Ensuring Reliable Valve Operation: The Role of Torque Safety Factors in Actuator Sizing

Pneumatic rack and pinion actuators are pivotal in automating industrial valves, enabling precise control over fluid flow in various processes. When engineers select these actuators for specific valve applications, they must ensure they can deliver sufficient torque to operate the valve under all expected conditions. This requirement leads to incorporating a torque safety factor in the sizing calculations. Understanding why this safety factor is essential involves examining the variables that affect valve torque requirements and the operational reliability of the actuator-valve system.

The Critical Role of Proper Actuator Sizing

Actuator sizing is not merely matching nominal torque values between the actuator and the valve. Valves often experience conditions that can significantly increase the torque required to open or close them. If the actuator cannot provide the necessary torque under these conditions, the valve may fail to operate as intended, leading to process interruptions, safety hazards, or equipment damage. Therefore, engineers must account for various factors influencing torque requirements to ensure reliable and safe valve operation.

Factors Influencing Valve Torque Requirements

Several factors can cause the torque required to operate a valve to exceed the nominal values provided by the manufacturer:

• Friction and Wear: Over time, valves can experience increased friction due to wear, corrosion, or the accumulation of deposits on sealing surfaces. This friction directly translates to higher torque requirements. For instance, sediment buildup in a butterfly valve can make it harder to turn, necessitating more torque from the actuator.
• Temperature Variations: Temperature changes can affect the materials of both the valve and the actuator. Thermal expansion or contraction can alter clearances and increase friction. Additionally, temperature changes can affect the viscosity of the process fluid, making it harder to move the valve.
• Pressure Fluctuations: The differential pressure across a valve influences the torque needed to operate it. Unexpected increases in upstream or downstream pressure can create additional forces that the actuator must overcome. For example, in a ball valve, higher pressure can increase the seating force, thus requiring more torque to unseat the ball.
• Valve Seat Aging: The degradation of valve seats over time can lead to increased torque requirements. Aging seats may harden, lose elasticity, or become damaged, making the valve harder to operate.
• Unanticipated Loads: External factors such as pipeline stresses, misalignment, or mechanical interference can impose additional loads on the valve stem, increasing the torque needed for operation.
• Supply Pressure Variations: Pneumatic actuators rely on a supply of compressed air at a specific pressure. Fluctuations in this supply pressure can reduce the actuator's output torque. For instance, if the air supply drops below the design pressure, the actuator may not produce enough torque to operate the valve.

The Justification for a Torque Safety Factor

Given the many variables that can increase the torque required to operate a valve, engineers incorporate a torque safety factor into the actuator sizing process. This safety factor is a multiplier, usually expressed as a percentage, applied to the nominal valve torque to ensure the actuator can handle the maximum expected torque under all conditions.

The torque safety factor accounts for the following:

• Operational Uncertainties: It compensates for unknown or unpredictable factors that may affect valve torque requirements during the valve's service life.
• Manufacturing Variances: This section considers tolerances and variations in the manufacturing of valves and actuators, which can affect performance.
• Maintenance Practices: It allows for less-than-ideal maintenance conditions, such as valves not being serviced as regularly as required.
• Extreme Conditions: It ensures that the actuator can operate the valve during extreme conditions, such as emergency shutdowns or start-ups, where conditions may not be typical.

By applying a torque safety factor, engineers build a margin of safety that enhances the reliability and longevity of the valve-actuator assembly. This practice helps prevent operational failures, reduces downtime, and maintains safety standards within the industrial facility.

Incorporating a torque safety factor when sizing pneumatic rack and pinion actuators for industrial valves is a critical engineering practice. It accounts for the myriad factors that can increase torque requirements beyond nominal values and ensures that actuators can reliably operate valves under all anticipated conditions. By doing so, engineers safeguard against operational failures, enhance system reliability, and uphold safety in industrial processes.

UNITORQ
2150 Boggs Road
Suite 410
Duluth, GA 30096
https://unitorq.com
Phone: 770-446-7074
Fax: 770-447-1825

Rack and Pinion Actuator Sizing

Sizing rack and pinion actuators for valves is a critical process that demands precise attention to detail to ensure optimal performance and longevity. In industrial applications, the correct sizing of these actuators is a matter of efficiency, safety, and reliability.

The foremost aspect to consider when sizing rack and pinion actuators is the torque requirements of the valve, meaning calculating the valve's torque demand during various phases of its operation, such as the breakaway torque, the running torque, and the seating torque. It's essential to understand that these torque values can vary significantly based on the type and condition of the valve, the process media, and the operational temperature. Underestimating the torque requirements can lead to the actuator being undersized, resulting in insufficient power to operate the valve effectively. Conversely, an oversized actuator can lead to unnecessary expenditure and potential control issues.

Another crucial factor is the actuator's air supply. The actuator needs an adequate and stable air supply to function correctly. The sizing of the actuator must account for the available air pressure and volume, ensuring that these parameters meet the requirements for the actuator to deliver the necessary torque.

Furthermore, the actuator's speed of operation is a vital consideration. The speed at which a valve opens or closes can significantly impact process performance and safety. A slow-acting valve may not respond quickly enough in emergency shutdown situations, while a too-rapid action might cause pressure surges or mechanical stresses.

Lastly, compatibility between the actuator and the valve is a non-negotiable aspect because it encompasses the physical connection and compatibility regarding the actuator's range of motion and required stroke.

The accurate sizing of rack and pinion actuators to valves hinges on a comprehensive understanding of the torque requirements, air supply specifications, operational speed, environmental conditions, and compatibility. These aspects ensure that the actuator operates efficiently, safely, and reliably, which is paramount in industrial valve applications.

UniTorq's Series M Rack and Pinion Actuator Online Sizing Tool introduces a practical solution for engineers in valve automation. This tool facilitates the selection of the most suitable actuator for specific applications. Users input the operational parameters and valve specifications, and the program employs advanced algorithms to suggest the appropriate Series M actuator. The program seeks to enhance the precision in actuator selection, contributing to improved efficiency and reliability in valve operations. UniTorq's Series M Online Sizing Program integrates technology and engineering expertise to optimize valve system performance.

UniTorq Actuators and Controls
2150 Boggs Road, Suite 410
Duluth, GA 30096
https://unitorq.com
Phone: (770) 446-7074
Fax: (770) 447-1825

Size It Right: Understanding the Risks of Oversized Valve Actuators

Undersizing valve actuators often lead to obvious problems, such as the inability to fully open or close a valve, which can significantly impact a system's operation and safety. However, the pitfalls of over-sizing valve actuators are less obvious but equally important to consider. Over-sized actuators, while seemingly a safer bet, bring many challenges, including higher costs, increased energy consumption, slower response times, and more. This article will delve into the often-overlooked disadvantages of oversizing valve actuators, shedding light on the importance of selecting the appropriate size for optimal system performance and efficiency.

Over-sizing valve actuators carries its own set of disadvantages.

• Higher Costs: Larger actuators are more expensive regarding the actual equipment, installation, and maintenance costs, unnecessarily increasing a project's capital and operational expenditure.
• Increased Energy Consumption: Larger actuators require more power to operate. This results in higher energy consumption, both economically and environmentally unfavorable.
• Slower Response Time: Oversized actuators may not respond as quickly to control signals as correctly sized ones, leading to slower operation and reduced system performance.
• Increased Wear and Tear: Operating an oversized actuator at less than its optimal capacity can lead to increased wear and tear because it may not operate in its most efficient range, leading to more frequent maintenance and repairs.
• Larger Footprint: Oversized actuators will occupy more space, which might be a critical issue in places where space is a premium.
• Higher Inertia: Larger actuators have higher inertia, which can make them less responsive to changes in control signals, making the control of the valve more complex and may lead to instability in the controlled process.
• Difficulty in Controlling Smaller Movements: Oversized actuators may have trouble controlling smaller valve movements as they are designed for larger forces and torques, leading to a lack of precision in the control of the valve.
• Compatibility Issues: There may be compatibility issues with the existing infrastructure, requiring additional modifications to the system to accommodate the larger actuator.
• Increased Weight: The increased weight of an oversized actuator may require additional support structures, increasing the complexity and cost of the installation.
• Suboptimal Performance: The actuator may not operate as efficiently as a properly sized one, leading to suboptimal performance of the valve and the overall system.

Selecting the correct actuator size is crucial for optimal system performance and efficiency. A proper sizing analysis is always recommended to choose the most appropriate actuator for a specific application.

UniTorq

https://unitorq.com

770-446-7074