Pneumatics

Summary

Pneumatics technology generates and uses compressed gas, normally air, to provide energy to mechanical equipment performing work. Pneumatic technology can be used in large-scale industrial applications, such as a drill for blasting rock, or on a much smaller scale, such as to move a prosthetic device such as an artificial leg. Pneumatics is based on the fact that all gases can be compressed, although the compression affects the volume and temperature. Air, the primary gaseous medium, is in endless supply, inexpensive, and environmentally safe.

Definition and Basic Principles

Pneumatics is a technology resulting from the molecular and chemical composition of a gas, a medium that can move machinery. The machinery can be very large, such as a marine hovercraft, or very small, such as a portable ventilator for a human being. Pneumatics is half of a technology labeled as fluid power, the other half being hydraulics. Hydraulics uses many liquids because liquids are also dependent on pressure and temperature for their volume, although not as much as gases. In scientific terms, the word "fluid" applies to both liquids and gases. Different laws govern the behavior of each medium.

Gases are molecular compounds. Molecules in a fluid are in constant motion. Matter in the gaseous state occupies a volume about one thousand times larger than the same amount of matter in the liquid state. The molecules in a gas are also much farther apart. Because they have no inherent shape, they can be easily confined.

Air is the most common gas used in pneumatics. It is composed of nitrogen (78.08 percent), oxygen (20.95 percent), argon (0.93 percent), and several other elements in trace amounts on the order of parts per million. Carbon dioxide and water vapor are also present in varying and unpredictable amounts. Because water can damage a system, most pneumatic systems have a component for drying the air. An important value is the weight of a one-inch-square column of air from sea level to the beginning of outer space (thermosphere). Expressed in a variety of international measuring systems, the unit one atmosphere (atm) weighs 101.3 kilopascals (kPa, named for French scientist Blaise Pascal), 14.7 pounds per square inch (psi), 760 torr (named for Italian physicist Evangelista Torricelli), or 29.9 inches of mercury (mmHg), so called because 1 atm can support a column of mercury that high.

Background and History

Pneumatics is derived from Latin words meaning "pertaining to air." The blacksmith's bellows pumping a fire is a primitive example. Windmills in twelfth-century central Europe exhibited the technology's first large-scale possibility. Development was dependent on discoveries made in the seventeenth and eighteenth centuries about gas properties, especially how the volume of a gas is affected by pressure and temperature. The Italian physicist Evangelista Torricelli invented the mercury barometer in 1643 and then measured atmospheric pressure. He also formed a vacuum by inverting a mercury-filled tube. The first vacuum pump was invented by German scientist Otto von Guericke.

Boyle's law, developed by Irish chemist Robert Boyle, states that the volume of a gaseous substance at constant temperature is inversely proportional to the pressure it is under. French physicist Jacques Charles contributed the insight that the volume of a given mass of gaseous substance increases or decreases by 1/273 for each degree Celsius of temperature change; this is known as Charles's law. French chemist Joseph Louis Gay-Lussac discovered the relationship between volume and temperature. He devised a hydrometer and calculated the volume of a gaseous compound is equal to or less than the sum of the volumes of the combined gases. Amedeo Avogadro, an Italian physicist, determined that at the same temperature and pressure, equal volumes of different gases contain equal numbers of molecules.

Once the gaseous state was understood, gases could be manipulated to do work, and the field of pneumatics was possible.

How It Works

Pneumatics works by compressing a quantity of air (or some other gas), filtering it to make sure it is clean, drying it, and sending it through a system with one or more valves. The compressed air is delivered to a mechanical apparatus that can then move a force through a distance. The air is an energy-transfer medium.

Pneumatic System Components. The major components of a pneumatic system include a compressor, an air storage tank (receiver), an air dryer, and a mainline filter, all connected by a series of hoses. These sections are followed by an air-conditioning section composed of a filter, regulator, and lubricator; then a controlling section made up of a directional control valve and a speed controller; and, finally, the actuator or operating system that the pneumatic system was designed to power.

This basic system is used in large factories where truck snow-plowing blades are spray painted. Such a system would be automated for mass production and include a timing apparatus, usually using digital logic, to control when and how much paint was sprayed. The paint is atomized and mixed with the pressurized air as it is released.

On a smaller scale, everyday handheld tools, such as a drill hammer for blasting slabs of concrete or an air hammer for pounding nails, use the same principle. Such tools have less need, and thus less capacity, for cleaning and removing moisture from the air sucked into the tool. The compressed air pressure supplied for pneumatic tools is normally about 90 pounds per square inch gauge (psig).

Valves.Valves control the way the gas is used, stopped, or directed. They must function under a range of temperatures. Control or proportional valves in a process system are power-operated mechanisms that can alter the fluid flow. A pneumatic valve actuator adjusts valve position by making the air pressure either linear or rotary motion. Ball valves provide the shutoff capability. Gas valves are specialized to control the flow of another medium, such as natural gas. A pressure-relief valve is a self-actuated safety valve that relieves pressure. A butterfly valve controls the flow of air or gas through a circular disk or vane by turning the valve's pivot axis at right angles to the directing flow in the pipe.

Gaseous Medium. The gas or energy medium traveling through the system is unique in its behavior. Charles's law states that a volume of a gas is proportional to the temperature. Boyle's law states the volume of a gas is inversely proportional to the pressure applied to it. If the amount of gas is calculated in moles (expressed as n), which is the amount of a substance that contains exactly 6.02214129 × 10²³ atoms or molecules of that substance; the temperature is in degrees Celsius (expressed as T); the volume of the gas is in liters (expressed as V); and the pressure is in atmospheres (expressed as p), then calculations can be made as to what happens to that gas changing one or more of those variables using the formula pV = nRT. R is called the molar gas constant and has the same value for all gases. When changes are made to the conditions of a gas, the calculation can be made to find out what will happen to any one or two values of the gas in question. This is expressed pV/T = pV/T. This is one of the most important formulas in pneumatics.

Pneumatic System Categories. One way of categorizing pneumatic systems is whether the actuator that the air drives is rotor or reciprocating. Compressed air enters a rotating compressor and pushes on the vanes, rotating a central shaft or spindle. Tools such as drills or grinding wheels use this system. In a reciprocating piston compressor, the air enters a cylinder, expands, and forces the piston to move. In a reciprocating tool, the piston also has a return stroke, which is actuated by compressed air on the other end of the piston or a spring action. A riveting hammer is a tool using this technique.

Another way to categorize pneumatic devices is as either portable or rock drills. Portable devices include buffers, drills, screwdrivers, wrenches, and paint mixers. This category is powered by a rotary-vane type of air motor. Rock drills or percussion hammers are composed of high-carbon steels. In this type, the compressed air drives a piston down onto a loosely held drill inside a cylinder.

Applications and Products

Pneumatic systems have positive and negative features. Potentially, pneumatics can be used in any situation where mechanical work needs to be done. Its overarching desirable quality is a boundless supply of free air. The desirable features include stability under temperature changes, cleanliness (leaks do not cause contamination), and work at high speeds measured in feet per second (fps); the tools stall when they are overloaded with pressure and are therefore inherently safe. Undesirable features are when a constant actuator velocity is not possible, when the force is limited to 4,500 and 6,700 pounds under normal conditions (usually 100 psi), and when the gas must be prepared by removing dirt and humidity as these degrade a system. Since pneumatics is so versatile, it can be used across industries.

Heavy Loads. This is the traditional area. Factories often deal in products weighing tons and under extreme temperatures. Pneumatic systems can open heavy or hot doors. They can unload hoppers (containers usually with sloping floors used to carry bulk goods) in construction, steelmaking, and chemical industries. Slab molding machines are usually lifted and moved with pneumatic systems. Road or large flat-surface construction is usually rammed or tamped with them. The capability of moving heavy loads proves the efficiency of pneumatic systems.

Spraying. Pneumatic valves can direct air and atomizing liquids into fine droplets for this application. Large- and small-scale surfaces needing coverage include agriculture, where crops are sprayed with chemicals or water, and painting, as in automobile, motorcycle, or bicycle manufacturing.

Repetition. Repetitive motion has been used since the first mass production and has grown with ever-larger quantities in ever-shorter periods. Pneumatics is advantageous because of its low cost of operation and maintenance. Both large-scale and small-scale tools are also examples. Both handheld and robotic riveters can secure bolts and screws at very fast speeds. Pneumatic systems are ideal for holding maneuvers where pieces are clamped while other work is accomplished likewoodworking, furniture making, gluing, heat sealing, or welding plastics. Guillotine blades for slicing precise quantities of a material by the millions are a classic example of this capability. Bottling and filling machines and household cleaners also use the systems.

Breaking and Smashing. The jackhammer, used for road repairs, is a pneumatic tool.

Medical Devices. Pneumatics is being used more in medical devices. When the dentist, drill or polisher in hand, steps on a small plate, a pneumatic system is activated that drives the instrument in a circular motion at a very high speed. Pneumatic systems are excellent for applications in patient ventilators. Ventilators can take over breathing for an extremely sick patient or assist a patient with some breathing ability.

Robotics.Robotics for work as well as entertainment is another application of pneumatics. Most movable monsters or lifelike creatures in theme parks or museums are operated pneumatically.

Careers and Course Work

Pneumatics is a subset of the field of fluid power. Fluid power is a subset of mechanical engineering and electrical engineering. Students earn an engineering degree in one of the two, then attend a university offering a master's program in pneumatics. The US Bureau of Labor Statistics listed 2023 median salaries for electrical engineers as $109,010 per year, while mechanical engineers made $99,510. The ultimate designation in the field is fluid power engineer, which requires a bachelor's degree, eight years of work in the field, and completion of other certifications. Jobs are also attained by having a good aptitude for mechanical and electrical work and passing short courses with exams to earn a certification from the International Fluid Power Society. Examples of certifications include fluid power connector and conductor, fluid power certified mechanic, fluid power certified technician, fluid power electronic controls, and fluid power specialist.

Certifications prepare people to be reliably expert in all stages of the pneumatic process from understanding theory, system design, schematics, efficiency improvement, controls, and safety.

Wherever tools are used, be they on an enormous scale as in mining or on a microscopic scale as in the biomedical field, opportunities exist for employment in the private sector and future growth is anticipated. Much of the growth will result from the miniaturization of systems through computers and advances in materials. The military also uses pneumatic systems in weaponry and transportation. Teaching and research at universities is another career track.

Social Context and Future Prospects

Energy awareness, conservation, and environmental protection are forces that will allow pneumatics to remain a promising field. Despite the commercial size of the field of pneumatics, few people know about it even though they use its technology daily.

From its inception, the industry has not changed much because the basic system remains the same. What does change is that component providers continue to improve on the efficiency and materials, as well as the advances made by computerization and miniaturization of parts. Hospital ventilators once took up as much room as a hospital bed. Now, they can be placed in a belt pack and the patient sent home.

The field of nanotechnology works with unusual matter located between molecules in the size range of 0.000000001 meter. It allows pneumatic parts such as pistons and seals to be manufactured with ultraprecision.

Bibliography

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