Exploring the Superior Features of Vane Actuators in Contrast to Rack & Pinion and Scotch-Yoke Designs

Pneumatic actuators are vital components in many industrial processes, enabling the automation of valve and damper operations. The three most commonly used types of pneumatic actuators are vane, rack and pinion, and scotch yoke. This post provides an analysis of the technical design differences between these actuators, focusing on the advantages of Kinetrol vane actuators. We will also discuss why Kinetrol vane actuators last longer in industrial valve and damper applications, and how they provide a lower cost of ownership than other types of pneumatic actuators.

Design Differences Between Vane Actuators, Rack and Pinion Actuators, and Scotch Yoke Actuators

Kinetrol Pneumatic Vane Actuators

Kinetrol pneumatic vane actuators utilize a simple yet effective design consisting of a central shaft connected to a flat vane inside a semi-cylindrical housing. When pressurized air is applied to the housing, the vane rotates the central shaft, creating a rotary motion that operates the valve or damper.

Pneumatic Rack and Pinion Actuators

Pneumatic rack and pinion actuators consist of a piston connected to a rack, which engages with a pinion gear on the output shaft. As the piston moves linearly, the rack converts this motion into rotation through the pinion gear, driving the output shaft.

Scotch Yoke Actuators

Scotch yoke actuators employ a slotted yoke mechanism that translates linear motion from a piston into rotary motion. The piston rod has a pin that engages with the yoke, which in turn is connected to the output shaft. As the piston moves, the pin slides within the yoke slot, causing the yoke to rotate the output shaft.

Advantages of Kinetrol Pneumatic Vane Actuators

Simplicity and Compactness

Kinetrol vane actuators boast a simple design with fewer moving parts compared to rack and pinion or scotch yoke actuators. This simplicity results in a more compact and lightweight unit, which requires less space and is easier to install and maintain.

High Torque-to-Size Ratio

Kinetrol vane actuators have an exceptional torque-to-size ratio, providing more torque per unit size compared to other actuators. This enables Kinetrol actuators to deliver powerful performance even in space-constrained applications.

Less Friction and Wear

The design of Kinetrol vane actuators minimizes contact between moving parts, resulting in reduced friction and wear. This leads to a longer service life and lower maintenance requirements.

Smooth, Precise Control

Kinetrol actuators provide smooth and precise control of the valve or damper position, with minimal backlash or hysteresis. This ensures accurate and consistent process control, essential for maintaining product quality and efficient operations.

Longer Life in Industrial Valve and Damper Applications and Lower Cost of Ownership

Kinetrol vane actuators last significantly longer in industrial valve and damper applications due to their design, which minimizes friction and wear. Their simple construction and fewer moving parts result in reduced likelihood of component failure and increased resistance to harsh operating conditions. This translates into fewer breakdowns, less downtime, and lower maintenance costs.

The cost advantages of Kinetrol pneumatic vane actuators stem from their durability, ease of maintenance, and lower energy consumption. With fewer components to replace, lower maintenance requirements, and longer service.

For more information, contact:
Kinetrol USA
https://kinetrolusa.com
972-447-9443

The Top Five Reasons Why Kinetrol is a Better Choice Than Rack and Pinion Actuators

1. Rotary vane actuators do not convert linear motion to rotary motion, unlike rack and pinion actuators. 

No additional gearing is required and no side loading is transferred to the actuator housing.

2. Vane actuator lip seals are the key for long life. 

The double opposing lip seal design, with stainless steel expanders, provides unmatched service life by using air pressure to improve the actuators seal-to-enclosure contact, and provide a “self cleaning” effect on the epoxy or PTFE internal finish.

3. The elimination of pressure bearing o-ring shaft seals. 

Rack and pinion actuators require shaft sealing o-rings that are exposed to the full supply air pressure used to operate the actuator. These o-rings wear, causing leaks, a drop in efficiency, and wasted energy through air consumption. Vane actuators' double opposing lip seals isolate the supply air pressure from the actuator shaft, requiring only a low friction bearing on the shaft.

4. Rotary vane actuators provide superior modulating accuracy. 

Because of the integral vane and shaft (machine from a single casting), lost motion or hysteresis is reduced dramatically which intern provides much tighter modulation and control. The vane actuators inherent low friction also reduces hunting and sticking.

5. Rotary vane actuator spring return units are designed to be virtually indestructible. 

Using low stress, clock springs reduces spring tension loss and metal fatigue. The housing for vane a actuator springs are sealed from the atmosphere, preventing corrosion of internal parts. Most importantly, these type of spring units provide the lowest torque loss which enables the section of smaller (less expensive) actuators.

Kinetrol USA
https://kinetrolusa.com
972-447-9443

Kinetrol Vane Actuators Lower Cost of Filter Operation at Power Plant

A Monoscour^® filter is a heavy duty, high-rate, gravity filter. It is designed for filtering high turbidity media and sticky particulates, and is commonly used in polymer chemical treatment, cooling tower side-stream filtration, and industrial wastewater filtering. This kind of filter is designed to be fully automatic and includes all piping and valves needed to change from filter mode to cleaning mode. Inexpensive rack and pinion actuators are installed as OEM components to divert flow between cycles. The actuators are mounted on 4" lug style butterfly valves.

A Midwestern power plant was experiencing failures with their filter's OEM rack and pinion actuators. The actuator cycle rate was moderate-to-high, approximately (1) cycle per hour, continuous.

While the cost of rack and pinion actuator replacement was relatively low, the cost of filter downtime and labor was very high for the utility. As part of an ongoing, long term cost savings effort, a more reliable and robust solution was required.

The local Kinetrol Distributor Salesperson was called in and immediately saw that replacing the rack and pinion actuators with Kinetrol vane actuators was the answer. Based on the countless applications around the world, where Kinetrol actuators perform reliably in the most challenging circumstances, this particular application was comparatively easy and straightforward.

The new Kinetrol actuators were retro-fitted to the existing valves with new mounting hardware and have been operating flawlessly for over a year now. Its expected the valves will wear out long before the actuators ever need service.

For more information about using Kinetrol vane actuators on filtration towers, contact Kinetrol USA by visiting https://kinetrolusa.com or by calling 972-447-9443.


Monoscour^® is a registered trademark of Graver Water Systems.

Kinetrol Vane Actuator Outperforms Rack and Pinion on Power Plant Filter-Demineralizer System

Kinetrol Vane Actuator on Power Plant
Filter-Demineralizer System

An important component of combined cycle power plant design and operation is condensate polishing, commonly referred to as "CP". CP is a process that purifies condensate. High purity condensate maximizes uptime in power plants by maintaining stable condensate chemistry and reducing corrosion transport. Power plants install specialized filter-demineralizer systems which remove both suspended solids and ionic contaminants to maintain optimal condensate  chemistry.

At one midwest power utility company, a valve controlling the flow of water (210 psi and 140 deg. F) that feeds the demineralizer was causing concern. The valve's accompanying rack and pinion actuator was creating a maintenance problem. While this isn't a high cycle application, the system must be 100% reliable, and the old actuator's performance was unreliable. The solution was to install a Kinetrol vane actuator. A new automated valve was installed 6 years ago (2012) and the Kinetrol actuator has operated flawlessly since then.

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:

1. Rotary vane
2. Scotch-yoke
3. Rack & pinion

All three categories provide the same basic function - converting air pressure to rotational movement intended to open, close, or position a quarter-turn valve (ball, plug, butterfly), louver or damper.

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.

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.

Why Vane Actuators Are Better - We'll Make This Easy

With millions of actuators performing reliably around the world, the Kinetrol vane actuators' outstanding cycle life, smooth and precise movement, and environmentally rugged design makes it the best choice for all of your valve actuation needs.

The rotary vane actuator 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.

Lower Total-Cost-of-Ownership in Poor Process Environments with Pneumatic Vane Actuators

Design advantages for use in poor process conditions (click for larger view).

Clean, dry instrument air is critical for pneumatic instruments and actuators to work properly. In remote, dirty process control environments, like refineries, chemical plants, power plants, water treatment facilities, pulp & paper mills, or mining facilities, providing clean instrument air is challenging,  costly and problematic.  Along with poor instrument air, the ambient air in these areas is generally filled with dust and contaminants. Process equipment must be engineered to withstand these conditions, and devices with low tolerance to dust, dirt, condensate, and poor ambient air quality (such as rack and pinion actuators) are to be avoided. Devices in these areas are costly to maintain as shut-downs and repairs are very expensive.

For the operation of pneumatically controlled valves, and as a better alternative to rack and pinion actuators, Kinetrol rotary vane actuators are an excellent choice. Their simple design, with one moving part, and an elegantly engineered vane, inherently protects the actuator from bad instrument air. Kinetrol's use of double opposed polyurethane lip seals, backed by stainless steel expanders, ensure long-term lip seal contact and effective sealing for years of maintenance free life. The vane, lip seals, and expanders actually provide a self-cleaning, or wiping, mechanism for any moisture, dirt or dust entering the interior of the actuator. In effect, the vane actuator's design "sweeps away" the debris that will cause other actuators to fail.

A considerable cost savings can be calculated given the trouble-free performance Kinetrol vane actuators provide. Assuming both a Kinetrol and standard rack and pinion actuator cost approximately the same, and that the life of a typical rack and pinion actuator in these environments is approximately 1 year, you can easily see the savings. By factoring in the replacement cost for an new actuator, and the cost of labor to install, you’ll find a standard rack and pinion is at least 2.5x the cost of Kinetrol over a 2 year period.

Kinetrol actuators have a well-earned reputation for operating trouble-free for years in the most difficult environments. Considering their years of maintenance-free service, it’s easy to understand the significantly lower total-cost-of-ownership they deliver.

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

Why Vane Actuators Outlast and Outperform Rack & Pinion and Scotch Yoke Designs

Kinetrol vane actuators perform
in the toughest applications.

Due to the use of gears, slides, pins, and yokes, rack & pinion and scotch-yoke design actuators are less reliable than Kinetrol vane actuators.

Kinetrol's 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

Vane Actuators Perform Better: Its All About the Gears (or Lack Thereof)

Why do vane actuators consistently outlast rack and pinion and scotch yoke actuators? The truth is in the gears.

Gears wear.

Surface wear, contact fatigue, scuffing and tooth bending are all real-life issues when dealing with gears. Surface wear affects gear contact in such a way that accelerates failure modes by increasing contact stresses and load distributions. This always leads to reduced accuracy and loss of smooth operation. Wear can never be completely eliminated, and over time, progresses at a more rapid rate.

Typical rack and pinion design - note gear arrangement

Types of Stress on a Gear

• Sliding stress - causes surface fatigue damage.
• Rolling stress - causes contact fatigue damage.
• Bending stress - like a cantilever beam, always deforms. 

Vane actuator - no gears

Pure simplicity - the rotary vane.

One moving part. No gears.

The rotary vane actuator design is based upon a single moving part which eliminates gears required to convert linear motion to rotary motion. This simple and innovative concept provides an extremely reliable mechanism for operating valves, drives and dampers.

More Accurate Control

Another advantage rotary vane actuators have over rack & pinion and scotch yoke actuators is in smoothness and accuracy of control. The more mechanical connections the actuator has, the greater the cumulative hysteresis, and the lower the control responsiveness and accuracy.

For long, trouble-free performance, choose a rotary vane actuator for your next valve actuation or damper drive requirement. You'll be very glad in the long run. 

6 Reasons Why Pneumatic Vane Actuators are Superior to Rack and Pinion Actuators

Rotary vane actuators offer distinct design and performance advantages.

1. Rotary vane actuators do not convert linear motion to rotary motion, unlike rack and pinion actuators. No additional gearing is required and no side loading is transferred to the actuator housing.
2. Vane actuator lip seals are the key to long life. The double opposing lip seal design, with stainless steel expanders, provides unmatched service life by using air pressure to improve the actuators seal-to-enclosure contact, and provide a “self cleaning” effect on the epoxy or PTFE internal finish.
3. The elimination of pressure bearing o-ring shaft seals. Rack and pinion actuators require shaft sealing o-rings that are exposed to the full supply air pressure used to operate the actuator. These o-rings wear, causing leaks, a drop in efficiency, and wasted energy through air consumption. Vane actuators' double opposing lip seals isolate the supply air pressure from the actuator shaft, requiring only a low friction bearing on the shaft.
4. Rotary vane actuators provide superior modulating accuracy. Because of the integral vane and shaft (machine from a single casting), lost motion or hysteresis is reduced dramatically which intern provides much tighter modulation and control. The vane actuators inherent low friction also reduces hunting and sticking.
5. Direct mount, modular design for springs, positioners, switches, and solenoids reduce space requirements and lower inventory costs. Since vane actuator accessories direct mount to various size actuators, there’s no need to inventory and keep track of mounting kits. 
6. Rotary vane actuator spring return units are designed to be virtually indestructible. Using low stress, clock springs reduces spring tension loss and metal fatigue. The housing for vane a actuator springs are sealed from the atmosphere, preventing corrosion of internal parts. Most importantly, these type of spring units provide the lowest torque loss which enables the section of smaller (less expensive) actuators.

Don't Get Racked Up ... Use Kinetrol Vane Actuators

Little video "commercial" about the virtue of Kinetrol Vane actuators over pneumatic rack and pinions actuators ...

Kinetrol vane actuators provide:

• Single moving part - Simplest and most reliable mechanism for quarter-turn rotary actuation.
• Close couple control modules - Fail-safe spring returns, limit switches, positioners and solenoid valves all close couple to the actuators.
• No cranks or gearing - No power loss or backlash - allows accurate positioning.
• Durable corrosion resistant finish
• Long maintenance-free life - Up to 4 million operations guaranteed.
• Compact - space saving - efficient: Best torque/size package available, fast operating speeds, best air consumption, proven design.

Kinetrol Actuator on Asphalt Plug Valve

Kinetrol actuator on asphalt valve.

A Mid-west asphalt manufacturer purchased Kinetrol actuators for use at two of their plants as a trial for possible standardization. This asphalt producer owns 7 asphalt mix plants and has been plagued with failing rack and pinion actuators. They're used to open and close their liquid asphalt valves (Homestead plug valves).

The service is extremely nasty, as the asphalt is hot, sticky and gets everywhere. The Kinetrol actuators were installed on 3” Homestead liquid asphalt plug valves with extended brackets and couplings to prevent the actuators from seeing over-temperatures. The valves are cycled 10 times per day.

Since the summer of 2014 they have installed 5 Kinetrol actuators and all are working without problems. The initial results are so positive the customer plans to standardize on Kinetrol Vane Actuators, and replace the rack and pinion actuators as they fail.

Elegantly Engineered Pneumatic Valve Actuators. A Simple, Single Moving Part

One moving part. Simple. Elegant.

According to Wikipedia, elegance is "a synonym for beauty that has come to acquire the additional connotations of unusual effectiveness and simplicity." In engineering terms, "a solution may be considered elegant if it uses a non-obvious method to produce a solution which is highly effective and simple. "

When you compare the mechanics of various other pneumatic valve actuators, such as rack and pinion or scotch yoke with their internal gears, bushings and bearings, you immediately understand that simplicity is sacrificed and the design is certainly not elegant.

Actuators with gears wear.

When gears mesh, there is friction. Friction causes heat and wear, which effects the mechanical life of the actuator. Friction converts kinetic energy into thermal energy and can have dramatic consequences if left unchecked. Another important consequence of friction is wear, which may lead to performance degradation and/or damage to the internal components of a rack and pinion or scotch yoke actuator.

"Fretting wear" is caused by the repeated cyclical rubbing between two surfaces (gears in the case of scotch yoke or rack and pinion actuators) and over a period of time, will remove material from one or both surfaces.

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".

A well designed vane actuator 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.

For more information, contact:

Kinetrol USA
1085 Ohio Drive
Plano, Texas 75093
(972) 447-9443 phone
(972) 447-9720 fax
sales@kinetrolusa.com

Why the Rotary Vane Actuator Design is Superior to Rack and Pinion & Scotch Yoke Designs

When it comes to pneumatically actuating an industrial quarter-turn valve, you basically have only three types of mechanical technologies to choose from: rack and pinion, scotch yoke and the rotary vane design. This post describes why a rotary vane design is the clear winner when it comes to efficiency and reliability.

First, let's describe how rack and pinion and scotch yoke actuators work.

A rack and pinion actuator is comprised of two opposing pistons, each with its own gear (referred to as the "rack"). The two piston racks are set against a round pinion gear. As pressure increases against one side of each piston, each rack moves linearly against the opposite sides of the pinion gear causing rotational movement. This rotational movement is used to open and close a valve. Pretty basic stuff. See the animation (provided by Wikipedia) below for a visual understanding.

Note rack and pinion gears
and how they are prone to
wear and slop.

A scotch yoke actuator relies on the scotch yoke mechanism to convert linear movement into rotary motion. In this case, a piston is coupled to the sliding yoke, which in turn moves a fixed pin on the shaft of the actuator to provide rotation. As one side of the piston is pressurized, the piston forces the yoke to move linearly, which allows a slot in the yoke to drive the pin on the actuator shaft. See the animation (from Wikipedia) below for clarification:

Scotch yoke operation. Easy to see its highly
susceptible to wear and resulting slop.

Both of these valve actuator mechanisms use several interconnected, mechanical moving parts. As a result, they are very susceptible to wear.

It All Comes Down to "A Single Moving Part"

The vane actuator has only one moving part and there is no linear-to-rotary conversion. An internal vane moves uniformly in response to inlet air pressure, without gears, slots, or levers. This is a clear advantage when you consider wear and tear, and also machine efficiency. See the video below for a visual explanation.

Vane = Simple, reliable design --------- Piston = Complicated, less reliable

One moving part --------------------------- Many moving parts
No O-rings ---------------------------------- Several sets of O-rings
Dynamic Memory Seals ------------------ Static seals
No linear to rotary motion ---------------- Linear to rotary = friction/wear
Spring isolated ------------------------------ Spring exposed to atmosphere
Very accurate control ---------------------- Hysteresis = poor control
Non-pressurized shafts -------------------- Pressurized shafts
4 million operations ------------------------ 500,000 to 1 million operations