Introduction to Industrial Automation

5.5   Pneumatic  Devices

Pneumatic devices can be split into two categories. The first contains the devices that are able to 

transform the energy of the pressurized air in a directional or rotational motion, such as pneu-

matic cylinders and motors, which are also called “pneumatic actuators”. The second category 

includes the devices that control or regulate the operation of pneumatic cylinders and motors, 

which mainly contains the various valve types.

5.5.1   Single-Acting  Cylinders

In the case of single-acting cylinders, pressurized air is applied only on one of the sides of the cylinder 

and mechanical work is produced only in one direction during cylinder extension. In Figure 5.3, 

1

2

3

4

5

Equivalent pi

pe

 leng

th (m)

80

60

50

40

30

20

10

8

6

5

3

2

1

0.8

0.6

0.5

0.4

0.3

0.2

15 20

30 40 50 60 80 100 150 200 300 400

1

2

3

4

5

Two-way valve

Angular valve

T-connector

Regulator valve

90°-curve connector

Figure 5.2  Nomogram for the equivalent length calculation of some types of equipment.

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  Introduction to Industrial Automation

a section of a single-acting cylinder is presented, where the basic parts of the cylinder are also depicted, 

such as the piston, the pressurized air inlet, the rod, the returning spring, and the elastic O-rings for 

the sealing of chambers, with the piston and the rod acting as the only moving parts of the cylinder. 

The application of pressurized air in the corresponding air inlet causes a corresponding extension 

of the piston rod. The return of the piston rod to the initial resting position takes place either based 

on the embedded return spring or with the application of an external force. Thus, the force applied 

from the return spring should be adequate in order to allow for a retraction of the cylinder with an 

increased speed. In the case of single-acting cylinders, the movement of the rod is restricted by the 

physical length of the spring, which is usually 10 cm in length. Some of the most common applica-

tions for single-acting cylinders include the cases of actuating materials, such as tightening, tossing, 

lifting, promoting, feeding, and vibrating. The single-acting cylinders are produced in two basic 

forms, presented in Figure 5.4. These types are contracted and elongated cylinders, and if no pressur-

ized air is energized to it, they are similar to the NO and NC types of electric contacts. The designs 

depicted in Figure 5.4 also indicate the symbols in the simple graphical representation of single-

acting cylinders that are used during the design of automations with pneumatics.