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Applied Industrial Technology

Pneumatics and Hydraulic Diagrams

     There is no record of manís first uses of air to do work.   One of the first pneumatic devices was the blow gun used by primitive man. In the latter part of the eighteenth century, heated air was used to carry the first balloon aloft. The heated air, being lighter than the surrounding air, caused the balloon to rise.  Every age of man has witnessed the development of devices which used air to do work. However, man used air to do work long before he understood it. The development of pneumatics depended on closely fitted parts and the development of gaskets and packings. Since the invention of the air compressor, pneumatics has become a very reliable way to transmit power.  Probably one of the most common uses of pneumatic power is in the operation of pneumatic tools. However, you should understand that pneumatics is also of great importance in large and complex systems as well.

     While having a knowledge of system components is essential, it is difficult to understand the interrelationship of these components by simply watching the system operate. The knowledge of system interrelation is required to effectively troubleshoot and maintain a pneumatic system. Diagrams or drawings are a valuable aid in understanding the operation of the system and in diagnosing the causes of malfunctions. To troubleshoot pneumatic systems intelligently, a technician must be familiar with the system on which he or she is working. The technologist must know the function of each component in the system and have a mental picture of its location in relation to other components. This can best be done by studying the diagrams of the system.  A diagram may be defined as a graphic representation of an assembly or system that indicates the various parts and expresses the methods or principles of operations. The ability to read diagrams is a basic requirement for understanding the operation of pneumatic systems. Understanding the diagrams of a system requires having a knowledge of the symbols used in the schematic diagrams.

     Some of the symbols frequently used in fluid power systems are available for review by clicking on this pneumatics and hydraulic symbols link.  Some rules applicable to graphical symbols for pneumatic and hydraulic diagrams are as follows:

1. Symbols show connections, flow paths, and the function of the component represented only. They do not indicate conditions occurring during transition from one flow path to another; nor do they indicate component construction or values, such as pressure or flow rate.

2. Symbols do not indicate the location of ports, direction of shifting of spools, or position of control elements on actual components.

3. Symbols may be rotated or reversed without altering their meaning except in cases of lines to reservoirs and vented manifolds.

4. Symbols may be drawn in any size.

5. Each symbol is drawn to show the normal or neutral condition of each component unless multiple circuit diagrams are furnished showing various phases of circuit operation.

Pictorial Diagrams

Pictorial diagrams show the general location and actual appearance of each component, all interconnecting piping, and the general piping arrangement. This type of diagram is sometimes referred to as an installation diagram. Diagrams of this type are invaluable to maintenance personnel in identifying and locating components of a system.

Cutaway Diagrams

Cutaway diagrams show the internal working parts of all pneumatic components in a system. This includes controls and actuating mechanisms and all interconnecting piping. Cutaway diagrams do not normally use symbols.

Graphic Diagrams

The primary purpose of a graphic schematic diagram is to enable the maintenance person to trace the flow of fluid from component to component within the system. This type of diagram uses standard symbols to show each component and includes all interconnecting piping. Additionally, the diagram contains a component list, pipe size, data on the sequence of operation, and other pertinent information. The graphic diagram does not indicate the physical location of the various components, but it does show the relation of each component to the other components within the system.