Safety, energy efficiency and high performance
- Pneumatic drives – performance, safety and environmental protection
- Pneumatic system design
- Compressed air preparation
- Valves for pneumatic systems
- Pneumatic drives
Energy efficiency, no standstills, human and machinery safety – these are prerequisites that define every state-of-the-art industrial plant designing process. Pneumatic drives address all such challenges effectively. This technology has been going hand-in-hand with industry for many decades, and it continues to support companies in their pursuit of the goals set by today’s markets and regulations. Safety, performance and environmental concerns are reasons why pneumatic drives play a central role in virtually every industry, machine design and other numerous applications.
Pneumatic drives operate based on a principle which involves transforming pressurised air (or other gas) energy into linear or rotational movement. This technology is in constant demand wherever there is a need for mechanical work to be performed. Pneumatic drives offer a plethora of possibilities, while being safe and easy to operate. The wide variety of market offerings makes them suitable for many industries, and designers can successfully match optimal components to their project requirements. The spectrum of potential applications is very wide.
Pneumatic actuators are used in a broad range of machine construction applications, from stationary devices used, for example, in manufacturing or heavy industry, to mobile machines used in transport or agriculture. All construction applications such as elevators, gates and mobile platforms also fall into this category. Pneumatic drives are also widely used in process and industrial automation systems where performance, reliability and safety are of key importance.
Pneumatic drives – performance, safety and environmental protection
Pneumatics is a well-established technology that is very familiar to designers and maintenance engineers. Simultaneously, it is an area which never ceases to amaze us with new solutions and possibilities. Manufacturers of components belonging to this group constantly develop their products to meet ever more demanding customers’ requirements and increasingly more stringent energy efficiency targets set for the industry. Today’s pneumatic drives are powerful yet highly efficient and reliable. Due to their resistance to harsh environmental conditions such as humidity, dirt and temperature fluctuations, they are suitable for demanding industrial, mining and construction applications. Simultaneously, taking into account the type of an energy carrier used (i.e. air), pneumatics is considered to be a clean technology, which is perfect for companies with high hygiene standards, especially in the pharmaceutical and food industry. Air is generally available and free of charge, generates no pollution and does not need to be regenerated or subjected to particular disposal operations after use. Low resistance and viscosity facilitate efficient transport in pneumatic lines, even over considerable distances.
Air storage and transportation are relatively easy and safe. Moreover, unlike electricity or liquids, air poses no risk of shock, fire or contamination. Therefore, system leakages pose no danger to people or equipment. In contrast to electric drives, pneumatic components are completely safe in explosive environments.
Minimal inspection and maintenance requirements significantly ease the burden on maintenance services and translate into low operating costs. Pneumatic systems have long been valued by design engineers for their ease of installation and replacement, resulting partly from a high degree of standarisation in the industry and the inclusion of actuator designs in ISO standards. Thus, users benefit from the fact that products from different suppliers are interchangeable and there is no risk of becoming dependent on one manufacturer. Due to a simple design and materials used (primarily aluminium), pneumatic components are small in size and weight, making them easy to fit into any project.
Pneumatic system design
A pneumatic system encompasses a number of components that generate and convey compressed air, as well as controls and actuators. Based on the function performed in a pneumatic system, we can distinguish between the following main component groups:
- Compressors – the first stage of the process is to compress the air in a single or several connected electric compressors and store it in a pressure vessel. Selection of a suitable compressor is crucial for achieving high pneumatic system efficiency and thus optimising the costs. Recent years have witnessed dynamic development of new solutions and methods of compressed air generation aimed at improving the process performance.
- Air preparation units – before compressed air is used in a pneumatic drive, it must first be properly prepared and free of water as well as other contaminants.
- Flow control valves – their function is to control actuator operation by controlling the direction and pressure of the air flow in the system.
- Power elements – pneumatic actuators where the energy of compressed air is converted into mechanical force.
Let us take a closer look at the structure of the latter three groups of pneumatics components below.
Compressed air preparation
The essential process of compressed air preparation is to ensure an appropriate working medium purity, which is crucial for ensuring failure-free operation and durability of pneumatic equipment. Compressed air contains particles of water, oil and solids, which penetrate lines, valves and actuators, leading to corrosion, mechanical damage and faster wear and tear of moving parts.
The change in air pressure due to compression causes it to heat up in a tank, while in the pipeline it cools down again, resulting in condensate formation. Therefore, coolers and dryers are installed in the system, at the compressor outlet, to remove water content from utilised air. Such systems also include filters responsible for contaminant removal. The ISO 8573-1: 2010 defines the class of air cleanliness required in a pneumatic system, with higher air cleanliness requirements for industries such as food processing and pharmaceuticals. The selection of appropriate filters and dryers depends on system performance, components used and amount of air that needs to be supplied to them.
Valves for pneumatic systems
Directional control valves are system components that control the direction of compressed air flow, perform logical functions, cut off or open the air flow or change its intensity. In pneumatic systems, such valves are, e.g. responsible for controlling actuator displacement or piston speed, and can also be used to implement sequential pneumatic systems.
Directional control valves control the air flow direction in systems. Basic parameters of valves belonging to this group include the number of flow paths, which is the number of possible combinations of element inputs and outputs that are linked by a valve control element; the number of positions of the control element; and the method and variety of control.
Valve operation may be controlled manually, by a pushbutton, pedal or another user interface. Fully automatic control is available for solenoid valves. In addition, a distinction is made between valves that return to their original position when the control signal is disconnected, i.e. monostable valves and those which retain their position, i.e. bistable valves. With respect to control method varieties, two groups can be differentiated. Directly controlled valves do not require connection of an additional valve with compressed air, but are limited to low pressures and flow rates.
Indirectly controlled elements require a supply of air at fixed pressure, often by means of an additional connection in the valve or connection plate, but thus can generate the force needed to overcome the high pressure of the working gas.
A separate group of valves encompasses throttle and flow control valves or throttle valves, whose function is to control the flow rate or shut it off completely. For every pneumatic actuator, there is a certain air pressure level that needs to be ensured for trouble-free operation, in most cases not exceeding 10 bar. Since air is stored at very high pressure in a tank, pressure regulators must be used to ensure stable air pressure at the input of a given element. When installed in the vicinity of actuators, they can also control the piston speed by throttling the air flow at the actuator inlet or outlet. For two-sided actuators, output intensity adjustment ensures more stable element operation. The most common operating pressure is up to 10 bar for actuators and much lower (less than 1 bar) for control elements.
To reduce system complexity, it is common to use valve islands that accommodate a series of solenoid valves as well as common power supply and controls in a single housing.
Pneumatic drives
Pneumatic drives are the most visible part of a pneumatic system, and a component that directly performs its primary function of moving parts, opening, closing and other movement types.
The most commonly used components are linear actuators and rotary actuators. In the former ones, the working element, usually the piston rod, performs a reciprocating motion. Designers can choose from among numerous types of such devices, including push or pull, piston or pistonless, single-sided or double-sided actuators. All are based on the same simple operating principle. Compressed air is supplied to the actuator chamber through a connection port, which moves the piston by a predetermined stroke. Typically, the piston travel distance amounts to a few to tens of millimetres, which is sufficient for most applications. Longer reach is possible, but it requires larger dimensions of the device.
In single-acting actuators, the piston movement in the opposite direction can be implemented by means of, e.g. a spring. This is an energy-efficient solution, but limited to a short distance, usually within a few dozen millimetres. For double-acting devices, the piston movement in the opposite direction requires air to be transferred to the opposite chamber while venting the other chamber.
Rotary actuators are devices in which the compressed air energy is converted into a rotary motion of a shaft or key. Depending on the nature of the motion performed, they are divided into swinging actuators that move within a specified angular range, and fully rotary actuators, also called air motors. As in the case of linear actuators, this group also includes single-acting and double-acting drives. A popular application for rotary actuators is flow control by opening and closing ball valves and throttling valves.
There is a wide range of actuators available on the market in various housing shapes and sizes, thanks to which designers have an extensive choice, including compact actuators intended for applications in hard-to-reach locations. It is worth remembering that the mounting hole spacing is included in ISO 15552, so it is possible to use products from different manufacturers interchangeably.
Correct pneumatic actuator selection for a project must be preceded by analysis of the required operating parameters and environmental conditions, such as the load magnitude and characteristics, temperature, clearance for mounting, and other potentially damaging environmental factors. The force generated by the piston rod can be calculated based on Pascal’s law – it is the product of its active surface and air differential pressure. Obviously, this is a simplified model, and in a real-life system this value will be smaller due to frictional and duct pressure losses. The final decision is not limited only to actuator operating parameters, but also determines the design materials used. Typically, an actuator body is made of aluminium, but various grades of stainless steel are also used for the harshest environmental conditions, such as exposure to chemicals, high salinity or extreme temperatures. Actuator piston rods are made of steel or stainless steel, the latter solution being used primarily in the food processing industry. Similarly, the sealing material determines the possible operating temperature range, but also the purity standards, and, as a result, for example, approval for operation in appliances coming in contact with foodstuffs.
Operation in a wide temperature range is actually a standard in this product group. Most actuators in TME’s assortment are suitable for operation in temperatures from -10 to 80°C, but if operation in more difficult conditions is required, devices adapted to temperatures from -40 to 150°C are also available.
In most cases, actuators are pre-lubricated and do not require external lubrication. However, it is important to note that if lubricators are used in the line, this process must be continued throughout the life of the machine.
See also our range of pneumatic tools and accessories:
Text prepared by Transfer Multisort Elektronik Sp. z o.o.
The original source of text: https://www.tme.com/in/en/news/library-articles/page/43313/industrial-pneumatic-drives/
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