Everything about pneumatics

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Pneumatic technology is technology which uses compressed air to control and carry out work processes in machines. Just like the compressed oil used in the hydraulic cylinders of large excavators and other construction machinery, compressed air can also be used to generate great amounts of force and fast movements. This offers a range of advantages – particularly in the classroom.

• Pneumatics is an easy to understand and easy to demonstrate type of technology – you can see what parts are moving and feel how different amounts of pressure produce different levels of force.
• Pneumatic cylinders always exercise the same force at the same pressure, regardless of how far extended they are. This makes it simple, for instance, to hold a workpiece with constant force, without damaging it as a result of excessive force.
• Pneumatic cylinders can be used to execute very fast movements.
• Valves can also be used to create fully pneumatic controls.
• Since these do not produce any sparks (such as can be the case with electric circuits), pneumatic systems are a good choice for use with flammable materials (such as bottling plants).
• In contrast to oil leaking from a hydraulic system, leaking compressed air is not an environmental contaminant.

For all of these reasons, pneumatic technology is used on countless industrial applications, to process workpieces, fill drink bottles, package, grip and handle parts, and much more.

History

Pneumatics has a surprisingly long tradition: Even as early as the third century BC, Greek mathematician and inventor Ctesibius was experimenting with compressed air and using it to power machines. His first pneumatic machine was a pump used to lift water. It was followed by clocks, catapults and organs all using compressed air.

Thereafter, the extreme versatility of compressed air was recognised as pneumatics began to be used in more and more areas. Steam engines, steam locomotives, diving with compressed air, painting, airbrush technologies, compressed air sirens, speed measurement with nozzles on aeroplanes – these are all applications of pneumatics, and show how useful and variable this relatively simple technology can be.

Today, pneumatics is part of all of our everyday lives. It serves countless purposes, from pumping up a balloon to operating jackhammers used to build streets, lightweight compressed air hammer drills for household use, vacuuming out air before sealing foods, and even large industrial systems. Pneumatics is a broad field of study!

Definition

Pneumatics is the field of compressed air technology which deals with doing work using compressed air (typically in pneumatic cylinders) and controlling machines used to work with this technology (via valves). This can be divided into the following areas:

• Compressed air generation delivers normal ambient air in a compressed form. This is achieved using compressors, which suction in air, then compress it in a pump and deliver it to compressed air lines (tubes or pipes). Low pressure pneumatics works within a range of approx. 100 mbar to 1 bar overpressure; at least around 6 bar overpressure is generally used to generate higher forces.
• For compressed air preparation, air is cleaned (e.g. filtered) and may have a fine oil mist added by atomizers, to ensure continuous lubrication of movable components like valves and cylinders.
• Compressed air distribution is handled by tubes, pipes, T-connectors and similar components.
• Controlling is handled by valves, which may be actuated manually (by an operator), mechanically (by a moving machine component) or pneumatically (by the compressed air signal of another valve). There are many different kinds of valves used to switch a signal on or off (i.e. to apply compressed air to it or vent compressed air from it), for time delay and for signal storage. Throttles regulate the air flow (causing a cylinder to retract or extend slowly).
• The actuators used in pneumatic systems are usually pneumatic cylinders. They consist primarily of a closed tube, which is divided by a tightly fitting disc inside. The cylinder rod (piston) sits on the disc. When compressed air is fed into one of the two halves of the cylinder (and air is vented out of the other), the disc and thus the cylinder piston will move. There are many different cylinder types, as well as other actuators, such as pneumatically activated counters.

Another interesting sub-field of pneumatics is fluidics: Switching and controlling systems using flowing media (gases, air or liquids). The unique thing about this type of pneumatics is that fluidic valves do not require any moving parts for logic circuits; instead, they function solely through the targeted shaping of flow channels. The pressure is not the key signal, but rather the flow of the medium. Pneumatic fluidic systems work with a pressure of just 100mbar, require no oil for lubrication, and result in valves that are self-cleaning thanks to the high flow speed. Fluidic signals are only converted into standard pneumatics or electrical systems if the controller ultimately requires a large force.

Pneumatics is related to the physics fields of mechanics, kinematics and thermodynamics (compressed air becomes warm), and fluid mechanics, as well as the mathematical field of logics for logistics circuits in pneumatic controllers, and therefore Boolean algebra.

Fundamentals

The following components are used to introduce pneumatics with fischertechnik:

• The fischertechnik compressor is small and quiet, yet powerful. It is operated with 9 V DC voltage and delivers approx. 1 bar pressure, as well as a sufficient flow rate to operate a wide range of functional models.
• The pneumatic tank stores compressed air. It is the pneumatic counterpart to a capacitor in electronic systems.
• Hoses which can easily be cut with a pair of scissors, T-connectors for distributing compressed air to multiple hoses, and plugs to close off connections, help ensure compressed air is available in the right place.
• The manometer is used to measure air pressure. It helps make pneumatic processes easier to understand.

• The fischertechnik manual valve is a “4/3 way valve” – it has four connections for the air inlet, air outlet and two outputs for cylinders, and offers three switching positions. It can be used, for instance, to retract or extend a cylinder, or hold a cylinder in a certain position.
• The solenoid valve allows users to connect a pneumatic valve to an electronic system. This connection can be used to create other kinds of mechanical controllers – even computer-controlled pneumatic machines.
• Various pneumatic cylinders do the work: Dual-action cylinders are moved in both directions (retracted and extended) actively using compressed air. Single-action cylinders have a built-in return spring. They are extended by compressed air, then automatically return to their home position once the compressed air is no longer present, due to the spring.

• Valves also include throttles, which allow either a strong or weak flow of compressed air through, depending on their setting. This ensures that the pneumatic cylinder extends or retracts at a desired speed, or fills a volume with compressed air slowly. They correspond to resistors in electronics.
• Check valves allow compressed air to pass through in only one direction. They are used to build up a compressed air source, or to allow a cylinder to work quickly in one direction, while throttling it in the other. This is the pneumatic counterpart to a diode in electronic systems.
• Of course, all of these are perfect for the fischertechnik system, which not only illustrates basic pneumatic functions but also allows students to build sturdy and realistic functional models of machines.