PNEUMATICS
PNEUMATIC FLOW CONTROL GETS SMART
Reliable flow control equipment plays an essential part in the control of many manufacturing and industrial processes. Control Engineering Europe takes a closer look.
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hen managing a liquid, gas or powder process, flow control equipment, such as actuators and instrumentation, are vital. Pneumatic actuators have long been an integral part of actuation solutions.
Low emission instrumentation Valve actuators are designed to automatically and remotely control valves. They can be pneumatically, hydraulically or electrically powered. Pneumatic actuators are well suited for use in critical high-speed fail-safe or emergency shutdown (ESD) duties in extreme or hazardous locations. There are also many instruments that are powered pneumatically which can be used as part of a smart, efficient and reliable flow control system, solenoid valves, controllers, positioners and regulators. Low emission pneumatic controllers and an overall carbon footprint reduction are increasingly important requirements for electro-pneumatic control systems. Natural gas is an abundant pressure source, so this gas is often used as the supply for pneumatic instruments. It is normal for pneumatic devices to bleed some natural gas into the atmosphere, but the allowable emission levels of natural gas from controllers is highly regulated. The bleed rate or emissions level will mostly depend on the design of the device used. Leonardo Ongetta, product manager Limit Switch Boxes and Positioners at Rotork, explains further: “Pneumatic flow control equipment and associated instrumentation can emit fugitive emissions, so there is an increased focus within the industry on efficient and innovative equipment that can reduce this as much as possible.
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February 2021
Low emission instruments that assist in efficient use of pneumatic flow control are becomming increasingly popular.”
Valve positioners Valve positioners play a key role within process control applications to control the position of a modulating valve. They are especially useful in process control applications thanks to their precision. They enable a rapid A smart positioner in use. response to position the valve when a command signal is received from a control system. When a control signal is different from the actuator’s position, the positioner changes the actuator to the correct position. Valve positioners are usually mounted on the yoke or top casing of a pneumatic actuator for linear control valves or on top of the actuator for rotary control valves. Positioners can be pneumatic or electro-pneumatic. Some have ‘smart’ digital technology with additional capabilities such as diagnostic, auto calibration and tuning functionality as well as connection to a current loop network.
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Smart positioners Pneumatic positioners receive pneumatic signals – usually 3-15 psig – from a control system. The positioner then supplies the valve actuator with the correct air pressure to move the valve to the required position. As they don’t have any electrical source, they are considered a fully mechanicalpneumatic device, following specific simplified regulations for hazardous area applications. Electro-pneumatic positioners convert current control signals to equivalent pneumatic signals. Digital/smart positioners use a microprocessor to position the valve actuator, while monitoring and recording data. They are accurate and Control Engineering Europe
