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S A F E T Y F I R S T

Learner Resource

Advanced Pumping

Reprinted under licence June 2009


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Advanced Pumping

LEARNERRESOURCE


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Reprinted, with minor amendments, by CFA under licence June 2009

Copyright 2005 Australasian Fire Authorities Council (AFAC)

All rights reserved. Except under the conditions described in theCopyright Act 1968 of Australia and subsequent amendments, no part ofthis publication may be reproduced, stored in a retrieval system ortransmitted in any form or by any means, electronic, mechanical,photocopying, recording or otherwise, without the prior permission of thecopyright owner.

Every effort has been made to trace and acknowledge copyright.However, should any infringement have occurred, the publishers tendertheir apologies and invite copyright holders to contact them.

The information contained in this learning manual has been carefullycompiled from sources believed to be reliable, but no warranty,guarantee or representation is made by AFAC Limited as to the accuracyof the information or its sufficiency or suitability for the application towhich any individual user may wish to put it, and no responsibility isaccepted for events or damages resulting from its use.

AFAC Limited (ABN 52 060 049 327)

Level 5, 340 Albert Street

East Melbourne Victoria 3002

Telephone: 03 9419 2388

Facsimile: 03 9419 2389

Email: [email protected]

Internet: http://www.afac.com.au
mailto:[email protected]://www.afac.com.au/http://www.afac.com.au/mailto:[email protected]


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Table of contents

Acknowledgements iOverview iiiLearning objectives iiiFirefighting hydraulics 1Characteristics of nozzle discharge 1

Function of the branch and nozzle 2Discharge through nozzles 2Advantages of optimum nozzle pressures 2Fog and foam nozzles 3Jet reaction 3Height of effective jets 3

Principles of pressure 3Pressure, head, and height loss/gain 6Loss of pressure due to friction 9

Estimating friction loss 10Typical friction loss at low flow rates 11Typical friction loss at higher flow rates 12Friction loss in delivery hose 13Friction loss in supply hose 13

Pressurised water supply 14Changing from tank to pressurised supply 14

Static/open water supply 15Negative pressure and suction lift 17Calculation of static/open water capacity 17

Section 1 summary 21Self assessment questions 23Centrifugal firefighting pumps 1Principles of operation 1

Impeller 2Casing 3Volute 3Guide vanes 3

Multi-stage pumps 3Series pump 4Series/parallel pumps 5

Peripheral pumps 6Section 2 summary 7Self assessment questions 9Priming the centrifugal pump 1Force and lift pumps 1Diaphragm primer 3Rotary vane primer 4

Water ring primer 5Ejector pump 5Section 3 summary 7Self assessment questions 9Pump gauges, valves and controls 1Gauges 1

Compound gauge 1Pressure gauge 2Flow meter 3Tachometer 3Tank gauge 3Oil pressure gauge 4Temperature gauge 4

Valves and control mechanisms 4Clack valve 5Ball valve 5Mushroom valve 6

Butterfly valve 7

Gate valve 7Drain valve 8Pressure-relief mechanism 8

Engine controls 8Throttle 8Emergency stop 9

Section 4 summary 11Self assessment questions 13Portable pumps 1Precautions 1Operation 2Maintenance 3High pressure, low volume pumps 3Section 5 summary 5Self assessment questions 7Appliance-mounted pumps 1Pump installation 1

Midship-mounted 1Rear-mounted 2

Power train 3Transmission 4

Powering the pump 4Transfer case 4Power take-off 5

Cooling systems 5Operation 6Pump with a transfer case 6Pump with a PTO 7

Maintenance 7Section 6 summary 9Self assessment questions 11Practical pump operation 1Positioning the appliance 1Pumping from the appliance tank 2Pumping from reticulated water 3Pumping from static/open water 4

Draughting 4Emergency priming 6Cavitation 7

Delivering water 8Water on 8Charging a hose line 8

Delivering optimum nozzle pressure 8Operating multiple lines 9Valve, throttle and pressure relief operation 9Shutting down and adding hose lines 9Hose reel operation 10

Gauge interpretation and fault-finding 10Appliance tank 11Reticulated water 12Static/open water 13

Relay pumping 14Open circuit 14Closed circuit 15Relaying over undulating ground 15Calculating the distance between pumps 16Setting up the relay 16Shutting down the relay 17Breakdown 17

Communications 18


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Section 7 summary 19Self assessment questions 21Foam systems 1Types of foam 1

Class A and Class B foams 2Low, medium and high expansion foams 2Protein, synthetic, fluoro-chemical, fluoro-protein and alcohol

type foams 2Low and high energy foams 3Foam-making equipment 3

Foam-making branchpipes 4Foam inductor and generator 6Round-the-pump proportioner 7Automatic foam-proportioning systems 8

Compressed air foam systems (CAFS) 9Section 8 summary 11Self assessment questions 13Self assessment answers 1Section 1 Firefighting hydraulics 1Section 2 Centrifugal firefighting pumps 1Section 3 Priming the centrifugal pump 2Section 4 Pump gauges, valves and controls 2Section 5 Portable pumps 3Section 6 Appliance mounted pumps 4Section 7 Practical pump operation 5Section 8 Foam systems 7Glossary/Acronyms 9Bibliography 13


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Acknowledgements

The Australasian Fire Authorities Council is deeply indebted to the officers and firefighters of member agencies

who developed this publication. Sources for the development of this material are listed in the bibliography

.

Council membersAirservices Australia

Australian Capital Territory Emergency Services

Authority

Bushfire Council of Northern Territory

Country Fire Authority, Victoria

Country Fire Service, South Australia

Department of Conservation and Land Management,

Western Australia

Department of Emergency Services, Queensland

Department of Primary Industry, Queensland

Department of Sustainability and Environment,

Victoria

Department of Environment and Heritage, South

Australia

Emergency Management Australia

Fire and Emergency Services Authority of Western

Australia

Forestry Tasmania

Metropolitan Fire and Emergency Services Board,

Melbourne

New South Wales Fire Brigades

National Parks and Wildlife Service, Department of

Environment and Conservation (New South Wales)

New South Wales Rural Fire Service

New Zealand Fire Service

Northern Territory Fire and Rescue Service

Parks and Wildlife Tasmania

Queensland Fire and Rescue Service

Queensland Parks and Wildlife Services

South Australian Metropolitan Fire Service

State Forests of New South Wales

Tasmania Fire Service

Associate membersArmy Emergency Response

Brisbane City Council

Bureau of Meteorology

Department of Conservation, New Zealand

East Timor Fire and Rescue and Emergency Services

Forestry and Forest Products CSIRO

Government Fire Service, Republic of Mauritius

Hong Kong Fire Services

Office of the Emergency Services Commissioner,

Victoria

Papua New Guinea Fire Service

United Kingdom Home Office


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ADVANCED PUMPING

iii

Overview

One of your roles as a firefighter may involve the directing of a stream of water from a branch or

nozzle onto a fire. The purpose of this learning resource is to provide the participant with the

knowledge and skills to operate portable and appliance-mounted pumps at an incident and

includes:

firefighting hydraulics centrifugal firefighting pumps priming the centrifugal pump pump gauges, valves and controls portable pumps appliance-mounted pumps practical pump operation foam systems.

Learning objectivesOn completion of this unit, you will be able to:

identify and apply the principles of hydraulics to practical pump operation describe the principle of operation, characteristics, limitations and representative types of

centrifugal firefighting pumps

locate, set up, prime and operate safely a firefighting pump to provide an effective andreliable water supply to firefighters

describe the operation and use of pump gauges, valves and controls describe the characteristics, operation and maintenance of typical portable and appliance-

mounted firefighting pumps

apply practical pump operation techniques, including operating from an appliance tank, openwater and reticulated water supply; fault finding and relay pumping

deal safely and effectively with a typical range of problems, within the scope of operatorcontrol, that might interrupt or diminish the safety and effectiveness of pump operation

describe the characteristics, use and limitations of typical firefighting foams and foam makingequipment

demonstrate the safe and effective operation of pumps, primers, valves, controls and foamsystems in a typical variety of firefighting scenarios.


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Firefighting Hydraulics

Section

1


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Firefighting hydraulics

Hydraulics deals with the physical characteristics exhibited by fluids at rest and in motion.

'Hydraulics' (Greek) = Hydro (water) aulos (a pipe)

In firefighting, hydraulics is generally used to describe the study and behaviour of water. Every

time you work with water you are employing hydraulics. Understanding the application of

hydraulics to your role as a pump operator is essential.

As a firefighter, you will already be aware that water is the most commonly used fire extinguishing

agent. For water to be used effectively it needs to be applied in a suitable form and at a rate high

enough to overcome the heat of a fire. To achieve this, a knowledge of hydraulics and pump

operation is important.

This section deals with the theory associated with hydraulics and includes:

characteristics of nozzle discharge principles of pressure pressure, head and height loss or gain loss of pressure due to friction pressurised water supply static/open water supply.

Note: In this learner resource the term friction loss is used, instead of the more formal termloss of pressure due to friction.

Characteristics of nozzle dischargeWater is usually applied in the form of either a jet or a fog/spray. Sometimes, it may be mixed

with a foam concentrate and air, and applied in the form of foam.

The energy in the water includes both the energy created by its flow and the energy created by its

pressure. Both are needed for effective firefighting. For example, an open-ended fire hose may be

able to supply a sufficient rate of flow of water, but unless a nozzle is added and water is supplied

at an appropriate pressure, it may not be in a suitable form (jet or spray) to apply to a fire.

Section

1


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Function of the branch and nozzle

The branch at the end of a hose line converts the water's pressure energy into velocity or kinetic

energy. The reducing cross-section through which the water must pass in the branch converts

pressure into velocity/kinetic energy so that it can form an effective firefighting jet or spray

pattern. The nozzle controls the size and pattern of the water being discharged.

The velocity of the water coming from the nozzle varies inversely with the size of the nozzle. For

the same rate of flow, if the size of nozzle is reduced, the velocity is increased, and vice versa.

Discharge through nozzles

Each nozzle should ideally be operated at the pressure generally accepted as giving the best jet

for the size of the nozzle. This is called best or optimum pressure. Note that the optimum

pressure cannot always be adopted during actual firefighting operations. The actual pressure used

may depend on the condition of the hose, the length of hose lines, height of the branch above the

pump, the capacity of the pump and many other factors.

It is important to know what the rate of discharge is, and hence the amount of water requiredfrom the pump, for each nozzle.

The formula for the rate of discharge through a nozzle is:

L/min = 2/3 d2 (P/100) (where L/min = Litres per minute, d = diameter in millimetres,and P = pressure at the nozzle in kPa.)

Table 1 indicates the generally accepted optimum nozzle pressures, discharge rates and jet

reaction forces (i.e. the force that must be held by the branch operator) for various sized nozzles.

Size of nozzle (mm) Nozzle pressure

(kPa)

Discharge

(L/min)

Jet reaction

(kg force)

12 250 150 6

15 350 280 12

20 500 600 31

25 700 1100 68

30 800 1700 113

32 800 1900 128

Figure 1: Discharge through nozzles

Advantages of optimum nozzle pressures

As previously mentioned, the optimum nozzle pressure is the pressure at which the nozzle

produces the best jet. The advantages of using optimum nozzle pressures are:

greater striking power longer reach larger volume of water avoidance of excessive turbulence in the water jet avoidance of excessive jet reaction.Exceeding the optimum nozzle pressure does not usually give any advantages. Excessive turbulence

in a water jet at a higher pressure may lead to premature break up of a water jet, and actually

reduce its effective range. Excessive pressure also creates an unnecessarily high jet reaction,

making the nozzle more difficult for firefighters to use and control.


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Fog and foam nozzles

Most fog nozzles operate best at a nozzle pressure of 700 kPa. Most foam nozzles operate best at a

nozzle pressure of around 550 kPa.

These pressures are generally higher than the optimum pressure for a straight stream nozzleoperating at the same rate of water flow. The additional pressure is needed to provide the energy

to break the water stream up into a fog or spray, or to induce and mix foam concentrate and air

with water to generate foam.

Some branches/nozzles are designed to operate at higher or lower pressures. Check your

organisation or manufacturer's instructions regarding the nozzles in use in your organisation.

Jet reaction

When water is projected from a nozzle, a reaction equal and opposite to the force of the jet takes

place at the nozzle and it tends to recoil in the opposite direction to the flow.

The whole of the reaction takes place as the water leaves the nozzle and whether or not the jet

strikes a nearby object has no effect on the reaction.

Branch operators must exert sufficient force (effort) towards the nozzle to overcome this reaction.

While it is often possible for one person to hold a small jet, several people are required to hold a

large jet. Though the velocity of the water in both jets may be the same, the mass of water

passing through a larger nozzle per minute is much greater.

The pump operator needs to be aware of the tiring effect that controlling jet reaction has on a

branch operator, particularly if the line has been in use for some time.

Height of effective jets

In theory, a jet of water discharging vertically from a nozzle should rise to a height equivalent to

its head pressure. In practice this is not the case. The atmosphere causes friction and the jet tends

to break up to some degree. The effective height of a firefighting jet is therefore considerably less

than its theoretical height.

The British Manual of Firemanship, Book 7, Hydraulics and Water Supplies quotes a formula that

gives the height of the highest drops of water in a jet, and notes that the height of a good

firefighting jet will extend to only about two thirds the height of the highest drops.

In a worked example quoted in that Manual, using a 20 mm nozzle operating at a pressure of 500

kPa (i.e. 50 metres head), the effective height of the jet is only 24 metres. In strong wind

conditions even this height might not be achieved.

Principles of pressurePressure is the force acting on a given surface area. It is usually measured in kilopascals (kPa).

Energy is needed to provide enough flow of water to the nozzle and to provide sufficient pressure

to form an effective jet, fog/spray or foam stream. Usually this energy is imparted to the water by

a pump. As a pump operator, you are the person in control of the flow and pressure of water being

supplied to firefighters at the nozzle.

Sometimes, water may be used directly from a hydrant without going through a firefighting pump.

In that case, the energy needed in the water is being supplied by the pumps or elevated tanks of

the water supply system.

Provided there are no leaks in the hose, the quantity of water leaving the pump per minute (the

rate of flow) and the rate of flow of water at the nozzle/s must be the same.


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However, as the water travels through the hose on its way to the nozzle, there is a loss of energy

due to:

the height of the branch/nozzle above the pump friction in the hose.Each of these is discussed later in this section.

Ideally, as a pump operator, you need to provide the correct pressure at the pump to overcome

both these losses so that the pressure delivered at the nozzle/s is sufficient to form an effective

jet, fog, spray or foam stream. To do this, you need to have a good understanding of the principles

of pressure.

There are six basic rules governing the principal characteristics of pressure in liquids.

Pressure is perpendicular to any surface on which it acts (that is, it acts at right angles).

Figure 2: Pressure is perpendicular to any surface on which it acts At any point, the pressure of a fluid at rest is of the same intensity in all directions.

Figure 3: The pressure in a fluid at rest is the same in all directions


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Pressure applied from outside to a fluid contained in a vessel is transmitted equally in alldirections.

Figure 4: Pressure applied from outside is transmitted equally in all directions The downward pressure of a fluid in an open vessel is proportional to its depth.

P=10kPa

P=20kPa

P=30kPa

1m

2m

3m

1m2 1m2 1m2

P=10kPa

P=20kPa

P=30kPa

1m

2m

3m

1m2 1m2 1m2

Figure 5: Downward pressure of a fluid in an open vessel is proportional to its depth

The downward pressure of a fluid in an open vessel is proportional to the density of the fluid.


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Figure 6: The pressure from a denser liquid (such as mercury) is greater than the pressure from a less dense liquid(such as water)

The downward pressure of a fluid on the bottom of a vessel is independent of the shape ofthat vessel.

Figure 7: Containers with the same depth of water exert the same downward pressure at their bases, irrespective ofthe shape of the vessel

Pressure, head, and height loss/gainAs already stated, pressure is defined as the force acting over an area. The depth of the water is

called the 'head'. As this section explains, the concepts of pressure and head are related to each

other. Some other terms are introduced in this section and you need to understand them. They

are:

Acceleration The rate of change of velocity of an object.

Force of gravity The force exerted by the earths gravity calculated by

multiplying an objects mass by the rate of acceleration

experienced by an object when it falls in the earths gravity.

Newton (N) The term used to describe a unit of force.

Pascal (Pa) The pressure exerted by a force of one Newton spread over

an area of one square metre (1 N/m2

).

Kilopascal (kPa) 1000 Pascals.


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Consider one cubic metre of water.

One cubic metre of water contains 1000 litres of water. Each litre of water has a mass of one

kilogram (kg), so one cubic metre of water has a mass of 1000 kg.

The force (F) exerted by 1000 kg is obtained by multiplying the mass of the water by the

acceleration due to the earth's gravity.

The acceleration due to gravity is 9.81 metres per second per second (9.81 m/sec2). That is, if you

drop an object from a height, its velocity will increase by 9.81 metres per second for every second

it falls. The 9.81 m/sec2

figure is usually rounded off as 10 m/sec2.

Therefore, Force (F) = mass x acceleration (due to gravity).

If you now apply this formula to our cubic metre of water, you get:

F = 1000 kg x 10 m/sec2

F = 10,000 Newtons (A Newton is the unit of force).

As previously stated, pressure is defined as the force acting over an area. In this case, the force is

acting on the base of one square metre, so we can say that the downward pressure due to gravity

is 10 000 Newtons per square metre (N/m2).

A Newton per square metre is also called a Pascal. 1 N/m2

= 1 Pascal. The downward pressure on

the cubic metre of water could also be stated as 10,000 Pascals. Both of these units are very small

units of pressure, so we usually measure pressure in kilopascals (kPa). Kilo means thousand, so

1000 Pascals equals one kPa. Therefore 10,000 pascals equals 10 kPa.

The pressure can now be expressed in terms of kPa, which is the unit of pressure that most fire

organisation personnel are familiar with. Remember that the term head (H) refers to the depth

of water.

So for a container with a head of one metre, the pressure exerted at its base is equal to 10 kPa.

Figure 8: One cubic metre of waterFrom this understanding, a basic formula reads:

P = 10 x H (Where P = pressure in kPa and H = head in metres)

If the formula is transposed:

H = P 10

Calculations become very simple with this formula.


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For example, suppose a firefighter requires 700 kPa at the nozzle and the nozzle is at a height of

16 metres above the pump. Neglecting losses other than those due to head, at what pressure

would the pump need to be operating?

Pressure required at pump = 700 kPa + Pressure loss due to head

Pressure loss = 10 x H

= 10 x 16 metres

= 160 kPa.

Pressure required = 700 + 160

= 860 kPa

In some organisations, the additional pressure to overcome head is referred to as height loss.

Note that if the nozzle is below the pump, head is working in your favour and you actually need to

reduce the pump output pressure by an amount equivalent to the head to get the desired pressure

at the nozzle.

For example, if a firefighter requires 700 kPa at the nozzle and the nozzle is at a height of 16

metres below the pump, then, neglecting losses other than those due to head:

Pressure required at pump = 700 kPa Pressure gain due to head

Pressure gain = 10 x H

= 10 x 16 metres

= 160 kPa.

Pressure required = 700 160

= 540 kPa

The simple rule for allowing for height loss or gain is to:

add 10 kPa for every metre the nozzle is higher than the pump, or subtract 10 kPa for every metre the nozzle is lower than the pump.Now, consider another vessel, this time with 2 cubic metres of water. The water depth is still

1 metre (see Figure 8).

The total force due to mass has now doubled, but the base area has also doubled to two square

metres. Doubling both the force and area will cancel each other out so the pressure remains the

same as in Figure 7 1000 kg of force (10 kPa).

Figure 9: Two cubic metres of water spread over two square metres


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However, stacking the second cube of water on top of the first would double the force, but not

the base area. Because you now have twice the force over the same area, the pressure at the base

is doubled. (See Figure 9)

Figure 10: Pressure depends on the head (depth)Remember that pressure due to head is determined by the depth of the water, not by the amount

of water.

Loss of pressure due to frictionTo propel water through a hose or pipe, energy (pressure) has to be used to overcome the friction

caused by the water molecules rubbing against each other and against the walls of the hose or

pipe. The energy to carry out this work is obtained from the difference in pressure or head existing

between the two ends of the hose or pipe.

Figure 11: Loss of pressure due to frictionAs previously stated, technical publications (including this one) usually shorten the term loss of

pressure due to friction to friction loss.

There are five principal laws governing loss of pressure due to friction (friction loss).

Friction loss varies directly with the length of the hose or pipe.


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The longer the hose, the more pressure is required to pump the water through it because of

the loss due to friction. If the length of hose is doubled, the loss of pressure due to friction is

doubled.

For the same velocity, friction loss decreases directly with the increase in diameter.If the diameter of a pipe is doubled, its internal surface area is doubled, but its cross-sectional area is quadrupled (the cross-sectional area being proportional to the square of the

diameter). Therefore, for any given velocity, if the diameter of the hose is doubled, the

quantity of water flow for the same velocity is increased by four times, and the friction loss is

consequently halved.

As a result, it is important to always use the largest diameter hose practicable.

Friction loss increases directly as the square of the velocity.If the velocity of the water is doubled, the friction loss is quadrupled. In other words,

increasing the velocity by a factor of 2, increases the friction loss by a factor of 2 x 2 = 4.

Conversely, if the velocity of the water is halved, the loss of pressure due to friction is

reduced to ()2

or one-quarter.

For example, if water is being delivered through one hose line at a particular rate of flow,

and a second parallel hose line (same diameter) is brought into operation, then each of the

parallel hoses will only need to flow half as fast to deliver the same total flow rate. However,

the friction loss will be reduced to a quarter of its original value in the single hose line.

Friction loss increases with the roughness of the interior of the hose.The friction increases according to the roughness of the interior of the hose or pipe. All other

things being equal, a hose which has a rough interior, for example an unlined hose, will have

greater friction loss than will a hose with a smooth interior, such as a rubber lined hose.

Friction loss, for all practical purposes, is independent of pressure.Experiments show that the loss of pressure due to friction is independent of the pressure orhead at which the system is operating.

Estimating friction loss

On many appliances today, there are charts or tables adjacent to the pump panel indicating to the

pump operator the required flow rates or pump pressure for various branches and nozzles through

different lengths and diameters of hose.

Alternatively, your organisation may have some rules of thumb for estimating friction loss in

various circumstances.

Table 2 gives examples of friction loss at low, medium and high flow rates for a range of hose

diameters that are commonly used in firefighting operations. The friction loss is expressed in kPaper 30 metre hose length (rounded off to the nearest 5 kPa).

Typical low

flow rates

(L/min)

25 mm lined

(kPa)

38 mm

unlined

(kPa)

38 mm lined

(kPa)

50 mm

unlined

(kPa)

50 mm lined

(kPa)

100 100 45 15 10 Negligible

150 250 100 35 25 Negligible

200 450 175 60 40 15


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Typical

medium flow

rates (L/min)

38 mm

unlined

(kPa)

38 mm

lined

(kPa)

50 mm

unlined

(kPa)

50 mm

lined

(kPa)

65 mm

unlined

(kPa)

65 mm

lined

(kPa)

70 mm

unlined

(kPa)

70 mm

lined

(kPa)

200 175 60 40 15 15 5 10 Negl.

350 500 180 125 45 40 15 25 10

500 1000 400 260 90 85 30 55 20

Typical high

flow rates

(L/min)

65 mm

unlined

(kPa)

65 mm

lined (kPa)

70 mm

unlined

(kPa)

70 mm

lined (kPa)

90 mm

unlined

(kPa)

90 mm

lined (kPa)

500 85 30 55 20 15 5

1000 350 120 200 75 65 25

2000 1400 500 850 300 260 90

Table 2: Effects of friction loss in a 30 metre length of hose

The rate of flow of water is determined by the diameter of the nozzle (remember Table 1) and the

nozzle pressure, not by the diameter of the hose. However, as you can see from Table 2 above,

because of friction loss, there is a limit to the practical water-carrying capacity of the hose.

Typical friction loss at low flow rates

A pump operator needs to supply water to a nozzle discharging 150 L/min at a nozzle pressure of

250 kPa through one 30 metre length of 25 mm hose. As shown in Table 2, the friction loss is

250 kPa. Disregarding any allowance for height loss/gain, the operator makes the following

calculations:

Pressure required at pump = nozzle pressure + friction loss

= 250 + 250 kPa

= 500 kPa

However, if the pump operator was supplying the same nozzle through four 30 metre lengths of

25 mm hose:


= 250 + (250 x 4) kPa

= 1250 kPa

Many firefighting pumps (apart from high pressure pumps) may not be capable of supplying a

substantial flow of water at pressures well above 1000 kPa. In addition, when using conventional

lay-flat fire hoses, there may be an increased risk of a hose bursting when pressures above 1000

kPa are used.

Remember that fire hose is normally rated at a particular short-length burst pressure. This is

when tested under ideal conditions. For operational use, it is normally recommended that

pressures not exceed 25% of the designated short-length burst pressure. Typical lay-flat fire hose

used by fire organisations has a short-length burst pressure of around 4000 kPa.


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If the pump operator was to use four 30 metre lengths of 38 mm lined hose to supply the same

nozzle described above (150 L/min):


= 250 + (35 x 4) kPa

= 390 kPa

Clearly this is a considerably lower pump pressure. The general rule is:

If you have to pump water over a significant distance, using a larger diameter hose gives you an

advantage.

Typical friction loss at higher flow rates

Let's now compare the friction loss involved in supplying a larger nozzle, delivering 500 L/min at a

nozzle pressure of 700 kPa through three 30 metre lengths of hose of various diameters.

Using three lengths of 38 mm lined hose:


= 700 + (400 x 3) kPa

= 1900 kPa

Using three lengths of 65 mm lined hose:


= 700 + (30 x 3) kPa

= 790 kPa

Obviously, the use of 65 mm hose would be preferred in order to reduce friction loss and

consequently maintain a lower pressure at the pump. However, a 38 mm hose line may be much

easier for firefighters to manoeuvre. A possible solution would be to use two lengths of 65 mm

hose and one length of 38 mm hose at the nozzle.


= 700 + (30 x 2 + 400 x 1) kPa

= 700 + (60 + 400) kPa

= 1160 kPa

Some fire organisations use 50 mm lined hose to give a good combination of manoeuvrability and

moderate friction loss. Using three lengths of 50 mm lined hose:


= 700 + (90 x 3) kPa

= 700 + 270 kPa

= 970 kPa


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Friction loss in delivery hose

Many firefighting organisations use fog nozzles of various sizes, all operating at 700 kPa. At a

typical fire a delivery hose line often consists of three 30 metre lengths of hose.

If the nozzle needs 700 kPa, then for the required pump pressure to be kept below 1000 kPa, the

total friction loss needs to be less than 300 kPa.

If there are three 30 metre lengths of hose, each would need to have a friction loss of no more

than 100 kPa.

In effect, this imposes a practical limit on the flow rate of the nozzle normally used in association

with a particular hose diameter on delivery lines. By referring to the friction loss tables in Table 2,

you can see that the flow rates for various diameter lined hoses which give 100 kPa or less friction

loss are as follows:

25 mm about 100 L/min 38 mm about 250 L/min 50 mm about 500 L/min 65 mm about 1000 L/min 70 mm about 1200 L/min 90 mm about 2000 L/min.These flow rates are used by some organisations to decide which size nozzle is provided for use

with various diameter hoses.

However, some appliances may have high pressure pumps supplying water to high pressure hose-

reels. In this case, higher flow rates will be possible in the hose-reels in spite of their relatively

small diameter, as the pump and/or hose is not as limited in the pressure at which it can operate.

Friction loss in supply hose

If you are using hose for supply hose lines, another option to reduce friction loss is to twin the

lines.

Let's say you need to supply 1000 L/min to a fire appliance through a single line of three 30 metre

lengths of 65 mm diameter, unlined hose.

Total friction loss = 3 x 350 kPa

= 1050 kPa.

If you were to twin the lines (that is provide a second parallel 65 mm line), each hose line would

now only need to deliver 500 L/min to achieve the same total flow rate. Thus the water in each

hose will now be travelling at only half the velocity it was in the single line, and, as already

mentioned, if the velocity is reduced by a factor of two (that is, halved), then the friction loss in

each hose is reduced by a factor of four (that is, it is a quarter of the original). In this case:

Total friction loss = 3 x 85 kPa

= 255 kPa.

Note that in this calculation, 85 kPa is slightly less than one quarter of 350 kPa as the figures in

Table 2 have been rounded off to the nearest 5 kPa.

An alternative would have been to use a larger diameter hose line. For example, for a single

90 mm unlined hose, the total friction loss over three 30 metre lengths would be only 195 kPa.


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In some overseas fire organisations, hose lines of 100 mm, 125 mm, 150 mm and even 200 mm

diameter may be used for supplying large volumes of water over a distance.

If you are already using your largest diameter hose, the general rule is:

To reduce friction loss in supply hose lines, twin the lines.

Pressurised water supplyThe water supply for firefighting may come from either a static/open source such as a dam or

creek, or from a pressurised source such as a hydrant, the pump of another firefighting appliance

or an elevated tank.

With your knowledge of the principles of pressure (see Section 3), you know that if your pump is

connected to a pressurised supply of water but there is no water flowing, all of the energy in the

water will be due to its pressure. The pressure at your pump will be the same as the pressure in

the water supply system. This is sometimes called the static pressure.

As already discussed, when you start using water from the pressurised supply, some of the energyin the water is now being used to make it flow. This means that, unless extra energy is added to

the system (for example, by increasing the output of the pumps that supply the hydrant water

system or of the pump in the appliance supplying you), the energy being used up to deliver the

water reduces the water's pressure.

The greater the flow of water, the further the pressure of the supply will drop. The pressure

remaining in the water supply when water is flowing at any particular rate is sometimes called the

residual pressure.

When you are taking as much water from the supply as it can provide, the residual pressure will

have dropped down to zero.

Attempting to take any more water will result in over-running the supply. If the supply is coming

in through lay-flat hose, the hose will collapse when the residual pressure reaches zero, as it isonly the residual pressure that keeps the hose inflated with water.

Remember that if you are connected to a pressurised water supply by an inadequately sized supply

hose, it could be the friction loss within that hose, not the capacity of the water supply that may

cause the residual pressure at your pump to be zero. Using a larger diameter supply line or

twinning the supply lines will improve the residual pressure.

If the supply is coming in through a hard suction hose, the hose will not collapse. However, over-

running the supply from a hydrant system when using hard suction hose may damage the hydrant

water supply pipes.

Some hydrant systems (for example, those on industrial sites) may be supplied by large firefighting

pumps that start automatically when water is drawn from the system, and may operate at

relatively high pressures. In some cases, hydrant systems may also use recycled water. Check yourorganisations procedures for any specific instructions or precautions to use in such situations.

Changing from tank to pressurised supply

Many organisations use a standard procedure in which a fire is initially attacked using water from

the appliance's tank, with a changeover made as soon as possible to the water supply from a

hydrant through the appliances pump.

When the changeover is made from tank to pressurised supply, the extra pressure of the latter will

be added to the pressure already being delivered to the nozzle by the appliance pump.


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Unless there is a pressure limiting mechanism or specific procedures are followed, the branch

operators may be given a sudden and potentially dangerous increase in pressure and jet reaction.

The pressure increase might also be enough to cause a hose to burst.

When changing over from tank to a pressurised supply, follow your organisations procedures to

minimise a sudden pressure increase. These may cover the use of pressure limiting devices,specific valve opening sequences and/or gradual opening and closing of relevant valves.

On some appliances, pressurised water supply may be fed into the tank, rather than directly into

the pump. In effect, the supply is keeping the water tank topped up. This avoids the risk of a

sudden pressure increase, but has the disadvantage of not being able to use the extra energy in

the external water supply. Unless the appliance tank inlets are fitted with automatic valves, you

will need to control the incoming supply to prevent overfilling of the tank.

Static/open water supplyAs already mentioned, the water supply for firefighting may come from a pressurised source, such

as a hydrant, the pump of another firefighting appliance or an elevated tank; or from a staticsource such as a dam, swimming pool or creek. Some organisations refer to the latter supply as

open water.

The pressure of the air from the atmosphere is used to force the water from a static source into

the pump of your appliance.

The air pressure at sea level in a standard atmosphere is 101.3 kPa (or 1013 hectopascals, using

the unit used in weather forecasts). This is often rounded off to 100 kPa or 1 bar. A bar is a larger

unit of pressure. (1 bar = 100 kPa)

From the previous discussion of pressure and head, you may recall that a head of one metre is

equivalent to a pressure of 10 kPa. Therefore, if atmospheric pressure is about 100 kPa, it should

be able to provide the pressure needed to create a head of water of about 10 metres.

In other words, if you were to lower a pipe vertically from a height down into the water sourceand remove all air from inside the pipe, the pressure of the air in the atmosphere should force

water up the pipe to a height of 10 metres.

No amount of further effort, whether by increasing the vacuum (which is impossible) or by

lengthening or widening the pipe, will induce the water to rise higher than 10 metres. Seawater is

slightly denser than fresh water, so that a shorter column of seawater would balance the

atmospheric pressure.


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Figure 12: The principle of lifting water by using atmospheric pressureIn practice, it is not possible to remove all the air from the pipe. So, if the air is not completely

exhausted from the pipe, the water only rises to a height sufficient to balance the pressure

difference existing between the inside and the outside of the pipe.

For example, if air pressure remains in the pipe equivalent to a column of water 7 metres high

(about 70 kPa), then the water will only rise 3 metres (see Figure 11). Water is not drawn up by

the formation of the vacuum, but is forced up by the external pressure of the air on the exposed

surface of the water.

This is precisely what happens when a pump is primed. A suction hose connected to the inlet ofthe pump takes the place of the vertical pipe. The primer is the device for exhausting or removing

the air from the suction hose and pump. As the pressure inside the hose and pump is reduced, so

the atmospheric pressure of the air on the exposed surface of the water forces the water up the

suction hose until it reaches the inlet of the pump.

Even under perfect working conditions, a pump will not lift water to a height greater than 10

metres above the waters surface. This height is measured from the surface of the water to the

centre of the pump inlet.

Although the maximum theoretical vertical lift is 10 metres and the maximum practical vertical

lift is 8 metres under perfect conditions, the maximum lift usually attempted is 7.5 metres. This is

due largely to the energy lost when the water enters the pump (known as entry loss), and in

moving the water through the suction strainers and suction hose.

The rated capacity of a pump is its output in litres per minute when working from a 3 metre lift.

As can be seen from the following figures, the greater the vertical lift to be overcome, the less

water that can be delivered to the incident:

3.0 metre lift rated capacity of the pump 4.5 metre lift 1/7 loss of capacity 6.0 metre lift 1/3 loss of capacity 7.0 metre lift 1/2 loss of capacity 7.5 metre lift 2/3 loss of capacity.


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Negative pressure and suction lift

Firefighters usually refer to pressure above atmospheric pressure as positive pressure, and

pressure below atmospheric pressure as negative pressure. (Strictly speaking the latter is not

negative, it's just lower than the normal atmospheric pressure.)

When the pump is using water from a static supply, there will be a negative pressure on the inlet

side of the pump. The amount of negative pressure will normally correspond to the lift of water

being achieved. For example, a pressure of minus 30 kPa would correspond to a lift of 3 metres,

due to 1 metre of head or lift being equal to 10 kPa of pressure.

If the suction hose or pump inlet were to become blocked, the negative pressure would increase as

the pump strains to lift against the blockage. If an air leak were to occur in the suction hose, the

negative pressure would be lost as the pressure in the suction hose equals atmospheric pressure.

Figure 13: Negative pressure and suction lift

Calculation of static/open water capacity

Static water supply sources may have a limited capacity. If one source has insufficient capacity,

you may have to locate another at some time during firefighting. The capacity of a static water

source can be calculated (in litres) by multiplying its volume (in cubic metres) by 1000.

Rectangular container

If the source is a rectangular container, such as a rectangular swimming pool or tank, the formula

for its capacity is:

Capacity (in litres) = length x breadth x depth x 1000

If it has an uneven depth, use the average depth in the calculation.


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For example, a rectangular swimming pool is 4 metres wide, 8 metres long and is 1 metre deep at

one end and 2 metres deep at the other.

Capacity (in litres) = length x breadth x depth x 1000

= 8 x 4 x (1+2) x 1000

2

= 8 x 4 x 1.5 x 1000

= 48 x 1000

= 48 000 litres

If you required, say, a total water supply of 2000 L/min to fight a particular fire, this pool would

supply that rate of flow for up to 24 minutes(48 000 2000 = 24).

Figure 14: Pumping from a swimming pool

Cylindrical container

If the source is a cylindrical container, such as rural domestic water tank, the formula for its

capacity is:

Capacity (in litres) = 0.8 x length (or depth) x (diameter)2

x 1000

For example, a cylindrical water tank (standing on end) is 3 metres deep and 4 metres in

diameter.

Capacity (in litres) = 0.8 x 3 x (4 x 4) x 1000

= 0.8 x 3 x 16 x 1000

= 0.8 x 48 x 1000

= 38.4 x 1000

= 38 400 litres

Figure 15: Pumping from a cylindrical water tank


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Flowing source

The capacity of a flowing water source can be calculated (in litres per minute) by multiplying the

volume (in cubic metres) flowing past any point per minute by 1000.

Capacity (in L/min) = volume (depth x width x rate of flow in metres per minute) x 1000

Firefighters often underestimate the water supply available from quite small streams. For

example, consider a creek that has a depth of 0.5 metres, a width of 4 metres and flowing past at

a speed of 5 metres per minute.

Rate of flow (litres per minute) = depth x width x speed of flow x 1000

= 0.5 x 4 x 5 x 1000

= 0.5 x 20 x 1000

= 10 x 1000

= 10 000 L/min.

It can be seen that the quiet creek shown in Figure 15 is in fact flowing at 2 to 3 times the pump

capacity of a typical pumper!

Figure 16: Pumping from a stream flowing at five metres per minute


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Section 1 summary

Hydraulics deals with the physical characteristics exhibited by fluids at rest and in motion. The branch at the end of a hose line converts the waters pressure energy into velocity or

kinetic energy so that it can form an effective jet or spray.

Each type/size of nozzle has an optimum operating pressure. Water discharging from a nozzle results in a jet reaction. Pressure is the force acting over a given surface area. It is usually measured in kilopascals

(kPa).

The principles of pressure are: Pressure is perpendicular to any surface on which it acts. At any point, the pressure of a fluid at rest is of the same intensity in all directions. Pressure applied from outside a fluid contained in a vessel is transmitted equally in all

directions.

The downward pressure of a fluid in an open vessel is proportional to its depth. The downward pressure of a fluid in an open vessel is proportional to the density of the

fluid.

The downward pressure of a fluid on the bottom of a vessel is independent of the shapeof that vessel.

The rule for allowing for height loss or gain when pumping is to add 10 kPa for every metrethe nozzle is higher than the pump, or subtract 10 kPa for every metre the nozzle is lower

than the pump.

The five principal laws governing loss of pressure due to friction are: Friction loss varies directly with the length of the hose or pipe. For the same velocity, friction loss decreases directly with the increase in diameter. Friction loss increases directly as a square of the velocity. Friction loss increases with the roughness of the interior of the hose. Friction loss, for all practical purposes, is independent of pressure.

Friction loss varies depending on the type of hose, diameter of hose, length of hose line andrate of flow involved.

For the same flow rate, larger diameter hoses have significantly lower friction loss thansmaller diameter hoses.

The friction loss in any particular diameter hose line will effectively limit the size of nozzleused in association with that diameter of hose.

Twinning the lines is a method of reducing friction loss in supply lines. Pressurised water supply may be obtained from a hydrant system, another appliance's pump or

an elevated tank.

When the residual pressure in a pressurised supply is approaching zero, it means you arealmost overrunning the supply.

Water may be obtained from a static or open source such as a dam, pool or stream.


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The capacity of a static water source can be calculated (in litres) by multiplying its volume (incubic metres) by 1000.

The capacity of a flowing water source can be calculated (in litres per minute) by multiplyingthe volume (in cubic metres) flowing past any point per minute by 1000.


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Self assessment questions

1. What are the functions of the branch and nozzle on a line of hose?2. If a 25 mm nozzle is operating at a nozzle pressure of 700 kPa what quantity of water is it

discharging per minute?

3. Would the friction loss increase or decrease if a line of hose was lengthened?4. For the same flow rate, would the friction loss increase or decrease if the diameter of the

hose is increased?

5. Calculate the pressure at the bottom of a tank that is filled with water to the height of 8metres.

6. A nozzle, supplied from a pump at street level 40 metres below, is being operated on theeleventh floor of a building. How much pressure would need to be added to compensate for

the head or height loss?

7. How long would a full rectangular water tank measuring 3 x 2 x 1 metres last if it was used tosupply a 20 mm nozzle operating at optimum pressure?

Activities1. Find out the optimum nozzle pressures and associated flow rates for the range of nozzles

typically used in your organisation.

2. Find out the rules of thumb used in your organisation for calculating friction loss, ordetermine the friction loss for the hose and nozzle combinations commonly used for

delivery lines in your organisation.

3. Find out the typical static pressures and flow rates that can be expected in any hydrantsystems in your area.

4. Find out the maximum flow rate of the pump/s (when operating at pressures of 700kPaand/or 1000kPa that are used by your organization.


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Centrifugal Firefighting Pumps

Section

2


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Centrifugal firefighting pumps

A pump is a machine, powered by an external source, which imparts energy to a fluid or gas. A

pump may be driven by hand, by an electric motor, by an internal combustion engine, or by

hydraulic or pneumatic means.

In a centrifugal pump, energy is imparted by centrifugal force that is, the force generated by the

rotation of an object. This force drives outwards from the centre of rotation.

This section explores the centrifugal pump in detail, including:

principles of operation multi-stage pumps peripheral pumps.

Principles of operationA centrifugal pump consists of an impeller, or impellers, rotating inside a pump casing. Water

enters at the centre, or eye, of the impeller and is flung out to the periphery (the outer edge of

the casing) by centrifugal force as the impeller rotates. The water is collected inside the pump

casing and discharged from the pump outlet.

Figure 17: Centrifugal pump

Section

2


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A centrifugal pump is ideally suited for firefighting work because it:

gives a steady flow operates at variable pressure depending on need

is simple in construction and operation is easily maintained and less likely to be damaged by bad pump operation is able to pump dirty or gritty water with minimal damage to the pump* is small and compact allows flow to be interrupted without stopping the engine can be connected to an internal combustion engine by direct drive.

*Note. Continuous pumping of contaminated water will result in damage to valves, seals, and

impeller and water passage surfaces.

A disadvantage, however, is that a centrifugal pump requires priming when using water from a

static or open source. Priming consists of filling the pump and associated suction hose with water.

Priming pumps are explained in Section 3.

It is sometimes said that centrifugal pumps can't pump air. This is not strictly correct. They can

pump air (a turbocharger on a high performance engine is an example), but they require different

design features, rotation speeds and engine power combinations that are compatible with pumping

water efficiently.

Lets now look in more detail at the main components of a centrifugal pump.

ImpellerA centrifugal pump has no valves, pistons or plungers. It makes use of an impeller that consists of a

number of curved radial vanes fitted between circular side plates to generate centrifugal force

when the impeller is rotated.

The impeller is the spinning part of a centrifugal pump that imparts energy to the water. It is

attached to a central rotating shaft.

Water received at its eye (inlet) is thrown outwards at high velocity by the radial vanes as the

impeller rotates, and is discharged at its periphery (outer edge). The flow through the impeller

passages causes a partial vacuum to be created at its inlet. This causes more water to be forced

into the impeller from the supply source.

Figure 18: Typical impeller


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Casing

The pump casing converts the kinetic (or velocity) energy of the water, when it leaves the

impeller, to pressure energy. The casing is designed to reduce the velocity of the water and to

produce a smooth and steady flow from the pump outlet.

The action of the impeller in thrusting water outwards creates considerable turbulence and

friction. As these factors represent wasted energy, two design features are used to minimise these

effects. These features are the volute and guide vanes. The volute and the guide vanes can also be

combined.

Volute

The volute is the cavity inside the casing of a centrifugal pump (see Figure 18). It is shaped like a

snail shell. The cross-sectional area increases in a circular direction toward the outlet. The effect

of this shape is to gradually reduce the velocity (kinetic energy) of the water and convert this

velocity into pressure.

The increasing space provided by the snail shell shape is also necessary because water is thrownfrom the impeller around its entire periphery, and the total quantity of water passing through the

casing increases nearer the discharge outlet. The volute is designed to handle this increasing

quantity of water.

Guide vanes

Fixed guide vanes in the casing may be used to guide the water along its correct path and to

reduce turbulence. Together, the vanes are sometimes known as a guide ring or diffuser. In many

pumps both guide vanes and a volute may be used.

Figure 19: Guide vanes and volute

Multi-stage pumpsThe output pressure of a centrifugal pump can be raised by increasing the speed of rotation or the

diameter of the impeller. The first method is limited by the power of the engine and the second is

relatively inefficient. Better results are obtained by using a multi-stage pump which imparts

energy to the water through two or more impellers.

Multi-stage pumps allow flexibility where a variation in capacity and pressure is required and

provide an appropriate option where delivery pressures exceeding those available from the single

stage centrifugal pump are necessary.

Multi-stage pumps also have the advantage of achieving higher delivery pressures while

maintaining moderate engine speeds. Examples of where higher delivery pressure could be


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required are in high-rise building incidents, or where it is desirable to deliver water through high

pressure hose reels.

Series pump

When two or more single-stage centrifugal pumps are arranged so that the discharge from the first

pump is connected directly to the inlet of the second pump, the pumping arrangement is said to

be in series.

A series pump is like having two or more separate single stage pumps back to back, each one

supplying the next with pressurised water.

Many multi-stage pumps used for firefighting are series pumps. The impellers of a multi-stage

pump are mounted on a common shaft, but in a divided casing, with each impeller representing an

additional stage of pumping.

The effect is similar to having one pump supplying water under pressure through to the inlet of

another pump. When the second pump is operating, the water pressure is further increased.

The amount of water passing through the second pump is the same as that passing through the firstpump. Neglecting friction loss and assuming the pump impellers are equal, each pump will add an

equal amount of pressure.

Figure 20 shows the flow of water through a typical two-stage series pump.

Low pressureHigh pressure

Waterinlet

Outlet

Outlet

Secondimpeller

Firstimpeller

Figure 20: Flow in a two-stage series pump

There may be a number of different stages and some variations in design for special uses. In some

types of pump, the first two stages provide water for the normal delivery outlets. Some of the

flow, however, is passed to further stages where the pressure is again increased. The output from

the final stage is at high pressure but the volume of flow is smaller.


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Series/parallel pumps

This type of multi-stage pump incorporates transfer or changeover valves between the various

stages. Depending on the position of the valves, the pump may either be operated in series mode

(the first impeller passing water to the second to build up pressure, see Figure 21), or parallel

mode (each impeller feeding directly to the pump outlet to produce high volume, see Figure 22).

In series mode, the transfer valve is closed and the discharge from the first impeller is directed to

the inlet of the second impeller, then to the pump discharge.

First stageimpeller2000L/min1050kPa

Second stageimpeller2000L/min1050kPa

Discharge2000L/min2100kPa

Intake

Transfer valve

Clapper valve

Figure 21: Series/parallel pump operating in series (or pressure) mode

In the parallel mode, water from the source enters the eyes of both impellers together at the

same pressure, and is discharged from both impellers together, into a common delivery.

First stageimpeller2000L/min1050kPa

Second stageimpeller2000L/min1050kPa

Discharge4000L/min1050kPa

Intake

Transfer valve

Clapper valve

Figure 22: Series/parallel pump operating in parallel (or volume) mode


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The series mode is selected when higher pressure is required, such as for a high pressure hose reel,

and the parallel mode is selected when a high volume is required, such as for a water relay (see

Section 6) or general pumping duties.

Peripheral pumpsA disadvantage of many high-pressure pumps is that they must operate at high speed to deliver the

required higher pressures.

One alternative is the peripheral pump, which is a variation of the normal centrifugal pump and

operates at the same speed. The peripheral pump is usually fitted in conjunction with a

centrifugal pump to provide a high pressure capability.

In the peripheral pump, the impeller has a ring of guide vanes around its outer edge. The pump

casing fits closely around the central part of the impeller but there is a channel surrounding the

guide vanes (see Figure 23).

When water enters the channel, it drops to the base of the guide vanes and is then flung outwards

between the vanes by centrifugal force. The water then moves to the base of the vanes again andthe process is repeated many times.

The spiralling water is dragged around in a circle by the impeller, and is finally expelled through

the outlet at a pressure which is the equivalent of a multi-stage pump operating in series mode.

At about the same rpm, the peripheral pump will deliver less water, but at considerably higher

pressures than will a conventional centrifugal pump.

Figure 23: Peripheral pump


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Section 2 summary

A centrifugal pump consists of an impeller, or impellers rotating inside a pump casing. A centrifugal pump is ideally suited for fire fighting work. A disadvantage of a centrifugal pump is that it needs to be primed. The impeller consists of a number of curved radial vanes fitted between circular side plates.

When the impeller rotates, the vanes fling the water from the centre out to the periphery by

centrifugal force.

The pump casing converts the kinetic (or velocity) energy of the water, when it leaves theimpeller, to pressure energy.

A volute and/or guide vanes may be included in the pump casing to guide the water along itscorrect path and reduce turbulence.

Multi-stage series pumps use a series of impellers to increase the pressure of the water in thepump.

Series/parallel pumps have a transfer valve which allows water to pass through multipleimpellers one after the other (giving high pressure); or to be drawn from a common inlet into

each impeller at the same time and to discharge through a common outlet (giving high

volume).

A peripheral pump impeller has a ring of guide vanes around its outer edge which raises thewater pressure to a much higher level than a normal centrifugal pump.


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1. How does a centrifugal pump operate, (including the function of the impeller and pumpcasing)?

2. List the advantages and disadvantages of a centrifugal pump for firefighting.3. Describe a centrifugal pump impeller.4. Describe the appearance and function of the volute and guide vanes.5. What is the advantage gained by using multi-stage series pumps?6. Describe the difference between a multi-stage series/parallel pump running in series mode

and running in parallel mode.

7. How does a peripheral pump produce higher pressures than is usual?

Activities1. Find out which appliances in your organisation use centrifugal pumps.2. Find out what type of centrifugal pump they are, (for example single stage, multi-stage

series, series/parallel or peripheral).

3. Compare the performance information for each type of pump (for example, rate of flow atvarious pressures).


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Priming the Centrifugal Pump

Section

3


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Priming the centrifugal pump

As mentioned in Section 2, a centrifugal pump designed for firefighting cannot usually pump air.

Priming pumps, or primers, can pump air. Therefore, when using a centrifugal pump to draught

water from a static/open water source, air in the pump and suction hose must be removed so that

atmospheric pressure can force water from its source up into the pump. This is achieved by using a

primer.

Firefighting organisations use a wide range of primers, but priming pumps generally fit into one of

the categories discussed in this section. In any case, you should refer to relevant appliance or

pump manuals for details. This section looks at the types of pumps commonly used as priming

pumps, including:

force and lift pumps diaphragm primer rotary vane primer water ring primer ejector pump.The practical use of primers is covered in more detail in Section 7, Practical Pump Operation.

Force and lift pumpsThe force (or reciprocating) pump is the simplest type of priming pump, consisting of a solid

plunger which moves up and down in a cylinder fitted with inlet and outlet valves. A single-actionforce pump (see Figure 23) draws in water or air on the upstroke and discharges it on the

downstroke. A disadvantage of this pump is the pulsating effect caused by the interval between

each discharge stroke.

An outlet valve enables the fluid to escape, while the inlet valve is held closed by the pressure of

the fluid during the downstroke. During the upstroke, the outlet valve closes and the inlet valve

opens, allowing more fluid to be drawn into the pump casing.

Section

3


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Figure 24: Single-action force pumpThere is also a double-action force pump, which discharges water (or air) both on the upstroke and

on the downstroke, thus lessening the pulsation (see Figure 25).

Inlet valve

Inlet valve

Outlet valve

Outlet valve

Figure 25: Double-action force pump

Lift pumps are similar to force pumps, but have a hollow plunger with a valve through which, in

the single-action type, water can pass freely in one direction, but cannot return. The pumps which

raise water from wells are usually lift pumps.

Some lift pumps also have a double-action. Water can be pumped on both the upstroke and

downstroke. The small hand pump on a knapsack spray used for wildfire fighting is a typical

example.


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DownstrokeUpstroke

Inlet valve

Outlet valve

Figure 26: Single-action lift pump

Another type of force pump is the semi-rotary pump, typically used for pumping out 200 litre

drums. This has two sets of valves operating within a circular casing. Pumping the lever backwards

and forwards allows fluid to be pumped on both strokes.

All force and lift pumps produce a pulsating flow of water. If a constant, steady flow of water is

needed, an air vessel can be fitted near the pump outlet (see Figure 26). As the water is pumped

out, some enters the air vessel and compresses the air within it. Between strokes, the compressed

air within the air vessel drives this water back out again, resulting in a fairly steady stream.

Frompump

Frompump

Airpressure

Waterpressure

Figure 27: Air vessel

Diaphragm primerA diaphragm primer consists of a metal housing (the chamber); an inlet and discharge port, each

containing a one-way valve; a flexible diaphragm (a thin partition); diaphragm actuating rod and

handle. It uses the same concept as a force pump, but a flexible diaphragm is used instead of a

moving plunger (see Figure 28).

When the handle is pulled up, the rod pulls the centre of the diaphragm upwards. This creates a

negative pressure in the chamber causing air from the pump and suction hose to be drawn into the

chamber. A one-way valve prevents air entering the pump from the discharge port.

When the handle is pushed down, the centre of the diaphragm is pushed downwards. This causes a

positive pressure within the chamber, below the diaphragm, forcing the inlet valve closed. The airinside the pump overcomes the tension of the spring-loaded discharge valve, and is expelled via


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the discharge port. Continuous operation of the handle will eventually remove all the air from the

pump system.

On an appliance, the diaphragm actuating rod (sometimes called a plunger rod) may be attached

to a motor which mechanically moves the diaphragm in and out. On portable pumps, however, it is

usually hand-operated.

Upstroke Downstroke

Inlet valve Discharge valve Inlet valve Discharge valve

Flexiblediaphragm

Air

Air

Figure 28: Diaphragm primer

Rotary vane primerThe rotary vane primer (also known as a sliding vane pump or primer) is driven by an electric

motor and controlled by a priming valve. The shaft on which the rotor is mounted is off-centre, or

eccentric, within the casing.

Within the rotor are several slots in which the vanes are inserted. As the rotor turns, the vanes

slide in and out, due to centrifugal force, maintaining contact with the casing. When the pump is

operating, oil from a reservoir automatically provides lubrication and an air seal between thevanes and pump casing.

The turning rotor causes the space between the vanes to increase, creating a partial vacuum, and

drawing in air from the main centrifugal pump and suction hose before the next vane meets with

the casing. Air is then carried between the vanes to the discharge, where the space between the

vanes decreases, thus forcing the air out through the discharge. This action is repeated as each

vane moves around.

Oilreservoir

Air from suction hose Discharge

Shaft

Casing

Sliding vanes

Rotor

Figure 29: Rotary vane primer


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Water ring primerA water ring primer consists of an elliptical housing that contains a stationary hollow boss or axle,

(incorporating an inlet from the pump and two discharge ports). The water in the housing is forced

to move outwards by centrifugal force created by the rotating impeller (see Figure 30).

At the widest parts of the housing, two areas of low pressure are created inside the ring of water.

These areas are filled with air forced in from the pump and suction hose by atmospheric pressure.

As the water moves inwards at the narrower section of the housing, the air is forced into the

discharge ports in the stationary boss. Since the impeller is located centrally in the elliptical

housing, there are two pumping actions for each revolution.

Figure 30: Water ring primer

Ejector pumpAn ejector pump consists of a passage or pipe which is constricted at one point so that fluid or gas

passing through it increases in velocity at the point of constriction. Speeding up increases the

energy in the liquid or gas accounted for by its velocity. The energy for this extra velocity is taken

from the static pressure of the liquid or gas. At the constriction, pressure drops below atmospheric

pressure. This is called the venturi effect and the device is called a venturi. You can simulate

this effect by blowing across the end of a straw inserted into a liquid. The velocity energy across

the end of the straw reduces the static pressure within the straw and the liquid is forced up the

straw by atmospheric pressure.

When used for priming, the lower pressure generated within the venturi throat is used to remove

air from the pump and suction hoses until priming is achieved. A common type uses the exhaust

from the pump engine as the gas flowing through the venturi. For that reason it is called an

exhaust ejector primer.

Note: Ejector pumps are sometimes used to pump water out of basements or ships' holds. In this

case the venturi has water flowing through it, supplied through a hose from a firefighting pump.

The venturi effect is also used in firefighting to induce foam concentrate into a foam inductor.

Rotating

impeller

Discharge ports

Inletfrom pump

Oval housing

Ring of water

Areas of low pressure

Air forced infrom pump

Air forced into

discharge nozzles


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ADVANCED PUMPING

3-6

Air

Passageor pipe

Increases in velocity

Point of constriction

Pressure drops belowatmospheric pressure

Main stream

Figure 31: Ejector pump


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Section 3 summary

A priming pump is a pump capable of pumping air. It is used to prime (fill with water) acentrifugal pump and associated suction hose when working from static/open water.

Priming pumps include: force and lift pumps diaphragm primers rotary vane primers water ring primers ejector pumps.

Force and lift pumps produce a pulsating flow of water. To provide a constant, steady flow,an air vessel can be fitted near the pump outlet.

The diaphragm primer uses the same concept of operation as a force pump, but a flexiblediaphragm is used instead of a moving plunger.

A rotary vane primer consists of an off-centre or electric turning shaft on which a rotor ismounted. Within the rotor are several slots in which vanes are inserted.

A water ring primer consists of an elliptical housing which contains a stationary hollow boss oraxle, (incorporating an inlet from the pump and two discharge ports). The water in the

housing is forced to move outwards by centrifugal force.

An ejector pump or primer consists of a passage or pipe which is constricted at one point sothat fluid or gas passing through it increases in velocity at the point of constriction and

generates a lowered static pressure. This is called the venturi effect.


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1. Why is a priming pump required?2. Describe how the pulsating effect of water in a force pump can be moderated.3. How does a water ring primer operate?4. How does an ejector pump work?

Activity1. Find out what types of priming pumps are used in your organisation.


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Priming the Centrifugal Pump

Section

4


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ADVANCED PUMPING

4-1

Pump gauges, valves and controls

Gauges display information you need to operate the pump effectively. Valves and controls enable

you to safely and effectively manipulate the water you are supplying. To help you better

understand this topic, it is divided into the following sections:

gauges valves engine controls.

GaugesFor pump operators, the most monitored gauges when pumping are the compound (inlet) and

pressure (delivery) gauges. On some pumps there may be more than one of each of these gauges.

Gauges are sensitive pieces of equipment. As with all firefighting equipment, care is required for

satisfactory operational service to be delivered. Sudden opening or closing of valves may cause

shock sufficient to damage some gauges, and such actions should be avoided.

Compound gauge

A compound gauge is used on the inlet or feed side of the pump and can measure pressure below

atmospheric (required when draughting from static/open water) and positive pressure (required

when water is being supplied from a hydrant or other pressurised source).

Compound gauges are usually diaphragm-type gauges. A diaphragm gauge has a flexible diaphragm

connected by a rocker bar and associated mechanisms (which magnify the movement) to a pointer.

As you look at the face of the diaphragm gauge, you will notice it has a long vacuum scale and a

short pressure scale. The scale on the vacuum side typically measures zero to negative 100 kPa

(1.00 x 100 kPa). This allows for more accuracy over a small range of vacuum readings (see Figure

32).

When a positive pressure is applied, (from water supplied from a hydrant or another appliance) a

small area of the diaphragm moves towards the small cavity in the front housing, thus giving a

reading on the smaller area of the gauge. On the other hand, if a negative (below atmospheric)

pressure is applied, a large area of the diaphragm shifts in the opposite direction within the larger

cavity of the rear housing, which magnifies the negative pressure reading.

Section

4


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Figure 32: Face and operating principle of a diaphragm-type compound gauge

Pressure gaugeThe pressure gauge is used to measure the pressure of water being delivered by the pump.

Pressure gauges are usually of the Bourdon tube type.

A Bourdon tube is a pressure responsive tube, that is, it reacts to pressures above and below

atmospheric pressure. This almost fully circular tube is oval in cross-section. At one end, it is

connected to the delivery side of the pump and, at its other end, to the gauge pointer by a link

and pivoting and toothed quadrant (see Figure 33). A hairspring keeps the teeth of the pinion in

close contact with those of the quadrant. This linkage magnifies the movement of the pointer on

the gauge dial.

Changes in pressure cause the Bourdon tube to either straighten out (caused by greater pressure),

or return to a more curved shape (lower pressure). More recent gauges are filled with glycerin,

which acts as a damper and reduces the fluctuation in the pointer's movement to give a moreaccurate reading.

01

2

3

4

5

67

89 10 11

1213

14

15

16

17

18

1920PressureX100 kPa

Toothedpinion

Pinion-activated pointer

Pivoting andtoothed quadrant

Link

Free end

Bourdon tubeunder pressure

Pressure Figure 33: Face and operating principle of a Bourdon tube type pressure gauge

Bourdon tube gauges are sometimes used for compound gauges, but the negative side (reading

down to 100 kPa) will be to the same scale, and therefore much smaller in overall size, than the

positive side of the gauge, which may read up to as much as several thousand kPa positive

pressure.


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ADVANCED PUMPING

4-3

Flow meter

Some types of fog nozzles are automatic in operation and will decrease or increase their flow

(within a set range) to maintain 700 kPa (or sometimes another set pressure) at the nozzle. While

adjusting the pump pressure (and taking into account friction and other losses) is an effective

means of controlling the flow to conventional nozzles, this is not the case with nozzles which willautomatically adjust to the changing pressure.

On some pumps, flow gauges or meters may be fitted. These indicate the rate of flow of water

being supplied. When used with automatic nozzles, a particular flow rate is supplied by the pump

operator, rather than a particular pressure. Usually, there will be a separate flow meter for each

outlet (see Figure 34).

Using a flow gauge or meter makes it possible for you to deliver the correct rate of flow to any

type of nozzle, without having to calculate pressure loss due to friction or height.

Litres per minute Litres per minuteLitres per minute Litres per minute

Figure 34: Flow meters showing different flow rates

Tachometer

The tachometer indicates the engine revolutions. The revolutions per minute (rpm) shown on the

gauge help the pump operator when performing various pump operations. The correct rpm settings

and/or limitations for your appliance will be indicated in the manufacturer's specifications.

When not actively pumping, you should set engine rpm so that the tachometer reads between 1200

and 1500 rpm. This is necessary when the pump is running and the deliveries are closed to:

keep the automatic priming pump (such as a water ring primer, if fitted) disengaged to avoidunnecessary wear on the primer drive wheel

maintain a high output from the alternator (particularly necessary when the appliance radio,flashing beacons or spotlights are in use)

run the engine-cooling system efficiently, whether or not the appliance is fitted with a coolingcircuit.

Note that if a pump is churning water against closed outlets, the water in the pump is not beingreplaced and may heat up to a point where damage may be caused to the pump seals or casing. To

avoid this, you should allow some water to escape from the pump or to re-circulate back to the

tank, if possible.

Tank gauge

Two types of gauges are typically used to indicate water level in an appliance's water tank: a sight

gauge, or an indicator light panel. (See Figure 35.)

The sight gauge, usually a clear plastic tube, is connected to the bottom and top of the water

tank, set vertically and positioned where it is visible from the pump panel. Whatever the level of

the water in the tank, it will be indicated in the tube (sight gauge).


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The indicator light panel uses a series of coloured lights to show when the water or foam

concentrate tank is full, and when the level is at three-quarters, half, one-quarter or empty.

These lights work as soon as the ignition is switched on. When the ignition is not on, a test can be

made to check the water contents by pressing the 'test' button.

In addition, some appliances are fitted with a low water level alarm which provides an audiblealert that the water level has dropped to a particular level.

Full

Empty

Test

Indicator light panel Tank gauge

Waterlevel

Valve

Full

Empty

Test

Indicator light panel Tank gauge

Waterlevel

Valve

Figure 35: Tank gauges

Oil pressure gauge

An oil pressure gauge is on the panel of all modern appliances. It uses an electrically transmitted

signal to indicate the oil pressure of the engine driving the pump. It is extremely important to

check this gauge frequently during operations. If oil fails to circulate, the engine can seize,

resulting in engine failure and extensive damage.

Any pronounced reduction in an oil pressure reading demands that the engine be closed down as

soon as possible after the branch operators safety has been assured. The Officer-in-Charge should

be advised of the close-down as well as what alternative arrangements can be made to ensure that

water continues to be delivered to the fireground.

Temperature gauge

The temperature gauge monitors the engine temperature. You should be aware of the normal

operating

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