a study of the hydraulic characteristics of control … · a study of the hydraulic characteristics...
TRANSCRIPT
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UNITED STATES
DEPARTMENT OF TH[ INTERIOR
BUREAU OF RECLAMATION
HYD-257 MASTER
FILE COPY BUR!:W OF RECLAMATION
HY DR.AGL TC L\W)P t/rORY
NOT 'l'O BE Rt:· ;;·1.·:_:: •·r,O:vl �'ILES
A STUDY OF THE HYDRAULIC CHARACTERISTICS
OF CONTROL DEV ICES FOR THE UNDERDRAIN
SYSTEM OF THE FRIANT-KERN CANAL
CENTRAL VALlEY PROJECT, CALIFORNIA
Hydraulic Laboratory Report No. Hyd.-257
RESEARCH AND GEOLOGY DIVISION
BRANCH OF DESIGN AND CONSTRUCTION
' DENVER, COLORADO
APRIL 18, 1949
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CONTENTS
Purpose of Study • • • • • • • • Conclusions • • • • • • • • • • Recommendations • • • • • o • • •
Acknowledgment • • • • • • • 1• •
Introduction • • • • • • • • • •
Description of Prototype Test Facilities • • • •
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. . . . . . . . . . . . . . . . . . . . . . . . . . Test Procedure • • • • . . . . . • • • . . . . . . . . .
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Preliminary Investigation . • • • • • • • • • • • • • • • • • 5
Ini�ial Tests of Flap Valve Control • • • • • • • • • • 5
Investigation of Seepf18e Quantity • • • • • . . . . . . . . .
. . . Flow of Seepage Water to Underdrains • • • • • Seepage Flow Equation • • • A • • • • • • • •
Computation of Seepage ::rl.ow • • • • • • • • • Pressure Distribution Under Canal Lining • • • �
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. . Investigation of Flap Valves . . . . . . . . . � . . . . . .
Seiection of Valve for .Alterations • • • • Capacity of Unaltered Valve • • • • • • •
. . . . � . . . Effect of Flap Counterbalance • • • • • • • • • • • • • Effect of Flap Weight • • • • • • • • • • • • . • • • • • Effect of Hinging Flap over. Center of Gravity • • • • • Effect of Seat Width • • ·• · o -.. • • • • • • • • • • • • ••
Characteristics of.Project Flap Valve • • • • • • • • • Characteristics of All�Brass Flap Valve · • • • • • • • • Characteristics of Rectangular Flap Valve • • • • • • •
Investigation of Weephole Type Underdrain Control· . . . . . . Weephole Und.erdrain Controls • • • • • • • • • Characteristics of Weephole with Rising Disk . Characteristics of Weephole with·Rubber Flap .
APPENDIX 1
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Flap Valves for 6-inch Drain Line--Friant-Kern·Canal-Central· Valley '.ProJect • • • • • • • • • • • •. • • • • • . .
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LIST OF FIGURES
Number
l Location Map 2 Concrete Canal Lining Und.erdrains 3A Electrical Analogy Tray Model. 3B Flap Valves 4 Curves fcYr Coef'ficient � 5 Capacity. Curves feyr Underdrain Flap Valves 6 Capacity Curves for Rectangular Flap Valve 7 Capacity Curves for Underdrain Weephole
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UNITED STATE3 DEPAR'IMENT OF TEE INTERIOR
BUREAU OF RECLAMATION
Branch of Design and Construction Research and Geology Division Denver, Colorado
Laboratory Report No. 257 Rydraulic Laboratory Compiled by: J. C . Schuster Reviewed by: J. W . Ball Date: April 18, 1949
Subject: A study of the hydraulic characteristics of conurol devices for the und.erdrain system of the Friant-Kern Canal--Central Valley Project, California.
PURroSE OF STUDY
The purpose of this study was to determine the adequacy of flap valves for controlling the flow of seepage water from the Friant-Kern can.aJ. lining und.erdrain system, without exceeding the maximum allowable pressure of 0 .67 foot of water-under the lining. The program was extended to_include· a study of the.hydraulic characteristics of two other types of underdrain control devices .
CONCLUSIONS
l. In any und.erdrain system, one of the first considerations should be the prevention of the underdrain control becoming inoperative because of· corrosion by oxidat.ion or electrolytic action, silting, bonding (such as rubber to metal), or biological growth.
2 . The quantity of seepage flow to each drain for an:y combination of factors of permeability, watertable, length of drainage section, and drain arrangement governing the flow quantity, should not. exceed the capacity of the control device for the critic·al head.
3 . The pressure conditions under the lining will be more critical with the can.aJ. empty than when l t contains enough water to submerge the · exits of the underdrains. With no water in the canal and the invert �f the flow passage of the exits placed 2 inches above the lining surfaces, the he�for producing fl.ow from the underdrains must not be greater than 0.21 of a foot or the buckling pressure of 0 . 67 of a foot will be exceeded. The allowable head differential will be increased to 0 .67 of a foot .for the buckling pressure when the exits are submerged.
4. Should a perfect seal occur between the contact surfaces of the valve seat, the ·head required to open the flap for any appreciable submergence would be cons�derably larger than the maximum of 0 . 67 foot used in this study. The effect of this type of sealing was negligible for all valves tested.
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5 . · The fl.ap valves purchased f'rom the Iowa Valve Company, the National Cast Iron Pipe Company, and the F;l.o,ckhart Valve Company will not operate satisfactorily under the low-pressure diffe�ential requ:lred in the Friant-Kern installation when �he canal is empty.
6 . The valve with the 4-pound. bronze flap, furnished by the project for testing, will operate satisfactorily provided that the seepage flow into a single drain does not exceed 0 . 01 cubic � per second,· and that there is no corrosion and a minimum frictional,. resistance in the hinge. By counterbalancing the flap of this valve, it is possible to make it open under extremely small heads and increase the capacity to 0.06 cubic foot per second for the 0 .21-foot head.
7 . Assuming no corrosion and_a minimum f'rictionaJ. resistance in the hinge, the three heavy commercial valves can be made to open at heads less than 0.21 foot by counterbalancing the flaps, but the discharge capacity for this maximum allowable head will be very small (approximately 0 . 03 cubic foot per second for the National Cast Iron Pipe Comp� valve).
8 . A "sloppy" fit should be provided in the hinge of any flap valve used in an und.erdrain system where operation under small heads is required.
9 . A lightweight flap (3 :Pounds or less) with its hinge over the center of gravity could be u ·aed to replace the heavy flaps of the valves al.ready installed.
10 . A flap valve with a recta.Dgular flow passage and lightweight flap will have better operating characteristics than one with a circular opening·having the same area and invert elevation.
11. A weephole through the canal lining, controlled by a rubber flap, is a feasible means of passing seepage flow f'rom beneath the canal. The material. of the :flap, the weight of the flap, and the position of the hinge point are important design factors •
. 12 . · An underdrain control consisting of a lightweight rising disk on a stem and supports, covering a weephole in the canal lining, might be us.ed in cases where the water is :f'ree of' moss, silt, or other ie br is .
RECOMMENDATIONS
1. Sufficient field information, including ground.water elevations and type and permeability of soils, be obtained for determining the adequacy of all canal underdrain systems prior to construction •
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2 . A 1ightweight flap (3 pounds or 1ess) with its hinge over the center of gravity be used to rep1ace the heavy flaps of the valves a1ready insta11ed in the Friant-Kern Cana1, and that additiona1 outlets be provided for the existing 1ong drains, should actua1 field conditions indicate seepage f1ow in excess of the capacity of the present insta11ation.
3 . A "s1oppy" fit be provided in the hinge of a;n;y flap valve used in an underdrain system operating under 1ow heads.
4 . ShouJ.d the f1ap valve be used to contro1 seepage flow from a canal. underdrain system, the valve should have a rectangular f1ow passage and 1ightweight f1ap and be insta11ed with the invert of the passage as near the surface of the 1ining as possib1e.
5 . If the use of a �onm.etal f1ap is contemp1ated, the sealing characteristics should be investigated before the design is adopted. Information concerning p1astic materials is contained in Appendix 1.
6. If the flap-controlled weepho1e underdrain is considered, a finished flap should be studied. in the laboratory before the design is adopted.
ACKNOWLEOOMENT
Engineers from the Cana1s and Mechanical Divisions and the Earth Materials Laboratory co1laborated in the cana1 underdrain investigations discussed in this repor�.
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INTRODUCTION
Description of Prototype
The Friant-Kern Canal., Central Valley Project, California, (Figure 1) has been designed with a 3-1/2-inch reinforced concrete lining. This lining can withstand. a maxim.um. differential water pressure of 0.67 of a foot without buckling. · To protect the lining against buckling due to a differential water pressure resulting from a high watertable or rainstorm, 6-inch open-jointed sewer pipe drains have been provided beneath the floor of the canal (Figure 2). At intervals along the
· course· of the canal, the drainpipes pass upward through the bottom lining and are vented by flap valves. F.ach valve consists of a body connected by a flange to the end of a drain and a flap which is free to swing out from the body seat when internal pressure from the drainpipe acts _upon it.· The invert of the valve flow passage has been placed approximately o.46 of a foot above the lower side of the bottom lining in order to facilitate the installation of the valve, -and to assure a minim.um interference by moss or accumulating· silt. For safety
· of the lining, the flap valve must open and be capable of discharging the drainage flow at heads not greater than 0.21 of a foot when the cana.1. is empty and the invert of the drain is 2 inches above the lining. The differential head should not be greater than 0.67 of a foot when there is sufficient water in the canal to submerge the valve. Since little was known of �he operating characteristics of flap valves at small heads, it was requested that several of the commercial designs inRtalled in the Friant-Kern Canal be tested in the.laboratory.
Test Facilities
A 20-foot horizontal length of 6-inch standara pipe terminated by a flange inside of a box in which the water depth could be varied was provided to test the gates in the laboratory. Water was supplied by a vertical 8-inch propeller pump and measured by an orifice-venturi meter. A 1-inch standard pipe vent was placed in the 6-inch pipe to facilitate applying pressure to the valve flap. Pressures were measured by a water manometer connected to a piezometer located one pipe diameter upstream from the extreme end of the valve body and in the bottom of the 6-inch pipe. To facilitate obtaining the pressure required to open the valve, a set of electrical contacts completing the circuit to a small light bulb was attached to the flap and body. The slightest movement of the flap would break the contact which would interrupt the current to the bulb and indicate the opening of the valve •
.An electric analogy tray was used to determine the amount of seepage flow which might be expected to enter the underdrains. The tray, l inch in deptp, having sides of strip plastic which represented
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a half section of the canal having a depth of 16 feet, a bottom width of 18 feet, and a side slope of 1-1/4 to l, was constructed on a 50- by 50- by 3/8-inch glass plate to a scale of i/2 inch = l foot· (Figure 3A). The rema,ining portion of the tray boundary was £ormed by.placing plastic strips on the vertical centerline below the canal bottom, along a horizontal line 8 inches above the floor and outside of the canal wall, and on an arc of 40-inch radius between these two lines. The center of the 40-inch radius was at the intersection of the canal centerline and the horizontal line 8 inches above the canal floor . An electrode was I placed along the curved boundary to represent the maximum potential of the groundwater . Two small electrodes represented one and one-half drain filters of a three-drain system and the minimum potential at the canal bottom . The electrolyte used in the model was tap water approximately 1/2 inch in depth.
Test Procedure
Each flap valve was bolted to the flange inside t�e box and water introduced slowly into the 6-inch pipe through the 1-inch vent until the flap w�s forced open by the pressure in the pipe. The head required to open-the flap was read from a water manometer at the instant the indicator light signified that the flap started to open . The same procedure was followed whether the valves were submerged or unsubmerged.
Accepted standard procedures were followed in the electric analogy tray tests.
PRELIMINARY INVESTIGATION
Initial Tests of Flap Valve Control
The initial tests on the four valves received from the project indicated that none would be entirely satisfactory for the underdrain system.
The opening heads were excessive for the unsubmerged condition for three of the valves, Table l, and it was not certain that the capacity of any of the valves was adequate, since the quantity of seepage flow was unknown •
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'· Manufacturer
Friant Va.l.ve No. l3l4l (lll&D,ufacturer unknown)
Iowa Valve Company
National. Cast Iron Pipe Company
Flockhart Val.ve Company No. 5149
Table 1
Differential head
Submerged
0.03
0.093
0.23
0 . 34
Pressure in feet of water, referred to invert of 6-inch pipe.
Unsubmerged
o.ll
0 . 31
o.48
o.47
Note: A check of the rel.iability of the values given above was made by computation using bal.anced moments about the hinge point, one for the weight of the flap and one for the force produced by the water pressure. Good agr-eement was obtained.
The investigation resol.ved into three parts: (l.) t;o determine what quantity of seepage flow might be expected to enter the drains; (2) to determine if the valves had sufficient capacity within the required head range; and (3) to determine if the install.ad valves could be made to operate satisfactorily by making lliinor alterations . The program was continued on the basis of these three problems.
mv.HSTIGATION OF SEEPAGE QUANTITY
Flow of Seepage Water· to Underdrains
The capacity of the Friant-Kern Canal. underdrain system was l.im:ited by the elevation of the drainpipe exits and the resistance of the flap valves; therefore, it was very important to determine the quantity of seepage flow to be e:x:pe.cted to enter the nnderdrains. Electric anal.ogy tests were made for that purpose.
Seepage Flow EQuation
The equation, Q == KHL'f:4, mey be used to compute the seepage flow to the canal underdrains, .providing al.l. its factors can be evaluated. In the equation
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Q = volume per unit tilne (cubic feet per year)
K .. percolation rate (f' eet- per year)
H = height of watert�ble in feet above drain filter
.L • length of canal section in feet, measured al.otig the longitudinal. centerline
� = shape factor, dependent upon design and foundation conditions
The f'actor, � , cannot be determined :ri:om physical meas11,..ements of an installation but can be obtained through electric �ogy studies which consider the flow of current in a conductor analogous to flow of water ,1
· through granular material. (Ohm' s Law and Darcy' s Law for seepage :f'low) .b In the case of the electrical analogy tray, ·� is the ratio of the resistance of a square unit of the model to the resistance of the model (both containing the same depth of electrolyte).
. Two conditions had to be considered in determining the value of � ·: (1) the.effect of·cha.nging the depth to an impervious layer; and (2) the effect of changing the height of the watertable·above the underdraih filter. Curves were plotted showing the variation in� for the two above conditions (Figure 4). The maximum value obtained was 0.77 for the one-half sec-cion of the canal which assumed pervious material. of· infinite dimenston� and a watertable coincident with the top of the canal.. A flow net constructed by using data from the electric ·. anal'ogy tray indicated that the discharge would be distributed so that approximately one-fifth of the seepage water flowing to the canal underdrain system would enter the center drain while two-fifths would' enter·each of·the two outs:l.de drains.
Computation of Seepage Flow
By using the f'low distribut.ion ratio and appropriate value$ of'� , it is possible to compute the seepage flow into any system of underdrains which is geometrically similar to the one tested, if the watertable, length.of drailla8e section, and percolation rate a.re known. All of these data a.re not avai�able for specific sections of the FriantKern Canal; thus it is not possible at this time to predict the discharge quantities for the underdrain systemsi of that structure.
Y E. W. Lane, ''Model Studies of the Imperial. Dam De silting Works and .Structures in All-American Canal, " Hydrau11c Laboratory Report No. Hyd 199, p. 93, Bureau.of Recl,amation, Denver, Colorado, May l, 1946.
J. �- Brag,ley, J. B. Drisko, and D. J . Hebert, Prel.iminary Report No. 2, 'lM l� 71, "Hydraulic and Electrical. Ana.logy Model Studies of the . Proposed Imperial Dam and Appurtenant Works--All-.America.n Canal Project," Bureau of Reclamation, Denver, Colorado, July 15, 1935 .
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The amount of seepage for a one-half section of the caruil computed from probable maximum val.ues of �, H, K, and L, which might occur al.ong the course of the canal, is 0. 80 cubic foot per second . The val.ues of�, H, K, and L used in computing this quantity are as follows:
H,' "' 0. 77 ma.x:imlllll val.ue from electric analogy tray tests (figure 4)
K = 4,125 feet per yea:r:, Table 2, Earth Materials Laboratory Report No . :EM-78, October 12, 1945
H = 16-foot depth of canal. or assuming watertable coincident with top of canal
L = 500 feet, Sec. AA, Figure 2
It seems very improbable that the above val.ues would ever exist at one location. If such conditions do exist, the most logical. solution would be to decrease the drain J..ength L. The height of the drain exits, being Q.46 foot above the bottom of the lining, limits the head for producing flow to 0.21 foot for the unsubmerged drain exit; thus the maximum. length of drain can be determined if the capacity of the drain under this head is known . The capacity must include the influence of any restriction, such as flap gates or other controls, placed at the exit of the drain. The discharge for an open unsubmerged drain under this head is 0 . 096 cubic foot per second, or about 15 percent of the maximum possible flow; thus, the pressure head for the ma.ximlll!l val.ues will be excessive, even for the unrestricted drain unless the length i.s Umited to about 65 feet or the permeability coefficJ.ent does not ex�eed 490 feet per year.
It must be pointed out that the val.ues of� determined in this study are applicable only to canal cross-sections geometrically similar to that tested and that these values are for a one-hal.f section of the.canal . Mditional. tests would be required to determine� val.ues for other cross-sections and underdrain arrangements.
Pressure Distribution Under Canal. Lining
A determination of the pressure distribution on the lining, that is the effectiveness of the drains for reducing pressures throughout the underside of the lining, was not made because of limitations imposed by the temporary electrical. analogy equipment used in this
•. study. It was believed that if pressure at any point under the lining exceeded the buckling pressure, the lining would raise slightly from the surrounding soil to form a free water path between the point in question and the und.erdrain filter, thereby relieving
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the excessive pressure. There probably will be some silt carried into this path by the seepage flow and so the number of pressure-relieving cycles without damage to the lining may be limited. A detailed pressure-distribution study could be made. if the need should ever arise in the design of underdrain systems.
INVESTIGATION OF FLAP VALVES
Selection of Valve for Alterations
It became evident during th� preceding tests, that nothing could be gained by using a valve with a greater capacity than an unobstructed drainpipe; therefore, this criterion was used for determining the adequacy of all valves tested . With a determination of approximate seepage flow quantities, it became necessary to find if any of the valves had sl,lf'ficient capacity to discharge this flow within the required head range, and to find if the installed valves could be made to operate satisfactorily by minor alteration of their parts. Since all of the valves were o:f similar design (Figure 3B) and had similar hydraulic characteristics, the National Cast Iron Pipe Company valve was studied for the effects of the various alterations . This valve was chosen because it required a greater head to open than any of the other valves when discharging unsubmerged, and any solution obtained from the uests on it would be applicable to the other valves.
Capacity of Unaltered Valve
A head-discharge curve for complete submergence was obtained for the National Cast Iron Pipe Compa!lJ'" flap valve (Curve a, Figure 5A). It was found that the differential head required to maintain flow was independent of the depth of tailwater, and that . the capacity of the valve for submerged flow was adequate for passing the seepage water.
The head-discharge relationship for the unsubmerged valve was obtained also (Curve a, Figure 5B). The heads to open tJ:ie· valve and maintain flow were excessive. A discontinuity existed in the curve at approximately 0.2 of a second-foot, which was believed caused by a change in the,flow conditions in the' passage formed between the body seat and flap.
It was believed that the discontinuity resulted from the contraction at the inner periphery of the body seat and the flow conditions in the expanding passage between the seat and flap. The decrease in pressure in the flow passage accompanied the contraction and expansion and created a hydraulic pull force which tended to close the flap, thus increasing the head required to maintain flow. This flow condition existed until the outward movement of the gate by the force of the
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water changed the dimensions of the passage so that the jet became aerated. When aeration occurred the flap moved out and the depth of water in the pipe decreased.
Effect of Flap Counterbalance
The first alteration made to the National Cast Iron Pipe Company flap valve was the addition of a 5.05-pound. counterweight suspended inside the pipe on the upstream side of flap (Figure·5A). The flap was balanced in air by the counterweight so that it might touch the seat or remain slightly open depe¢ing upon the action in the hinge. In this condition of balance, the valve starts opening at practically zero head. The discontinuity in the discharge curve was. not discernible, probably due to the fact that the balancing of the flap permitted it to be forced open beyond the critical point by a very low head and permitted the jet to aerate at a very small discharge. The discharge was approximately 0.03 of a second-foot when the head in the pipe reached the ma.:x:imllll allowable of 0.21 of a foot (0.67-foot water on bottom of lining) (Curve b, Figure 5B). Calibration for the submerged condition showed the capacity to be satisfactory, 0.27 cubic foot per second for a differential head of 0.010 foot (Curve b, Figure 5A).
Effect of Flap Weight
.An 8- by 8- by 1/8-inch brass flap with the same hinge point was made for the National Cast Iron Pipe Campany valve (Figure 5C). This flap weighed 2.59 pounds compared to the 10.60 pounds of the originaL. A discontinuity in tha discharge curve similar to that observed for the original flap was still apparent, but occurred at a lower head and a discharge of approximately 0.04 of a second-foot (Curve a, Figure 5c). At a discharge of approximately 0.25 of a second-foot and a head of 0.81 foot, the flap ceased to affect the head at the piezometer and the discharge curve coincided with that for free flow from the pipe. This alteration was not a solution because the head to open the valve and maintain flow was excessive when the valve was. not submerged.
Effect of Hinging Flap.over Center of Gravity
The 8- by 8- by 1/8-inch brass flap was altered to move the hinge point over its center of gravity (Figure 5C). This change reduced the head required to matntain_a given discharge such that the discharge for the 0.21-foot head was.approximately 0.10 cubic foot per second, the same as for an l.llll:'estricted drain (Curve b, Figure 5c). However, a discontinuity still occurred in the discharge curve and the maximllll head under the lining, at the discontinuity, was O·. 62 of a foot, wh-ich was only slightly less than the ma.:x:imllll a.lldwable. It was desirable to either reduce t�e-head. at the discontinuity or elimin,a.te the discontinuity, so further tests were made.
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Ef'fect of Seat Wid�h
It was reasoned that the discontinuity caused by the flow condition occurring between the body seat and flap could be eliminated by redu�ing the width of the seat. The reduction was made by machining the original seat of the National Cast Iron Pipe Company valve to an annular ring 1/8 inch wide by 1/4 inch deep having an inside diameter of 7.12 inches (Figure 5B). The pressure-discharge relationship for the original flap with the altered seat ring is shown by Curve c, Figure 5B. The discontinuity in the discharge curve was eliminated, but the opening head was decreased only slightly. This slight decrease was attributed to the fact that the water pressure acts over a larger area on the inside of the flap.
Data obtained for the 8- by 8- by 1/8-inch brass flap having the �ame hinge point as the original flap, but with an altered body seat, are shown by Curve c, Figure 5c. There was no discontinuity in the discharge curve but the head to open and maintain flow against the moment of the gate about the hinge point was still too large. With the hinge point moved forward, the head-nischarge relationship was the same as for f'ree discharge from an open drain (Curve d, Figure 5c). It is believed that any of the four valves listed in Table l.could be made to operate satisfactorily by reducing the seat width and providing a lightweight flap hinged over its center of gravity. From these tests, it was concluded .alsu that the most satisfactory flap valve for the underdrain system would be one which has a narrow seat a.nd. a lightweight flap with the hinge placed over or near its center of grayity.
Characterist.ics of Project Flap Valve
Although the heads to open the flap valve with cast-steel body and 4-pound bronze flap received from the project and identified by the number, 13141, were within the specified limits for the submerged and unsubmerged co;nditions, the discharge capacity was very small for the unsubmergea condition and there was a small discontinuity in the discharge curve at about 0.04 cubic foot per second (Curve a, Figure 5D). Tests were made .to determine if the capacity could be increased sufficiently by minor alterations to permit the use of the valve in the Friant-Kern Canal underdrain system. The alteratio�s consisted of: (l) counterbalancing of the bronze flap (Figure 5D), and (2) decreasing the width of the seat by machining the inner periphery of the flap seat ring (Figure "SD) .
The capacity of the valve was increased by counterbalancing the bronze flap with a piece of 3/8-inch-diameter brass rod 10-1/2 inches long. The increase in capacity for the submerged valve was substantial while that for the unsubmerged condition was small (about 0.05 cubic foot per second)_ (Curve b, Figure 5D). The head required to open the valve was negligible for both cases.
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The capacity of the valve was not increased materially by the machining of the inner periphery of the flap seat (Curve c, Figure 5D), but the discontinuity in the discharge curve for unsubmerged flow was practically eliminated.
The water from the reservoir at Friant Dam is considered to have a salt content great enough to produce an electrolytic action between the cast-steel body and bronze flap of· this valve. This action would make the life of this valve questionable, if the valve were to remain submerged for long periods.
The loose fit in the hinge of this valve will lessen any possibility of its becoming inoperable due to corrosion.
Characteristics of All-brass Flap Valve • I
An all-brass flap valve, having a bod� of 6-inch-inside-diameter by 1/4 inch wall brass pipe and a circular flap of 1/8-inch brass plate with the hinge placed vertically above the center of gravity, was constructed and tested (Valve e, Figure 3 B). Its design was based upon the results of the tests completed thus far on the four flap valves received from the project. No discontinuity was observed in the discharge curve which, for all practical purposes, coincided with that.for an unobstructed drain (Curve e, Figure 5c). This valve was cc>nsidered enti-..ely satisfactory s_o far as hydraulic characteristics were concerned. It does have the disadvantage in that cast iron is anodic to brass.
Characteristics of Rectangular Flap Valve
Since it was found that most flap valves are unsatisfactory for installation in low-pressure und.erdrain systems:, a valve for replacing those already installed in._the Friant-Kern Canal was proposed by the Mechanical Design Section (Figure 6). This flap valve included a cast-iron adapter flange that lowered the valve flow passage invert l-l/4 inches below the invert of the underdrain exit, and a 1/8',..inch rectangular bronze flap and hinge weighing approximately 1.5 pounds. The seat on the body of this valve was a rectangle with inside dimensions 3-1/4 inches high by 7 inches wide, and a seat width of 9/32 inch. A clearance of 1/16 inch bet't-leen the hinge pin and .bearing was provided to minimize the possibility of corrosion freezing the hinge. The rectangular exit of this valve provided a greater area in contact with the water for small heads, thus for a given depth of water, the opening force is larger than for the circular exit.
The opening head for the unsubmerged rectangular flap valve was 0.06 of a foot of water. Since the invert of the water passage of the valve body was about 0.10 foot below the invert of the drainpipe exit, the opening head for the flap did not affect the depth in the drain (Figure 6).
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The rating curves based on the total head on the drain exit and on the total head in the valve body, show that the capacity for this arrangement is essentially the same as an unobstructed drain (Curve a, Figure 6). The capacity of an unsubmerged Friant-Kern Can.al underdrain, using this flap valve arrangement, will therefore be limited by· the elevation of the drain exit rather than the resistance of the flap valve. The critical heads and corresponding capacities for three drain-exit elevations are shown on Figure 6. The maximum capacity for the drain exits placed 2, 3, and 4 inches above the canal floor are 0.094, 0.036, and 0.004 cubic foot per second, respectively. This valve, as constructed in the laboratory, exhibited good sealing qualities in preventing a reverse flow of water into the µnderdrain. The only disadvantage was the possibility of corrosion resulting from the use of two dissimilar metals.
INVESTIGATION OF WEEPHOLE TYPE UNDERDRAIN CONTROL
We.ephole Underdrain Controls
I A weephole type of underdrain was investigated because of the unfavorable opening heads and operating cha:r--acteristics noted for many of the flap valves in.the tests discussed pre--viously in this report. The ·advantages of this type of und"erdrain, over that planned for the Friant-Kern Canal, were: (1) that its exit was at a low elevation with respect to the floor of the canal, permitting utilization of more of the ma:x:imlml allowable underlining pressure for producing flow from the drains, and (2) possible elimination of drain tile. Two devices for controlling, the flow frqm the weephole were tested: (1) a rising rubber disk and (2) a rubber flap (Figure 7).
Characteristics of W�ephole with Rising Disk
A rising-disk control for the weephole, tested in the laboratory, consisted of a rubber disk seal; a circular metal plate on top of the rubber disk to prevent its being pushed into the weephole by water pressure from the canal; a guide_stem; and a guide bearing with clips to facilitate the removal· of the device for inspection (Figure 7A). This control was placed in a 2-inch plastic tube which represented the weephole.
The opening head for the,disk was recorded as that which produced an evinent flow and not that which caused slight leakage from beneath the disk. This head was recorded by a piezometer installed in the 6-inch conduit supplying the water·to the underside of. the disk. Water was introduced into the supply conduit slowly and the piezometer reading taken when the disk opened. Since the head required to open
13
._ .
...
•
this device'was somewhat dependent upon the weight of its moving parts, tests were made with various weights placed on top of the disk.
The opening head for the submerged condition appeared to be constant at about 0.03 of a foot for moving parts weighing from O. ll to 0.65 of a pound, while that for the unsubmerged condition varied from 0.02 to 0.22 of a foot.· The fact that the opening head for the submerged condition appeared to remain constant was attributed to the difficulty of determining when the opening actually ocourred.
The capacities of the unsubmerged weephole underdrain for weights of 0.11, 0.23, and 0.65 of a pound were approximately 0.01, 0. 03, and 0.05 of a cubic foot per second for the maximum allowable lining pressure. The three separate curves at the left of Figure 7C show the effect of the weight of the moving parts upon the head required to 'produce a given discharge, while the single curve at the right into which the three merge shows the effeGt of the disk reaching its maximum rise. The high points in the curves are caused by flow conditions between the seating surface of the rubber disk and the lining surface, similar to that described for the flap valve under section "C.apacity of Unaltered Valvell of this report. · The capacity of the unsubmerged rising disk control, with moving parts weighing up to 0.2 of a pound, would be half that for an uncontrolled 6-inch underdrain of the type placed in the Friant-Kern Canal�
The pattern of the capacity curves for the submerged weephole and three different weights of the moving parts was similar to that for the unsubmerged condition (Figure 7D). How�ver, the head to produce flow remained substantially below the maximum allowable until after the disk reached its maximum rise and the curves merged, thus giving the same maximum capacity of 0.067 of a cubic foot per second for the three weights. The weight of the moving parts is not so critical when the weephole is submerged. The possibility of increasing the capacity of this device by increasing the rise or the size of the weephole was not investigated.
The disadvantages of this control were that moss streamers might entangle the disk when it is in the raised position releasing seepage flow during the time that the canal carries water, and that it was on the floor of the canal where sediment could interfere with its operation. A protective hood could be added but no tests were made to determine its feasibility.
Characteristics of Weephole with Rubber Flap
A second device considered for controlling the flow through a weephole was a rubber flap bolted to the canal lining (Figure 7-B). 'A metal reinforcing disk was placed 011 top of the 1/8-inch rubber flap to
14
•
... . ...
prevent its being pushed into the tube which represented the weephole. The head to open this rubber flap was determined in the same manner as that for the rising disk and it was found to be negligible (Figure 7E). Discharge curves for the submerged and unsubmerged condition were obtained.for flaps with hinge distances of 2 and 3 inches and reinforcing disks weighing 0.04, 0.13, and 0.31 of a pound. The weight of the portion of the rubber flaps affecting the operating heads was 0.07 and 0.09 of a pound for the 2- and 3-inch hinge distances.
I
There were discontinuities in the curves similar to those observed for small openings in the initial flap gate study. It was believed that a reduction in pressure occurred between the rubber flap and lining as the water passed from the tube, thus increasing the head required to force water through the weephole. This reduction in pressure continued until the force of the water lifted the flap and changed the flowlines. The discontinuity of flow is reflected in the discharge curves for both the submerged and unsubmerged weephole.
The maximum capacity at the allowable underlining pressure ·obtained for this type of control was 0.06 of a cubic foot per second for the unsubmerged condition and O.l2 of a cubic foot per second for the submerged condition.
' The head-discharge relationship of the rubber flap might follow
two paths, depending upon whether the seepage flow from the weephole is decreasing or increasing. In either case, the head might becom� sufficient to endanger a 3-l/2-inch-thick lining, unless the hinge distance and weight of the flap are properly designed. The fiap should be lightweight and the hinge distance made small enough to eliminate objectionable head ri�es in the region of discontinuity. Further improvement might b� realized by using other hinge and seal designs
..
. •
..
APPENDIX l
J. K. Richardson March 8, 1949 Through W . T . Moran and R. F . Blanks
J. L. Gilliland
Flap valves for 6-inch drain lines--Friant-Kern Canal--Central Valley Project.
1. During .December 1948 , we had several discussions on the question of a suitable material for fabricating the flaps of the drain valves on the Friant-Kern Canal . At that time, I suggested that certain plastics appeared to have the desired properties and should be given· consideration .
2. King Plastics and Ingerwerson Manufacturing Company, both of' whom are local plastics fabricators, were consulted . Both concerns expressed the belief that certain plastics were suitable :f'or this purpose. Particularly, polyethylene , polystyrene, and saran were proposed . However, since these :f'abr�cators were not completely familiar with the long-time behavior of' these materials, it was considered advisable to· write the manufacturers for their recommendations.
J . After a considerable delay, we have now received replies to our three letters of inquiry . Although the original problem has been eliminated by a change in design, this memorandum has been prepared to summarize the manu.:f'acturer · s recommendation in the event a similar problem arises .
4. Monsanto Chemical · Company says flatly that · they would recommend. no plastic material where the flaps will not be available for examination or replacement for a period of years . They fear also, that plastics have not sufficient impact strength.
5 . Dow Chemical Company suggests that either saran or polystyrene might be used if' the impact conditions are not too severe.. However, they lack aging _information, and can only suggest that we answer this question by trial.
6. DuPont is somewhat. doubtful of the aging characteristics of polyethylene, as well as the possibility of cold flow distorting the vaives •
7. In view of these opinions, I have now concluded that we have not su.:f'ficient data at this time on the aging characteristics of these materials to warrant a field installation on a very large scale. There is no proof that the materials would not be suitable, and I would not , hesitate to chance one of these materials if' we had no alternate. However, until the manu.:f'acturers gain more experience, there is no advantage in our pres sing for an installation at this time .
16
, •
...
Ref'erences: Letter of' December 31, 1948, f'ram Monsanto Chemical Company (04881 January 10, 1949)
Letter of' January 5, 1949? f'rom Dow Chemical Company Letter of' February 15, 1949, f'ram DuPont and Company
(10013 February 18, 1949)
/
17
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LO CAT I O N M A P
F R I A N T - K E R N CAN AL
F I G U R E I
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Sand and gravel filled t rench (a) to' crs. ------------- -
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mortar over trans- // ,: Sand and gravel filled A \ not shown ,' �A\ verse drain - -- - - trenches (continuous ) _ _ _, \ 'Sand and gravel filled
7c
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over 6" sewer pipe drain.
E r Unreinforced protective hood --
\ Short radius ,, - Mortar jo int
,- t" Layer cement mortar ' I ' '
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'
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Unreinforced box 2 ' x 2 '-6" / (Graded sand and
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I � ' --. gravel ' 30" Precast reinforced : concrete p ipe unit. - - '
- ---compacted backfill
S EC T I O N A -A A T OUTL E T B O X - 5oo' MAX. C R S.
Unreinforced protective hood - ' ,, FL O W�
i-- - · �-------\o r -
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Underdrain
\ . :J ECTIO N A-A
A LTERNA TI VE SECTION AT O U TL E T B O X - 5oo 'MAX. CRS.
t = 2£"Min. for cenfrifuqal pipe. t = 3f'Min for precast pipe.
Unreinforced protective hood - , , FLOW
- --',>-
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6"F lap valve , ,,,,
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P LA N C-C P L A N E - E A LT ERN A TI VE S EC TION
FIGURE 2
r" -2 , · - -� -.J 10 1." k- __ L r. U nderdrain 1 2 j - / I I£.
A lternative transverse
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S EC T I O N B - B ( TRA NSVERSE DRA IN )
:,<--20" _,,, ---] 1 0" 1:/+-f Underdrain
I I I •
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THIS DRA WING SUPERSEDES D WG. 214-D-1479O
U N I T£ D S TA T£ S
DEPA R T M E N T O F TH£ I N T E R I O R
B U R E A U O F R EC L A M A TI O N
CEN T R A L VA L L E Y PROJEC T- CA L I FO R N IA
FR/ANT-KERN CANAL-STA. 4646 +06 TO 6 0 76 + / 5 .00
C O NCR ETE C A NA L LINING
U ND E R D RA I N S
D£N V£R , CO L O R A D O. A PR I L 30, 1 948 214-D-148 14
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A. Electric .Analogy Tray Model
F. K . C A N A L
B. a . Friant Valve b . Iowa Valve c. National Cast Iron Pipe Valve d . Flockhart Valve e. All Brass Valve
FRIANT-KERN CANAL
FIGURE 3
1-w w
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8 0
7 0
.!:=. 60
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B . 16 Feet-- I '
----� '- 0. 7 7 Max imum va lue I of ':,S"- 16 foot water--
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I C U R V E S FO R CO E F F IC I E NT j!J
I N E Q U AT I O N Q = K H fl L
S E EPAGE F LOW STU D l ES
F R I A N T - K E RN CA N A L
0. 20 0.40 9.60 0 . 80 1 .00
ft
1 8
1 6
1 4
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FIGURE 5
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6-inch Standard Pipe - •
� /
Piezometer - ' ' COUNTERWEIGHT
l-------
pounds
- - - 12,¾ inch Rod
Flop weight ro.6 pounds
: o.-As furnished
Maximum a l lowable d i fferential head 0.67 foot
f- b -With .:
Counterweight
:J z 0 0 " W Q.4
0.2
,-Invert of drainpipe flow passage
�:
m
\� en ..u SE�T D;�: I L
- I nvert o f lining ALTERED SEAT
r
0 0.05 0.10 015 0.20 0.25 0.30 0 � � M M W D ISCHARGE CFS DI SC H ARGE C F S
A .CAPf,CITY CURVES SUBMERGED N.C.I.P. VALVE B. CAPACITY CURVES UNSUBMERGED N.C. I .P VALVE
0.9
0.8
0.7
CCo.G w
n ·, /
I L----
_,,,. ,/: _ _ -- - --
/ I ,...__ I
a.-Hinge and Body seat OS furnished.
" - - -. , --- .,._ - ---- -- - - - -
·/ /4ximum
/
V ........ ------V - --
./ AS FURNISHED COUNTERWEIGHT
V c.-Hinge as furnished , i · inch Body seat. FRIANT VALV E No. 1 3 1 4 1
a l lowable head 0.8
Maximum allowable head a.-As furnished I I I ----:_:,.-- - - - - 1 I I --
�� - b.- Hinge over C. G. of f lop, Body seat as furnished I
I -" r·d.· Hinge over C.G. of flop ,i ·inch Body seat
Q'. w 1-� 0.6 -:x ��---1-- -- - --�:- b.-With Counterweight
u. 0 1-0.5 w w !::. "' z Z o. 4 :J z 0 ·� �0.3
0.2
'/ ---- - - - - - - - -
..( e. -Al I brass Valve �.f.· Unrestricted Drain
.·Invert of ' drainpipe flow po�ge
lfi
8x8.1ij-rnch - - -\ Bross Flop- --
I� HINGE AS FURNISHED
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SEAT DETA I L
u. 0 1-w w �0.4
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0 " w I
;::: �0.2 u.
0 ct w I t=µ 0. 1 __lO.I
HINGE OVER CENTER OF GR AV ITY
f/· - - --
c.-Flop seat width reduced
_ _ __ j, '•,invert of drainpipe flow passage
U N SUB ME RGED
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0 •1 �: 5 ·,,?,, �(
s �(( a: ,,;,,, u, , ,, ,, ,
=Y.... ,-:,",, ?··· ;,;, ·.,. ;, Metal '; __ _ ,.� removed FLAP SEAT
I I 0.02 0.04 0.06 0.08 0.10
DISCHARGE CFS
Maximum al lowable d ifferential head 0.67 foot
I SUBMERGED
d.-As furnished --.,_
--
-
0.12
-
,:· - Invert of I ining
ct .::: z w Q'. w u.. --- I ,,
I - e.-With Counterweight
0 0.05 0.10 0. 15 020 0.25 0.30 �- 0 0.02 0.04 0.06 0.08 0.10 D I S CHARGE C F S DISCHA RGE CFS
I I I
C. CAPACITY CURVES UNSUBMERGED N.C. 1.P. VALVE WITH BRASS FLAP D . CAPACITY CURVES FRIANT VALVE No. 13 14 1 CAPACITY CU RVES FOR UN O E RORAI N F LAP VALVES
F R IA NT - K E R N C A NA L
0.12
�· ' � ·""
6 - Inch dra inpipe ------
. 2 8
� -24
.32- f-l
a: w .20 > - z f- .28- -
w LL.
w e> .1 6 <(
f- .24- (f) a:: (/) w <( >
a.. .1 2 z - .20- z w <( <!> a:: .08 '(},
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z Q..
0 0 .04
w <( >' . 1 2 - W :..J :r;
z .oeo 0
·� .04-
0-
0
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'--- -
1-i,
�
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0
,-Water surface ' '
P i pe P iezometer---· .......
Cr it_i ca l head for p i pe f low passage ._ _ 2 - i nches above su rface of bottom l i n ing - -
(ba sed on 8 - inch l i n i n g upl ift pressure) .--J...-:""
�v � -L/
i...,.---
- -3 - lnches - 1- - ,<' ,.,,
/ � -l/ /
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1- -
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,;f-- -We ight 1 .5 pounds _:f_',, 4' by 1f by f brass f lap
.--
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.--
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dra inp i pe, va lve attached (Based on head at pipe p i ezometer )
--i- ---· ------
>--
-
K4-lnches ... - -� ,, 1-b. Discharge curve, dra inpipe and
�-� /
,, '·
'
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i- .... -Hnvert s - inch dra inpipe f low po ssoge
I I I l l I I I I I
1a 1vi9 1
pe1
i n� hj
adl
= 1. oj foot
l/, l nvert v a l ve f low passage
I .02 .04 .06 .08
D I SCHARGE CFS
f lap va lve f low passage inverts same e levat ion
'
CAPAC I TY CURVES FOR -RECTA NGULAR FLAP VA LVE
� FRIANT- KERN CANAL
I I . 10 . 12 . 14 . 16
"Tl G') C ::0 IT1 m
.,
er w
1.2
1.0
i o.e u. 0 1-w w
"' z z ::; z 0
0,6
0.4 0 <( w r
0.2
1 .2
1.0
er w I-<( ;<a.a u. 0 1-w t:' C)
0.6 z z ::; z 0
0.4 0 <( w r
0.2
-7 V/
/� '/ - - - -
-, '
- � -:.C-- - -3"--- >! l K-2t_� �,--,Reinforcing disk : : 4 1 ·: -a inch Rubber
Stem--·--- -Guide bearing·····- ·,S:.--Canal l i ning
" ·· ·Filter
A.RISING D ISK
I 0.648 PJund .!._ /,,, I ,
/ ··- 1¾ Inch stem rise Weight of moving parts)'!--
/ 11 / I
/ .-0.2 2�ound I - - - - -7- -- - -y
,C:Mo_x�m_um_ ���w_able head
./ / 1
I / I V ,-0. 109 Pound
I
I · - --.<;urfnre �f_ lj�in_g _ _ _ - - - - - - - - - - -
c. U N S U B M E R G E D
·I nvert o f l ining I I
0.02 0.04 Q0G 0.08 DISCHARGE CFS
0. 1 0
FIGURE 7
--T - �r __ :,'_
Hinge d istance-- ·· ·:1.
· ," , .-·R einforcing disk :--- -- · -�'1:'- ·i i nch Rubbe r
-.::: .. -Canal l i nl ng
2
.c-
er w I<( ;o o u. 0 1-w w �o 0 "' w :,:
.8
.6
_J "' j:: O.
-
8. RUBBER FLAP
Maximum a l lowable head �"- - - - -1 - - - - - - - - - - - - - -
/ J
I/ o . 648 Pound---� V
z w 0: w u. u. i5 /- I
/ 0
·- F i lter
/ I
- - -
I
- - -
I
·2
/ 0.226Pound·--
'.,.-t- ./ V D. S U B M E R G E D
0.1 2 0
�- ,,-·O,r
PoT
d
0 002 0.04 o:os 0.08 DISCHARGE CFS
0.18 0. 12
CA PA CITY C U RV E S FOR R ! S I N G D I SK
1.2
/ . 0 I / .1 V _.3-inch hinge ,0.3�8 pord flop
• (Increasing head
7 I I / /L:1/ 1/ .,, , 2-inch 0.378Pound �-1 .0
- -� .
I
N OT E S
Effective weight of rubber flop For 2- inch ___ 0.07Pound For 3- inch ••. _0.09 Pound
Total weight includes disk and rubber
' J, / I!
I I
I I I I 2-inch hinge 0.203 pound flop-
I I I 2 - in c h ,0. I I 2 Pound--
I /
/
0··
. 1/ ,... , ....
---- / / < • / er
UJ 1- I I I I I
2-inch;°-378Pound--:;/ ! .. -r tr ;j '// �
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,s / V v·
i/- - -p k--:'.-1'' / + • •/
0 v- 1- - -� .... ,..
V'-/
IX� . ...-/�' ,- • , • v ·· 2·inch,0.1 I2Paund V. / ./ I ---: _ ��-t"+ X ¥:·����i�:1:'! �l!�wo_b�e_ �eo_d_�
- _,..,-:-- '··3-inch ,0.398Pound _ ', ( Decreasing head) V - I _ 2-inch, 0.203Pound
··-3 •inch,0.2 43 Pound • (Increasing head) ···-(Decreasing head)
; o.a u. 0 1-w w �0.6
0 "' w :z:
' ,i,1 Maximum ollowa le
c-:_�e_a�--��- , J--
I I /
- - - - ----
-/
/
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I · - - - - - - -r· 1 ·- - · I / l y I /;, / I V / : / / /
/ ,:r, /--. · - /
- ----/· - -; / 0 1/
1/" / ·-- 3 -inch, 0 . 1 3 2 Pound
_J So.4 >-z w
I / / ,...---� V _,..,) :;<-3-inch,0.132 Pound / /: �--- Sur_face o_f l in_i�g I 0: I I w u. u. 'I /
/ / v· V,, V ··-3 - inch,0. 243 Pound / v,,--
E . U N S U B M E RGED I I
i5 0,2 ft
/
� I; I v·' 1/ I � - F. S U B M E R G E D � ·....-- I I
- Invert of l i ning � � r;::::. -0.02 o.o4 0.06 a.pa
DISCHARGE C F S 0.10 0.12 0.02
CAPACITY CURVES FOR RUB B E R F LA P
0.04 0.06 0.0 8 DISCHARGE C F S
CAPAC ITY C U RVES FOR U N D E RDRA I N WEEPHOLE F R IA NT- K E R N C A N A L
0.10 0.12
. .
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