Introduction to Industrial Automation

Table 5.1  Symbolic Representations of Directional Valves and Their Operations

The switching positions of a valve are represented by a 

rectangle

The number of adjacent rectangles expresses the equal 

number of switching positions of the valve

The air flow path and its direction at each switching 

position inside the valve, is represented by an arrowed 

line

The air flow shut-off is indicated by a ‘T’ symbol

The outer connections of air flow, usually called inlet 

or outlet ports, are indicated by lines drawn on the 

outside of the rectangle representing the normal or 

initial position

The other positions of the valve operation are obtained 

by shifting the rectangles until the flow paths inside 

the valve correspond to the outer connections

(a) The air exhaust flow path without pipe connection 

(free exhaust in the environment), (b) air exhaust flow 

path with pipe connection (closed pressurized-air 

network), (c) symbol of a pressurized-air source

(a)

(b)

(c)

Compressed airway

 is open

Compressed airway

 is closed

Pneumatic symbol of a

two-port, two-position

directional control valve

Outlet

Figure 5.9  The two operation states of a two-port, two-position directional control valve and