Monthly Archives: August 2018

Sizing & Selection Criteria for Control Valve Actuators

Valves are used to control the flow of fluid in process systems. During routine operations, the position of valves often needs to be opened or closed regularly. In large plants, manually adjusting these valves can be time-consuming and largely impractical.

In these cases, valve actuators are used in place of hand-operated wheels and levers. Valve actuators are mechanical devices used to adjust valve positions. Instead of having operators physically locate and reposition valves, valve positions can be adjusted from a remotely located control room.

The actuator itself is a mechanism that produces a particular motion to control a valve. This motion can be either:

  • Linear

Forward/backward or up/down in a fixed plane (such as in a globe valve)

  • Rotary

Revolving around a fixed axis (similar to butterfly valves)

Valve actuators can be used with control valves to throttle or regulate process flows, or they can be used in isolation valves to stop the flow of fluid at a given location. These devices are commonly used in a variety of industrial plants, including:

  • Water/wastewater treatment facilities
  • Power plants
  • Oil refineries
  • Food and beverage
  • Oil and gas

Types of Valve Actuators

The working principle of actuator valves primarily depends on their driving force. The two most common types of valve actuators are pneumatic and electric.

  • Pneumatic Valve Actuators

Pneumatic valve actuators are the most common type of actuator used in process systems. These actuators use air (or other gas) pressure as a main power source. Air pressure is used to produce motion to control the position of the valve.

For double acting and spring return models, we offer two different styles of rack and pinion pneumatic actuators. Rack and pinion pneumatics are excellent for a variety of industrial applications in fields such as chemical & plastic, food & beverage, and a whole breadth of general industrial sectors.

Our rack and pinion actuators are available in the PN Series or the SS Series with two different body material options (hard anodized extruded aluminum or stainless steel), plus feature ISO and NAMUR mounting to meet international standards.

  • Electric Valve Actuators (Motor Driven Actuators)

Electric actuators use electricity as their primary power source. Electricity is used to produce the motion which opens or closes the valve as required. These types of actuators fall into two general classifications: solenoid actuators or motor driven actuators.

In solenoid actuators, an electric current is applied to a wire coil (solenoid) which produces a magnetic field. This magnetic field pulls on a metal plunger which pushes the valve stem downward. When the solenoid is de-energized, the spring retracts the plunger upwards and reopens the valve.

In motor driven actuators, the valve stem is controlled by an electric motor. A servo amplifier provides a DC signal to the motor which moves the valve stem in a linear motion to the desired position.

 

Valve Actuator Selection Guide

Valve actuators are an essential element in the efficiency of process systems and also play a significant role in process plant safety. It is therefore crucial that the right type of valve is selected for the given environment to ensure optimal valve operation.

The following factors must be taken into consideration when determining the most appropriate type of valve:

  • Power source

One of the first factors to consider is the most effective power source for the actuator. Power source availability, control access, valve size, frequency of operation, and required torque are all factors to consider when choosing between pneumatic or electric actuators. For pneumatic actuators, an air pressure generally between 40 and 120 psi would need to be provided. Most electric actuators would require available access to a 110 AC power supply, although different sized AC and DC motors are available.

  • Temperature range

The operating temperature range for pneumatic actuators is typically between -4° and 174° F (-20° to 80° C). With appropriately rated seals, bearings, and grease, this temperature range may increase to -40° to 250° F (-40° to 121° C). In low temperatures, the dew point in relation to the environmental temperature should be considered, as frozen condensate can affect the ability of the air supply port to provide sufficient air pressure.

Electric motors are typically available in temperature ranges between -40° to 150°F (-40° to 65°C). Special care should be given to electric motors in outdoor applications. The unit should be properly enclosed to prevent the accumulation of condensation and rainwater which can negatively affect the actuator.

  • Hazardous locations

Pneumatic actuators are preferred in areas with hazardous, explosive, or flammable gases, vapor, or dust due to their lack of ignition source. Electric actuators, on the other hand, work with electricity, which is a classified as a source of ignition. Therefore, electric actuators need to be contained in NEMA, UL, or CSA-approved enclosures to prevent ignition of the external environment.

Learn More

BI-TORQ Valve Automation has served countless industrial, commercial, and municipal clients for over 35 years. Since our valve automation department began operations over 23 years ago, we have supplied thousands of butterfly valves, electric and pneumatic actuators, limit switches, and proximity sensors to customers worldwide.

We are proud members of the Valve Manufacturers Association of America (VMA), and our proficient technical team is well-versed in valve actuators of all types. Our 25,000-square-foot manufacturing facilities allow us to operate efficiently to meet even the strictest client requirements without compromising quality or service.

If you would like to know more about our valve actuators, services, or other products, please contact us or request a quote.