HYDRAULICS BRANCH OFFICIAL FILE COPY

,

UNITED STATES DEPARTMENT OF THE INTERIOR

BUREAU OF RECLAMATION

FLOW CHARACTERISTICS OF 8- , 10 - , 12 -

AND 18 - INCH CONCRETE FRESNO

, I RRIGATION . FLOWME T ER S

Hy dr aulic Laboratory Report No o Hy d o - 340

ENGINEERING LABORATORIES BRANCH

DESIGN AND CONSTRUCTION DIVISION DENVER, COLORADO

D e cemb er :d 9, 19 5 2

. UNITED STATES DEPARTMENT OF THE INTERIOR

BUREAU OF RECLAMATION

Design and Construction Division Engineering Laboratories Branch Denver. Colorado · · December 29. 1952

Laboratory Report No. Hyd-340 Hydraulic Laboratory Section Written by: J. B. Summers Reviewed and

checked by: W. C. Case J; W. Ball

Subject: Flow characteristics of 8-. 10-. 12-. and 18-inch concrete Fresnoirrigation flowmeters ·

PURPOSE

1. · Determine rating curves. head losses due to meters. and installa­tion limitations.

2. Compare the Hydraulic Laboratory test results with information given in the booklet published in 1928 by the Fresno Irrigation District and titled "Methods and Devices Used in the Measurement and Re~ulation of Flow to Service Ditch~s, Together with Tables for Field Use, ' abbreviated _edition, pages 26 to 39. inclusive.

CONCLUSIONS

1. The meter rating curves based on the laboratory tests agree closelwith the rating curves in the Fresno publication (Figure 5).

2. . Head losses through these meters. which contain sudden enlarge­ments, are high. The head loss can be reduced by forming a gradual expan:sion from the throat of each meter to the inside diameter of the concrete ·pipe (Figures 6B and 7).

3. A pipe outlet must have the submergence given in the following tableto insure a water surface in the downstream measuring well when the head difference (~H) in the measuring wells is 18 inches. . ·

Minimum submergence above Meter size Discharge cfs Location of down- pipe center in inches

inches for H • 18" ~ tream well tap .ttya Lat> l4 resno publ1cat1on

8 1. 73 Top of pipe 17.4 --10 2.50 Top of pipe 19.9 --12. 3.68· Side of plpe lL 3 11-1/8 18 8.52 Side of pipe 10. 6 14-3/ 4

The conditions under which the above listed values were obtained and the submergence required for various discharges· are-'shown on Figure 8.

4. The variation in the ratio of pipe inside diameter to throat diameter (ratio designated as R) results in different calibration curves fo:r meters- of ··: the same nominal size. This is an undesirable feature. · · ·

5. If a single calibration curve applicable to all meters of a given size is desired, forms which will give a constant ratio of pipe inside diameter to throat diameter will have to be used.

. ACKNOWLEDGMENT

The laboratory tests of Fresno flowmeters were- initiated by Mr. E. C. Fortier of the Tulare Basin District in a letter to the Chief Engineer dated April 28, 1949. Concrete flowmeters in sizes 8, 10, 12, and 18 inches were furnished qy the Fresno Irrigation District, F~esno, California. The study was ~ade jointly by members of the Canals Branch, and the Engineering Laboratories Branch. · ·

INTRODUCTION

The Bureau of Reclamation in recent years initiated a program for the development and standardization of various water-measuring devices. Among the devices investigated for feasibility, flow characteristics, and operational limitations was the concrete. flowmeter used by the Fresno Irri-gation District, Fresno, California. ·

The Fresno meter consists of a standard length of concrete pipe into which ha.$ been formed a circular throat section to give a reduction in cross­sectional area so that the principle of the venturi meter is applicable for the measurement of flow. The cylindrical throat section and the conical approach immediately upstream are cast by means of metal forms into standard pipe (Figure 1). The difference in static head taken one diameter upstream of the conical approach and 2 inches downstream of the throat section is the differ­ential head (b.H) across the meter. The publication by the Fresno Irrigation · District shows the static head taps located on the side of the pipe for the 12-· to 24-inch diameter meters and on the top of the pipe for the 8- and 10-inch diameter meters. The meters are available in 8-, 10-, 12-, 14-, 16-. 18-, . 20-, and 24-inch sizes.

INVESTIGATION

The Labora~or:y Installation

The test installation us_ed for the investigation in the Hydraulic Lab­oratory is shown on Figure 2. The flow was provided by a ·12-inch centrifugal pump and measured by volumetrically calibrated venturi meters. For the four sizes of Fresno meters tested, two or more sections of concrete pipe

2

were placed upstream of the meter section to make certain of the developmeof a representative velocity distribution for concrete pipe. ·The joint betweethe steel pipe and concrete pipe was ·made watertight by first passing the concrete pipe through a diamond saw to get a smooth surface., then greasing thesurface and holding it tight against a ~teel pipe flange by six tie rods to a similar flange at the opposite end of the concrete section (Figure 3). Prior to installing the concrete pipe., all rough edges were smoothed and recessiongrouted. A static head tap was. installed in the steel pipe at 5 diamete,rs dowstream from the metering section in order that the head loss due to the metecould be computed. A tailbox with a tailgate was installed on the outlet of thinstallation to control the elevation of the hydraulic grade line. This outlet arrangement permitted the· determination of the submergence requ~rements of the meter.

Test Results

Capacities. --Logarithmic plots of differential head (~H) versus discharge were made for the four meters (Figure 5). Prior to establishing the curve which would average these data., the coefficient of discharge for each plotted point was computed from the following relationship which can be de­rived from Bernoulli's equation applied immediately upstream of the meter throat and in the meter throat:

where

Cd= coefficient of discharge

Q = discharge., cfs

A1 = flow area of meter pipe., ft2

A2 = flow area of meter throat., ft2

g = gravitational force., 32. 2 ft/ sec2

~ H = differential head across meter, ft

A plot of Cd versus the throat velocity is shown on Figure 4. Using the average value for Cd at a particular velocity or discharge., the curve was then established on the logarithmic plot., Figure 5. The- equation of the curve for each meter tested is given on this figure. Previously in thisreport it was stated that any v.ariation ·of the ratio R., D1 ,was an undesirable

D2 characteristic. For example., in the equation for the 8-inch meter:

Q = 1. 49 cd~Ho. 502

3

The constant 1. 49 is a factor called K for the meter, which comprises Ai, A2, and g, thus: · · ' · · ·

Any variation in R will change the value of K, making it necessary to pre­pare another rating curve for a meter of the same nominal size but with slightly different value for R. • · ·

Head Losses. --The head loss due to each meter was computed (Fig­ure 7). To evaluate this head loss, the difference in static head at points P 1 and P3, Figure 2, was determined anq from this value was deducted the fric-:­tion loss in the pipe downstream of the metering section to the P 3 station. The friction loss was determined using the Darcy equation, ·

· 1 v2 HL = f d 2g

with the applicable values of "f" taken from King's Handbook of Hydraulics,. 1939 edition Since the resulting value of head loss was high, ways to de.;. , crease this head loss·were considered. A gradual expansion was formed on the 18-inch meter by placing concrete downstream of the throat section for a distance of 1 foot (Figure 6B). The lower head loss resulting from this gradual expansion rather than a sudden enlargement is shown on Figure 7.

Downstream submer~ence. --With insufficient submergence on the outlet of a turnout it is possib~e not to have a measurable water surface in th.e downstream well. The tailgate on the tailbox of the laboratory installa­tion was used to determine the amount of submergence necessary to maintain a water surface at the downstream tap as noted on Figure 8. The submer­gence v.aries with the different meter sizes because of the location of the well taps. In the 8- and 10-inch meters the taps were on the top while in the 12-and 18-inch sizes the taps were on· the sides. An examination of the figure shows an intersection of the 8- and 10-inch submergence curves in the lower flow range. This intersection results when the curves are passed through zero discharge. At zero discharge, the distance from the pipe center to the top of the piezometer used in these tests is greater for the 10-inch meter than for the 8-inch. This does not occur on the 12- and 18-inch meters since the measuring taps are located on the side of the pipe.

If the static pressure shown on Figure 8 does not give sufficient depth in the measuring well for certain recording devices such as a hook -gage, the submergence must be increased over that shown.

The pipe outlet should fl.ow full to have the meters operate as intended. On the 12- and 18-inch meters, with the well taps on the side of the pipe, it was possible to have a positive pressure at the taps and yet have the pipe not fl.owing full.

4

(A.) Looking Upstream

(B.) Looking Downstream TESTS OF FRESNO IRRIGATION FLOWMETERS

18-Inch Fresno Meter

Figure I Report Hyd. 340

,,flow straightener, 3 vanes,

,,aH = Pi- P2\ I I \ I \ I . \

.,,concrete pipe v ; ,-Stee I pipe

I I I I I I

~ I '

ltJ(:J : ', I q . I I j j il J J:io. - . - t \ / : Steel pipe/-,, ;; ~ . , = ; I J Submergencel

f. 120°apart,3'1ong. ,' P1 P2 '·

FLOW-:>-

' P3

, 1 I '--T1 e rods , 1 • • , *------------L,----------->t<--------------L _____ 1 Meter : 1 '-To supply · 2 ------->t<Sec-tio~-----L3 --->t

ME·TER o;~~ D2i~ R=~ L1 SltE 02

8" 7. 94" 5.4711 1.45 22'

1011 9.9411 6.67'' 1.49 21'

12· 11. 78 11 8, 13 II 1.45 191

1811 17. 9411 12.1411 1.48 10'

i~Av·erage of 6 measurements.

L2

6'

6'

8'

161

L3

5'

5'

5'

8'

TESTS OF FRESNO IRRIGATION FLOW METERS

LABORATORY INSTALLATION DRAWING

::0 CD

li:J "Tl 0-., (i)

-+c I~ <m 0: 'N (1,1

~ 0

(A.) 18-inch meter

(B.) Plastic measuring wells (laboratory use only) used for all meters tested.

TESTS OF FRESNO IRRIGATION FLOWMETERS Laboratory Installation

Figure 3 Report Hyd. 340

.98 • ,.. 0

0

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OAT -l l l 1 l l l 1 1 l 1 .860 2 3 4 5 6 7 8 9 10 I( 18-INCH METERS

THROAT VELOCITY - FT./SEC.

4.0

3

2

1.5

0: 1.0 w 1- 0.9

; 0.8

LI. 0.7 0 1-.0.6 w w LL. 0.5 I

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FIGURE 5 Report Hyd.34O

J V I Limit of Fresno Publication- -I -~ j

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--~ I I I

01

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02 I I I

~---,--i

Q=Cd A1A2· '1f2gtiH 'VA~-A~

Q - Discharge, c.f,.s.

Cd- Coefficient of discharge.

A,- Area of section at o,-ft~

A2- Area of section at o2-ft.2

FLOW ---:>

g - Gravitational force, 32.2 ft./sec.2

IIH- Di'fferentiol Head across meter-ft.

R - Rotioofpipedio.tothrootdio., ~~ K - Constant for meter A, A2ffl I

. . ,J A~-A~

Q- c.f.s.

METER D1 D2 R K SIZE

0" 7.94" 5.47" 1.45 1.49 10" ·9_94" 6.67" 1.49 2.18 12" 11.78" 8.13" 1.45 3.29 18" 17.9411 12.14" 1_.48 · 7.25

NOTE Dashed lines represent the data contained in the

publication, by Fresno Irrigation District,titled "Methods and Devices used in the Meosurementond Regulation of the Flow to Service Ditches,Together with Tables for Field Use;' Page 26 to 39, 1928. Doto for the 8 and 1O-inch meters was token from Tobie x, Page 33. Doto for the 12ond 10-inchmeters was token from Tobie IX, Page 31. Plotted points represent the data of the Bureo.u's Hydraulic Lo borotory.

TESTS OF FRESNO IRRIGATION FLOW METERS RATING CURVES 8,10,12 AND 18-INCH ~ETERS

(A.) Original metering section

(B.) After gradual expansion was added TESTS OF FRESNO IRRIGATION FLOWMETERS

Head Loss Study- -18 Inch Meter

Figure 6 Report Hyd. 340 .

1.4

• 1.2

a:: ILi I­<( 3: 1.0 IL 0 I-' IL I

~ 0.8

1-w ::i: 0 1-w 0.6 ::::, 0

en en 0 J o 0.4 <( w J:

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I HL = (P1 -P3) -Hj

Hj=J.&, y2 ,. II n d 2g

""" -12" Meter i taken from King's Handbook --/ of Hydraulics, 1939 edition.

J. I

.I_/ ~ Id" ,l- V

/ ..... .,,

J' V 1a"Meter- .,,/

~ I/ ~" A'

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L--" ~ -I/ i--- ·v -i,..,- ----

~ D""' - -k .... ,.,. 'IL

,.,. ... ' 1a"Meter with gradual expansion ----- -

" ~ I~ .,... as shown on Figure 68.

I '--" - :z-~ """'" -

"

4 5 6 7 8 9 10 DI SCH A R G E - c. f. s.

TESTS OF FRESNO IRRIGATION FLOWMEt-ERS HEAD LOSS CURVES

::0 Cl)

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FIGURE 8 Report Hyd. 340

, . • • • ··•· ; :·:·:--~- :±:+.::. ~.:.· t.·:·:.; ·:··;: ~.;.· ·: ;-r: • • •; 1: •· C : ;.~i. • .:.::~ r: .:. . .. •·• .... ,.. ·:. :__;-~· _;· ~ • ·.~ p:·:·~-_.: :_: ;:; : ....

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__ -·· _ _ -~.::· --Note: For occur ate wote r meo sure ment, ?Ll the submergence sh.ould be sufficient

1.

2

:::=::::~:::~:::::::::~:1::~::::~r: .. ~:~~:::~ .. -~:~~~~=:=::::::~_::~~~.:_--.:-.:-.-.:-.:~-.:-.:::::-.:-.::-.:~~~~ to have the pipe f I ow in g f u 11.

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3 4 5 ' 7 8 9 ·10

01 SCH ARG E - C.F. S.

, ,..-Measuring well tops, 12 and 18-inch meters. ,--w.s. / ,-Measuring well tops, 8 and 10-inch meters. , I t., I

~ ',:-----3~,---------- : ,-This depth of water \ ~-1

'i ~' plotted on ordinate ,, . ••• •• • .. .... ,.. I

, ', · ... · · ·· · · · , of above gro ph. \ ',, ~= I

' -- I

', ----------- FLOW. : ~ . --¾ --~ y -----o--i-----...... >---- __;;_ ___ .._____ - 0 u t I et

,;;., .. , ...................... ~"'··· ii',· ~"7':tt .--~-~~ 2 22222222222222222224

NOTES The required submergence was that which just

gave a pressure slightly above the downstream piezometer located on top of the pipe for the a and 10-inch meters and on the side for the 12 and 18- in ch mete rs. All resu Its ore for horizontal installation only.

TESTS OF FRESNO IRRIGATION FLOW METERS OUTLET SUBMERGENCE REQUIREMENTS

Interior - Reclamation - Denver, Colo.