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| 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.
Industrial valves, dampers and louvers are operated either electrically or pneumatically. This post compares the three major categories of pneumatic valve actuators, namely:
Scotch Yoke
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.
In higher quality vane actuators, the vane and shaft are machined from a single piece of steel. Casting and machining adds cost, but also adds performance. Lower quality actuators save cost by using a 2-piece vane/shaft combination. These are more likely to be affected by backlash or lost motion. In other words, a one-piece shaft and vane assembly transfers 100 percent of the vane movement directly to the shaft. Two-piece designs may lose movement over time, reducing control and accuracy.
Higher quality pneumatic vane actuators incorporate a pair of “lip seals” around the vane. The durable and resilient polyurethane seals provide two key benefits; eliminating the need for o-rings; and eliminating shaft seals. Dual, opposing lip seals are located each side of the vane. They isolate the vane and shaft from the air supply and create an area from the shaft through the center of the vane that remains unpressurized, eliminating the need for pressure seals around the top and bottom of the shaft.
The heart of the pneumatic vane actuator is simple design. Manufacturers often promote the concept of "a single moving part", referring to the vane/shaft/seal assembly. But despite this claim, all pneumatic vane actuators are not the same. You owe it to yourself and your organization to "look under the hood". See what level of engineering and quality you're really getting.
As they have in a past MythBuster episode, the MythBusters team turned to Kinetrol for the crucial piece of equipment - the Kinetrol pneumatic rotary vane actuator.
