The Principles of Rotary Actuators

Variation of the rotary actuator.
(Kinetrol pneumatic vane actuator.)

A rotary actuator is an output device for a fluid power system that delivers an oscillating motion over a limited range in less than one full revolution of the circle.

A true rotary actuator produces work by direct action of fluid pressure against internal vanes. Work is defined as a force applied over a distance. Rotary actuators produce a special type of rotational work called torque.

Torque occurs when a force acts on a radius. Since rotary actuators operate at low speed with high torque, torque output rather than the horsepower is used for the rating and identification purposes. Speed is a secondary consideration when choosing a rotary actuator for a particular application.

The typical units of measurement for torque are foot pounds (lb·ft). For example, if a rotary actuator with an arm length or radius of two feet were used to lift the two hundred-pound weight, then the resultant torque required to accomplish the work would be 400 lb·ft.

Understanding the relationship between the output torque required and the physical set up a fluid system enables designers to determine the appropriate rotary actuator for each unique application.

The following video does an excellent job of illustrating the mechanics and the physics behind rotary actuators.

Water Recycling Application at Iron Ore Mine

Mining corporations need water - a lot of water - to make bare rock give up its valuable minerals.

Water is used for the extraction of minerals that may be in the form of solids, such as coal, iron, sand, and gravel. The category includes quarrying, and milling (crushing, screening, washing, and flotation of mined materials).

Not only is water used to expose the mineral, it must be carefully managed to prevent the release of contaminated water back into the environment.

There are multiple processes involving the management of water that require piping, valves and automation for water management.

• The reuse of water used to extract the minerals from the other solids.
• Managing surface water from rain, snow, and streams.
• Capturing and recycling water from the mine site.
• Storing water in evaporation ponds.

At a large Midwest iron ore mining facility, a Kinetrol Distributor was contacted to look at ways to lower the overall consumption of water in the main water treatment plant.

The Distributor designed and provided this characterized butterfly control valve, with a Kinetrol actuator, pneumatic positioner, and cone indicator.  The valve is used to recycle processed water back into the plant for reuse in the extraction process. The valve and actuator experiences a very high cycle rate (400 cycles per day).

Intercepting and diverting surface water

• Intercepting and diverting surface water (rain and snowmelt runoff, streams, and creeks) from entering the mine site by building upstream dams to reduce the potential for water contamination from exposed ore and waste rock
• Recycling water used for processing ore in order to reduce the volume of water requiring treatment
• Capturing drainage water from precipitation at the mine site through the use of liners and pipes and directing the water to tailings dams in order to prevent potentially contaminated water from entering groundwater or flowing off site
• Allowing the water to evaporate in ponds to reduce the volume of contaminated water; in dry regions, enough water may be evaporated that no water needs to be discharged, resulting in the containment of contaminates at the mine site
• Installing liners and covers on waste rock and ore piles to reduce the potential for contact with precipitation and contamination of groundwater

- See more at: http://www.miningfacts.org/Environment/How-is-water-managed-and-treated-in-mining/#sthash.0qMpVdHr.dpuf

Segment Ball Control Valve with Vane Actuator, Pneumatic Positioner, and I/P Transmitter

Actuator and Positioner

Ball, plug and butterfly valves all belong to a class of valves commonly referred to as "quarter-turn" valves. This refers the 90 deg (angular) rotation required to go from full closed, to full open position.

In most cases standard ball, plug, or butterfly valves are not the best choice as control valves (where the process media has to be modulated or throttled). Standard ball, plug and butterfly valves usually introduce very non-linear, dynamic flow coefficients. Furthermore, they can introduce undesirable turbulence to your piping system.

As a means to linearize flow coefficients and reduce turbulent flow, the machining, or characterization, of the valve disk is done so that the machined shape allows for more optimized flow.

For ball valves in particular, machining the ball's flow port with a "V", or even by machining the ball more radically, can deliver excellent flow curves. A term for a more radically machined ball is the "segment ball" (sometimes called "segmented").  In the following video you can see how a Kinetrol pneumatic actuator, postioner, and I/P transmitter team up with a segment ball valve foe an excellent control valve.

Very High Cycle, Coal Power Plant Butterfly Valve Application

One moving part. Simply the best.

A coal fired power plant was using old Powell gate valves with dual air cylinders and volume tanks. Because of high cycle rate (the valve cycles open/closed every 30 seconds), the Powell gate valves were breaking down constantly - leaking at first, then failing. Downtime for repair was costing a fortune.

Kinetrol Model 12

A local Kinetrol Distributor was called in to recommend a better solution. After discussing the capabilities of Kinetrol, the power plant decided to replace the gate valves with 6" high performance butterfly valves actuated with Kinetrol size 12 actuators, spring returns and limit switch packages. 

The result was a robust valve/actuator package that could handle the 120 cycles per hour required - truly a difficult application. As of two years in operation, both valve and actuator have been running reliably much to the delight of the power plant maintenance crew. 

High cycle coal fired power plant Kinetrol / HPBV application.