What is a Valve Actuator?
A valve actuator is a type of mechanical device that opens and closes a valve’s flow passageways as required. A manual operator or an external power source (such as electricity, compressed air, or compressed hydraulic fluid) can initiate the machine’s movements. Its design determines whether it best suits on/off flow control or flow throttling.
What Do Valve Actuators Do?
Seat The Valve with Sufficient Torque:
The actuator must induce and maintain enough torque to keep the valve in the closed position during shutoff operations.
Maintain The Closure Element Position:
In addition to moving the closure parts, the actuator must be able to keep it in the required position. It may use a spring, fluid power, or mechanical difficulty for this purpose, depending on its type.
Move the Closure Element:
The closure element refers to the parts (e.g., the ball, disc, or plug) employed to partially or entirely block fluid flow through the valve. The valve’s actuator must be able to offer the force to move and position the closure element as needed, even under demanding process conditions.
Operate at Appropriate Speed:
Unique control circuit elements can be applied to keep the cycle speed of a valve actuator. It is essential to carefully select the valve for fast cycle speeds below half the standard actuator cycle time to avoid shock-related damage to its parts.
Have A Failure Mode:
In a power failure, the actuator should have failure mode (e.g., fully closed, fully open) to make sure the system does not undergo excessive damage.
Provide Rotational Capabilities:
Actuators must be able to accommodate their valves’ rotational capacities (generally 90 or 180 degrees).
Seat the Valve with Enough Torque:
The actuator needs to make and keep up enough torque to keep the valve closed during shutdown activities.
Keep the position of the closure element:
The actuator must be able to keep the closing piece in the right place and move it. Depending on what kind it is, it might do this with a spring, fluid power, or mechanical difficulty.
Move the Component of Closure:
The closing element is the valve part that stops or slows fluid flow, like the ball, disc, or plugs. The valve’s actuator must be strong enough to move and place the close element as needed, even when the process is very tough.
Operate at Accurate Speed:
You can change the cycle speed of a valve actuator by using particular parts of the control circuit. So that shock does not damage the parts, it’s important to carefully choose the valve for fast cycle speeds that are less than half of the normal actuator cycle time.
If the power goes out, the actuator should have a good failure mode so that the system doesn’t take too much damage.
Offer the ability to rotate:
Actuators must be able to handle the valves’ rotating ranges, usually 90 or 180 degrees.
Types of Valve Actuators
- Manual Valve Actuators
Hand-operated handles or wheels turn a set of gears to open or close the valve. Manual valve actuator tends to be cheap and easy to use. However, they can only be used where automatic or remote valve control is unnecessary. There are different kinds of manual valve actuators, such as:
- Basic Levers:
Lever actuators are the most common type. They have a long handle that connects to the valve stem. The primary lever is the most common method to turn smaller quarter-turn valves manually. The stem has a long handle connected to it, which gives you the force you need to turn the valve. On tiny valves where you don’t need pressure, ovals, tees, and other shaped knobs can be used instead.
Handwheel actuators have a large handwheel and a gearbox. The gearbox makes the mechanical advantage bigger. Geared hand wheels are often used to handle larger valves that need much power. These have a big hand wheel with a gearbox. However, this makes the technical edge even larger. The amount of mechanical advantage is based on the wheel’s diameter and the gearing ratio. To turn the valve only 90 degrees, these wheels must turn many times. Most butterfly valves 8 inches or more in length have these kinds of operators. They are often used in large valves that need more torque to open and close.
- Manual Valves with Limit Switches:
Limit switches can be added to manual valves to let the control system know where the valve is set—limit switches on manual valves. Manual valves often do work that doesn’t require automated actuation, but the system still requires to know their position. We utilize manual valves with limit switches (“position indicators”) in these situations. Even though you still have to move the valve by hand, the switches indicate the control system where the valve is.
- What Is the Advantage of a Manual Valve Actuator?
Using a manual valve actuator has many benefits, including being cheap, reliable, and not needing electricity. They are often self-contained, and because they employ the same actions to open and close, it is usually easy to determine the source of any variations or errors. The lack of automation requires regular human supervision, which is a disadvantage.
- Pneumatic Valve Actuators
Pneumatic valve actuators turn valves on and off automatically or semi-automatic by turning the energy from compressed air into mechanical motion. They work by introducing air into a chamber and making it expand. This makes the pressure inside the chamber higher than the pressure outside. The pressure difference gives the air energy. Then, it can be sent out of the chamber and toward the valve part used to open and close it.
There are different kinds of pneumatic valve actuators, such as:
- Rotary Pneumatic Valve Actuators
Rotary pneumatic valve actuators use the energy in compressed air to turn rotary valves (like ball, butterfly, and plug valves) to open and close them. You may categorize them into two main groups: rack-and-pinion actuators and Scotch yoke actuators.
- Linear Pneumatic Valve Actuators:
Linear pneumatic valve actuators use compressed air to turn linear valves, like gate and globe valves, in a straight line. There are two main types: diaphragm actuators and cylinder actuators.
- Electric Valve actuators
Electric valve actuators create the torque necessary for valve operation using an alternating current (AC) or direct current (DC) motor. A cam-activated limit switch connects the motor to the valve stem through gears. All of these parts working together allow for fine-tuned valve regulation. Electric valve actuators come in different types.
- Linear Electric Valve Actuators
(Electric Linear Actuator Proportional Ball Valve for Water 12v 24v)
To control linear valves, electrical actuators transform electrical power into linear motion. ACME screws are often less efficient than ball screws but may retain loads without power. Power screws, known as “ball screws,” have a series of ball bearings that rotate between the screw and the nut. Compared to lead screws, they are more efficient and have lesser friction. Linear electric valve actuators suspend the load at the end of an unsupported screw or rod. Belts or gears usually drive the screw. The linear electric actuator will consist of a motor, a reduction gear set, a nut and bushing to drive the valve stem, and a way of limiting its range of operation.
Specifications for Linear Electric Valve Actuators Include:
- · Valve Stem Stroke Length
The stroke length of the valve stem is measured in inches (in) and is one of the critical parameters for linear electric valve actuators. The distance a valve needs to move from its open to fully closed position is known as its “stroke.” By using an actuator with fewer strokes than the valve, you will “short-stroke” the valve and prevent it from reaching its maximum CV rating.
- · Actuating Force or Seating Thrust
The force of an actuator is measured in pounds (lbs). The closing element cannot shut and remain closed until the actuator provides enough force to offset the pressure in the system.
- · Number of turns
The number of revolutions a multi-turn actuator takes as it rotates a valve stem from its closed to open state.
Rotary Electric Valve Actuators
Electric rotary valve actuators use electric energy to operate rotary valves and transform them into rotational motion. Electric rotary valve actuators use electromagnetic force from a motor to rotate parts. They usually have control and indexing features that let you pause at different points along a stroke. Electrical housing, electric motor, reduction gearing, drive coupling between the final drive gear and valve stem, and travel limiting mechanisms make up a rotary electric valve actuator. The rotating part might be a shaft or a flat table. The bolt pattern on the tables and the keyways on the circular shafts make it possible to attach various parts.
Characteristics of Rotary Electric Valve Actuators
- · Actuators’ Torque
Multiplying the applied force by the radial distance between the pivot and the point of application yields the actuator torque, the force that causes axis rotation.
- · Range of Motion
The complete extent of motion may be 90° (quarter-turn), 180° (nominal), 270° (nominal), or 360° (multi-turn).
Most manufacturers of electric actuators manufacture items at the following standard voltages: 12, 24, 48 VDC; 24, 48, 120, 240 VAC. The S4 series is one example of a multi-voltage or “Universal Voltage” actuator that can work with any power source. These parts can detect voltage as well as react accordingly.
- Hydraulic Valve Actuators
Hydraulic actuators are hydraulic devices that move due to pressurized fluids like hydraulic fluid. Similar in size, hydraulic-operated valves tend to be more robust than their pneumatic.
Types of Hydraulic Valve Actuators Rotary Hydraulic Valve Actuators
Butterfly, ball, and plug valves, among others, need rotating actuators because their opening and closing motions require at least a quarter turn. The closing element is often a disc or an ellipse that rotates around a shaft at a right angle.
Properties of Valves with Rotary Include:
- Toque of Actuator:
Torque is defined as the amount of force necessary to cause a rotation. Multiplying the applied force by the distance between the pivot point and the point of application of the force gives the solution.
- Rotary Motion Range:
Quarter-turns (90 degrees), full-turns (180 degrees), half-turns (270 degrees), and multiple-turns (360 degrees) are typical rotational motion ranges.
- Hydraulic Linear Valve Actuators
To operate linear valves, including gate, pinch, globe, and diaphragm valves, linear actuators slide a stem that controls the closing element.
- General Specifications for All Types of Valve Actuators:
- Source of Power
Actuators are typically powered by electricity or fluid (air-pneumatic or liquid-hydraulic). The amount of electricity required for actuators is proportional to their size, with larger actuators requiring a three-phase supply and smaller valves requiring a single-phase supply. Occasionally, a DC supply is available as a secondary power source. When selecting a fluid-powered actuator, it is necessary to consider the media type, available pressure, and the cylinder’s capacity.
The type of valve is another essential factor to consider. Proper actuator sizing is only possible if the user is aware of the type of valve it will be installed on, whether the valve is multi-turn or quarter-turn, whether the stem rises or does not rise, and the power requirements of the valve. To calculate the torque requirement of a valve, it is also necessary to know the valve’s variety. The manufacturer of the valve can typically provide this information.
- Type of control signal input
Three fundamental control signal input types are milli-ampere, voltage, and pressure.
Devices utilizing either AC or DC voltage are widely available. The signal is typically a 120/240 VAC or 12/24 VAC discrete voltage supply.
- Supply pressure
The supply pressure is the input pressure required to produce the intended torque or thrust. Companies determine the air supply pressure for pneumatic actuators and the liquid supply pressure for hydraulic actuators. Typically, compressed air in pneumatic actuators ranges between 60 and 100 psi.
- Valve stem diameter
The valve stem diameter and the lead and pitch of the valve stem thread can be used to determine the required valve automation size. In conjunction with the valve size and pressure loss across the valve, it can also be used to calculate torque demand.
- Number of turns
The number of turns applies to actuators with multiple turns. It specifies the number of revolutions the valve stem makes as it rotates from the completely closed to the fully open position.
- Location kind
Valve actuators for hazardous environments are designed for environments with flammable or potentially explosive atmospheres. There is no risk of combustion or detonation in environments where non-hazardous devices are utilized. Because condensation can form inside electric actuators, they are not recommended for outdoor applications or hazardous environments; compressed air should be used whenever possible.
- Operating temperature
The entire operating temperature range. In a broad spectrum of temperatures, pneumatic and electric actuators can be utilized.
Speed of Power Actuators
Actuators can operate at various speeds. The rate should be determined by the power and speed demands of the system, as well as the energy availability of the actuator.
Utilize fast-acting actuators when a system must be rapidly isolated or opened. Actuators such as hydraulic, pneumatic, and solenoid provide rapid action. Installing the correct orifice in the lines determines the rate of actuation, and the valve is closed by spring pressure, which is opposed to hydraulic or pneumatic pressure to set the valve open. Electrical motors can also provide rapid actuation when the motor speed and gear ratio are used to determine the desired speed.
Utilize slow-acting actuators when injecting frigid water into a hot system or when a prolonged opening is required.
There is an immediate connection between the actuator’s pace and the required amount of electricity. An increase in the rate of the valve/actuator needs an increase in horsepower. Motor operators for three-phase electric motors have a fixed speed, whereas smaller DC motors may have variable speeds. A fluid control valve can regulate the rate of fluid-powered actuators.
How to Choose the Right Valve Actuator?
A wide variety of valve actuators are on the market, so it’s crucial to research before choosing. Consider the following when determining if a product is suitable for your needs:
Availability of a Power Source:
Do you have access to a suitable power supply for the actuator at your facility? A powered valve actuator requires a source of electricity to function, so be sure you have one available. Pneumatic actuators require a compressed air source, whereas electric actuators require an electric motor.
Do you intend to use valve automation? Valve automation enables remote management and monitoring. Powered actuators allow for automation, whereas manual ones do not.
How significant are the environmental obstacles that the actuator must face? Regarding temperature ranges, electric actuators can work between -40 and 150 degrees Fahrenheit, whereas pneumatic actuators may work between -4 and 150 degrees Fahrenheit. Pneumatic actuators are the best option for use in potentially explosive settings. NEMA-rated enclosures are required for usage with electric actuators.
Do you want to reduce the amount of emissions coming from your building? When in use, pneumatic actuators release varying amounts of methane gas into the air, which can be problematic for areas subject to severe standards for emissions. Electric actuators give a zero-emissions alternative to pneumatic systems to help businesses meet the requirements of stricter environmental legislation.
Valve Actuator Usage Factors: What You Must Know
It is essential to consider the usage factors to choose the correct valve actuator. Several of these factors are detailed below.
What energy source is available? As discussed previously, electric actuators require electricity to function. It is necessary to consider the type of available electricity source. Electric actuators require electricity for regular operation. If there is no approaching source of electricity, a pneumatic or hydraulic valve actuator is the most reasonable choice. The air supply pressure must be between 40 and 120 psi for pneumatic actuators.
Obtaining elevated pressures can be complex. A diaphragm or piston must have a larger diameter to provide the required torque at a lower pressure. While valve actuators are available with DC and AC motors of varying capacities, the electric actuators require a 110 VAC power source.
Pneumatic actuators can operate between -4 and 150 degrees Fahrenheit (-20 and 70 degrees Celsius). Electric actuators can operate between -40 and 150 degrees Fahrenheit (-40 and 65 degrees Celsius).
• Hazardous Regions
Due to their explosion-proof nature, pneumatic actuators are frequently chosen for use in hazardous environments. However, electric actuators may be used if compressed air is lacking or a pneumatic actuator cannot meet specific operational requirements.
The differential pressure across the valve and the valve’s size and design are also factors to consider. Supply pressure is one of the most important things to consider when planning.
What We Solve in this Article?
- Valve actuators are essential for any process because they help automate valve operations.
- Choosing the suitable valve actuator depends on the working condition. The force or torque needed, the control’s accuracy, and the available power sources.
- Each type of actuator—manual, pneumatic, hydraulic, or electric has pros and cons.
- The type of valve and its needs determine the actuator type. These are multi-turn, quarter-turn, diaphragm, or another type.