vane actuator is well suited for driving this type of valve, with its own 90 degree arc of movement.

A rotary vane actuator operates quarter turn valves, dampers and louvers. A pressure tight housing contains a movable vane which is sealed to the sides of the pressure chamber by means of a low friction gasket. Inlets into the chamber on opposing sides of the vane allow a controller to produce a pressure differential across the vane. The vane will move, in response to the pressure differential, in either direction. A shaft is connected to the vane and the vane acts like a lever to rotate the shaft as the vane is moved by fluid pressure. The torque produced by the actuator assembly is primarily dependent upon the applied fluid pressure.

Hydraulic rotary vane actuators have the ability to handle large amounts of fluid and dynamic motions, exhibiting also qualities of durability and compactness. Pneumatic vane actuators use plant air pressure as the motive force. Both types generally have few moving parts and require little regular maintenance. A variety of typical automation accessories and options are available to customize a unit for a particular application.

Pneumatic Vane Actuators Can Now Be Used in Foodservice Wash-down Applications

Kinetrol Blueline Foodservice Actuator
(Double-acting)

Finally, food and beverage processing companies can take advantage of the long-life and headache-free performance of Kinetrol vane actuators.

Kinetrol USA has officially introduced it's "Blueline" Series of pneumatic vane actuators for use in foodservice and beverage processing. The actuators are intended to be installed in areas where harsh chemical wash-down is required. These areas are very tough on most types of pneumatic actuators because the caustic or acidic chemicals used in cleaning adversely effect the actuator. All stainless steel actuators are an alternative, but they are prohibitively expensive. Kinetrol's Blueline Series provides a very economical option.

Kinetrol Blueline Actuator
(Spring-return)

Blueline Actuators are permitted for use in contact with food in compliance with the Federal Food, Drug and Cosmetic Act (FDA) and all applicable regulations, including 21 CR 175.300 (Code of Federal Regulations). The new actuator has an applied coating that meets with the FDA's allowance whereby "Resinous and polymeric coatings may be safely used as the food-contact surface of articles intended for use in producing, manufacturing, packing, processing, preparing, treating, packaging, transporting, or holding food ...".

The Blueline Series provides food and beverage processors all the time-proven benefits of the Kinetrol PLUS provides an affordable option for tough chemical wash-down areas. 

Kinetrol Blueline Features:

• Very good resistance to "caustic wash-down" procedures as typically performed in the food industry.
• Very good resistance to corrosion In salt laden environments.
• Very good non-stick properties.

For more information, contact Kinetrol at 972-447-9443.

More Kinetrol Vane Actuators Hard at Work!

Here is a another short video of Kinetrol pneumatic vane actuators taking on some of the toughest industrial valve and damper applications.

Kinetrol engineered the first rotary vane actuators in 1958. The rotary design is based upon a single moving part which eliminates additional parts required to convert linear motion to rotary motion. This simple and innovative design provides a highly accurate and extremely reliable actuator for operating valves, drives and dampers, and is perfectly suited for the most demanding process control control applications.

For more information visit http://www.kinetrolusa.com or call 972-447-9443.

Rotary Vane Actuators for Corrosive Marine Environments: The Right Choice

Corrosive marine environments present problems for
valve actuators.

Corrosive marine environments such as offshore oil rigs, shipyards, and maritime facilities present special challenges for pneumatic actuators. Proper selection of actuator design is important for long, trouble-free life. Salt-laden dust and high humidity take a harsh toll on the internal and external parts of any industrial equipment if not properly designed and protected. For example, rack & pinion and scotch-yoke actuators are particularly susceptible because of the relative ease of penetrating the actuator and affecting their critical components, such as metallic gears and coil springs. Spring-return rack & pinion and scotch-yoke actuators further complicate the issue because they require the intake and venting of ambient air, along with any contaminants in the air.

Rotary vane actuators, (such as Kinetrol) provide strong immunity to internal corrosion. First, they have no internal gears or springs to corrode. Second, the internal surfaces are coated with a very durable, epoxy enamel finish and all internal hardware is made from stainless steel. Additionally, the “wiping” action of the vane and lip-seals provide a self-cleaning effect that prevents corrosion in the working areas. Finally, unlike rack & pinion and scotch-yoke actuators whose coil springs are bathed in ambient air, (Kinetrol) vane actuators use externally mounted clock type springs that are 100% sealed from ambient air/gasses and are unaffected by corrosive atmospheres.

For any application where corrosion is a problem, such as those in offshore platforms or other marine facilities, engineers should strongly consider rotary vane actuators as the preferred choice for any quarter-turn valve application.

The video below illustrates the difference in construction in actuator types and illustrates the inherent advantages of vane style actuators: