UNIVERSITY OF MAURITIUS
FACULTY OF ENGINEERING
MECHANICAL AND PRODUCTION ENGINEERING DEPARTMENT
COMPILED by S. Venkannah
Let’s Talk PNEUMATICS – FTOSP 1261
Lecture 3
TYPES OF DIAGRAMS
There are many types of diagrams. Those that are most pertinent to fluid power systems are discussed below.
SCHEMATIC LAYOUT: The purpose of the schematic layout is to demonstrate the position of the working units on
a machine or other kind of device, simultaneously giving precise information on the type and position of mounting.
PROGRAM FLOW: chronological relationships between steps in an operation which add up in sequence to form the
complete work program.
PROGRAM FLOWCHART: A program flowchart groups together all t he steps of a program and the motions
involved illustrating them diagrammatically in chronological sequence starting from the top.
LOGIC PLAN: It clearly states the interlinking interdependencies and flow of signals within a control system. The
logic plan serves as a means of communication between electrical, electronic and pneumatic engineers. It dose not
specify the actual equipment components of a control system.
FUNCTION DIAGRAM: e.g. travel-step diagram, travel-time diagram, travel-step-time diagram.
Travel-step diagram: Diagram representing the state of the most important elements , primarily working
elements, of the complete elements of a control system as a function of the separate control steps.
Travel-time diagram: Diagram representing the state of the most important elements , primarily working
elements, of the complete elements of a control system as a function of time.
Travel-step-time diagram: Diagram representing the state of the most important elements , primarily
working elements, of the complete elements of a control system as a function of time and control steps.
CIRCUIT DIAGRAM: Diagram representing all components of a control system together with their lines and
connections.
S. Venkannah
Jan 2006
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UNIVERSITY OF MAURITIUS
FACULTY OF ENGINEERING
MECHANICAL AND PRODUCTION ENGINEERING DEPARTMENT
COMPILED by S. Venkannah
Pictorial Diagrams
Pictorial diagrams show the general location and actual appearance of each component, all interconnecting
piping, and the general piping arrangement. This type of diagram is sometimes referred to as an installation
diagram. Diagrams of this type are invaluable to maintenance personnel in identifying and locating
components of a system.
S. Venkannah
Jan 2006
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UNIVERSITY OF MAURITIUS
FACULTY OF ENGINEERING
MECHANICAL AND PRODUCTION ENGINEERING DEPARTMENT
COMPILED by S. Venkannah
Cutaway Diagrams
Cutaway diagrams show the internal working parts of all fluid power components in a system. This includes controls
and actuating mechanisms and all interconnecting piping. Cutaway diagrams do not normally use symbols.
S. Venkannah
Jan 2006
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UNIVERSITY OF MAURITIUS
FACULTY OF ENGINEERING
MECHANICAL AND PRODUCTION ENGINEERING DEPARTMENT
COMPILED by S. Venkannah
Graphic Diagrams
Graphic Diagram
The primary purpose of a graphic (schematic) diagram is to enable the maintenance person to trace the flow of fluid
from component to component within the system. This type of diagram uses standard symbols to show each
component and includes all interconnecting piping. Additionally, the diagram contains a component list, pipe size,
data on the sequence of operation, and other pertinent information. The graphic diagram does not indicate the
physical location of the various components, but it does show the relation of each component to the other
components within the system.
Combination Diagrams
A combination drawing uses a combination of graphic, cutaway, and pictorial symbols. This drawing also includes
all interconnecting piping.
NOTE: 1 bar = 14.7 psi
S. Venkannah
Jan 2006
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UNIVERSITY OF MAURITIUS
FACULTY OF ENGINEERING
MECHANICAL AND PRODUCTION ENGINEERING DEPARTMENT
COMPILED by S. Venkannah
Example 1: The piston rod of a single acting cylinder is to advance when the air is applied. When the air is
removed, the piston is to automatically return to the initial position.
Soln.: A valve is to create the signal when a pushbutton is pressed and to cancel this signal when the pushbutton is
released.
Single acting cylinder with one supply connection and one exhaust and spring return
3/2 way DCV, pushbutton for operation and spring return
Supply air source
Example 2: The piston rod of a double acting cylinder is to advance when a pushbutton is operated and to return to
the initial position when the pushbutton is released. The double acting cylinder can carry out work in both directions
of motion due to the full air supply pressure being available for extension and retraction..
Soln. A valve is to create a signal and cancel another when the pushbutton is pressed and to change over the signals
when the pushbutton is released. The circuit would consist of the following:
Double acting cylinder with 2 supply connections
4/2 way DCV; pushbutton for operation and spring return
Supply air
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Jan 2006
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UNIVERSITY OF MAURITIUS
FACULTY OF ENGINEERING
MECHANICAL AND PRODUCTION ENGINEERING DEPARTMENT
COMPILED by S. Venkannah
SYMBOLS: Symbols are used to represent all t he components used in fluid power to simplify the circuits. The
elements are represented by symbols which indicate the function of the element. There are a number of important
symbols for accessories which are utilised in conjunction with pneumatics e.g. exhaust air symbols, visual
indicators and the methods of connection of components. There are standards available for the representation of
circuits and all design should be made according to the specified standard. Some of the symbols frequently used in
fluid power systems are shown below.
While the symbols shown below are not all encompassing, they do provide a basis for an individual working with
fluid power systems to build upon. Some rules applicable to graphical symbols for
fluid diagrams are as follows:
Symbols show connections, flow paths, and the function of the component represented only. They do not
indicate conditions occurring during transition from one flow path to another; nor do they indicate
component construction or values, such as pressure or flow rate.
Symbols do not indicate the location of ports, direction of shifting of spools, or position of control elements
on actual components.
Symbols may be rotated or reversed without altering their meaning except in cases of lines to reservoirs and
vented manifolds.
Symbols may be drawn in any size.
Each symbol is drawn to show the normal or neutral condition of each component unless multiple circuit
diagrams are furnished showing various phases of circuit operation.
S. Venkannah
Jan 2006
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UNIVERSITY OF MAURITIUS
FACULTY OF ENGINEERING
MECHANICAL AND PRODUCTION ENGINEERING DEPARTMENT
COMPILED by S. Venkannah
S. Venkannah
Jan 2006
7
UNIVERSITY OF MAURITIUS
FACULTY OF ENGINEERING
MECHANICAL AND PRODUCTION ENGINEERING DEPARTMENT
COMPILED by S. Venkannah
S. Venkannah
Jan 2006
8
UNIVERSITY OF MAURITIUS
FACULTY OF ENGINEERING
MECHANICAL AND PRODUCTION ENGINEERING DEPARTMENT
COMPILED by S. Venkannah
The energy supply and air preparation unit usually consist of the compressor, air reservoir and air service unit. The
symbols for the energy supply system can be represented as individual elements or as combined elements. The
choice between using simplified or detailed symbols is dependent upon the purpose of the circuit and its complexity.
In general where specific technical details are to be given such as requirements for non lubricated air or micro
filtering, then the complete detailed symbol should be used. If a standard and common air supply is used for all
components, then the simplified symbols can be used. For trouble shooting the detailed symbols are more suitable.
But the details might add to the complexity of the circuit.
The DCV is represented by the number of controlled connections and the number of positions. Each position is
shown as a separate square. The designation of the ports is important when interpreting the circuit symbols and the
valves as fitted to the physical system. To ensure that the correct lines, connections and valves are physically in
place, there must be a relationship between the circuit and the components used. Therefore all symbols on the
circuit must be designated and the components used should be labelled with the correct symbol and designations.
The methods of actuation of pneumatic DCV is dependent upon the requirements of the task. The Directional
Control Valve (DCV) may have a sensing, a processing or an alternating control function. The types of actuation
vary, i.e. mechanical, pneumatic, electrical and combined actuation. The symbols for the method of actuation is
detailed in ISO 1219.
When applied to DCV, consideration must be given to the method of initial actuation of the valve and also the
method of return actuation.
The Non return valve is the basis for the development of many combined components.
configurations for NRV, with and without spring return.
There are 2 main
Most flow control valves are adjustable. The one way flow control valve permits flow adjustment in one direction
only with the non return fitted. The arrow shows that the component is adjustable but does not refer to the direction
of the flow.
Pressure regulating valves are generally adjustable against spring compression. The symbols are distinguished
according to the following;
Pressure sensing downstream, upstream or external
Relieving or non relieving and fluctuating pressure
Adjustable or fixed settings
The symbol represents the pressure valve as a single position valve with a flow path that is either open or closed
initially. In the case of the pressure regulator the flow is always open, whereas the pressure sequence valve is closed
until the pressure reaches the limit value as set on the adjustable spring.
The linear actuators or cylinders are described by their type of construction and method of operation. The single
acting cylinder and the double acting cylinder form the basis for design variations. The use of cushioning to reduce
loads on the end caps and mountings during deceleration of the piston is important for long life and smooth
operation. The cushioning can be either fixed or adjustable. The cushioning piston is shown on the exhaust side of
the piston. The arrow indicates adjustable cushioning and not the direction of cushioned motion.
Rotary actuators are divided into continuous motion and limited angle of rotation. The air motor is normally a high
speed device with either fixed or adjustable speed control. Units with limited angle of rotation are fixed or
adjustable in angular displacement. The rotary actuator may be cushioned depending upon the load and speed of
operation.
REFERENCE:
1. Educational Materials + CDROM from FESTO Ltd.
2. Fluid Power with Applications by A. Esposito 5th Ed. Published by Prentice Hall
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