Introduction to Industrial Automation

tank automatic filling.

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Elements of Electro-Pneumatic Components 

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175

5.8   Circuits for Electro-Pneumatic Automation

In every electro-pneumatic application of automation, initially the pneumatic operation diagram 

should be designed. This diagram includes the pneumatic circuit for the flow of the pressurized air, 

pneumatic cylinders, valves, control devices, and the corresponding connection of all of them. In 

general, the pneumatic circuit expresses the logical flow of the pressurized air, as well as the logic 

behind the operation of the pneumatic cylinders, due to the action of the pressurized air.

If the pneumatic automation circuit also includes valves with solenoids, then a separate electrical 

automation circuit should also be designed for proper completion of the industrial automation, a 

circuit that will solely control the operation of the electro-valves. For example, in Figure 5.18 a simple 

pneumatic and electrical circuit is presented for controlling the operation of a single-acting cylinder 

with an automatic return. When the cylinder is connected to the pressurized air source, the piston 

rod is extracted, while when the cylinder is connected with the air exhaust line, the rod returns to 

its initial position due to the return spring. The electromagnetic valve supplies pressurized air to the 

cylinder when it is energized, while it connects the cylinder to the exhaust line when it is not ener-

gized. This operation is presented in the pneumatic circuit of Figure 5.18a. In this case, the extension 

of the piston rod activates a limit switch, whose contact should be utilized for the automatic return of 

the piston to its initial position. The implementation solution for this problem is presented in Figure 

5.18b, which consists of the electrical circuit of the pneumatic automation. If the extension of the 

piston rod lasts a long time, this movement can be interrupted through a STOP button.

In Figure 5.19, the pneumatic and electrical automation circuit for the control of a lifting ramp 

of light objects is presented. We would also like the ramp to stop in any position of this lifting 

stroke. For this automation problem, the pneumatic equipment contains, as shown in Figure 5.19a, 

a double-acting cylinder, a four-way, three-position electro-valve, and an air compressor with the 

pressurized air tank. In Figure 5.19b, the corresponding electrical circuit of the automation is also 

presented. Except from the classical START-STOP operation of the air compressor, the rest of the 

Limit

switch

Coil a

 

(a)

Pneumatic components and limit switch

N

d

R

d

START

 

STOP

a

Limit

switch

d

(b)

Automation circuit