Fluid power schematic diagrams

These diagrams cover both pneumatic and hydraulic circuits. The symbols that we shall use do not illustrate the physical make-up, construction or shape of the components. Neither are the symbols to scale or orientated in any particular position. They are only intended to show the `function' of the component they portray, the connections and the fluid flow path.

Complete symbols are made up from one or more basic symbols and from one or more functional symbols. Examples of some basic symbols and some functional symbol.

Energy converters

Let us now see how we can combine some of these basic and functional symbols to produce a complete symbol representing a component. For example, let us start with a motor. The complete symbol.

The large circle indicates that we have an energy conversion unit such as a motor or pump. Notice that the fluid flow is into the device and that it  

is pneumatic. The direction of the arrowhead indicates the direction of flow. The fact that the arrowhead is clear (open) indicates that the fluid is air. Therefore, the device must be a motor. If it were a pump the fluid flow would be out of the circle. The single line at the bottom of the circle is the outlet (exhaust) from the motor and the double line is the mechanical output from the motor.

Now let us analyse the symbol 

• The circle tells us that it is an energy conversion unit.
• The arrowheads show that the flow is from the unit so it must be a pump.
•  The arrowheads are solid so it must be a hydraulic pump.
• . The arrowheads point in opposite directions so the pump can deliver the hydraulic fluid in either direction depending upon its direction of rotation.

• The arrow slanting across the pump is the variability symbol, so the pump has variable displacement.
• The double lines indicate the mechanical input to the pump from some engine or motor.

Summing up, we have a variable displacement, hydraulic pump that is bi-directional.