March 11, 2026
Understanding an Actuator’s Cycle Life (and Why You Should Care)
Part Two: A Practical Look at Actuator Types and the Advantages of One Versus Another
Contributed by Dave Hurley, Product Information Manager
An “actuation cycle” is defined as the result of an actuator powering a valve open and then closed in an installed process environment. The total expected number of times the actuator can cycle a given valve open/closed under ideal conditions is the actuator’s cycle life. An actuator’s cycle life is not fixed, however, and varies greatly depending on the operating conditions of the valve attached to the actuator. Other factors, such as duty cycle, environment and enclosure ratings, power supply and control signal, proper sizing of the actuator, and frequency of use, can all influence the actuator’s cycle life.
Manufacturers design actuators to be robust, long-term automated valve operating solutions. Environments where actuators are used can vary widely, including both indoor and outdoor processes. Actuator operation can range from the simple task of cycling quarter-turn ball valves or butterfly valves to more advanced multi-turn operations found on diaphragm valves or gate valves. Whatever the application or environment, you should always make sure that an actuator is up to the task of repeatedly opening and closing a valve.
There are two main types of actuators we will discuss: pneumatic and electric—both of which offer distinct performance benefits in specific applications. Actuation is chosen based on cost, availability of resources, and the ability to manually override the valve to an open or closed position in the event of a power loss.
Actuators are not one-size-fits-all; they are ideally paired with valves that meet the appropriate size and torque requirements. As a general rule, an actuator should be able to provide about 25% more available output torque than the requirements of the valve it is operating. This buffer ensures reliable operation across the range of conditions the valve is required to perform under. Now, let’s take a closer look at what should influence your decision in choosing between a pneumatic and an electric actuator.
Pneumatic actuators are also an excellent solution for many valve automation needs. They can be supplied as single-acting (Air to Open, Spring to Close) or double-acting (Air to Open, Air to Close), and are available in a rack-and-pinion design. Additionally, pneumatic actuators feature a NAMUR solenoid interface for routing the air supply and a NAMUR limit switch mounting interface. Since a pneumatic actuator requires compressed air to function, a compressor and a compressed air piping system would need to be installed and maintained, in addition to the electrical requirements for the solenoid to operate the actuator. Most pneumatic actuators do not include a declutchable manual override as a standard feature. Pneumatic actuators are well-suited for rapid, repeated opening/closing cycles of the valve and do not come with any duty cycle concerns.
Electric actuators are an excellent solution for many valve automation needs. Electric actuators are available in a variety of input voltages and typically include built-in declutchable manual overrides as a standard feature. They are calibrated to open/closed end stops, and include a 90-degree fixed cycle time. Other features include an enclosure rating based on environmental location, visual position indicators, and position confirmation sequencing back to a PLC. Electric actuators are ideal for indoor applications, as they can be used wherever a power source is available. Electric-type actuators also require resting time to limit internal heat buildup, resulting in a rated duty cycle that accounts for the necessary cool-down time to prevent the motor from overheating. These actuators are available in Open/Closed, Modulating, Failsafe, or Modulating Failsafe designs, suitable for varying application requirements.
Duty cycle applies exclusively to electric actuators. It is a balance between the percentage of time the actuator’s motor is running and the time the actuator is at rest. Duty cycle can be expressed in the formula below:
Adhering to a duty cycle rating prevents the motor from overheating, thereby extending the actuator’s lifespan by providing it with cool-down time. Factors such as following the general rule of “valve torque output rating plus 25%” also help to ensure the actuator remains within the rated duty cycle range. In addition, environmental temperature and humidity can negatively affect the actuators’ ability to dissipate heat, thereby reducing the ability to maintain the rated duty cycle.
The operating environment of the actuator can negatively impact its cycle life. Electric actuators prefer dry, low-humidity environments whenever possible. Pneumatic actuators are less susceptible to these adverse effects and can be found in some of the harshest and most challenging environments.
Enclosure rating is primarily a concern for electric actuators, but it can also apply to pneumatic actuators. When a limit switch, solenoid, or positioner is added to the valve and actuator, each accessory has its own electrical enclosure rating. The NEMA Enclosure Ratings standard is listed below for reference:
Generally speaking, NEMA Type 4 and NEMA Type 4X ratings with added corrosion resistance (for general locations) are the most common enclosure design targets. They provide a good range of working environments, provided a hazardous location is not a consideration for the actuator. Some actuators can be rated NEMA Type 6 for temporary submersion; however, a pneumatic actuator with a remote-mounted solenoid is a far better solution for temporary submersion environments, as it will provide an increased product lifetime.
Both pneumatic and electric actuators require an operating power supply and a switchable control signal to operate the actuated valve (and, as previously mentioned, pneumatic actuators also require a compressed air system). Electric actuators require steady power, free of power spikes, surges, or cross-feeds. When setting up a group of reversing-motor, capacitor-driven electric actuators, each actuator will require its own switch or relay contacts to avoid cross-feed between actuators. This phenomenon would cause both windings to be powered, creating an internal power struggle and generating extreme heat in the motor. Pneumatic actuators do not have this problem because their solenoid can be bank-mounted and powered collectively. Cross-feed instances can drastically shorten an electric actuator’s cycle life, so preventing them is critical for reliability, position-stopping accuracy, and performance predictability.
Both pneumatic and electric designs require proper sizing of the actuator to the valve they operate. All actuators have a rated output torque, while all valves have torque requirements for opening and closing. To sustain the desired cycle life, it is crucial to ensure that a valve is initially paired with an actuator capable of outputting a torque greater than 25% of the “greatest capable” valve operating torque. What is the “greatest capable” operating torque, and why isn’t this a consistent requirement? With a ball valve, torque is typically stable throughout the 90-degree rotation from open to closed; however, a butterfly valve has different considerations. Butterfly valves have additional torque value(s): break-away torque and seating torque. These values are far greater than the running torque when turning the disc intermediate of open and closed positions. The break-away and seating torque values may differ slightly, so Asahi considers the higher of the two for actuation consideration. Any actuator that is underpowered for the valve will experience a shorter cycle life than an appropriately sized valve and actuator package.
Frequency of use is a consideration for both pneumatic and electric actuators, with pneumatic actuators the clear winner when rapid, frequent valve actuation is required, thanks to the aforementioned duty cycle advantage. In the first installment of my Cycle Life duology, I looked at a bottle-filling application and the actuation frequency of the ball valve used to fill bottles with product. In that specific application, pneumatic actuation would be the preference. Electric actuators need a break to cool down, but pneumatic actuators open and close quickly and are free of duty cycle concerns, making them ideal for applications requiring repeated actuation. Conversely, the opposite can also be true. A valve that sits in a closed position for an extended period tends to set in place. It then takes greater force to initiate the actuation cycle and open the valve. When running exclusively from open to closed and back, pneumatic is faster. However, if you are simply making small, incremental position changes in an actuated valve, electric actuators are typically well within their duty cycle range. Both pneumatic and electric actuators, when balanced adequately to the application, can provide a long cycle life.
Oftentimes throughout my 35-year career, customers would call me to tell me that their actuator “wore out” or “burnt up,” and that they intended to replace just the actuator. While in some cases this may prove advantageous, in my experience it never yields anything near equivalent to the original actuator cycle life. A valve that has been in service for a given amount of time and has been subjected to temperature changes, chemicals, environmental influences, UV exposure, etc., may become sticky or internally deformed, generally operating at a lower performance level than when new or failing altogether. When installing a new actuator, it is essential to check the manual operation of the valve, verify the manufacturer’s specifications (to ensure the valve is operating within torque requirements), and confirm that the lubrication is still effectively lubricating the valve. Taking these factors into account and ensuring these requirements are met leads to a better-performing actuator and a longer actuator cycle life.