chapter 03

© 2008 Delmar, Cengage Learning

Water Supplies for Fire Protection Systems

Chapter 3


Learning Objectives

• Define the terms pressure, flow, and duration as they relate to the movement of water

• Identify and describe the components of a water supply and distribution network

• Discuss the difference between a municipal/public water system and private water system


Learning Objectives (continued)

• Describe how gravity, pumped, and combined supply systems operate

• Define friction loss and discuss how it affects water flow

• Define static pressure and residual pressure• List and discuss the characteristics of the two

types of NFPA-approved stationary fire pumps• Define churn, rated performance, and peak

performance


Introduction

• Some areas have access to ground and surface water sources– Other areas have only one source of water available

• Demand for water changes by day, week, month and year– Engineers determine community’s demands

• Water-based fire protection depends on water pressure, flow, and duration– Must be adequate to support proposed design


Water Supply Systems

• Most water supply systems divided into source/supply network and distribution network

• Components of the source/supply network:– Water source, water intake, pumping– Treatment, purification system, transmission mains


Water Supply Systems (continued)

• Components of the distribution network:– Water storage facilities, distribution pumps, water

distribution mains

• Municipal public water systems responsible for water system supply


Source/Supply Network

• Gravity system: water at a higher elevation than the location it serves– Eliminates the need for pumping equipment

• Pumped system: lower elevation than the location it serves– Water from a well, or from a surface source

• Combined system: pumps fill water towers – Feed water distribution system by gravity

• Majority of systems treat and purify the water


Figure 3-1 Gravity-fed water distribution system


Figure 3-2 Direct pump water distribution system


Figure 3-3 Combination gravity-pumped water distribution system


Distribution Network

• Water purveyor treats water to make it potable• Treated water flows into distribution system

water main piping network– Transmission mains, distribution mains, service

laterals/lines

• Transmission mains: very large piping that transport the bulk of the water

• Distribution mains transport water from transmission mains to smaller areas


Distribution Network (continued)

• Service laterals/lines take water from distribution mains to individual properties– Supply fire hydrants and water storage facilities

• Water flows from different directions connected in loops and grids– Minimizes service interruption and improves reliability

• Fire lines or fire mains describe service laterals/lines that feed fire protection systems– In many jurisdictions, no other lines can connect


Figure 3-4 Schematic of grid or looped piping


Distribution Network (continued)• Water in sprinkler system stagnates and must be

kept separate from domestic lines– Must provide adequate flow, pressure and duration

• Developer or property owner responsible for installation of new water and fire mains– Water company taps into distribution line– Installs a control valve and piping to reach the

property line– Water lines constructed from ductile iron

polyvinylchloride and polyethylene plastics


Distribution Network (continued)• Approving authority handles all installations,

tests, and certification of new water lines– Water lines on private property the responsibility of

the property owner– Water lines in public right-of-way or easement the

responsibility of local jurisdiction

• Fire flow: number of gallons of water per minute needed to fight a fire

• If amount of water inadequate, need larger lines or looping of dead-end mains


Water Distribution System Valves• Two types of valves:

– Control the water flow– Control the direction of water flow

• Valves that control water flow – public water systems– Gate valve

• Buried under the street

• Access by removing valve box or roadway box

• Street key, valve key, T-wrench opens the valve

• Usually non-indicating valves


Figure 3-6 Valve box for a non-indicating gate valve feeding a fire hydrant from a water main


Water Distribution System Valves (continued)

• Valves that control water flow – private water systems:– Usually indicating valves

• Most are post indicator valves (PIVs) or outside screw and yoke valves (OS&Y)

– PIVs can be gate- or butterfly-type valves– OS&Y valves are only gate valves



• Valves that control the direction of water flow– Check valves and backflow prevention devices

• Prevent water from flowing in the wrong direction

• Prevent potable and non-potable water from mixing

– Check valves have a clapper that swings in the direction of water flow

– Two common backflow prevention devices• Double check valve assembly

• Reduced pressure principle devices



• Valves that control the direction of water flow (continued)– Water purveyors install double detector check valve

assembly – Reduced pressure principle/zone type backflow

devices• Offer best protection

• Install on any water system but are common to systems where hazard levels are higher than normal


Fire Hydrants

• Provide a point of connection to a water supply– Support manual firefighting operations

• Upon arrival, firefighters connect fire hoses to outlets on the fire hydrant

• Opening the hydrant and removing the caps requires a hydrant wrench

• Water flows from hydrant through hoses• Hydrant location and number determined by

local building and fire codes


Types of Hydrants

• Dry barrel and wet barrel most common types of hydrant

• Dry barrel commonly found where temperature drops below freezing– Water held in the ground below frost line

• Wet barrel has water up in the barrel at all times– Entire hydrant need not be shut off

• Outlet size varies– Steamer outlet usually four to four and a half inches


Figure 3-15 Typical schematic of a dry barrel hydrant


Types of Hydrants (continued)• Bollards surround hydrants to protect them• Wall hydrant: installed on the structure• Flush hydrant: installed in belowground vault• Yard hydrant: common at industrial facilities• Hydrants painted a specific color

– Caps and bonnet painted a different color

• Hydrants require different inspections and tests to ensure operability– Responsibility varies by jurisdiction


Water Flow Tests of Water Supplies

• May be simple or complex• Water information obtained from tests is valid for

design– Most water flow test information for new structures

comes from fire hydrant flow tests

• Important to perform water flow tests after system installed

• Perform tests at frequent intervals


Water Supply Design Considerations for Water-Based

Fire Protection Systems• Adequacy of water determined by evaluating:

– Flow– Pressure– Duration of water flow test

• When water supply is inadequate, further test determine if there are impairments– Designer has many parameters to explore


Water Pressurization for Water-Based Fire Protection Systems

• Many fire protection systems take water directly from the municipal network– Pressure determined by water purveyor

• Designer must know the static and residual pressure and flow rate at residual pressure

• If residual pressure is inadequate:– Installation of gravity tanks, pressure tanks, and

stationary fire pumps helps to support the design


Gravity and Pressure Tanks

• Gravity tank: freestanding tank elevated above a community– Tank capacities can be small or large– Tanks must be engineered to withstand

environmental conditions– Every foot of elevation exerts a pressure of 0.433 psi

• Pressure tank uses compressed air to push water out of the tank– Tank sizes range from 2000 – 9000 gallons

• Air is one-third total capacity


Stationary Fire Pumps• Fire pump boosts the pressure to desired level

– Delivers a certain amount of flow – Water supply must be deemed to be capable of

meeting demand

• Stationary fire pump part of an assembly that includes the driver and controller

• Three categories of stationary fire pumps:– Fire pumps– Booster pumps– Special fire service pumps


Fire Pump Impairments

• Fire pumps with an electric driver should be exercised for ten minutes per week

• Fire pumps with diesel drivers should be exercised for 30 minutes per week

• Pump flow-tested by owner annually• Insufficient water discharge could indicate an

obstruction• Preferable to uncover a problem during testing

than during a fire emergency


Summary• Water system is divided into supply/source

network and distribution network• Various types of valves control water flow and

direction of water flow• Two common barrel types: dry barrel, wet barrel• Water flow tests extremely important when

designing fire protection systems• Two types of fire pumps: centrifugal and positive

displacement

chapter 03

Documents

water pressure

water changes

water intake

water inadequate

water supplies

movement of water

water system supply

municipalpublic water