Introduction to Industrial Automation

5.6   Calculations in the Case of Pneumatic Cylinders

In Figure 5.8a, the internal state of a pneumatic cylinder is depicted; the pressurized air of pressure 

P has been applied, and the moving piston has an area of A. In general, the force that is generated 

in a surface A, under a pressure P is provided by:

 

F AP

=

where F is the force in N, A is the area in m

2

, and P is the pressure in N/m

2

 (1 bar = 10

5

 N/m

2

).

If the area A is representing the area of the piston in a pneumatic cylinder, the friction that is 

generated on the walls of the cylindrical surface due to the movement of the piston and the force 

of the spring (if it exists) should be taken into consideration. The friction is in general calculated as 

a percentage (%) of the nominal force F and varies from 5–20%, depending on the type of fitting 

for the piston in the internal surface of the cylinder. Thus, we have:

 

Single-acting cylinders:

F

F F

F

real

friction

sprin

= −

−

gg

friction

spring

where

F

F

F

the spring force

= −

=

5 20%

Air inlet

Air inlet

Piston seal

Figure 5.7  Cylinder for altering the translation movement into a rotational one.

A

P

F

(a)

Out stroke

In stroke

D

d

(b)

P

P

P

Figure 5.8  Calculation of the force applied by a pneumatic cylinder (a), and the difference