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.