Paper 360
Food, pulp and paper, pharmaceutical, and chemical plants often operate around the clock. To manufacture these products, high-speed, high cycle actuators open, close, or throttle valves to 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 need 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.
With an actuator specifically designed for reliable and long-lasting performance, mills can reduce costs associated with a labor-intensive manufacturing component.
However, some processors are beginning to reassess this expectation. The truth is that 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 crucial, 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 use and demand placed on the actuator. Actuators come in different styles, but all involve moving parts that experience considerable force, wear, and stress. Some actuators are 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.
There are exceptions—including what Howard refers to as the “Ferrari” of actuators: those from Tomball, TX-based QTRCO. 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. This makes them perfect for demanding applications in extreme temperature, corrosive, or submerged environments.
NO MORE LUNCHBOX
Among QTRCO’s more innovative designs is its answer to the common aluminum “lunchbox” actuator. This type of actuator, which gets its name from its one-piece aluminum extruded body and cylinder that resembles a lunchbox, is popular because it is compact, inexpensive, and works well. Yet aluminum lunchbox actuators are not very reliable and often break 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 in 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 outward, 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.
REPLACEMENT FREQUENCY
With an actuator specifically designed for reliable and long-lasting performance, processors can save on costs associated with more frequent replacements. When preventive 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.
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 preventive 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,” he adds. “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.”
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.
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
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,” he notes. That does not even take into consideration the plant’s number one expense: downtime.
Design advancements in high speed, high cycle actuators make things easier for processors, including pulp and paper mills. With an actuator specifically designed for reliable and long-lasting performance, mills can reduce costs associated with a labor-intensive manufacturing component that today too often requires frequent maintenance, repairs, and replacement.
