MEM341_Chapter 13_Pneumatic circuits

13.0 Pneumatic circuits

A pneumatic circuit consists of a variety of components arranged so that a useful task can

be performed, such as:

o compressors

o receivers

o filters

o pressure regulators

o lubricators

o mufflers

o air dryers

o actuators

o control valves

o conductors

In a pneumatic circuit the force delivered by a cylinder and the torque delivered by a

motor are determined by the pressure levels established by pressure regulators placed at

the desired location in the circuit.

The linear speed of the pneumatic cylinder and the rotational speed of an air motor is

determined by flow control valves placed at the desired locations in the circuit.

The direction of flow in various flow paths is established by the proper location of

directional control valves. After the pressurized air is spent driving the actuators, it is

then exhausted back into the atmosphere.

When analyzing or designing a pneumatic circuit, the following four important

considerations must be taken into account:

o Safety of operation

o Performance of desired function

o Efficiency of operation

o Cost

MEM341_Chapter 13_Pneumatic circuits

13.1 Graphical symbols

Component Symbol

Filter

Regulator

Lubricator

FRL (filter, regulator, lubricator)

Silencer

Check valve

Shuttle valve

MEM341_Chapter 13_Pneumatic circuits

Component Symbol

Three way push button valve

Four way push button valve

Palm button valve

Limit valve

Hand lever operated four way valve

MEM341_Chapter 13_Pneumatic circuits

Component Symbol

Solenoid actuated DCV

Double acting pneumatic cylinder

Air motor

13.2 Basic pneumatic circuits

Pneumatic circuits are similar to hydraulic circuits

One difference is that no return lines are used in pneumatic circuits because the exhausted

air is released directly into the atmosphere.

Also, no input device (i.e. pump) is shown, because pneumatic circuits use a centralized

compressor as their source of energy.

MEM341_Chapter 13_Pneumatic circuits

Basic pneumatic circuit

Figure above shows a basic pneumatic circuit consisting of a 2-way DCV, single acting

cylinder.

o The return stroke is accomplished by a compression spring located at the rod end

of the cylinder

o When the push button valve is actuated, the cylinder extends

o The cylinder retracts when the valve is deactivated

o Needle valves V1 and V2 permit speed control of the cylinder extension and

retraction strokes

Basic pneumatic circuit (double acting)

Figure above shows a basic pneumatic circuit consisting of a 2-way DCV, double acting

cylinder.

o double acting cylinder requires a 4-way DCV

o Actuation of the push-button valve extends the cylinder

MEM341_Chapter 13_Pneumatic circuits

o The spring offset mode causes the cylinder to retract under air power.

Air-pilot control of a double acting cylinder

MEM341_Chapter 13_Pneumatic circuits

MEM341_Chapter 13_Pneumatic circuits

MEM341_Chapter 13_Pneumatic circuits

MEM341_Chapter 13_Pneumatic circuits

13.3 Pneumatic circuit application

The application of pneumatic circuits is very extensive. The following are some

examples.

a. Transport system

i. Figure below shows a simplified industrial transport system.

ii. When the button is pushed, the cylinder will push one of the goods from the shelf

onto the transport belt.

iii. When the button switch is released, the cylinder will retract automatically.

MEM341_Chapter 13_Pneumatic circuits

b. Vehicle door operation system

i. Pneumatic circuits can be used to operate the doors of public vehicles.

ii. Assuming the opening and closing of the doors are controlled by two button

switches ON and OFF.

iii. When the button is switch ON is pressed, the doors will open. When the button

switch OFF is pushed, the doors will close.

iv. Figure below shows a pneumatic circuit that can be used to operate the doors of

vehicles.

MEM341_Chapter 13_Pneumatic circuits

Tutorial Questions

1. What does the circuit of Figure 1 accomplish when the manual shutoff valve V1 is opened?

Figure 1

2. Consider the circuit of Figure 2

a. What happens to the cylinder when valve V4 is depressed?

b. What happens to the cylinder when valve V5 is depressed?

Figure 2

MEM341_Chapter 13_Pneumatic circuits

3. For the circuit of Figure 3, what happens to the cylinders in each case?

a. Valve V1 is actuated and held

b. Valve V1 is released and valve V2 is actuated and held. Valves V3 and V4 are sequence

valves.

Figure 3

4. For the circuit in Question 3, based on Figure 3, cylinder 1 will not hold against a load while

cylinder 2 is retracting. Modify this circuit by adding a pilot check valve and appropriate piping

so that cylinder 1 will hold while cylinder 2 is retracting.

MEM341_Chapter 13_Pneumatic circuits

5. The pneumatic system of Figure 4 contains a double-rod cylinder controlled by two three-way,

two-position directional control valves. Describe the four operating conditions for this system.

Figure 4