Saturday, April 28, 2018

Pneumatic Valve and Damper Actuators: A Design Comparison

Industrial valve applicationIndustrial valves, dampers and louvers are operated either electrically or pneumatically. This post compares the three major categories of  pneumatic valve actuators, namely:
  1. Rotary vane
  2. Scotch-yoke
  3. Rack & pinion
All three categories provide the same basic function - converting air pressure to rotational movement intended to open, close, or position a quarter-turn valve (ball, plug, butterfly), louver or damper.

All three can be configured in either direct acting or spring return versions. Direct acting actuators use the air supply to move the actuator in both directions (open and close). Spring return actuators, as the name implies, uses springs to move the actuator back to its "resting" state. Converting from direct acting to spring return is done through simple modifications, typically just adding an external spring module, or removing the end caps from rack and pinion actuators and installing several coil springs.

Vane Actuator
Rotary Vane Actuator

Rotary Vane Actuators

Vane actuators generally provide the most space savings when comparing size-to-torque with rack and pinion and scotch yoke. They have an outstanding reputation for long life because then contain only one moving part, as opposed to rack and pinion and scotch yoke actuators that have many. They tend to withstand dirty and corrosive atmospheres better than rack and pinion and scotch yoke actuators. Vane actuators also use externally mounted, helically wound "clock springs" for their spring return mechanism.

Scotch YokeScotch Yoke

Scotch-yoke actuators use a pneumatic piston mechanism to transfer movement to a linear push rod, that in turn engages a pivoting lever arm to provide rotation. They come in a wide variety of sizes, but are very often used on larger valves because they are capable of producing very high torque output. Spring return units have a large return spring module mounted on the opposite end of the piston mechanism working directly against the pressurized cylinder.

Rack and Pinion

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.

The practical difference between these three types of pneumatic actuators comes down to size, power, torque curve and ease of adding peripherals. For the best selection of valve actuator for any quarter turn valve application, you should seek the advice of a qualified valve automation specialist. By doing so your valve actuation package will be optimized for safety, longevity, and performance.

Scotch yoke mechanism image courtesy of Wikipedia.
Rack and pinion mechanism image courtesy of Wikipedia.

Monday, April 9, 2018

Kinetrol Blueline Actuator Stands Up to Harsh Conditions in Cheese Factory

mozzarella cheeseA very large mozzarella cheese producer in the USA had an actuator problem with their EFV’s (Enclosed Finishing Vats). The flow of the curds being blown into the EFV’s is controlled by star valves and pneumatic actuators. The actuators and valves serve (2) critical purposes: 1) The shut off of the star valve; and 2) controlling the air flow of the blower.

The cheese plant had continuous service problems with their existing actuators. Some had to be replaced within one week of installation. Failure of the actuators caused the curd line to be plugged, and when replacement of the actuator was needed, it would result in a huge mess to be cleaned up off of the production floor. With a 24/7 production timetable, a solution needed to be found to keep the EFV’s up and running.

Kinetrol Blueline vane actuators were recommended because of their 4 million operation guarantee and the new proprietary coating that meets FDA specifications and is permitted for use in food service.

The Kinetrol Blueline actuators eliminated the maintenance issues completely and the Blueline coating has held up excellently after caustic wash-down, with no signs of degradation or fading.


https://kinetrolusa.com
972-447-9443