Valve actuators built for longevity

High cycle actuators are often seen as having a short lifespan, with costly installation and maintenance requirements. However, many leading processors are realizing that well-designed actuators can offer reliable performance for years with minimal maintenance or repair.

In food, pulp and paper, pharmaceutical, and chemical plants, processors often operate around the clock to produce chemicals, paints, resins, lubricants, ingredients, and other raw materials. To manufacture these products, high-speed, high cycle actuators open, close, or throttle valves to regulate, direct, or control the flow of gases, liquids, fluidized solids, or slurries.

Many processors have become accustomed to the idea that high cycle actuators have a short lifespan and necessitate regular maintenance to replace parts prone to wear, such as O-Rings, springs, cylinders, and others. In some facilities, this task can consume a technician’s entire work schedule.

However, many leading processors are beginning to reassess this expectation, given the high costs for installation and maintenance.

A well-designed actuator should be able to provide reliable performance for many years beyond the warranty period. If maintenance or repair is needed, it should be infrequent and simple enough for a single technician to handle, using common tools. For maintenance or repair purposes, the actuator should be easily accessible without the need to remove it from the valve. This is a crucial factor, as valve manufacturers will invalidate warranties if the actuator is detached from its mount.

High demands on actuators
Actuator usage and stress are often linked to the frequency of valve opening and closing cycles. The cycle count often varies based on the environment or application. Some actuators are seldom used, while others operate regularly. High cycle, high-speed valve actuators – often found in processor operations – can fire rapidly and repeatedly many times per hour, non-stop throughout the year.

The core issue lies in the high utilization and demand placed on the actuator.

Actuators come in different styles based on the mechanical action required, such as linear or rotary, but all involve moving parts that experience considerable force, wear, and stress. In processing plants, actuators are also installed in highly corrosive industrial settings. Many designs fail to account for these factors and are poorly engineered, leading to excessive side loading, wear on non-wearing parts, and various other issues.

High reliability is another crucial factor that holds significance for Scott Howard of NewGen Products, a specialist in valve automation. Many of his customers are in the aerospace industry, where valves with actuators regulate the flow of cryogenic gases for fueling and storage operations.

For critical applications like these, Howard often recommends a top-of-the-line actuator, purpose built for the application. Although there may be a higher initial cost, these actuators are designed to perform reliably in challenging and harsh environments. Even within this category, however, many actuators are not expected to last. “Many of the higher end actuators are rebuilt every three to four years,” says Howard.

Founded in 1998, QTRCO has innovated designs specifically for high cycle, high speed, high reliability applications.

The actuators are built with a robust mechanical design that eliminates common failure points like sliding parts, side load forces, and multiple seals.

No more lunchbox
Among the more innovative designs from QTRCO is its answer to the common aluminum “lunchbox” actuator and its inherent design limitations.

The actuator, which gets its name from its one-piece aluminum extruded body and cylinder that resembles a lunchbox and is compact as so. Aluminum lunchbox actuators are not very reliable and often break, however, in more demanding environments or applications.

To resolve many of these issues, QTRCO designed an actuator with an internal “rack and gear” mechanism as an alternative to its traditional rack and pinion design.

The actuators are designed with offset cylinders that align the piston axis with the pinion gear pitch circle diameter, eliminating cantilever forces and friction. The company also replaced the sliding blocks, wear pads, and bushings with specialized rollers. As a result, the rack and gear actuators have extremely low internal friction.

The new design also eliminates one of the primary causes of failure of a lunchbox actuator: the O-rings on the shaft. In a lunchbox actuator, air is forced through ports in the body. The air pushes the piston outwards, and springs push the piston back in. Each cycle pressurizes the shaft, which typically has two O-rings, one at the top and one at the bottom. As the shaft cycles back and forth 90 degrees, the reciprocating motion places significant stress on the O-rings.

In QTRCO’s design, this action is reversed, and the air is forced inward through the end cap. The spring return applies no pressure to the shaft seals, which prevents premature O-ring wear.

This configuration also has benefits when valve throttling is required. Due to the design of the company’s Q Series and because the piston is located close to the end cap, much less air fill volume is required, and the actuator responds much quicker and is easier when throttling.

QTRCO took a similar approach as an alternative to Scotch yoke actuators. Also known as a slotted link mechanism, the Scotch Yoke is a simple and effective mechanism that has been used for a long time. However, with typical Scotch Yoke actuators, the force applied to the piston rod is also applied to the shaft and shaft bushings, resulting in friction and bushing wear.

To resolve these issues, QTRCO designed a patented Flat Yoke mechanism that can accurately and reliably position any rotary control valve requiring up to 500,000-inch lbs. of torque.

The Flat Yoke is designed with quad body slots that absorb the mechanism’s side loading forces, leaving the piston rod completely free of bending stresses while allowing termination of the rod at the yoke. Like the Q Series, these F Series actuators also have extremely low internal friction, consume minimal air volume, and can handle the most severe throttling applications.

Frequent Replacement
With an actuator specifically designed for reliable and long-lasting performance, processors can save on costs associated with more frequent replacements.

In one processing plant he visited, Howard says the actuator fired twice a minute throughout the entire year, adding up to over a million cycles per year. Given the usage, the plant would replace the actuator annually during planned outages.

According to Howard, the replacement of an actuator typically requires an entire day for a single technician, often with the help of at least two additional individuals. If the actuator is large enough, a crane is required. Considering the potential costs for hourly labor rates and rentals, a plant could save thousands of dollars every time it eliminates the need to replace an actuator.

“If a plant doesn’t have to change the actuator every year, they just saved a fortune,” says Howard.

When preventative maintenance or repair is required, it should be easily conducted using common tools and without removing the actuator from the valve. With large, metal-seated ball valves, it is critical to mount the actuator with extreme precision. A slight misalignment during mounting can result in severe damage to a valve that carries a hefty price tag of hundreds of thousands of dollars. The connection is so crucial that most major valve manufacturers will void warranties if the actuator is removed.

In rare cases, like with QTRCO designs, the actuators can be easily maintained without removal from the valve. This enables hassle-free removal and replacement of end caps, cylinders, and O-rings, often without special tools.

Safety
According to Ross Evans, also with NewGen Products, safety is another concern during preventative maintenance and repair. Actuators of considerable size may require two people for lifting and moving.

“Imagine being in a plant environment and climbing six flights of stairs to a catwalk to service an actuator. With that kind of weight, what does it take to get your cranes and rigging in place to safely take off the actuator? You have to remove all the pneumatic airlines, disconnect the electrical, and you need a couple hands. There’s a lot of cost and time and risk involved,” explains Evans.

“The alternative is, I can do maintenance on the valve while it is in place,” adds Evans. “I shut down the unit, tag it out, take off the end cap, inspect the cylinder, remove an O-ring, grease it, and put it back in place. In about 10 minutes per cylinder, we are back and running.”

The actuator’s design can also contribute to safety concerns. Many Scotch Yoke designs feature a lone piston assembly on one side of the unit. Lifting or rigging an unbalanced, single piston assembly is challenging due to its significant lean on one side.

For high speed, high cycle processing applications, QTRCO recommends sizing up to a two-piston version of its Flat Yoke design. The two pistons balance the forces on both sides of the shaft, preventing bushing wear. The design also includes the addition of a weight and force balancing second force module diagonally offset from the first.

By balancing the forces, there is less friction and wear and no net force applied to shaft bushings. The balanced weight also makes lifting and handling of the actuators safer and easier, while reducing valve neck stress that can occur in unbalanced scotch yoke actuators.

Another issue is the spring set used in many lunchbox actuators, which are under load and must safely be controlled once the end cap is removed. If the spring becomes jammed and the mechanism that contains the spring fails, the force exerted can be equivalent to a shotgun.

“In one actuator, the end cap corroded and failed. It discharged the spring out of the actuator across the shop,” says Evans.

He says he has personally observed experienced field technicians that regularly work on actuators, who move out of the line of the cylinder to remove the end cap on the actuator.

“Anybody that’s done any type of maintenance on an actuator, they know the potential energy contained in the spring,” says Evans.

With QTRCO, the spring is fully captured using a solid stainless-steel rod that goes through the spring retainers and there is a safety collar that locks it into place. Replacing the springs simply requires removing the end cap and replacing the cartridge.

“Once they capture those springs, it is designed not to ever come apart again – it remains captured. It is a big safety feature,” says Evans.

Cost-Effective Solution for Processors
Installing actuators that are built to last and require minimal maintenance or repair not only brings significant benefits, but also proves to be more cost-effective in the long run, even if the initial cost of ownership is higher. When multiple actuators are installed in a processing plant, the savings can add up.

“If you put a well designed actuator in one of these demanding applications and rarely have to do any maintenance or replace it very quickly, the total cost of ownership is far less,” says Evans.

“If you can get an extra three or four years of run time on an actuator, you just made up whatever cost difference you had on the initial price,” notes Evans, adding that does not even take into consideration the number one thing that costs the plant money: downtime.

Today, design advancements in high speed, high cycle actuators make it easier for food, pulp and paper, pharmaceutical, and chemical processors to create high-quality products.

With an actuator specifically designed for reliable and long-lasting performance, processors can reduce costs associated with a labor-intensive manufacturing component that today too often requires frequent maintenance, repairs, and replacement.

Jeff Elliott is a Torrance, Calif.-based technical writer. He has researched and written about industrial technologies and issues for the past 20 years.