Valve actuators are a vital component of industrialization. This explains why, according to Future Market Insights, the global market for pneumatic actuators alone will attain a market value of $16 billion in 2023. Although valve actuators come in various forms, they only work as expected in specific applications. This article examines pneumatic, electric and hydraulic valve actuators and provides the advantages and disadvantages of each to help in the purchasing journey.
Pneumatic Valve Actuators
As the name suggests, pneumatic valve actuators use the energy generated by compressed air into rotary or linear mechanical motion. The typical use for rotary pneumatic valve actuators is on plug, butterfly and ball valves, and the two primary types are scotch yoke and rack and pinion pneumatic valve actuators. Both can operate in single or dual versions, relying on either spring return or direct (single or double) action. In double-acting actuators, the configuration requires the supplied air to drive the pistons in the primary direction of operation and in the reciprocal direction of operation.
Alternatively, spring-return actuators only require the supplied air to drive the action of the pistons in one direction and instead rely on the mechanical force of a spring to return the pistons to their original position. This spring-return configuration consequently yields a failsafe position, a designated orientation to which the actuator will return the stroking valve upon loss of air supply to the actuator. Double-acting rack and pinion actuators deliver linear torque outputs, offering consistency throughout the valve stroke. However, a scotch yoke actuator would deliver a torque output curve reflective of its ability to deliver its maximal torque outputs at the beginning and end of its stroke with diminished torque mid-stroke.
To ensure a user selects the right pneumatic valve type for their application, they must consider features such as the method of valve actuation, valve configuration, flow capacity, type of return action and media of control. Valve configuration could mean opting for either 2, 3 or 4-way valves, and a user could choose a spring-return or direct actuation valve. The gas or liquid used to control the valve and how the user will actuate the valve also play a pivotal role in the selection process.
Electric Valve Actuators
An electric actuator device converts electricity into kinetic or mechanical energy that can control butterfly and ball quarter-turn valves. Most use a motor that can travel in both directions and a limit switch that turns it off when it achieves the final position. There are two basic types of electric valve actuators: rotary and linear. Rotary electric actuators can be used with plug, ball and butterfly valves that rotate 90 degrees (quarter-turn) open to close, typically used in the packaging industry. Linear electric valve actuators work best with diaphragm, pinch, gate, angle and globe valves requiring a sliding stem to open or close the valve. These work well where tight tolerances are the goal.
To get the selection of an electric actuator right, a user must consider the motion profile. That is, the force required to move the load, the travel distance and minimum and maximum speeds required. Additionally, they have to take into account the load, duty cycle/cycling rate and positional accuracy requirements.
These use the same principles of operations as pneumatic actuators, except hydraulic actuator valves use a liquid in the place of air. Therefore, a hydraulic actuator converts fluid pressure energy into linear, rotary or oscillatory mechanical motion. Since they use incompressible fluid, they are ideal for heavy loads. Hydraulic actuators come in several forms, including rotary, linear, throttling, start-stop and semi-rotary valves. Piston-type actuators have the most widespread usage. Unlike the other actuators, users need several components to run hydraulic actuators. For instance, a piston-type actuator contains a cylinder, spring, stem, piston, control valve, hydraulic fluid and hydraulic supply and return line.
The most suitable hydraulic actuator will depend on its use case. Users will need to consider factors such as operating pressure range, force and direction of force and cylinder mounting style. Other factors include actuation time (the time it takes to open and close), range of motion, sealing thrust and actuator force and the number of turns.