Choosing the Right Valve Actuator
Valve actuators are mechanical devices that allow remote and automatic control of valves without direct human involvement. Despite their relatively simple design, these devices play a vital role in the overall efficiency and safety of a process system. Because valve and actuator designs vary significantly, taking the time to research and identify the right actuator for your system's specific requirements is critical to ensuring smooth and successful operation. Some of these factors include:
Valve Type: (Manual, Electric, Pneumatic, Hydraulic - must also be compatible with the power source.
Desired motion: rotary (quarter turn or multiple turns) or linear
Operating mode: double acting, spring return (spring close, spring open)
Desired value operating thrust or torque
Power sources: e.g. voltage, available air supply
On/off, throttling, or proportional control
Corrosion resistance: materials, coatings, tubing
Frequency of operation
Special requirements: e.g. marking, testing
Accessories: e.g. limit switches, positioners, solenoids, valves, sensors, manual overrides
Here we discuss several key factors and considerations to keep in mind during the actuator selection process.
Compatibility with Power Supply
One of the first factors to consider when researching valve actuator options is power. Pneumatic and electric actuators are two of the most common options for process systems. Each has its own benefits, limitations, and requirements to consider.
Pneumatic actuators. Pneumatic actuators that use pressurized air or gas to generate powered motion require an air supply of 40-120 psi to function. However, it is important to remember that higher air pressures may be difficult to achieve, while lower pressures require large-diameter pistons or diaphragms to generate the required force.
Electric actuators. Electric actuators work by converting electrical energy into kinetic energy. Most require a 110-115 VAC power supply, although some can use AC and DC motors of different sizes.
Given the variety of power requirements for actuators, it is important to choose an option based on your available power supply. For example, pneumatic or hydraulic actuators are the most logical choice when no power source is available. Frequency of operation and valve size should also be considered when determining which power supply will be most efficient for your actuator.
Pneumatic actuators typically withstand operating temperatures from -4 to 174℉ (-20 to 80℃), although specialized seals, bearings, and greases can extend this range to -40 to 250℉ (-40 to 121℉). In cryogenic applications, it is important to know the dew point as it relates to the air supply to the actuator. Condensation that forms when the temperature is below the dew point can freeze in the air supply line and block airflow to the actuator.
Electric actuators are capable of operating in temperatures ranging from 40-150℉(-40 to 65℃). When used in outdoor applications, it is important to properly encapsulate the actuator to prevent condensation, rain, and forms of moisture that can damage internal components.
Bear in mind that condensation may also enter the actuator through the power conduit if any moisture was present prior to installation. Additionally, as the motor naturally heats up and cools down during actuator operation, the resulting temperature fluctuations can create condensation. Fitting a heater to the actuator can help prevent this type of problem.
The National Electrical Manufacturers Association (NEMA) develops guidelines for the manufacture and installation of electrical equipment, including electric actuators. NEMA 7-rated enclosures can be used with electric actuators for added explosion protection in a range of hazardous environments. Choosing an electric actuator with the NEMA 7 marking is a smart choice, especially for high-risk applications. Another option is to use pneumatic actuators, which are inherently explosion-proof since there is no ignition source. Using a pneumatic actuator with electric control is often a more cost-effective solution. the
The speed at which an actuator can perform a function is directly related to the power input. Increasing the speed of a task, such as opening or closing a valve, requires increased power. Fast-acting actuators are ideal when immediate isolation or opening of a system is required, and this fast action is typically provided by pneumatic, hydraulic, or solenoid actuators. In contrast, slow actuators are a better choice for applications that benefit from slower, more controlled motion, such as gradually injecting cold water into a heating system.
For pneumatic actuators, the desired operating speed will determine how much airflow they require. An advantage of these actuators is that their speed can be easily controlled, usually by fitting a variable orifice (such as a needle valve) to the exhaust port of the air pilot. While the geared motor of an electric actuator makes speed control more difficult, it can be achieved by adjusting the gears. In some cases, pulse circuits can be incorporated for slower operation.
Movement Frequency (Duty Cycle)
The frequency of operation is an important consideration because it affects the amount of stress and wears on mechanical and control components within the system. For example, isolation and regulating valves that only need to be operated occasionally wear much less than those that are operated almost continuously or continuously. Where continuous use is required, stronger, more resilient valve and actuator assemblies should be selected.
Expressed as a percentage, the duty cycle of an operation is the ratio of the operating time to the rest time. Pneumatic actuators have a 100% duty cycle, making them ideal for applications requiring frequent valve operation. In contrast, most electric actuator motors have a duty cycle of only 25%, which means they need frequent breaks to avoid overheating. The duty cycle is less important in automatic on-off valves as they are ideal 95% or more of the time.
When determining the ideal actuator size for your application, the following factors should be considered:
Valve type and torque requirements. Actuators are sized according to the specific valve being used and its calculated torque requirements. The torque requirement of a valve is the amount of force required to open or close it.
Minimum and maximum pressure. Pressure is another important factor to consider when sizing an actuator for a system. It is important to test the actuator at the minimum supply pressure to ensure that even at the lowest pressure point it is producing enough torque for proper operation. Likewise, valves should be able to operate safely at their maximum potential pressure.
Power requirements. The amount of electricity required to power the actuator will depend on its size. While large actuators typically require three-phase power, single-phase power is sufficient for smaller actuators.
When selecting an actuator, ensure that the equipment complies with all relevant safety guidelines to reduce the risk of explosion and other safety hazards. NEMA, CSA, and other regulatory agencies provide various ratings that indicate the suitability of an actuator for a particular type of environment.
Higher levels of safety can be achieved by using fail-safe actuator designs. Pneumatic spring return actuators provide fail-safe functionality by forcing the valve into a safe position in the event of a power or signal failure. Likewise, a battery backup can be a reliable fail-safe option for electric actuators.
Valve Actuators from UG Controls
Valve actuators have a significant impact on the performance of the valve as well as the overall system. Choosing the right actuator can help ensure safer, more cost-effective operations, reducing valve replacements, downtime, and maintenance frequency. Contact us to learn more about our wide selection of actuators.
UG Controls is a professional custom valve actuator manufacturer. We use our engineering expertise and industry experience to continuously improve our products, striving to provide efficient solutions and competitive prices. UG is also a global supplier of highly engineered actuators and accessories to the Oil & Gas, Mining, Chemical, Pharmaceutical, Water & Power, Food & Beverage, and general industrial markets.
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