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Small but mighty: pneumatic actuator sizing and selection simplified: in mines and mills, installation space is often at a premium for pneumatic actuators used in valve automation.

Although space has been a long-standing hurdle in the actuator industry, innovation around this restriction didn't take place until recently. In fact, up until the late 2000s, no fundamental improvements or disruptions to pneumatic actuator designs occurred. The old generation of valve actuators typically relied on internal springs. In this design, when the actuator moves the flow control element away from Its starting position (open or closed), it compresses the internal spring and then uses the energy stored in the spring to move the control element back toward its starting position.

There are a few reasons why spring-controlled actuators are less-than-ideal for the mining industry. First, they are inherently neither size- nor cost-effective, because the actuators must be sized to overcome the spring tension and account for the necessary torque of the valve and system. This translates to oversized actuators, which in addition to taking up unnecessary space, also means a higher price tag. Add the spring assembly to these costs and the price quickly climbs to 30% to 80% more than the standard double-acting actuator assembly. Additionally, springs are subject to corrosion from atmospheric conditions and degradation from constant compression.

Alternatives are available. They use air reservoirs to store compressed air needed to supply the required force to fail the valve to the fail-safe position. However, air reservoirs have traditionally been supplied as an added piece of equipment that requires custom brackets and mounting hardware. External reservoirs require ASME code-certified tanks that are mounted to the actuator assembly. These reservoirs not only add to the size and cost of the system, but they also require a considerable amount of external tubing. These considerations add to the overall footprint, which limits the usefulness and cost efficiencies.

A new generation of pneumatic actuators addresses these hurdles. Instead of springs or external reservoirs, the new generation of actuators relies on internal air reservoirs to store the compressed air needed to supply the force to fail the valve to the fail-safe position. Unlike spring-based designs, the new generation of actuators is not oversized to overcome spring tension. And unlike external reservoirs, internal reservoirs do not require space-consuming brackets, mounting hardware or external tubing. These developments lead to an exponential reduction in the actuator's size and weight, while reducing air consumption.

The Easytork model integrates the reservoir into the pneumatic actuator housing, resulting in one compact package. With the proper pilot assembly, the reservoir is constantly pressurized and able to perform the fail-safe operation during a power failure or catastrophic air failure. When those situations arise, sufficient air is maintained in the reservoir to fail the valve in the pre-selected fail position.

The introduction of spring-less pneumatic fail-safe actuators opens up new possibilities for effective, streamlined designs. Freed from the mechanical restrictions and space requirements needed for springs, actuator designers can now use the space once reserved for springs for more user-focused design elements, such as friendlier valve adaptation, simplified inventory, tighter repeatability on control valves and air consumption efficiency designs. These are also the crucial factors that mining operators must consider when planning and maintaining their facilities.

Actuator manufacturers may for example build double-acting or fail-safe in fail-close or fail-open functioning all in the same package, thereby reducing inventory complexity by threefold.

Further, the design improves valve adaptation. For example, Easytork actuators use the additional real estate from the internal air reservoir to create more room for valve mounting without the need for space-consuming third-party components such as brackets and a coupler. All these elements combined make for a more efficient, user-friendly valve automation package size.

The introduction of the pneumatic fail-safe actuator without the use of springs, external reservoirs, and an emergency backup operating medium has significantly changed the pneumatic fail-safe industry. End users aware of this new innovation of pneumatic actuators are best-positioned to maintain more efficient valve automation systems and simplified operations.

George Wang is president of Easytork Automation Corp. Prior to founding Easytork, Wang was part of the group that founded Taiwan Ball Valve, which was sold to Tyco in 2002. Jack Dovenbarger is head of sales at Easytork. They can be reached at info@easytork.com.

Caption: Drawings and charts reflect data comparing fail-safe actuator without the use of springs (highlighted in red) versus single-acting actuators of various designs with the use of springs (highlighted in grey).

Caption: While other spring-return actuators require different packages for different functions, fail-safe actuators can layer multiple functions through properly ported solenoid valves.

Caption: On the left: Singular actuator body with an integral air reservoir and vane compartment. Source: Easytork

Caption: On the right: Both actuators with similar torque. The actuator on the left saves space through direct-mount to valve.
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Title Annotation:VALVE SELECTION
Author:Wang, George; Dovenbarger, Jack
Publication:E&MJ - Engineering & Mining Journal
Geographic Code:1USA
Date:Aug 1, 2017
Words:778
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