Introduction to Industrial Automation

noid and return spring (a), and with two solenoids and a return spring (b).

(a)

Non-energized

Energized

(b)

Non-energized

s

1

s

2

Solenoid S

1

 energized

s

1

s

2

Solenoid S

2

 energized

s

1

s

2

Figure 5.16  Operation of two basic direction control valves: (a) a 3/2 direction valve, (b) a 4/3 

directional valve, and the air flow paths in energized or non-energized state.

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  Introduction to Industrial Automation

5.7.5   Pneumatic Actuation of a Valve

As mentioned in Section 5.1, a pneumatic automation system can be fully pneumatic. In this case, 

the pneumatic equivalents of the electrical buttons, the limit switches, the selecting switches, etc., as 

well as the logical units (based on Boolean algebra) such as AND, OR, etc., exist, thus allowing the 

implementation of simple or complex functions with the physical magnitude to be pressurized air 

and not an electrical current. This enables the synthesis of a complete pneumatic industrial automa-

tion system, without the utilization of electrical components.

The pressurized air, the flow direction of which is being controlled by a valve, can be uti-

lized also for valve actuation. In Figure 5.17a, a pure pneumatic circuit for the extension and 

retraction of a single-acting cylinder is presented. Furthermore, in Figure 5.17b the automatic 

execution of a tank filling with only pneumatic devices is indicated. In all these cases, either 

in a full pneumatic or electro-pneumatic circuit, the logic that describes the operation of the 

automation is exactly the same. The only differing factor is the physical variable, pressurized 

air, or electrical current.

(b)

(a)

Pressure  signal

(air pilot)

No pressure signal 

Figure 5.17  Pure pneumatic actuation of a valve and a corresponding application: (a) Pneumatic 

actuation of a 3/2 valve by another button-type 3/2 valve and (b) pure pneumatic circuit for