Scales

A scale can be used to increase the detail of a small object or to accurately represent a large object on a smaller piece of paper.  The majority of scaled work done in the construction industry is to reduce objects to a smaller more suitable size that will fit on a sheet of paper.
The list below shows the scales used in BS 1192:

• Block Plans 1:2500 – These show the outlines of buildings and may also indicate roads, railway lines or rivers.
• Site Plans: Between 1:500 and 1:2500 – Although often drawn at the same scale as the block plan site plans only give details relevant to the actual project.  These details could relate to landscaping arrangements or show underground drainage pipe-work.
• General Location Drawings 1:200 or 1:100 – These drawings can show pipe runs within the building and the location of radiators and sanitary fixtures.
• When details of boiler houses or plant rooms are given the scale may increase to 1:50.  This enables greater detail to be shown.
• Where particular detail is necessary the scale could be as high as 1:20 or 1:10.  This could be in the case of a bracket or support for a piece of equipment.

Here is a drawing of Block Plan originally drawn at 1:2500 but printed not to scale (NTS).

 

• Block Plan

Scale Rulers

As already stated, the scale of the drawing will be indicated in the block.  To take measurements from such a drawing a ‘Scale Rule’ is used.  Scale rules are usually manufactured from plastic and have several scales indicated on the ends as shown below.

 

• Scale Rulers

Graphical Symbols and Abbreviations

In order to read a drawing properly, and to understand what is happening, an agreed set of graphical symbols and abbreviations are used.  All the different trades have a set of symbols pertaining to their respective works.  The works of the plumber is often referred to as the “Mechanical Services”.
The Mechanical Services includes:

• Hot and Cold Water Services.
• Central Heating Installations.
• Air Conditioning Pipe-work.
• Compressed Air Lines.
• Oil and Gas Supply Lines.
• Above and Below Grounds Drainage.
• Medical Gas Services.
• Sheet Metal Roof Coverings.

When pipes and their relative components are shown on a drawing it is vitally important that the craftsperson can correctly identify their locations and positions.  The symbols for the location of pipes in a building are as follows:
Pipes at low level                                           _________________________________
Pipes at high level                                          ___    ___    ___    ___    ___    ___    ___
Pipes in roof or above ceiling                        ___       ___       ___       ___       ___      __
Pipes below floor or underground                 _  _  _  _  _  _  _  _  _  _  _  _  _  _  _  _  _
When pipes rise or drop to a different level they are shown

To show the direction of flow                      
In order to know if the pipe rises or drops the following abbreviations will be used:

• Abbreviations for Pipe Rises/Drops

TA	To Above
FB	From Below
RTA	Rise To Above
DTB	Drop To Below

To identify individual services some of the following abbreviations may be used.

• Service Abbreviations

MWS	Mains Water Services
DW	Drinking Water
CWF	Cold Water Flow
CWS	Cold Water Service
HWSF	Hot Water Service Flow
HWSR	Hot Water Service Return
HWSVP	Hot Water Service Vent Pipe
FF	Fire Fighting Services
HRS	Hose Reel Service
CA	Compressed Air
F&R	Flow and Return

The symbols on the following pages are from the British Standards Institution and are used extensively in drawings relating to mechanical services.

 

• British Standards Institution Symbols

• BSI Symbols

Symbol	Description	Application
	Draw-off tap
	Shower head
	Sprinkler head
	Float-operated valve
	Float switch (Hydraulic type)
	Float switch (Magnetic type)
	Filter or screen
	Supply stopvalve (SV)
	Servicing valve (SV)
	Water meter

• BSI Symbols

Symbol	Description	Application
	Draining valve (BS 1192) (Drain valve) (drain cock)
	Draining valve   (Abbreviated version used in this book)
	Line Strainer
	Pressure reducing valve (Small end denotes high pressure)
	Expansion vessel
	Pressure relief valve (Expansion relief valve)
	Check valve or non-return valve (NRV)
	Double check valve assembly
	Combined check and anti-vacuum valve  (check valve and vacuum breaker)
	Air inlet valve

• BSI Symbols

Symbol	Description	Application
	Cold water storage cistern (Storage and feed cistern) (Feed Cistern)
	Feed and expansion cistern
	Hot water storage cylinder or tank (plan)
	Hot water storage cylinder or hot store vessel (Direct types) (elevation)
	Hot water storage cylinder or hot store vessel (indirect types) (elevation)
	Boiler (elevation)
	Temperature relief valve
	Tundish

Specifications

In addition to installing drawings most large construction projects will also have a ‘SPECIFICATION’ to which the craftsman will have to refer.  The specification will give more information relating to the installation. 
There are many advantages to having a specification for a project, for example:

• When tendering or pricing a job the specified standards must be followed.  This ensures that no one can use sub-standard materials to keep a price low.
• The specification is also referred to at the installation stage.  This means that the client is guaranteed that all materials are up to the required standard.

Specification will normally include the following information:

• The different materials that pipes and equipment are to be manufactured from.
• The spacing of brackets.
• The type of valves to be used.
• The standard and type of sanitary fixtures.
• The type of radiators.
• Type of boiler, cylinder and storage cistern.

Identification of Pipework

In large plumbing and heating installations it may be difficult to correctly identify what services pipes are supplying.  A system of colour coding has been designed which enables pipe contents to be identified.  The chart below shows the different colours that apply to the various services.

• Identification of Pipework

Pipe Contents	Basic Colour	Specific Colour	Basic Colour
Untreated Water	Green	Green	Green
Drinking Water	Green	Blue	Green
Hot Water Supply	Green	Whit-Crimson-White	Green
Heating Pipes	Green	White-Crimson-Blue	Green
Steam	Silver Grey	Silver Grey	Silver Grey
Condensate	Green	Crimson-Green-Crimson	Green
Natural Gas	Yellow	Yellow	Yellow
Diesel Fuel Oil	Brown	White	Brown
Compressed Air	Light Blue	Light Blue	Light Blue

Occasionally it will also be necessary to indicate the direction of flow on a pipe. This is shown by an arrow situated close to the colour code.  In the case of central heating pipe-work the word FLOW or the letter F may be shown on one pipe and RETURN or R on the other.
 

• Direction of Flow

Systems of Representation

Orthographic Projection

Orthographic projection shows the views of an object in three different positions, namely:                                 PLAN – ELEVATION – END VIEW.
The plan is an outline of the object when viewed from above.
The elevation is what is seen when looking from the front.
The end view shows the view from one of the ends.
Orthographic projection is generally not used in the construction industry.  It is more commonly found in the engineering sector where precise measurement is essential.
Try drawing the object below in orthographic projection i.e. draw a plan (z) an elevation (x) and an end view (y).
 

 

 

• Orthographic Projection

Isometric Projection

In isometric projection all the horizontal lines are drawn at 30° to the horizontal plane while vertical lines are drawn vertical.
Isometric projection embraces the three views from orthographic projection in the one drawing.  In the drawing of the matchbox below you can see the plan, elevation and end view.

 

 

• Isometric Projection

Isometric projection is often used in the plumbing industry to show pipe runs. 
The drawing on the next page is an extract from BS 1192 Part 2 : 1987 with the pipe-work shown in the isometric projection.

 

• Isometric Projection

 

Self Assessment

Symbol exercises

Complete the symbol and applications boxes in the table below.

• Symbol Exercises

Symbol	Description	Application
	Draw-off tap
	Shower head
	Sprinkler head
	Float-operated valve
	Float switch (Hydraulic type)
	Float switch (Magnetic type)
	Filter or screen
	Supply stopvalve (SV)
	Servicing valve (SV)
	Water meter

Symbol	Description	Application
	Draining valve (BS 1192) (Drain valve) (drain cock)
	Draining valve   (Abbreviated version used in this book)
	Line Strainer
	Pressure reducing valve (Small end denotes high pressure)
	Expansion vessel
	Pressure relief valve (Expansion relief valve)
	Check valve or non-return valve (NRV)
	Double check valve assembly
	Combined check and anti-vacuum valve  (check valve and vacuum breaker)
	Air inlet valve

•  

Symbol	Description	Application
	Cold water storage cistern (Storage and feed cistern) (Feed Cistern)
	Feed and expansion cistern
	Hot water storage cylinder or tank (plan)
	Hot water storage cylinder or hot store vessel (Direct types) (elevation)
	Hot water storage cylinder or hot store vessel (indirect types) (elevation)
	Boiler (elevation)
	Temperature relief valve
	Tundish