Graphic Representations of Electro-Pneumatic Circuits

Pneumatic and Electric Circuit Diagrams


Circuit diagrams for electro-pneumatic control systems consist of a pneumatic plan that shows how the individual pneumatic components are connected to one another and interact and an electrical circuit diagram that illustrates how the electric components are combined.

Pneumatic Circuit Diagram

In pneumatic diagrams the elements are represented by standardized symbols. These are arranged in the diagram according to their function:

Working elements at the top of the diagram (e.g. cylinders)
Restrictor and return valves underneath them
Actuators (directional control valves) underneath them
Power supply at the bottom left

Every component has a unique label consisting of the following elements:

Machine number followed by a hyphen (only required when the diagram includes more than one machine)
Circuit number (numeral)
Component label (letter from the following table)
Component number (numeral)

The following table lists the labels for different component types.

Component Label
Compressors P
Working elements A
Drive motors M
Signal sensors S
Valves V
Valve solenoids Y
Other components Z

Within each circuit the components of the same component type are labeled in numerical order from bottom to top and from left to right.

Electric Circuit Diagrams

There are various types of circuit diagram available for representing electrical circuits. These are used depending on the application. The following considers only that type of circuit diagram relevant to the representation of electro-pneumatic control circuits. All electrical components are represented (as in the pneumatic diagrams) by schematic symbols and the electrical connections between them are also shown. Various parts of a single component may be shown in a variety of different places. Such a diagram is said to have an exploded view. Normally open and normally closed relay contacts can thus be shown distributed throughout the diagram, to make it easier to understand.

The symbols are drawn from bottom to top and from left to right. Relays and valve solenoids are always shown beneath their contacts.

Labeling of the elements is similar to that used in the pneumatic diagram. The following table lists the corresponding component labels. Circuit numbers are only required if the corresponding element (e.g. a valve solenoid) also appears in the pneumatic diagram.

Component Label
Limit switch, operating switch S
Reed switch, pressure switch B
Indicator H
Relays, fuses and circuit breakers K
Valve solenoids Y


The electric circuit diagram is drawn in its inactive state (i.e. with the power switched off). Any limit switches that are activated in this state are labelled with a double arrow. The relevant contacts are also shown in their active state. The graphics below should clarify this.

Activated normally closed contact activated-normally-closed-contact.jpg
Activated normally open contact activated-normally-open-contact.jpg


The graphic below shows an example of a circuit diagram for a pneumatic control system, consisting of a pneumatic diagram (top) and an electric circuit diagram (bottom). It can be seen that the solenoid 1Y1 of valve 1V1 appears in both diagrams and so it is labeled identically in both.



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