m7-drawings and diagrams
DESCRIPTION
MnulTRANSCRIPT
Abu Dhabi Gas Liquefaction Company Ltd
Basic Maintenance Technician Course
Module 7
Drawings and Diagrams
ADGAS Personnel & Training Division
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 2 of 61
Contents Page No. Abbreviations and Terminology ................................................ 4 1 Introduction ………………………………………………………….. 5 2 Engineering Drawings…………………………………………....... 7 3 Electrical Circuit Diagrams………………………………………... 11 4 Process Diagrams………………………………………..............… 15 4.1 Process Flow Diagrams (PFDs)…………………………... 18 4.2 Piping and Instrumentation Diagrams (P&IDs)………… 20 5 Title Blocks…………………………...........……………..............… 26 6 Pictorial Drawings………………………………………..............… 28 6.1 Oblique Drawings…………............................................... 29 6.2 Isometric Drawings…………............................................ 31 6.3 Freehand Sketching…………........................................... 33 6.4 Exploded Drawings…………............................................ 36 7 Orthographic Drawings………………………………………......... 37 7.1 Layout of Views………….................................................. 39 7.2 Types of Line…………...................................................... 45 7.3 Dimensions…………......................................................... 46 7.4 Sections…………............................................................... 48 7.5 Drawing Springs and Screws…………............................ 54 8 Piping Layout Drawings…………………………………............... 56 9 Summary………………………………….......................……......... 59
10 Glossary……………........................…………………………......... 60 Exercises 1 – 8............................................................................. 61
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 3 of 61
Pre-Requisite Completion of A.T.I. Maintenance Programme and ADGAS Induction Course
Course Objectives
The Basic Maintenance Technician Course is the first phase of the development programme intended specifically for the maintenance developee.
On completion of the Course the developee will have acquired an awareness of the equipment, terminology, and safety requirements related to the ADGAS LNG plant and Maintenance Training Workshops.
Module Objectives
On completion of this module, the developee will have an appreciation of the types of drawings and diagrams encountered by the Maintenance Technician.
He will be able to correctly :
• identify and state the purposes of engineering drawings, piping layouts, electrical circuit diagrams, PFDs and P&IDs
• identify information given in title blocks
• produce simple oblique and isometric freehand sketches
• identify and state the purposes of detail and assembly drawings
• identify types of lines used on orthographic drawings
• interpret information from simple orthographic drawings including sections and threaded components
• produce simple, dimensioned freehand orthographic sketches
Methodology The above will be achieved through the following:
• pre-test
• classroom instruction
• audio visual support
• tasks & exercises
• post-test
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 4 of 61
Abbreviations and Terminology
ANSI American National Standards Institute
BSI British Standards Institute
ISO International Standards Organisation
LNG Liquefied natural gas
P&ID Piping and instrumentation diagram
PFD Process flow diagram
R Radius
φ Diameter
Assembly A group of components fitted together
Component A part of a machine, electric circuit, etc.
Diagonal A sloping line, e.g. a line joining opposite corners of a square
Fittings (pipe) Items used to join sections of pipe, e.g. elbows, tees,
Flange Circular item for joining pipes or fitting pipes to equipment
Impurities Anything in a substance that stops it from being pure
Isometric A type of pictorial drawing
Legend A list giving the meanings of symbols used in a drawing
Liquefaction The process of turning something into liquid form
Oblique A type of pictorial drawing
Offset Not in line
Orthographic A type of drawing showing an object viewed from different directions, usually at 90o to each other, e.g. front, top, side
Projection A type of engineering drawing, e.g. isometric projection, orthographic projection.
Also the way that orthographic views are constructed by drawing horizontal and vertical lines between views.
Schematic A simplified diagram using symbols, particularly of an electric circuit
Signal A message, usually electrical, that causes something to happen
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 5 of 61
1 Introduction
Drawings and diagrams are one of the most important ways in
which engineers and technicians communicate.
They use international symbols instead of words wherever possible and are drawn
using rules, just like a language. If you understand the symbols and know the rules,
you can read most drawings and diagrams, whatever language you speak.
You can find all the rules and symbols that are needed to make and read drawings and
diagrams in International, National and Company Standards, e.g.:
• ISO (International Standards Organisation)
• ANSI (American National Standards Institute)
• BSI (British Standards Institute)
There is an important difference between a drawing and a diagram:
• A drawing shows the shape and size of an object or group of objects. Some
symbols may be used but, with practice, you can recognise the appearance of
an object from its drawing.
• A diagram, sometimes called a schematic, shows the flow of something and
what it flows through. This ‘something’ may be water, gas, electricity, or
anything else that can flow. It flows through pipes or wires and through
equipment such as pumps, instruments, resistors, etc. A diagram uses many
more symbols to represent objects than a drawing. It need not
show correct shape, size, distances or locations but does show
the correct order of equipment in the flow, i.e. what comes first, second, etc.
To represent is to stand in the place of something.
You communicate with someone when you give or receive information.
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 6 of 61
You will find that in practice, the word ‘drawing’ is often used to describe both
drawings and diagrams.
In this module you will look at the types of drawings and diagrams that you will see
while working as a technician for ADGAS. You will need to work with some more
than others, depending on whether you are a mechanical, electrical or instrumentation
technician. But, all maintenance technicians should be able to recognise all of these
types of drawings and diagrams. You should also know what type of information they
show and why they are needed.
The drawings described in this module are:
• engineering drawings (including piping layout drawings)
• electrical circuit diagrams
• process flow diagrams (PFDs)
• piping and instrumentation diagrams (P&IDs)
It is unlikely that any of you will have to produce these drawings but you will all need
to read drawings and make sketches at some time.
All technicians should be able to read engineering drawings as these are used to
describe the equipment you work with: pumps and compressors, electric motors and
switchgear, process instruments, etc.
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 7 of 61
2 Engineering Drawings
There are many types of engineering drawing and you will look at these in more detail
later in this module. Engineering drawings show the shape and size of an object and
can give enough information to make the object. They may also show how a group of
objects fit together to form an assembly. This information is important if you are
going to take something apart for maintenance and even more important if you want
to re-assemble it correctly afterwards.
The two main types of engineering drawings are:
• pictorial drawings
• orthographic drawings
You will easily recognise an object from a pictorial drawing. They show a single
view that is something like a photograph. Figure 2.1 shows a photograph of an object
and a pictorial drawing of the same object.
Pictorial drawings give a good general idea of what an object looks like but some
parts will always be hidden. If you want to make the object, or if you want someone
else to make it for you, these drawings do not show enough information unless the
object is very simple.
Figure 2.1: Pictorial Drawing and Photograph of a Casting
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 8 of 61
Orthographic drawings show the object looked at from different directions: the front,
top, side, etc. Each of these drawings is called a view and they are drawn on the same
sheet. Three views are enough for many simple objects but more can be added if
needed.
Figure 2.2 shows an orthographic drawing of something you will recognise.
Figure 2.2: Orthographic Drawing of Aircraft
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 9 of 61
Figure 2.3 shows an orthographic drawing of the object in Figure 2.1.
See how the three views are located in the orthographic drawing in Figure 2.3.
• The front is chosen to show the general shape most clearly. The front view is
what you see if you look from directly in front of the object.
• The top view, or plan, is what you see if you look directly down from above
the object. See how it is drawn exactly above the front view.
• The side view is shown on the right of the front view. That means it is what
you see if you look from that side (the right side).
This layout of the three views is called ‘third-angle orthographic projection’. This is
the layout you will find on most orthographic drawings.
Figure 2.3: Third-angle Orthographic Projection of Figure 2.1
CASTING
Top view
Side viewFront view
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 10 of 61
Orthographic drawings can show all the details and all the dimensions needed to make
the object. But, you need to look carefully at all the views and to use your
imagination to picture the final shape of the object from the drawing (Fig. 2.4).
Figure 2.4: Imagining an Object from an Orthographic Drawing
CASTING
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 11 of 61
3 Electrical Circuit Diagrams
Electrical circuit diagrams show the connections and components in an electric
circuit. Electrical technicians use circuit diagrams to build circuits, search for faults
when troubleshooting and to identify isolation points to make electrical equipment
safe for maintenance or removal.
Unlike drawings, circuit diagrams do not show you what the finished circuit looks
like. They show you the path of the electricity as it flows through components and
equipment and the order in which it flows through them.
They use lines to represent wires and symbols to represent equipment and
components.
Wires are drawn as single straight lines on the diagram.
If two wires cross but are not joined, so electricity can not flow from one to the other,
they may be drawn in two ways, as shown in Figure 3.1.
OR
If two wires are joined so that electricity can flow from one to the other, they are
drawn as in Figure 3.2.
OR
Figure 3.1: Crossing Wires
Figure 3.2: Joined Wires
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 12 of 61
Some common electrical symbols for equipment and components are shown in Table
3.1.
Symbol Component
Battery
Alternating current supply
Switch
Light bulb
Indicator lamp
or
Resistor (fixed value)
or
Resistor (variable) Capacitor
Earth
Motor
Transformer
Fuse
Circuit breaker
Transistors
The best way to read any diagram that shows the flow of something around a circuit is
to start at the point where the flow starts. For a circuit diagram, flow starts at a power
supply.
Table 3.1: Circuit Diagram Symbols
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 13 of 61
Figure 3.3(a) shows a drawing of a simple electric circuit with a battery of cells
supplying a lamp through a switch. Figure 3.3(b) shows a diagram of the same
circuit.
Can you identify:
• the battery
• the switch
• the lamp
in the circuit diagram?
(a) Drawing of Lighting Circuit (b) Lighting Circuit Diagram
Figure 3.3: Simple Lighting Circuit
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 14 of 61
Figure 3.4 shows a circuit for an amplifier
Can you identify:
• resistors?
• capacitors?
• transformer?
• transistors?
• where wires cross without connecting?
• where wires are joined?
Figure 3.4: Amplifier Circuit
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 15 of 61
4 Process Diagrams
The LNG liquefaction process on Das Island takes a mixture of gases coming from
the gas fields or from ADMA-OPCO, removes the impurities,
separates the gases and turns them into liquids for export.
The main product from the process is liquefied natural gas (LNG).
There are two types of diagrams that describe the gas liquefaction process on the
plant:
• process flow diagrams (PFDs)
• piping and instrumentation diagrams (P&IDs)
Both of these types of diagram show the flow of fluid through pipes
and equipment as the gas is processed.
The purpose of a PFD is to describe the changes that are made to the fluid and the
main items of equipment that make those changes.
The purpose of a P&ID is to describe the way the process is controlled.
Both types of diagram use similar lines and symbols.
A fluid is something that flows, like a gas or a liquid.
To export something is to sell it to another country.
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 16 of 61
Pipes and wires are drawn as straight lines.
Some of these lines are shown in Table 4.1.
Line Type of pipe or wire
Pipes carrying the main fluid being processed
Pipes carrying other process fluids, cooling water, refrigerant, etc.
L L L L Pipes carrying hydraulic fluid (water or oil) to operate valves etc.
// // // // Pipes carrying air to operate valves etc.
Wires carrying low-voltage electrical signals for controllers, switches, etc.
Two pipes that cross but are not joined, so that fluid can not flow from one to the
other, are drawn as shown in Figure 4.1.
Two pipes that are joined, so that fluid can flow from one to the other, are drawn as
shown in Figure 4.2.
Table 4.1: Lines on PFDs and P&IDs
Figure 4.1: Crossing Pipes
(a) Fluid from the vertical pipe joins the flow in the horizontal pipe
(a) Fluid from both horizontal pipes flows into the vertical pipe
Figure 4.2: Joined Pipes
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 17 of 61
Some examples of common symbols for process equipment are shown in Table 4.2.
Symbol Equipment
Vessel (typical)
Valve (typical)
Pump (centrifugal)
Heat Exchanger
Compressors (centrifugal)
or Turbine/turbo-expander
The meanings of the symbols used may be shown on the diagram sheet in a section
called the legend. This is normally on the right of the diagram sheet, in the area above
the title block (Section 5).
The size of the symbol does not tell you the size of the equipment. A small valve has
exactly the same size symbol as a big one.
The best way to read a flow diagram is to follow the flow, starting where the fluid
enters the diagram. You will normally see the fluid entering the process at the left of
the diagram and flowing from left to right. In the ADGAS process, where lighter
fluids (gases) are separated from heavier fluids (liquids), the lighter fluids flow
towards the top of the diagram and heavier fluids towards the bottom (Fig. 4.3)
Table 4.2: Equipment Symbols
General flow direction
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 18 of 61
Remember, diagrams show how the fluid flows through pipes and equipment but they
do not show you what the system looks like on the plant.
4.1 Process Flow Diagrams (PFDs)
PFDs are diagrams that describe a process. They show what is happening to the fluid
in the simplest way.
PFDs show:
• the path of the fluids as they go through a process or part of a process
• the main items of equipment in the process
• some important instruments and controls may be shown
• important temperatures and pressures in the process may be shown
Process flow diagrams are very useful for process operators, but everyone working for
ADGAS should know what the plant does and how it does it. All maintenance
technicians maintain the equipment that processes the gas. You should know what
job each item of equipment does in the process.
Figure 4.4 shows a PFD of the Train III production process on Das Island.
Figure 4.3: General Flow Directions
General product flow direction
Ligh
t pro
duct
s H
eavy
pro
duct
s
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 19 of 61
Figure 4.4: Simplified PFD of Train III
FEED
52 b
ar g
REGE
NERA
TION
MRU
-350 C
ACID
GAS
CO2 /
H2S
-160
0 CTO
MAR
INE
LOAD
ING
LNG
1420 C
SULP
HUR
PIT
HEAT
ER50
%
50%
MAIN
COMB
USTI
ONCH
AMBE
R
COND
ENSE
R
COND
ENSE
R
REAC
TOR
TO M
ARIN
ELO
ADIN
GSU
LPHU
R
-70 C
TO M
ARIN
ELO
ADIN
GBU
TANE
-450 C
TO M
ARIN
ELO
ADIN
GPR
OPAN
E
AMBI
ENT
TEMP
ERAT
URE
(10-
430 C
)
TO M
ARIN
ELO
ADIN
GPE
NTAN
E
MCR
COMP
RESS
OR
FUEL
GAS
HPFL
ASH
DRUM
LPFL
ASH
DRUM
COLD
BOX
C3 R
EFRI
GERA
TION
ACID
GAS
TREA
TMEN
TDR
YING
REGE
NERA
TION
SEPA
RATO
RDE
A
PROP
ANE
CHILL
ERPR
OPAN
E
PROP
ANE
POTA
SSI
UM
CAR
BO
NAT
E
TOTR
AIN
I & II
MCR
CRYO
GENI
CEX
CHAN
GER
KO DRUM
GAS
MCR
LIQUI
D MC
R
INCI
NERA
TOR
TAIL
GAS
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 20 of 61
Can you identify:
• where the gas enters the process?
• different types of vessels and tanks—how many are there?
• pumps—how many are there?
• compressors—how many are there?
• heat exchangers—how many are there?
• where the main product (LNG) leaves the system?
• what other products does the process produce—where do they leave?
4.2 Piping and Instrumentation Diagrams (P&IDs)
P&IDs describe how the process equipment is controlled.
They show:
• pipes, hydraulic lines, instrument air lines, electric wires for instrument
signals
• equipment, valves, drain points
• instruments, where they are located and where their readings are displayed
• alarm, emergency shutdown and process control systems
P&IDs have many uses for the maintenance department as they identify equipment
and instruments and show where in the system you can find them. A P&ID does not
show you the exact place in the plant where these things are located but, if you follow
a pipeline from any point in the process, you will find everything in the same order as
it is shown on the diagram.
You should be able to locate the correct isolation valves and drain points on a P&ID
before working on any equipment in the plant.
Figure 4.5(a) is a drawing of the pipes and instrumentation on a small section of a
process.
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 21 of 61
Figure 4.5(b) shows the same information on a P&ID.
Look at this figure to see how the components shown on the drawing in Figure 4.5(a)
are represented on the P&ID in Figure 4.5(b).
(a) Drawing of Piping and Instrumentation
Figure 4.5: System Drawing and P&ID
(b) P&ID of the Same System
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 22 of 61
Three types of line are shown:
• main process line
• by-pass line around the pressure control valve
• control signal lines
Five valves are shown: they are different types (gate and globe valves) but the
symbols are similar.
They all use the same basic valve symbol with additions to show the
type of valve, e.g. for a ‘globe’ valve.
The pressure control valve, PCV 123, is operated by the control room pressure
recording controller, PIRC 123.
Instrument symbols are circles. They show where the instrument is located and
contain information to identify the instrument.
Instrument symbols are shown in Table 4.3.
Symbol Instrument Location
Mounted locally (fitted on or near the pipe or equipment where the reading is taken)
On a local panel (close to the pipe or equipment where the reading is taken)
Behind a local panel
On main control room panel
Behind main control room panel
Part of a computerised control system
Table 4.3: P&ID Instrument Symbols
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 23 of 61
Each item of equipment and instrument has its own identification made up of:
• letters at the beginning that identify the type of equipment or instrument, e.g.
pressure gauge, valve, etc.
• numbers that identify each item separately, as there are usually many similar
items in a process, e.g. there will be many pressure gauges with the same
identity letters but different numbers
• there may be more letters at the end that give other information
Some examples of typical identity letters are shown in Table 4.4.
Identification letters Instrument
FCV Flow Control Valve
LCV Level Control Valve
PCV Pressure Control Valve
PT Pressure Transmitter
PI Pressure Indicator
PRC Pressure Recording Controller
PC Pressure Controller
TI Temperature Indicator
Table 4.4: Instrument Symbols
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 24 of 61
If you look at Figure 4.5 you will see that there are five instruments shown:
(Figure 4.5 is repeated below)
• PI 123—Pressure Indicator
• TI 123—Temperature Indicator
• PT 123—Pressure Transmitter
• PIRC 123 —control room Pressure (Indicating and) Recording Controller
• PCV 123—Pressure Control Valve
You can see where these instrument are located by their symbols:
• PI 123; TI 123; PT 123 and PCV 123 are mounted locally on the pipes
• PIRC 123 is panel-mounted in the main control room
• PCV 123 is a valve. Because it is automatically controlled from PIRC 123 it
is a part of the instrumentation system so it is identified in an instrument
circle
Notice that the P&ID is not exactly the same shape as the drawing in Figure 4.5(a).
Now try Exercise 1 & 2
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 25 of 61
Figure 4.6 shows a P&ID of the plant simulator located at the ADGAS Training
Workshop.
This system pumps water from one drum to another and back again. The water can be
heated in drum 01-X-D-02. Because the fluid can flow in both directions, this
diagram does not follow the general rule of flow from left to right.
Your instructor will take you to the simulator where you can follow the flow of the
fluid on the P&ID and in the plant. Identify all the items shown on the P&ID and find
them on the plant simulator.
Now try Exercise 3
Figure 4.6: P&ID of Plant Simulator
M
M
S
S
S
S
SCALE ISSUE DATE REMARKS DRN ENGCHK
HV10
NOTES:
1. LSL-01/02 STOPS 01-X-G-01/02 RESPECTIVELY
2. HIGH PRESSURE ON PT-01/02 OPENS XV1/2RESPECTIVELY
3. LSHH-02 CLOSES FV1 AND OPEN XV1 AT THE SAME TIME
4. LSL-02 SWITCHES THE HEATER OFF
5. LSHH-01 CLOSES FV2AND OPENS XV2
6. XVI/2 ARE RE-CYCLE VALVES
LEGEND:
S
GATE VALVE
CONTROL VALVE
SOLENOIDOPERATED VALVE
PRESSURE RELIEFVALVE
HEATER ELEMENT
M
ELECTRIC MOTOROPERATED PUMP
LOGIC CONTROLLER
LOCALLY MOUNTEDINSTRUMENT
FRONT PANELMOUNTEDINSTRUMENT (IN CONTROL ROOM)
ABU DHABI GAS LIQUEFACTION COMPANY LIMITED
P&ID PLANT 01 - TRAIN X (SIMULATOR)TITLEMOD. No.
TRAIN - X DRG. No. EX3.1 ISSUE 1
01-X-G-02
K8PIC02
PT02
K4
K1
K6
LSHH 02
LSH 02
TT01
LSL 02
TY01
TY01
01-X-D-02
01-X-D-01
01-X-E-01
FY02A
FC02
FT02
FC01
FY01A
FT01 K3
K7
K2
K5
PIC01
PT01
LSHH 01
LSH 01
LSL 01
LT01
HV11
HV12
HV1
HV2HV3FV1
HV4
XY1
XV1
01-X-G-O1
FY1
HV5
HV6
XV2XY2
HV7
HV8
HV9
FV2 FY2 FEED WATER
PSV1
1 12.05.03 PNS
P R O V I S I O N A L
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 26 of 61
A
B
C D F
E
H
G
5 Title Blocks
All drawings and diagrams have a title block in the bottom right corner of the drawing
sheet. This title block shows standard information for all types of drawings and
diagrams. Figure 5.1 shows the standard ADGAS title block.
The information located in the sections A to H shown in Figure 5.1 is described in
Table 5.1.
Section Information
A Company Name
B Title or brief description of the drawing or diagram
C Drawing number to identify this drawing sheet
D Gas production train number: 1, 2, 3,etc. Used for process diagrams.
E Used for drawings but not diagrams. Shows the size of the drawn object relative to the actual object
F, G and H Modifications and issues tell you about changes made to the drawing
Additional information is written here: • Legend • Parts or Items List • Notes
ABU DHABI GAS LIQUEFACTION COMPANY LIMITED
0 2003 ISSUED FOR APPROVAL/COMMENTS
MOD No. TITLE
ISSUE DATE REMARKS DRN CHK ENG
DO NOT SCALE THIS PRINT ALL DIMENSIONS ARE IN mm UNLESS OTHERWISE STATED
SCALE TRAIN DRG No. ISSUE
Figure 5.1: Standard ADGAS Title Block
Table 5.1: Standard ADGAS Title Block Information
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 27 of 61
The title block often continues upwards above section A. This part can contain extra
information and notes including:
• the legend—symbols used on a diagram and their meanings
• materials and items list—identification of components and materials on a
drawing
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 28 of 61
(a) Cutaway of Piston Engine (b) Heavy Vehicle Axle
6 Pictorial Drawings
Pictorial drawings show as much of an object as possible in a single view. There are
two main types of pictorial drawings:
• oblique
• isometric
The same object is drawn using both these projections in Figure 6.1. The difference
is explained in Sections 6.1 and 6.2.
These drawings give a general idea of the appearance of an object and you may see
them in manufacturers’ manuals to illustrate a piece of equipment (Figure 6.2).
(a) Oblique Projection (b) Isometric Projection
Figure 6.1: Pictorial Drawings of a Turnkey
Figure 6.2: Isometric Technical Illustrations
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 29 of 61
Pictorial sketches of simple objects can be very useful in helping you to describe
something to someone. You can make quick, simple sketches using oblique drawings.
6.1 Oblique Drawings
An oblique drawing shows the true shape of the front face of the object. All vertical
edges are drawn as vertical lines but side edges are drawn at an angle, often 45o, to the
horizontal. This makes your drawing look like a solid object, even though you are
drawing it on a flat piece of paper.
To make the object look more realistic, you can draw the side edges that are going
away from you shorter than they really are. If you draw these about half their true
length the drawing looks better.
In Figure 6.3, which block looks like its edges are all the same length, (a) or (b)?
Now check them.
Block (b)’s edges are all the same length. Block (a)’s edges look all the same length,
but the side edges are half the length of the front and back edges.
If there are any circular parts or holes on the object, try to show them on the front
face. Any circles on the sides are not drawn as true circles.
(b)
Figure 6.3: Shortened Edges in Oblique Projection
(a)
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 30 of 61
The procedure for making an oblique drawing of the object in Figure 6.4 is described
below.
Draw the view you see if you are looking in the direction
of arrow A in Figure 6.4.
Draw the side edges that are going away from you all
at the same angle (B) to the horizontal. Angle B is
usually 45o.
Draw edges that are parallel to the front edges to
form a framework that contains the object.
Draw circular parts of the object.
Go over the outline of the object with a darker line.
You can then erase the lines you do not want.
Notice that the circles and half-circles on faces parallel
to the front are true shapes. Those drawn on the other faces are not,
they are distorted. If you sketch objects with circular parts you must
practice sketching true circles and distorted circles. There is some
help for this in Section 6.3.
Figure 6.4: Making an Oblique Drawing
A distorted shape has been changed from its original shape.
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 31 of 61
6.2 Isometric Drawings
Isometric drawings look even more realistic than oblique drawings, but they are a
little harder to draw. All vertical edges are drawn as vertical lines, but all horizontal
edges are drawn at 30o to the horizontal. These edges are drawn parallel to the
isometric axes shown in Figure 6.5.
The next step is to find the overall dimensions of the object you are drawing. Draw a
box that would just contain the object. Draw the edges of the box parallel to the
isometric axes. The size of the box you draw depends on the scale of your drawing.
For sketches, you can estimate lengths as long as they are in proportion, i.e. if one
edge is twice as long as another, draw it twice as long. The actual length is not so
important on a sketch.
Figure 6.6 shows an isometric drawing of an object. Its overall dimensions are
84mmx30mmx25mm.
Can you work that out from the
dimensions on the drawing?
Figure 6.5: Isometric Axes
Figure 6.6: Dimensioned Isometric
30o 30oHorizontal
Isometric axis Isometric axis
Isometric axis
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 32 of 61
This is how to make the drawing:
• Draw a box with its edges parallel to the
isometric axes. The length is about three
times the width and the height is a little less
than the width; this gives the correct
proportions.
• Next, draw the edges of the object. You can
imagine that the box you have drawn is a block
of material and you are cutting the object out of
that block.
• Now sketch in any curves or other details.
Notice that all the lines drawn so far are thin,
light lines. These are called construction lines.
Some are not wanted on the final drawing and, if
you draw them lightly, you can easily erase them
later.
• Now decide which lines make the outline of the
object. Go over these again, making them darker
and thicker. Then you can clean up your sketch
by erasing the construction lines you do not want.
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 33 of 61
6.3 Freehand Sketching
You do not have to be an artist to make good pictorial freehand sketches. Anybody
can do it if they take some care and follow the steps described.
Always start your drawing with light construction lines. You can make the final
outline darker when you are pleased with your drawing.
When you freehand sketch straight lines, start by marking
the start and end points of the line as shown in Figure
6.7. Then draw the line, always looking at the point
where the line will end.
For short lines, draw the line in one go, without taking
your pencil from the paper.
For long lines, draw the line using a number of short strokes of your pencil. This
helps to keep the line straight.
Remember, you can always turn the paper so that it is at a better angle for drawing the
line you want.
Curves are the most difficult part but there are some things you can do to help you to
sketch better curves.
Use your wrist as a turning point (Fig 6.8(a)), like the centre point of a compass.
Turn the paper as you draw the curve so that your wrist is in the most comfortable
position (Fig. 6.8(b))
Figure 6.7: Sketching a Straight Line
(a) (b) Figure 6.8: Drawing Curves
start end
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 34 of 61
Draw circles inside a square.
Draw lines joining the mid-points of the sides.
Draw the circle so that it just touches, but does not cross, the mid-
point of each side.
Go over the circle again to make it darker.
Then erase your construction lines.
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 35 of 61
If you need more points to draw your circle through, join opposite corners of the
square, these lines are the diagonals of the square. Now divide each line from the
centre to the corner roughly into three, as shown in Figure 6.9.
Draw the circle so that it just touches the marks farthest from the centre and is
perpendicular to the diagonals.
To draw the distorted circles on isometric and oblique drawings, draw them inside an
isometric or oblique square, as shown in Figure 6.10.
Figure 6.9: Extra Points for Sketching Circles
Figure 6.10: Sketching Oblique and Isometric Circles
Now try Exercise 4
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 36 of 61
6.4 Exploded Drawings
Manufacturers often use exploded drawings in their manuals to show the parts of an
assembly and how they fit together. Figure 6.11(a) and (b) shows exploded drawings
of two types of pump.
Perhaps you can see why they are called ‘exploded’ drawings. The parts that make up
the assembly are all separated but they are shown in their correct relative positions.
You can imagine that this is how something would look if it had been photographed
just as an explosion took place.
Exploded drawings are very useful for maintenance work as they show
the order of dismantling and re-assembling equipment.
(a) Vane Pump
Figure 6.11: Exploded Drawings
(b) Gear Pump
To dismantle something is to take it apart.
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 37 of 61
7 Orthographic Drawings
To show enough information for most engineering purposes, orthographic drawings
are needed.
There are two main types of orthographic drawing:
• detail drawings
• assembly drawings
Detail drawings show a single part with all the dimensions needed to make that part.
Any other information needed is also put on the detail drawing. Most items of
equipment are made of many parts. Each part has its own detail drawing.
Assembly drawings show a group of parts fixed together. They may show some
important dimensions that can not be shown on the detail drawings, like the overall
size of the assembly. Assembly drawings have an items list where all the parts and
their detail drawing numbers are identified. Any other information needed for the
assembly is shown on the assembly drawing.
Sometimes, when you dismantle a piece of equipment, you can remove a section that
is a number of parts fixed together. This is called a sub-assembly, as it is a part of the
main assembly. Sub-assemblies have their own sub-assembly drawings.
Every piece of equipment that you work on will have its own set of drawings that may
include all of these:
• assembly drawings of the whole item
• sub-assembly drawings of groups of parts that can be removed as one piece
• detail drawings of each separate part
Standard parts like nuts, bolts, washers, etc. are listed in the items list of the assembly
and sub-assembly drawings. They will not usually have their own detail drawings.
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 38 of 61
Figure 7.1 shows a typical assembly drawing with its sub-assembly and detail
drawings.
DRG No A/0001
ABU DHABI GAS LIQUEFACTION COMPANY TITLE
PULLEY
ALL DIMENSIONS IN mm
DRG No A/0001
ABU DHABI GAS LIQUEFACTION COMPANY LIMITED
TITLE PULLEY ASSEMBLY
DRG No A/0007
ABU DHABI GAS LIQUEFACTION COMPANY LIMITED
TITLE PULLEY SUB-ASSEMBLY
(c) Assembly Drawing
(b) Sub-assembly Drawing (a) Detail Drawing
Figure 7.1: Full Set of Orthographic Drawings
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 39 of 61
7.1 Layout of Views
You saw how three views of a third-angle orthographic drawing are arranged on the
paper in Section 2. Some objects need more views to show all their details, some
need fewer. Figure 7.2 shows an object and the six directions that you could view it
from to look at all its sides. The man is shown viewing it from the normal three sides
only.
To draw all these orthographic views, follow the rules you learnt in Section 2.
Choose the side that best shows the shape of the object and make that the front view.
This side is coloured red in Figure 7.2.
In third-angle projection:
• the view of the object you see when you look from above the front view, you
draw above the front view
• the view of the object that you see from the right of the front view, you draw
on the right of the front view
Figure 7.2: Six Possible Orthographic Viewing Directions
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 40 of 61
Figure 7.3 shows a third-angle projection drawing of the object shown in Figure 7.2
showing views from all six sides.
Remember that when you read a third-angle drawing:
• a view drawn above is what you see when you look from above
• a view drawn on the right is what you see when you look from the right
• a view drawn on the left is what you see when you look from the left
• etc.
For most objects, three views are enough:
• front view
• top view or plan
• one end view—viewed from the side where you can see the most detail
Notice again how the views are lined up exactly. This is done by ‘projecting’ lines
from one view to another as shown in Figure 7.4.
Figure 7.3: Six possible Orthographic Views
A
B
D D
E C
C E
F
F
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 41 of 61
Notice also in Figure 7.4 the symbol at the bottom.
You will find some orthographic drawings that have views arranged differently.
These are first-angle orthographic projections. Most drawings are now made in third-
angle projection, but you may see some first-angle drawings so it is best to know how
to recognise them.
Figure 7.5 shows the same object again, but this time drawn in first-angle projection.
Figure 7.5: Three-view First-angle Orthographic
Figure 7.4: Three-view Third-angle Orthographic
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 42 of 61
FrontLeft side
Notice that the views look the same, but are located in different places.
In first-angle drawings the views are positioned on the opposite side:
• a view drawn below is what you see when you look from above
• a view drawn on the right is what you see when you look from the left
• etc.
Notice the symbols at the bottom of Figures 7.4 and 7.5.
They are similar but not quite the same. These symbols tell
you if a drawing is in first or third-angle projection. Can
you see the difference?
The symbol represents a cone with its top cut off.
Look at it from the front and you see a triangle with its top cut off.
Look at it from the left side and you see two circles: one is the small end
and the other the big end.
In third angle, you would draw this end view, seen from the
left, on the left.
This symbol means that the drawing is in third-angle
projection.
In first angle you would draw this end view, seen from the
left, on the right.
This symbol means that the drawing is in first-angle
projection.
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 43 of 61
Always look for this symbol on an orthographic drawing, usually in the title block. If
it is not there you will have to use your knowledge to decide if the drawing you are
looking at is in first- or third-angle projection.
Figure 7.6 shows six examples of orthographic drawings labelled A to F. An
isometric of the object drawn is shown next to each one. An arrow points to the
‘front’ of each object.
Are these drawings in first or third-angle projection?
Cover the orthographic views. See if you can imagine the three orthographic views
by looking at the isometric.
Now cover the isometric views. See if you can imagine what the object looks like in
the isometric view.
Do this for each of the objects in Figure 7.6.
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 44 of 61
Figure 7.6: Orthographic Drawings
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 45 of 61
7.2 Types of Line
Two things help to tell you what a line represents an orthographic drawing:
• whether the line is broken or unbroken
• the thickness of the line
The main lines used are shown in Table 7.1.
Line Description Use
Thick, unbroken line Outlines and edges that can be seen
Thin, unbroken Dimension, extension and leader
lines. Also cross hatching for sections
Thin, unbroken and not straight
Edges of parts that are cut away to see inside or behind
Thin, broken with equal length short dashes
Outlines and edges that are hidden
——— - ——— - ——— Thin, broken with long and short dashes
Centre lines. Also extreme positions of moveable parts
Thin, broken with long and short dashes—thick ends
Cutting planes for sections
Figure 7.7 shows examples of some of these lines on a single-view drawing.
Table 7.1: Line Types for Orthographic Drawings
Figure 7.7: Use of Line Types
Now try Exercise 5
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 46 of 61
7.3 Dimensions
Dimensions show the size of the object and the positions of holes, etc. Dimensions
are drawn outside the main outline of a drawing wherever possible.
Extension lines are drawn from the object outlines. Dimension lines, ending in
arrowheads, touch the extension lines. Figure 7.8 shows a simple outline with
extension lines and dimension lines.
Notice that:
• there are no dimension lines inside the outline
• dimension lines end in arrowheads that just touch extension lines
• there is a small gap between the outline and the extension lines
• extension lines end just past the dimension line arrowheads
• there is plenty of space between dimension lines and they are not too close to
the outline
• larger dimensions are put outside smaller ones so that extension lines or
dimension lines do not cross
• hole positions are dimensioned to centre lines
Figure 7.8: Dimensions
Diameter
Extension line
Dimension line Dimension lines
well spaced
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 47 of 61
Figure 7.8 shows one way of dimensioning a hole diameter. Other ways of
dimensioning circular parts are shown in Figure 7.9. Notice the symbol φ, which
stands for diameter, and R, which stands for radius.
Dimensions are written neatly, usually above the dimension lines, never below.
Always add dimensions so that they can be read from the bottom or from the right
side of the drawing as shown in Figure 7.10
Figure 7.9: Dimensioning Diameters and Radii
Figure 7.9: Dimensioning Diameters and Radii
Figure 7.10: Dimensions Read from Bottom or Right of Drawing
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 48 of 61
Notice how the very small distances (6 and 3) are dimensioned in Figure 7.10, with
arrowheads outside the extension lines.
Two ways of dimensioning outside diameters are shown in the figure.
Follow the same rules when you put dimensions on any sketches you make,
orthographic and pictorial.
7.4 Sections
One way to show details that you can not see from the outside of an object is by using
thin dashed lines to show outlines and edges that are hidden; these are called hidden
detail lines.
Another way to show parts that can not be seen from the outside is to use sections.
You saw a cutaway drawing of an engine in Figure 6.2. A cutaway drawing is a
section shown on a pictorial drawing. Figure 7.11 shows another cutaway section,
this time showing the inside of a hydraulic cylinder.
Figure 7.11: Cutaway Section in Isometric Drawing
Now try Exercise 6
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 49 of 61
Sections are mentioned in Table 7.1 and Figure 7.7 shows two sections. Sections
show what is hidden inside or behind something.
To understand sections, imagine that the object is cut through and the front is
removed. The part of the object left behind is the section. The imaginary surface that
you cut along is the cutting plane. Any metal that is cut through is
shaded with diagonal lines called cross-hatching.
Figure 7.12(a) shows an object actually being cut through to see the inside. The saw
cuts along the section plane. In Figure 7.12(b) the front is removed to show the
section that is left. See how any material that has been cut is cross-hatched. In
section drawings you just imagine that this cut has been made.
In Figure 7.13 you can see two orthographic views of the object shown in the last
figure.
In Figure 7.13(a), the hidden edges are shown using hidden detail lines.
In Figure 7.13(b), they are shown using a section view. Note how the cutting plane
and the direction you look in to see the section are shown.
Is first- or third-angle projection being used in Figure 7.13(b)?
(a) Making the Imaginary Cut (b) The Section
Figure 7.12: Imaginary Cut to make a Section View
A plane is a flat surface.
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 50 of 61
A Section A-A
A
Sometimes, to see more detail you need to make a ‘cut’ that is not straight. Figure
7.14 shows a section taken to see both the holes.
(a) Hidden Detail in Side View
(b) Sectioned Side View
Figure 7.13: Two Ways to ‘See’ Inside an Object
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 51 of 61
Notice that where the cutting plane is bent, or offset:
• there is a centre line on the section view where this happens
• cross hatching lines do not line up where they meet this centre line
Is first- or third-angle projection used in Figure 7.14?
Sometimes, when an object is symmetrical it is enough to section just
one side. It would waste time to draw both sides as they are the same.
Figure 7.15 shows a half-section of a symmetrical object.
Figure 7.14: Offset Cutting Plane
Figure 7.15: Half-section
A symmetrical object is exactly the same on both sides of a line called the line of symmetry
Bend in cutting plane
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 52 of 61
If it is enough to cut away a small area to show a detail, local or part-sections are
used. You saw a part-section in Figure 7.7. Figure 7.16 shows another example of a
part-section.
To show the shape of some items, it is enough to turn or revolve the section through
90o. If the section is drawn on the same view, it is called a revolved section (Fig.
7.17(a)). If it is drawn somewhere else, it is called a removed section (Fig. 7.17(b)).
Figure 7.16: Part-section
(b) Removed Section (a) Revolved Section
Figure 7.17: Revolved and Removed Sections
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 53 of 61
Two things are not cross-hatched, even when they are cut by a section plane. These
are:
• shafts, and anything similar to a shaft including nuts and bolts—when cut
along their length
• thin strengthening parts called webs and ribs—when cut along their length
Figure 7.18 shows examples of parts that are not cut through in a section view.
Is first- or third-angle projection used in Figure 7.18?
Section A-A
Figure 7.18: Items Not Sectioned
Now try Exercise 7
Nut
Bolt
Shaft
Web
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 54 of 61
7.5 Drawing Springs and Screws
Some items that are often used in equipment are drawn in a special way to save time.
Screw threads and springs are examples of these. The ways in which they are drawn
are shown in Table 7.2.
Item Simplified drawing Description
Compression spring
Tension spring
External thread
Internal thread
Thread assembly
Threads may be:
• external—cut on the outside of a round shaft, e.g. a bolt
• internal—cut on the inside of a hole, e.g. a nut
Notice that:
• when you look at the end of an external thread, you see the outside diameter
of the shaft. This is drawn as a thick, unbroken circle. The thread is cut into
this material and is drawn as a thin broken circle on the inside.
• when you look on the end of an internal thread, the hole you see is the inside
diameter of the thread. This is drawn as a thick, unbroken circle. The thread
is cut into the material and is drawn as a thin broken circle on the outside.
Table 7.2: Spring and Thread Drawings
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 55 of 61
Look back at Figure 7.14. Notice how the left hand hole is drawn. What can you say
about this hole?
Now try Exercise 8
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 56 of 61
8 Piping Layout Drawings
These drawings show the actual path, or shape, of a piping layout, the lengths of pipe
runs and distances between valves and fittings. They may also show pipe sizes.
Simple piping layouts can be double-line drawings. These show pipes and fittings
more realistically but take longer to produce so are only used where appearance is
important and layouts are simple. Figure 8.1 shows a simple double-line piping
layout drawing.
For most piping layouts, single-line drawings are used. These show pipes as a single
thick line, drawn where the centre of the pipe would run. Symbols are used to
represent valves and fittings. Symbols for valves are the same as or similar to those
used on PFDs and P&IDs. Figure 8.2 shows a single line drawing of the pipe layout
shown in Figure 8.1.
Figure 8.1: Double-line Piping Layout Drawing
Figure 8.2: Single-line Piping Drawing
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 57 of 61
Figure 8.3: Isometric Showing Piping in More than One Plane
Figures 8.1 and 8.2 show simple layouts that are in a single plane, i.e. they can be laid
flat on a surface.
If the layout is in more than one plane, isometric or
orthographic projections are needed to describe it.
Figure 8.3 shows a section of piping that is in more than
one plane. You could not describe this with the simple
piping layout drawings shown in Figures 8.1 and 8.2.
Figure 8.4 shows a single-line isometric piping layout drawing.
Figure 8.4: Isometric Piping Layout
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 58 of 61
Notice the way that two crossing pipes are shown on this drawing. The pipe that is
shown ‘broken’ passes behind another pipe.
Also notice how equipment that is connected to the pipeline is shown using long and
short dashes, like a centre line.
Figure 8.5 shows a third-angle orthographic drawing of the same pipe layout.
Notice how flanges on pipes that are coming towards you or going away from you are
shown as circles. You can see the open end of the pipe on flange C in the side view;
the open end of a flange is shown as two circles to represent the flange and the pipe.
You are looking at the back of flange A in the side view; the back of a flange is shown
as a single circle.
Figure 8.5: Orthographic Piping Layout
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 59 of 61
Figure 8.6 shows a manually operated gate valve with flanges on either side, like the
valves shown in Figure 8.5.
9 Summary
You have now seen some of the most important types of drawings and diagrams used
by ADGAS. You should be able to recognise them when you see them and be able to
identify the type of drawing or diagram by looking at the lines and symbols used.
You should also be able to read simple orthographic drawings and make your own
dimensioned sketches of simple objects.
Figure 8.6: Flange-mounted Valve
Flanges
Valve
Now try Exercise 9
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 60 of 61
10 Glossary
Here are some words used in this module that might be new to you. You will find
these words in coloured italics in the notes. There is a short definition in a box near
the word in the notes.
Word First Used on
Page:
Part of Speech Meaning Example of Use
Dismantle 36 verb To take to pieces The equipment had to be dismantled before the fault could be found.
Distorted 30 adjective Pull or twist out of shape
He was not going fast, but the front of his car was completely distorted when he hit the car in front.
Fluid 15 noun A substance that can flow, e.g. gas or liquid
Hydraulic fluid is usually a thin oil.
Plane 49 noun A flat surface that might be real or imaginary
The U.A.E. forms a flat plane with mountains along its eastern edge.
Represent 5 verb To stand in place of something.
The ADGAS logo represents a burning gas flame.
Symmetrical 51 adjective Having two identical halves, as if reflected in a mirror
He folded his ‘gil’ neatly, so that it was exactly symmetrical on his head.
Personnel & Training Division Basic Maintenance Technician
Drawings and Diagrams/Rev. 1.0 Page 61 of 61
Exercises