4.1 Fire Protection Measuring Water Supplies for Fire Protection Systems - Michael Klemenz, UFPE

8/4/2019 4.1 Fire Protection Measuring Water Supplies for Fire Protection Systems - Michael Klemenz, UFPE

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Measuring Water Supplies for

Michael J. Klemenz, PEFire Protection Engineer

. .

November 2010


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Fluid Hydraulics Formulas (10 min) Fire Code of NYS 10 min

NFPA 291- Overview Flow Test Basics (10

min)

Planning a Flow Test (10 min)

Performin a Flow Test 10 min

Calculating Flow Rates (5 min)

&A 5 min


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A brief review of Freeman, Bernoulli and

Hazen-Williams is in order to prove thevalidity of common flow-measuring

formulas


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For steady state, incompressible, frictionless

flow along a single streamline;

dp/ + gz + V2/2 = constantor

[p1/ + gz1 + V12/2]-[p2/ + gz2 + V22/2]=0

p1/ + gz1 + V12/2 = p2/ + gz2 + V22/2


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Determination of the head loss term is not covered

here. However, most fluid mechanics texts containthe derivation of this term using Reynolds Number,

, .


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For the flowing head loss across a standard

underwriters playpipe using the measuredflow velocity;

hf = (1-Cv-1)(V2/2g)

where:

hf = head loss across nozzle in ft.Cv= velocity coefficient (dimensionless)

V = Flow velocity in ft/s

g = gravitational acceleration in ft/s2


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With Q=AV, apply the Bernoulli Equation,

transpose units [cf/s to gpm], velocity [ft/s toft/min] and combine terms, simplify for

approximation purposes, etc. Freeman

Formula becomes


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Q=29.84cd2p

where:

c = coefficient of discharge *

d= diameter of the outlet in inchesp = pitot pressure (velocity pressure) in psi

*Include large orifice coefficient (0.84) if d 4


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-

P=4.52 1.85/C1.85d4.87 x L

where:

P= pressure loss from friction in psi= fluid flow rate in m

C= roughness coefficient

d= internal i e diameter in inches

L = pipe length in feet


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-

NFPA 13 Table 14.4.4.5

Pipe or Tube C ValueUnlined cast or ductile iron 100

Black steel (dry systems) 100

Black steel (wet systems) 120Galvanized steel 120

Plastic 150

cas or uc e ronCopper tube or stainless steel 150

Concrete 140


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-

Since pipe diameter, length and roughness

remain constant regardless of flow rate,

P=K Q1.85

If K is constant, then

P= Q1.85

Use Q1.85 logarithmic graph paper to plot P

vs. Q


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Section 508 states requirements for hydrantsand water su lies

Code enforcement official shall be notified

rior to water flow test. Tests shall bewitnessed by the CEO or approved

documentation shall be rovided 508.4


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Recommended Practice forFire Flow Testing and Marking of Hydrants

2007 Edition

Provides uidance for waterflow testin usin

pitot tubes and gauges

.This is up to the designer


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3.3.2 Residual Pressure. The pressure that exists inthe distribution system, measured at the residual

hydrant at the time the flow readings are taken at

the flow hydrants. 3.3.3 Static Pressure. The pressure that exists at a

given point under normal distribution system

no hydrants flowing.


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Flow Test Basics

When is a flow testrequired...? Whenever

NFPA 14 requiresflow test < 9 months

you are designing a

water-based fire

before installation

Tests must besuppress on sys em,

thats whenconducted during

periods of peak water

.recent and accurate Use test equipment in


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Flow Test Basics

Flow tests indicate therelative strength of awater su l

Dont assume watersupplier knows proper

Flow tests determine if Protect yourself and your

pump systems are neededto achieve system design

client conduct your own

water flow test

Flow testing can help

Specify that fire protectioncontractor perform a flow

closed underground valves& flow obstructions


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Flow Test Basics

Many water systemsexperience normal

Minimum residualpressure = 20 psi

time of day and season Plan for water disposal.

Prevent erosion or damage Flow test measures only

one point during the

dail /seasonal c cle

Avoid or plan for freezing

conditions

Get water supplier to


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1. Notify/request water supplier

2. If possible, obtain water utility maps of the water line to be

tested

.protected

4. Select a flow hydrant preferably downstream of the

5. Note any significant elevation differences betweengauge hydrant and building (1 ft. = 0.433 psi)

6. Plan for safe disposal of water


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Hydrant Wrench

Ca Assembl Liquid-filled GaugeScale/Ruler/Tape

Pitot Tube & Gauge


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1. Record date, time and location of test

2. Remove cap from gauge hydrant. Tighten the * .

3. Install cap gauge.

.

5. Open air release valve to vent air from hydrant. Whenwater emerges, close the air release valve

6. Observe and record the static water pressure indicated onthe gauge

* - .psi static pressure


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7. Remove cap from flow hydrant. Tighten the

remaining caps so they dont blow off.

8. Measure the actual internal diameter of hydrantoutlet(s) to be flowed

. ee n er or o ou e o es ma e y ran coe c en(see Figure)

10. O en h drant full and wait for clear water

11. Insert blade of pitot tube into center of stream about the outlet diameter away from the discharging

ou e see gure12. Observe and record the average pitot pressure on the

au e

13. Observe and record the residual pressure at thegauge hydrant


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Hydrant Coefficients

Vertical Section Through Hydrant Barrel


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14. Flow rate must be sufficient to reduce the residual

pressure to 75% of static pressure

15. Open additional outlets as needed to increase flowrate necessary to achieve pressure reduction

. pp y y ran coe c en o ow ra e ca cu a onresult

17. When usin lar e steamer outlets d 4 a ladditional 0.84 large orifice coefficient

18. Need minimum pitot pressure of 10 psi. If not, use

app ance o sma er ame er .e., p ay p pe,nozzle, etc.)


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Gauge Hydrant Flow Hydrant

Static Pressure, P si Outlet Diameter, D (inches)

Residual Pressure, PR(psi)Coefficient, C

Pitot (velocity) Pressure, PV (psi)


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Correct pitot position

D

D/2


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19. When all readings have been recorded, slowly close

ow y ran o preven wa er ammer one urn

every four seconds). Verify that the hydrant barreldrains

20. Reinstall hydrant cap

. ose gauge y rant an remove cap gauge

22. Verify that the hydrant barrel drains

23. Reinstall hydrant cap

.


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Diffuser equipment allows better control of water

No need to feel for hydrant coefficient or measurethe hydrant outlet diameter

Use lengths of 2-1/2 fire hose to get diffuser to catchbasin, ditch or other convenient water termination

Diffuser does not whip around during flow testbecause equal flow forces oppose and cancel

Length of fire hose between hydrant and diffuser doesnot affect overall flow test results


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2-1/2 Fire HosePressure Gauge

1-1/8 Insert

Pitot Tube

Hose Monster Appliance


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Q=29.84cd2p

where:

c = coefficient of discharge *

d= diameter of the outlet in inchesp = pitot pressure (velocity pressure) in psi

*Include large orifice coefficient (0.84) if d 4


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Q2=Q1 x (PS-20)

0.54

(PS-PR)0.54

where:

Q1= measured water flow in gpm

Ps = measured static pressure in psiPR = measured residual pressure in psi


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Or use values frompublished tables


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D=2-7/16105 psi

18 psi

70 ps

Gauge Hydrant Flow Hydrant

Static Pressure = 105 si Outlet Diameter = 2-7/16 inches

Residual Pressure = 70 psi Coefficient = 0.9 (rounded edge)

Pitot (velocity) Pressure = 18 psi


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Other Suggestions

When testing watersupplies served by a If test results are notas expected, look for

fire pump, shut off

jockey pumps and

closed valves, partially

closed valves,

manua y s ar e re

pump so it is running

un ergroun

obstructions, etc.


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References

1. Introduction to Fluid

Mechanics 3rd Edition (Fox &

McDonald)

2. Hydraulics for Fire Protection

(Hickey)

3. NFPA 291-2007 Edition(National Fire Protection

Association)


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the Old Days


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Measuring Water Supplies for

Michael J. Klemenz, PEFire Protection Engineer

. .

November 2010

4.1 Fire Protection Measuring Water Supplies for Fire Protection Systems - Michael Klemenz, UFPE

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