Devices called valve actuators are utilized to position valves, and they can completely open and close off a valve. They can be utilized to regulate the position of the valve in applications that call for constant and accurate control, like controlling the liquid flow to a gas turbine.
In procedure control applications, valves are utilized to open, close, or partially restrict the flow of liquids while managing the line pressure. The pneumatic actuator valve manufacturers produce various types of actuator valves in different sizes and models. Check out this guide to know about the various types of actuator valves.
What Is A Valve Actuator?
A mechanical device that shifts or regulates a device like a control valve is referred to as a valve actuator. Actuators lessen the requirement for operators to physically move each valve that has to be repositioned. The valve actuators are utilized to control valves, and the actuator can be controlled remotely from a place like the control room.
Valve actuators make it simple to swiftly and correctly operate the valves. Actuators for control valves are utilized with flow-regulating or throttling valves. Flow control valves are typically referred to as control valves since they automatically reduce flow. There are many actuator valve types that one needs to be aware of.
Actuators are a common component in a variety of process factories and are utilized to automate industrial valves. They are utilized in pipelines, food plants, mining, and nuclear procedures, power plants, refineries, and wastewater treatment facilities. In automating procedure control, valve actuators are crucial. The automatic valves come in a variety of shapes and sizes. The valves’ diameters vary from 1/100 of an inch to many feet diameters.
Types Of Valve Operation
The early step in selecting the right actuator is to have a thorough understanding of how a valve functions. Control valves come in a plethora of varieties. However, there are two main ways that a valve operates from the standpoint of a valve actuator.
- Rotary (Quarter-Turn) Operation
It applies to butterfly, ball, and plug valves. This would also include quarter-turn dampers. Since the operation is quite straightforward and only calls for a 90-degree rotation at the proper torque, these sorts of valves are typically simpler to install with the right actuator.
- Multi-Turn Operation
In order to shift the valve closure element from the open to the closed position, these sets of valves retain rising non-rotating stems or non-rising rotating stems. Globe valves, sluice gates, knife gates, gate valves, and other valve types are a few that can be found in this group.
Valve Method of Control and Function
When choosing valve actuators, it is crucial to take valve motion and operation style into account.
- Valve Method of Control
Ball, butterfly, and plug valves are examples of rotary motion valves or rotary valves that revolve at least a quarter revolution before closing.
Gate, pinch, globe, diaphragm, and angle-style linear motion valves or linear valves retain a sliding stem structure that shoves the closure element to remain empty or shut down. It is possible for the valve stem to surge with and without rotation.
- Valve Function
The air actuated valves can operate in one of two ways:
- Start or stop valves, sometimes referred to as on or off or isolating devices, restrict the motion of the actuator to predetermined open and closed positions.
- Devices that throttle or control motion give valves the ability to be throttled as needed. This kind of actuator works in tandem with a positioner to precisely move to the desired position.
Manual Valve Actuators
Manual valve actuators can shift a valve to the right position without using an external power source. Rather, they operate a set of gears whose percentage produces an output torque greater than the input torque by utilizing a handwheel, chain wheel, lever, or declutchable device. Worm gears, which are mechanical devices that disseminate motion between non-intersecting right-angle axes, are used by many manual valve actuators.
The benefit of employing a manual valve actuator is that they are affordable, dependable, and independent of a power source. They are typically self-contained, and because they open and shut with a similar motion, it is frequently simple to identify a mistake or the source of an error. The major drawback is that they require manual control every time because they are not automated.
- Basic Lever
The basic lever is the manual control that is used the most frequently on tiny quarter-turn valves. The valve can be rotated with the help of a long handle that is fastened to the stem. These can be swapped out for oval, tee, and different-shaped knobs on extremely tiny valves where leverage is not required.
- Latching-Lockable Lever Handle
It has a handle on the lever that keeps the valve from inadvertently opening or closing.
- Oval Handles
For applications where the valve may be close to other equipment, there is a tiny handle alternative. The layout reduces the likelihood of the valve being unintentionally opened or shut down.
- Hand Wheels
Larger valves that require a lot of torque frequently employ hand wheels, and they are frequently used on butterfly valves as actuators. Chain wheels can be put into a gearbox for simple on-the-ground function if a valve seems too elevated to reach.
- Manual Valves with Limit Switches
Manual valves frequently carry out tasks that do not employ automated actuation, but the system still has to be aware of their current positions. In these circumstances, manual valves with limit switches or position indications are employed. The switches inform the control system of the valve’s current position even though it is still manually actuated.
Pneumatic valve actuators
Pressurized air is utilized by pneumatic actuators to turn a valve. They accomplish this by exerting air pressure on a piston or a diaphragm that is fastened to the valve stem. Because of their durability and straightforward construction, pneumatic actuators are the most often utilized type of device for automatic or semi-automatic valve operation.
In order to automate the control of a valve, pneumatic actuation needs a power supply of compressed air or gas. Although this method of actuation does not require a motor, power is required if the part is used in conjunction with a solenoid valve or an inbuilt pilot.
Air pressure is converted into linear or rotary motion by pneumatic valve actuators, which then modify valve position.
- Piston Valve Actuator
If the stroke of a diaphragm actuator is too low or the thrust is insufficient, piston actuators are employed. A solid piston inside a solid cylinder is subjected to compressed air. The reasonable designs urge the piston higher by pressing air into a central chamber.
The reverse force spring causes the shaft to shift in the opposite direction when the air pressure is released. Since there is no return spring, the piston actuators’ double-acting models are also accessible, allowing air to be fed into either side of the piston.
- Diaphragm Valve Actuator
A diaphragm actuator is a device that uses compressed air to move a thin, flexible membrane. Since only one direction of the diaphragm receives air from this type of actuator, it is available in single-acting models. These actuators can either be direct acting or reverse acting. Pneumatic valve actuators have the benefits of being powerful, light, straightforward, and quick. The drawback is that unless at entire stops, precise position control is not achievable.
- Double-Acting Valves
The valves in question are operated by compressed air. The ball valve will flip back to its closed state if there is a power outage. Double-acting valves are perfect for applications with low to high cycle counts.
- Spring-Return Valves
A failsafe spring urges the ball valve to remain closed in a spring-return ball valve while air is utilized to unlock the valve. It guarantees that in the case of a power outage or a pressurized air failure, the valve will stay closed. These valves are designed for applications with low to moderate cycle rates.
- Solenoid Valves
The pneumatic actuator’s airflow is regulated by these valves. The actuator can be remotely piloted with solenoid valves or flush mounted with the actuator itself. Solenoid valves are frequently employed in applications that make use of numerous pneumatically operated valves in order to eliminate the need for a solenoid valve for every single actuator.
Electric Valve Actuators
The electric valve actuators will be mounted on the valves and employ an outer power source to push the valves automatically to the ideal position after receiving a signal. In order to produce the required torque level, a set of gears are driven by single-phase, three-phase, AC, or DC motors. The most often utilized actuators are electric valve actuators because of their high level of precision and quick response times.
Electric valve actuators can be divided into two categories: rotary and linear. Special valves are used by specific actuator types.
- Rotary electric valve actuators
Ball, butterfly, and plug valves that revolve at least a quarter revolution from open to closure use rotary electric valve actuators. Applications in high-power switching gears, the electric power sector, and packing sectors all utilize rotary electric valve actuators.
- Linear electric valve actuators
With a gate, pinch, globe, diaphragm, and angle valves that have a moving stem that opens or shuts down the valve, linear electric valve actuators are utilized. Actuators for linear electric valves work effectively when operating with small tolerances.
Hydraulic Valve Actuators
Hydraulic actuators are hydraulic devices that are propelled by pressured fluids like hydraulic fluid. The hydraulic actuated valves of the same size are typically more powerful than pneumatic actuators.
- Rotary hydraulic valve actuators
With a quarter turn or more from open to closure, rotary actuators are employed for valves with rotating motion like butterfly, ball, and plug valves. A disc or an ellipse that revolves around an angular shaft typically serves as the closing element.
Specifications for rotary motion valves include:
- Actuator torque: The amount of force required to induce rotary motion is known as torque. The applied force multiplied by the separation between the pivot point and the point of application of the force yields the answer.
- Rotary motion range: Typical rotary motion ranges include 90 degrees (quarter turns), 180 degrees, 270 degrees, and 360 degrees (multi-turn).
- Linear hydraulic valve actuators
Linear actuators slide a stem that controls the closing element to move linear valves, including gate, pinch, globe, and diaphragm valves.
Specifications for linear motion valves include:
- Valve stem stroke length: The term “stroke” refers to the distance that a valve must travel from its totally open position to its totally closed position. If the chosen actuator has a stroke that is smaller than the valve’s stroke, the actuator will specify the stroke of an activated valve. The valve will be “shortly stroked” if an actuator with fewer strokes than the valve is utilized, and the entire CV rating of the valve might not be realized.
- Actuator force or sealing thrust: Actuator force, also known as sealing thrust, is required to shut down the closing element and maintain it shut by pushing against the system’s pressure.
What Are The Functions Of Valve Actuators
The actuator types should have the following functions:
- In order to move the closure mechanism in both mild and drastic situations, actuators need to retain the proper direction controls and enough torque or thrust.
- Keep the valve closed in a targeted manner. Actuators should possess the required spring tension, liquid force, or mechanical stiffness to maintain the valve’s closed position even during throttling operations where liquids exert an unnecessary amount of torque on it.
- Seat the valve appropriately. Butterfly valves are deemed to be correctly seated after their disc has been set in the liner or robust seat.
- Based on the application, valve actuators should be able to completely open, shut down, or remain in the open position in the case of a catastrophe or system failure.
- The majority of the valves need to be rotated 90 or 180 degrees. Understanding the necessary rotational travel will help you choose the best valve actuator.
- The ability to function at the needed speed. The valve actuator is controlled by the cycle speed.
What Are The Actuator Valve Specifications
The following are essential details for valve actuators:
Rotary Actuator Specifications
Rotational motion or torque is produced by rotary actuators. The mechanical gadget rotates by creating motion in a single direction. The servo or step motors are employed to set the actuator at a steady angular point, while the electric versions of the rotary actuator rotate continuously.
A rack with cylinder pistons on either end steers a pinion, which is supported by housing in a rack and pinion actuator. Racks come in single, double, and multiple design options. Actuators with rack and pinion gearing typically operate at 85 to 90 percent efficiency. They can rotate between a few degrees and five revolutions or more, and they can handle a broad span of torque productions.
Rotary actuators with rotations of 90 degrees, 180 degrees, or 360 degrees can be employed in pressures of up to 210 bar for hydraulic actuators and 18 bar for pneumatic actuators. Due to the non-uniform static pressure distribution on the closure (spinning) element of a quarter-turn valve, the media moves and generates dynamic torque.
Pressure is proportional to the resultant force acting at the same distance from the stem axis because the pressure is not equally distributed. Dynamic torque, which is the product of each resulting force and its corrective distance, conducts on the valve stem. The valve actuator may benefit or be hampered by it. If the friction torque is left unchecked and is smaller than the dynamic torque, it will lead to rotary motion.
The beginning of shock and surge pressures over the unit’s maximum rated working pressure is the most frequent reason for rotary actuator failure. Actuators with rotational speeds greater than 10 RPM, those that control heavy masses in the horizontal plane or that shift over their centers, and those that operate lengthy lever arms frequently fail.
Linear Actuator Specifications
An assembly known as a linear actuator generates force and motion in a straight line. In order to produce this motion, linear actuators employ a number of different techniques and an outer energy source. Actuators that are mechanical, electrical, hydraulic, and pneumatic can be created as linear actuators.
Other types of actuators rely on rotating motors to create linear motion, while hydraulic and pneumatic actuators do it naturally. The valve stem stroke length, actuation duration, amount of turns, and actuator pressure or seating thrust are among the performance requirements for linear actuators.
Valve stem stroke length: The length of the valve stem stroke is referred to as the distance the valve must travel to close completely. If the chosen actuator has a stroke that is tinier than the valve’s stroke, the actuator will deduce the stroke of an activated valve. The valve will be “short stroked” if an actuator with occasional strokes than the valve is used.
Actuation time: It is the time required for the linear motion valve to completely close.
Actuator force: Actuator force or the seating thrust is the amount of force required by the actuator to close and maintain the closure of the closing element in the presence of system pressure.
Load capacity: Actuators may deal with both static and moving loads. The actuator’s capacity to support a certain load when the system is stationary is known as its static load capacity. The load that an actuator can support while it is in practice is known as its dynamic load capacity.
What To Know About Valve Actuator Usage Factors
In order to pick the proper valve actuator, it is vital to consider the usage factors. Some of those factors are listed here.
It is necessary to consider what type of power source is available. Electricity is needed to run the electric actuators. The rational option is a pneumatic or hydraulic valve actuator if there is not an immediate source of electricity. Air supply pressure for pneumatic actuators must be between 40 and 120 psi.
Elevated pressures can be challenging to get. To provide the required torque at less pressure, a diaphragm or piston must have a larger diameter. While valve actuators can be bought with DC and AC motors in various capacities, the electric actuators need a power source that is 110 VAC.
- Temperature Range
Electric actuators can function between -40 degrees Fahrenheit and 150 degrees Fahrenheit temperature conditions. If the proper seals, grease, and bearings are used, pneumatic actuators can function in temperatures ranging from -40 to 250 degrees Fahrenheit. However, in general cases, they can work in conditions between-40 degrees Fahrenheit and 150 degrees Fahrenheit.
- Hazardous Regions
Because of their explosion-proof character, pneumatic actuators are frequently chosen in hazardous or harmful atmospheres. However, electric actuators might be utilized if compressed air is not available or if a pneumatic actuator cannot fulfill some operating requirements. NEMA VII enclosures are required for electric actuators used in risky locations in order to safeguard them from outbursts.
Valve actuators depend on the valves and employ an outside power source to drag a valve to the accurate position. Choosing the right valve actuator is vital in order to enhance plant security, increase uptime, and reduce maintenance costs.
The majority of types of actuator valves are always lubricated, and instrument-quality air is optimal for their operation. Additionally, they can be packaged with motor protection, digital communication capabilities, and location sensing tools. Make sure to contact an industrial valve manufacturer to get sturdy and best-quality valves.