Understanding Basic Fluid Power & Electrical Symbols and Their Analogies

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Graphic symbols are used to indicate the components that make up a circuit. While they do not indicate the physical layout of the components on a machine, they provide an indication of how the components interface and interact within the system. As illustrated in Fig. 1.6, hydraulic, pneumatic, and electrical systems are analogous in many ways.

Fluid power and electrical symbols and schematic diagrams are introduced throughout this study manual. The internationally recognized standard for fluid power symbology (including some associated electrical components) is ISO 1219-1 Graphical Symbols and ISO-1219-2 Circuit Diagrams. In the United States and much of North America, the standard for electrical symbology is IEEE 315 (former ANSI Y32.2 and CSA Z99) Graphic Symbols for Electrical and Electronics Diagrams and to a lesser extent, NEMA ICS 19, Diagrams, Device Designations and Symbols. Internationally, IEC 60617 Graphical Symbols for Diagrams is the recog-nized reference. Component-level references for hydraulic, pneumatic, and electrical symbols can also be found in the Fluid Power Symbology Guide and the Fluid Power Reference Handbook, both available from the IFPS.

General rules of symbology worth noting:

Symbols represent functions, methods of operation, and external connections. They are not intended to show component construction, physical location, or orientation.
Unless noted, symbols are normally drawn in the unactuated or neutral condition.
For complex symbols, only functional connections need be shown.
Two or more symbols indicating a single device are typically enclosed inside a thin line.

Test Your Skills

1. Graphic symbols:
a. Reference the metric system of units.
b. Show the exact location and layout of components.
c. Are a symbolic representation of the components that make up a circuit.
d. Are drawn in their actuated condition.
e. Are identical for pneumatic and hydraulic components.