Know Your Pneumatics: Rotary Actuator Basics

Know Your Pneumatics: Rotary Actuator Basics

  Pneumatic actuators are commonly used to convert compressed air pressure (in the form of a cylinder stroke)  into an oscillating rotary motion. Like other pneumatic components, they are durable, offer simplicity and high force for their size, and can operate in hazardous environments.

    There are two main types of pneumatic rotary actuators: rack and pinion, and vane – both are available in either single or double actuation:

    Rack and pinion rotary actuators use a cylinder piston attached to a rack gear. When actuated, the piston and rack move in a linear fashion rotating the pinion gear and output shaft. A double rack unit utilizes two racks on opposite sides of the pinion gear, in effect, doubling the output torque of the unit.

    Vane actuators have a cylindrical chamber in which a vane is mounted on a central shaft. Air pressure applied on one side of the vane forces it to rotate until it reaches the end of the stroke. Alternatively, air pressure from the opposite side of the vane drives the shaft in the opposite direction until it reaches the end of stroke. In a single vane style, the rotary motion is typically limited to 280 degrees. In a double vane style, the motion is typically 90 or 100 degrees, offering less rotational range with double the force of the single vane construction. Our Series is an example of a vane actuator available in 9 sizes in single or double vane versions.

    Rotary actuators can often be overlooked in the specification process as common pneumatic cylinders are specified with a pivot arm to achieve the necessary rotary motion. However, rotary actuators have the potential to greatly simplify applications because they are self-contained components capable of supporting loads due to the internal bearing sets.

    Additionally, there is no need to design and construct external pillow block bearings. Unlike piston rods exposed to airborne contaminants, rotary actuators can reduce maintenance headaches in dirty environments.

    A butterfly valve is a quarter-turn rotational motion device that utilizes a rotary disc to allow, obstruct, or control the flow of fluids in a piping system. It features a rotating disc that is situated on the passageway of the flowing media. The disc is rotated and controlled by an external actuating mechanism through the stem attached to it. When the disc is coplanar to the flow cross-sectional area, the flow is fully obstructed. Otherwise, the fluid is fully or partially allowed to pass through the butterfly valve. It takes a 900 turn to fully open a butterfly valve from a closed position, which means the disc should lie perpendicular to the flow cross-sectional area.

    Butterfly valves are quarter-turn valves like ball valves and plug valves. They have a fairly simple construction and operation mechanism, and they have a compact size designed to fit two pipe flanges.

    They can be operated manually or by an automatic actuating mechanism that is integrated into the process control system of the pipeline. They are ideal for on-and-off applications, but their applications to flow throttling are limited.

    There are several types and designs of butterfly valves available, rated in varying temperatures, pressures, and flow rates to suit the needs of pipeline systems handling liquids and gases.

    A limit switch box is an electromechanical device operated by a physical force applied to it by an object. Limit switches are used to detect the presence or absence of an object. These switches were originally used to define the limit of travel of an object, and as a result, they were named Limit Switch.

    A solenoid valve is an electrically controlled valve. The valve features a solenoid, which is an electric coil with a movable ferromagnetic core (plunger) in its center. In the rest position, the plunger closes off a small orifice. An electric current through the coil creates a magnetic field. The magnetic field exerts an upwards force on the plunger opening the orifice. This is the basic principle that is used to open and close solenoid valves.

    There are several features of a filter regulator, all as important as the last. The point of an airline filter, regulator, lubricator is to ensure that every component or process is receiving a clean and lubricated supply of compressed air. But, this must also be done at the correct pressure to achieve peak performance. It is stated that every 2-psi increase in operating pressure adds an additional 1% to compression energy cost. Therefore, unregulated or incorrect pressure settings can result in increased compressed air demand and consequently high energy consumption. This excess of pressure can also create equipment wear, causing a rise in maintenance costs and a limited application lifespan. Air filter regulators maximize longevity and reliability, making them an essential component of many applications.

    There are a few different types of valve positioners available. Depending on the type of positioner, it either uses air or electricity to move the actuator. Let’s discuss some of the popular options. Pneumatic positioners receive pneumatic signals (usually 3-15 psig). The positioner then supplies the valve actuator with the correct air pressure to move the valve to the required position. Pneumatic positioners are intrinsically safe and can provide a large amount of force to close a valve. Electric valve positioners receive electric (usually 4-20 mA) signals. They perform the same function as pneumatic positioners do, but use electricity instead of air pressure as an input signal. There are three electric actuation types: single-phase and three-phase alternating current (AC), and direct current (DC) voltage. Electric-pneumatic valve positionerss convert current control signals to equivalent pneumatic signals. It uses a mix of both electricity and air, as implied by the name.