Actuator Options: More Than Meets the Eye

Submitted by Corey Foster || Valin Corporation
Actuator Options
For both process and discrete motion control applications of actuators, many of the terminologies uttered and the base technologies utilized are similar. The differences come in with the application and evolution of these base technologies. However, there is often an opportunity for a crossover of the two. With a little bit of knowledge, it is possible to take advantage of the strengths of one for the applications of the other.

In process applications, many users prefer a pneumatic actuator.  They have a long, reliable history, and the sentiment of “if it ain’t broke, don’t fix it” certainly applies here.  However, when air supply isn’t a realistic option, electromechanical actuators
can be used.  These are less ideal for performance reasons.

However, in discrete applications, the technological evolution and expectations are very different. In this world, pneumatics are the least expensive option with the lowest expected performance. In fact, as many people want to go “all electric”, they are much more in favor of an electromechanical option.

The key is that there are in fact times when some crossover is ideal.  For a process application, if the available pneumatic solution doesn’t meet the performance requirements, an electromechanical solution from the world of discrete automation may be exactly what you need.

So, what kind of other applications would benefit from electromechanical actuators?  Mostly, an application where you would receive financial benefits from higher performance.  Whether we’re talking about higher accuracy, better repeatability, more controlled motion or lower maintenance, these all could benefit from an electromechanical approach as opposed to a pneumatic one.

How do we know if a solution will work? For better or worse, trial-and-error is a common method in some industries. Try an actuator and if it doesn’t work, try a larger one.  In the discrete automation industry, trial-and-error isn’t an effective method due to the cost and lead times of these high-precision products.  Proper sizing and selection is the preferred method, but this can mean digging up or guessing at information that isn’t readily available. An alternative, of course, is grossly over-sizing the solution, but then this makes it more expensive than otherwise needed.  

Another pit-fall to avoid is that very few electromechanical servo-motor controlled actuators will include manual over-rides. This is certainly possible but isn’t the default design of these actuators.  Manual over-rides are so commonplace on valve actuators that people assume they will be included with any actuator. While the solution of an extended shaft on the back of the motor with a hand-wheel mounted to it is simple, this just isn’t commonly used in the discrete automation world.  If your application needs it, make sure you specify it.

I broke down this topic far more thoroughly in a recent article penned, along with colleague Peter Jessee, P.E., for Processing Magazine.  To view the full article, follow this link.

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