ABSTRACT: This article discusses the most common types of spillway gates including radial gates, vertical liftgates, and flap gates including inflatable gates, and their application. Design considerations for each type areexplained. Design and application considerations for different types of spillway gate operators are also included.Items covered for gates include gate geometry, gate proportions, location of gate hoists, location of gate trunnions, trunnion anchorage arrangements, gate seals and sealing arrangements, use of dogging devices, wavedeflectors, flow splitters, corrosion protection including use of cathodic protection, and ice problems associatedwith spillway gates. Items covered for hoists include selection criteria for hydraulic and mechanical hoists,functional requirements of the hoists, use and type of position indicators, normal speed of opening and closing,use of automatic controls, the need for maximizing the minimum opening, and automatic stopping of the gatesat set intervals to prevent unintentional spilling. Permissible leakage rate through the gates is also included.
GENERAL
A number of gate types can be used for the spillway of ahydro project. The common types include radial, vertical lift,and flap-type gates. Each type has specific advantages depending on the control requirements and operating conditions.Under certain conditions, variations of the common gate typesare also used. The purpose of this paper is to provide designguidelines for the types of gates most commonly used atspillways.
APPLICATION
Radial Gates
Radial gates are the most common type of spillway gates.They are the least expensive type for most applications. Because they do not require slots in the piers for their support,radial gates also result in lower flow disturbance and a bettercoefficient of discharge than the vertical lift gates. In addition,radial gates are generally superior to vertical lift gates for coldregions because of the absence of slots that can accumulateice; also, it is easier to install heaters on the radial gate bodybecause the radial gate trunnion presents a point of zero rotation for feeding the heaters. Unlike vertical lift gates, radialgates do not require a high overhead structure, usually calleda gate tower, which the vertical lift gates require to supportthe gate hoist above the fully raised position of the gate. Figs.1 and 2, respectively, show the typical layout of a crest-typespillway radial gate and an orifice-type spillway radial gate.Orifice spillways are used where economics dictate that thespillway be combined with another structure such as an irrigation release structure, low-level outlet structure, diversionstructure, or sediment passage structure. Crest-type radial gateshave been constructed in very large sizes, with areas up to 560m2
, widths up to 56.5 m, and heights up to 22.5 m. Orificetype radial gates have been constructed with areas up to 114m, widths up to 12.8 m, heights up to 9.5 m, and heads upto 135 m.
With radial gates, the gate trunnion is located above the flownappe to reduce the possibility of debris impinging upon anddamaging the trunnion, and, in icy conditions, to prevent thetrunnion from freezing. Under high-tailwater situations, thehigh location of the trunnion could result either in larger gate
'Sr. Assoc. and Head, Gates, Cranes and Hoists Section, Harza Engineering Co., Chicago, IL 60606.
radius or in the gate tilted upstream, causing larger verticalhydrostatic forces. This condition could cause the radial gateto be more costly than a vertical lift gate.
Vertical Lift Gates
Before radial gates were developed, most spillway gateswere of the vertical lift type. Some users still prefer verticallift gates because they are simpler to construct and install anddo not require support girders embedded in piers. Also, forthe reasons stated, in spillways with high tailwater, vertical liftgates are generally superior to radial gates.
Vertical spillway gates are usually designed as wheeledgates rather than slide gates to allow them to close under gravity and to reduce the required hoisting force. The seals andskinplate on the vertical lift gates are usually provided on theupstream side of the gate slot to minimize flow disruption bygate slots. The slots for downstream sealing gates are deeperin the direction perpendicular to the flow than for upstreamsealing gates because, for downstream sealing gates, thewheels and the seals are located on the same side, and forupstream sealing gates, they are located on opposite sides. Fig.3 shows the typical arrangement of a vertical lift gate. Verticalgates have been constructed in overall area sizes comparableto crest-type radial gates.
Flap Gates
Flap-type gates are usually used when the reservoir levelmust be accurately maintained or when floating debris and/orice have to be skimmed. Flap gates can be built in very largewidths, up to 100 m and larger, because they are fitted withhinges and can be equipped with hydraulic operators at regularintervals to support the gate throughout its width. Flap gates,however, cannot replace radial or vertical gates for routinespillway application because of the costs associated with fabrication and installation. Flap gates require very high hoistingforces to raise them from the fully opened (lowered) positionbecause besides the mass of the gate and friction, the mass ofthe water flowing over the gate must be overcome. In addition,the downstream side of the gate is prevented from being naturally aerated by the sheet of water flowing over it; aerationrequires that flow breakers be welded at the top of the gateskinplate at regular intervals and/or vents of considerable sizebe located in the side piers. The provision for aeration is necessary in order to reduce cavitation damage, downpull, andvibration. Because of the cost, the height of flap gates is usually limited to 4 m. Flap gates are usually inclined 20° to thevertical, when in fully raised position. Fig. 4 shows the typicalarrangements for flap gates.
FIG. 1. General Arrangement of Crest-Type Radial Gate
DETAIL A
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GATE GEOMETRY AND GENERAL DESIGNCONSIDERATIONS
Width to Height Ratio
The width to height ratio of a gate is not a critical designconsideration. Gates have been successfully designed withwidth to height ratios less than equal to, and greater than 1.For a given area of opening, however, gates with smaller width
Inflatable Gates
An inflatable gate is basically a seal~d tube made of a flexible material, such as synthetic fiber, rubber, or laminated plastic. The gate is usually called a rubber dam and is laid acrossthe full width of a waterway. It is anchored to the sill andwalls by means of anchor bolts and an airtight and watertightclamping system. The gate is inflated with air, water, or acombination of the two. The gate is deflated by dischargingthe air and/or water from the gate. When fully deflated, thebody folds flat against the downstream sill, minimizing hydraulic losses. The inflation or deflation is achieved by the useof gravity, a pump or a compressor. The air-type inflatable gateis the one most commonly used because it can be rapidlyraised and lowered using a simple compressor arrangement;problems arising from freezing of water inside the gate arealso eliminated. Fig. 7 shows typical arrangements of inflatable gates.
Inflatable gates can be made in widths of 150 m or more.They are convenient for quick releases of water and for passage of silt, debris, and ice. Because inflatable gate installations eliminate the need for several piers and stainless steelembedded parts typically required for steel gates, they are usually quite economical. The disadvantages include limited design head (usually limited to 5 m), susceptibility to damageby floating debris, and limited life. According to some manufacturers, a life expectancy of 30 yr can be expected basedon the modern day chemical makeup of the rubber. However,there does not appear to be any installation in service for morethan 20 yr. Inflatable gates have difficulty in regulating discharge in a partially open/closed situation, although, accordingto the claims of one manufacturer, several inflatable gate installations have been used for regulation. Fins similar to thoseshown in Fig. 7 are provided to help reduce the vibrationscaused by water flowing over the gate.
Inflatable gates should generally be considered for shortterm use, unless replacement of an inflatable gate installationis considered economical. Present-day steel gates are designedfor a life of 75 to 100 yr. The effect of replacement costs,including cost of disrupting services, should be considered inthe economic evaluation.
An inflatable gate that includes a reinforced steel plateraised and lowered by an inflatable rubber bladder has beenrecently developed. Hydraulically, this version appears to bean improvement over the rubber dams because the steel platehelps control flow when the gate is partially open. The steelplate also protects the rubber bladder from debris. To limit thelength of the rubber bladder, the gate is fabricated in approximately 3 m wide panels. Adjacent panels are connected byreinforced rubber webs. Disadvantages of this system compared to a plain rubber dam include the need for maintenancepainting of the steel plate and the possibilities of individualpanels not moving in unison, debris being caught between thepanels, and ice forming due to leakage at the ends and betweenthe panels. All inflatable gates are more easily subjected todamage by vandalism than steel gates.
If an inflatable gate system is chosen, it is best to use astandard inflatable gate package that includes the gate body,piping, and power unit for inflating and deflating. These packages are available from several manufacturers.
One advantage of a flap gate is the high discharge coefficient, similar to ungated spillways, when the gate is fully lowered. Disadvantages include possible damage to hydraulic operators located downstream of the gate due to debris or icefalling over a partially open gate and difficulty in their maintenance due to access problems. The damage may be prevented by locating the operators on the piers at each end ofthe gate, or by selecting a gate equipped at the bottom with atorque tube that is rotated by a hydraulic cylinder located atone end of the gate. The end location of the operators limitsthe width of the gate that can be provided because of therequirement for structural rigidity of the gate. Flap gates areusually difficult to maintain because the wide stoplogs or bulkheads required would be difficult to handle, especially in theabsence of an overhead bridge not usually provided where flapgates are used.
In many applications, small flap gates are installed withinthe upper portion of a radial gate to facilitate skimming ofdebris/ice. This results in considerable savings over installinga separate radial gate and/or a flap gate. Vertical lift gates, onwhich it is not convenient to install a flap gate, can be designedin sections, with the upper section raised separately to skimdebris. To pass debris, radial gates may also be designed tobe submersible with the gate moving down from the crest instead of upward. Fig. 5 shows a radial gate with a flap andFig. 6 shows the schematic of a submersible radial gate.
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-,- HOIST HOUSING
I ~"'-'--GATE HOIST
..'., .., -:---:---:--1.~ .. :.. ~.:: £.. ::"
--:'.--':" -~-... ... .."
SECTlON THROUGH ~ OPENING
WELDING PAD lTYPI
GUIDE BAR -j-........-,..SECONDSTAGECONCRETE -+--....,..-\.
--IE:;IIl.._--+-CORROSION RESISTANTBOLTS AND WASHERS
:----:+-SILL BEAM
DETAIL ADETAIL B
FIG. 3. Typical Arrangement of Vertical Lift Spillway Gate
to height ratios are cheaper; the cost of a gate is proportionalto approximately (width)1.28 X height. Also, gates with smallerwidth to height proportions are less subject to cocking, andthey provide better flow regulation because of greater heightof opening for a given flow. The overall cost of a spillway,however, is generally smaller for wider gates because widergates permit fewer and smaller height piers.
The gate proportions should be based on the overall plan ofthe project and not on the gate itself, except that the gate'sstructural design limitations must be considered in the overallplan. For radial gates, the structural size is limited by the loadtransferred to the trunnion anchorage and hence to the piers.For wheel gates, the structural size is limited by the load transferred to the wheels and the ability of the wheel material towithstand the resulting contact stress. For radial and wheel aswell as flap gates, the size is also limited by the maximumoperating loads for which the operator and the support structures can be economically designed.
Gate Slot SizelEdge Distance of Wheel Tracks
Wheel gate slot size must be kept to a minimum to minimizedisruption of the flow and cavitation damage. Gate slot size isespecially critical for wheel gates installed in cold regionswhere ice could accumulate in the slot. Wheel size, whichinfluences the slot size, should be kept to a minimum withindesign limitations. The distance between consecutive wheelsshould increase from the bottom towards the top of the gate,since the wheel load is maximum at the bottom and negligibleat the top. The variation in distance also applies to the locationof horizontal main load bearing structural beams for all typesof spillway gates, except high-head orifice-type spillway gates.
Wheel tracks should be installed an adequate distance intothe slot to prevent concrete failure, as shown in Fig. 3.
158/ JOURNAL OF HYDRAULIC ENGINEERING / MARCH 1996
Location of Gate Hoist and Gate Handling Criteria
Radial and vertical lift spillway gates are usually connectedto their operators (hoists) at two points. Flap gates may haveone, two, or more connection points, depending on their width.
For vertical lift gates, an overhead structure above the pier,with a height slightly more than that of the vertical gate, isnecessary to support the hoist so the gate can be lifted abovethe maximum water level and, for maintenance, out of the gateslot. If hydraulic cylinders are provided to operate a verticallift gate, either the gate must be provided with openings toaccommodate the cylinders as the gate moves up. or the fullheight of the cylinders must be extended above the top of theoverhead structure. The two cylinders of a vertical lift gatemust be electronically coordinated by use of proportionalvalves in the hydraulic system to prevent cocking of the gate.Because of these requirements, hydraulic hoists are not commonly provided for vertical lift spillway gates. Wire ropehoists are more acceptable because the hoist drums do notextend much above the top of the overhead structure. Also,with a wire rope hoist, coordination between the two liftingpoints can be readily accomplished by providing only one motor for the two hoisting drums, with the two drums interconnected by a common shaft. For very wide gates where aninterconnecting shaft is not practical, two separate synchronized motors must be provided.
If a hydraulic hoist is provided for a vertical lift gate, eitherthe hydraulic power unit should be equipped with a hydraulicaccumulator or the cylinders should be equipped with overhead tanks. This allows the upper chamber of the cylinders toremain full of hydraulic fluid during gravity closure of thegate, even when the gate is lowered without power (pump notrunning). In colder climates, the cylinders are usually installedwith the piston rod up and with the cylinder barrel connectedto the bottom of the gate. With this configuration, the heating
11 Air Admission Pipe12 Field Joint Rib13 Downstream Skin
Plate14 Cylinder Operator15 Lever16 Main Bearing17 Packing Box18 Seal Contact Surface
(tube)19 Cylinder Hood20 Cylinder Base Plate
Overhead CylinderArrangement
FIG. 4. "lYplcal Arrangement for Flap Gates (Pictures courtesy of Rodney Hunt Co.)
system used to keep the gate free from ice also keeps thehydraulic fluid in the barrel from freezing.
For radial gates, no overhead structure is generally needed,except in the case of a wire rope hoist. Wire rope hoists maybe connected either on the upstream or on the downstream
side of the gate. Where a wire rope hoist is connected upstreamof the gate, the wire rope should lie against the radial skinplateto eliminate the possibility of debris becoming caught betweenthe wire rope and the skinplate. Upstream conne.::ted hoistsrequire a smaller hoisting capacity than the downstream con-
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indicat?r arran~ement options. The height of the cylinderabove Its trunmon should be less than the height below, sothat the cylinder does not flip over when disconnected from~e gate. If this cannot be done, limiting stops must be pro~lded to. prevent the cylinder from flipping over. Some existingmstallatI?ns have the cylinder pivot point at the upper cylinderhead. Thls.~nsures adequate moment arm in both the open andclosed poSItions of the gate. However, this arrangement is notpreferable because it results in a larger unsupported length ofthe cylinder and extended piston rod.
In s~me. instances, the radial gate trunnions are providedeccentnc WIth respect to the center of the skinplate radius. Thisarrangement uses the moment of the resultant hydrostatic loadabou~ the gate trunnion in reducing the hoisting load requiredto ralse the gate. However, the eccentric trunnion complicatesthe fabrication and installation of the gate and embedded partsand should be avoided except for very large gates. With aneccentric trunnion, the gravity closure force of the gate shouldbe verified.
For fl.ap gates, the preferred hoist is the hydraulic type. Wirerope hOISts are usually not provided because their installationis difficult. A~ shown in Fig. 4, the hydraulic cylinder(s) maybe arranged eIther downstream of the flap gate or on the side.Cylinders loc~ted on the downstream side (wicket arrangement) are deSIrable for gate structural design, but are undesirable due to the possibility of damage by debris falling overthe gate and maintenance difficulties because of lack of access.Cylinders located on the sides and supported on the piers aregenerally much more convenient to maintain as is the casewi~ a cylin.der located on one end of a structurally stiff gateeqUIpped WIth a torque tube. Preference should be given toprovide the cylinders on the sides or one end. If structuraldesign with the gate supported only on the two sides or operated only from one end becomes uneconomical, cylindersmay be provided downstream of the gate. However, a schememust be worked out for access to the cylinders for normalmaintenance and for removal during major maintenance.
The hoist controls are usually located on the top of the pier?r a hoist deck. Th~y may be provided as self standing units10 weatherproof cabmets or within a control building. With acontrol building, common practice is to provide a window forvie~ing the gate in operation. For radial and flap gates, thecyhnders are usually below the power units, and therefore,there is usually no need for accumulators or overhead tanksas with the vertical lift gates during gravity closure withoutpower.
Use of Dogging Devices
Dogging devices are helpful during gate installation beforethe hoist is connected to the gate or in cases where the gateis to be maintained in an open position for an extended period.
Use of Wave Deflectors and Flow Splitters
Depending on the nature and size of the waves in a reservoir, wave deflectors are provided on the top of the spillway
Use of Common Hoist For Vertical and Radial Gates
The use of a common hoist, such as a gantry crane or hoistcar, for several gates is quite prevalent on many old projects.A chain is usually provided between the hoist and the gate;chain is convenient for dogging the gate in a partially openposition as the gate is raised in steps. Depending on the liftof the gate, a long length of chain may need to be stored onthe top of the pier as the gate moves up. Although economical,a common hoist is an undesirable arrangement, unless gatesare operated infrequently. In addition to being extremely slowand cumbersome, especially in an emergency, a common hoistsystem is unsafe.
TRUNNION
HYDRAUUCCYUNDER
- SlOE SEAl PLATE
GATEUPPER ARM
FIG. 5. Radial Gate with Flap
SILL
DIRECTION OF TRAVEL
FIG. 6. Schematic of Submersible Radial Gate
SKINPLATE
necte? hoists because of the larger moment arm about the gatetrunmon for upstream connection. Also, upstream connectionof the hoist can result in a smaller pier length. The disadvantages of ?pstream connec~on include the possibility of damageto the WIre ropes by debns or by galvanic corrosion, damageby the wire rope to the paint on the skinplate upstream surfaceflow-induced vibrations due to the presence of large wire rop~brackets for large gates, and difficulty in inspecting the ropec~mnection, which normally remains underwater. Despite thesedIsadvantages, the common practice is to connect the wirerope hoist upstream of a radial gate because of the cost savingsresulting from the smaller hoisting capacity. Wire rope maintenance is necessary regardless of the location of the hoist. Forlonger life, stainless steel wire ropes are usually provided.With radial gate wire rope hoists, the synchronization provisions for the two lifting points are similar to those for wheelgate wire rope hoists.
With hydraulic hoist-equipped radial gates, the two hydraulic cylinders are usually interconnected by hydraulic piping. In most cases, the rigidity of the gate structure and theguidance of the gate movement by the gate trunnions is usedto provide automatic synchronization between the two liftingpomts. If the gate is extra wide and the cylinders cannot beeasily interconnected, synchronization of movement is accomplished by the use of proportional valves in the hydraulic syste~. The cylinders are located close to the ends of the gateWIdth, so that they can be supported on the piers.
Hydraulic cylinders are usually provided downstream of theradial gates, because of the difficulty of their installation upstream. The location of the hydraulic cylinder trunnion and thepoint of connection between the radial gate and the cylinderaffects the structural design of the gate, gate trunnion, gatetrunnion anchorage, cylinder, hydraulic system, cylinder trunnion, cylinder trunnion anchorage, and the piers. The cylinderlocation is usually selected such that the hoisting load is assmall as practical and remains nearly the same for all positionsof the gate, without the cylinder stroke being excessively high(usually under 10 m). Excessive stroke is detrimental to thelife of the cylinder rod end seal and bearings because of theside load caused by bending of the rod when it is inclined tothe vertical. Excessive stroke also limits the cylinder position
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y<..... . ~. ~
." " ..Air Supply and exhaust pipe
(b) Weather resistantrubber
Nylon fabric
FIG. 7. Inflatable Dam (a) Typical Arrangement (Courtesy Bridgestone Corp.); (b) Alternative Arrangement (Courtesy Rodney HuntCo.)
gates to prevent waves from overtopping the gate. Usually,0.3-0.6 m high wave deflectors are provided above the maximum storage level of the reservoir as shown in Fig. I. A gateequipped with wave deflectors must be designed for the increased head on the gate due to the presence of the wavedeflector.
Flow splitters are provided on overtopping gates to breakthe flow and aerate the underside of the flow nappe. Without
proper aeration, the nappe may cause severe gate vibrations.Vibrations may still occur if the design of the flow splitters isnot adequate.
Corrosion Protection
Although some installations have used cathodic protectionfor corrosion protection, a good painting system alone, main-
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15I'
J TYPE (HOLLOW)
~BRll
~~;J TYPE
DOUBLE BULB SEAL
.~113R161
~~~'. ,
165
BAR TYPE
L TYPE
143
DOUBLE STEM TYPE
~r~~rr:;!=~:i:
,..,
25 R
Radial Gate Trunnion Support and Anchorage
The radial gate trunnion support and anchorage are the critical items in radial gate design because all the load acting on
FIG. 8. 'TYpical Seals (All Dimensions In Millimeters)
type (Fig. 2, detail A). Side seals of all radial gates and the topseal attached to an orifice-type radial gate should be adjustableto account for fabrication and installation tolerances. For theorifice spillway radial gate, square bulb seals (Fig. 2, detail C)may be used as side seals to help maintain better contact withthe top seal attached to the lintel so that leakage is reduced atthe top comers when the gate is in an open position. If the headon the top seal is not too large, the top seal may be hollow toprovide more flexibility for better sealing.
Embedded stainless steel side seal plates (Fig. 5) are provided on flap gates to prevent leakage from the sides of partially open gates. These plates may be eliminated if it is certainthat the gate would be used only in the fully raised or fullylowered position, and, instead, smaller plates may be embedded in the concrete for the gate to seal against when fullyraised. Some installations seal against the pier concrete insteadof using side seal plates. This requires smooth concrete surfaces. Without a side seal plate, frequent seal replacement maybe needed due to faster wear of the seal. The flap gate bottomseal arrangement needs to be carefully designed because therotating bottom comer of the skinplate can trap debris anddamage the bottom seal.
Fluorocarbon cladding is usually provided on the gate sealsto reduce seal friction and the required hoisting capacity. Except for orifice-type spillway gates, the weight of spillwaygates is usually large compared to seal friction, and therefore,seal friction does not significantly affect the hoisting capacity.Fluorocarbon cladding should, however, be provided on allspillway gate side seals to prolong the seal life.
tained every 10-15 yr, is usually the most economical and convenient method of providing corrosion protection. An impressedcurrent system of cathodic protection is usually impractical.Even for a sacrificial anode system, estimating the number, dimensions, and locations of the sacrificial anodes required forproper cathodic protection is difficult. If the spent anodes arenot replaced promptly, corrosion can progress rapidly, especiallyif cathodic protection is heavily relied on. Properly applied andmaintained paint eliminates the need for cathodic protection,except in cases where the gates are not readily accessible forregular maintenance or the water resistivity is very low, suchas in seawater applications. The design of the cathodic protection is affected, in addition to the water resistivity, by the watervelocity, abrasiveness of water, and coating efficiency.
The exposed surfaces of the embedded items in permanentinstallations should be constructed of stainless steel, becausepaint is difficult to maintain on these items. All gate and hoistequipment including pins, wheels, hoist piston rods, anchorbolts, and other similar items that are critical for proper gateoperation should also be of stainless steel. The type of stainlesssteel should be carefully selected, especially for mating surfaces, to eliminate galling or crevice corrosion problems.
Self-lubricating bronze bearings mating with stainless steelpins should be used as much as possible. On all submergedparts, insulators should be provided to separate the surfaces ofdifferent materials such as stainless steel and carbon steel toprevent galvanic corrosion.
Radial Gate Proportions and Location of Radial GateTrunnions
Gate trunnions of radial gates must be located sufficiently(usually 1.0 to 1.5 m) above the maximum flow nappe to prevent damage to the trunnion by debris or ice. The radius ofthe gate is usually 1.25 times the vertical height of the gateabove the crest. The sill of the gate is usually located slightlydownstream of the crest. Based on the statistical study of several gates, the center of gravity of most radial gates can beassumed to be located at a horizontal distance from the gatetrunnion of about 0.75 times the gate skinplate radius and ata vertical distance from the gate sill of about 0.45 times thegate vertical height.
Gate Seals
Refer to Fig. 8 for a configuration of seals commonly usedon spillway gates. J-type side seals perform satisfactorily onvertical lift wheel gates. L-type seals, because of their betterresilience, are preferred for radial gate side seals. Bar-typebottom seals, chamfered as shown in Fig. 8 are used on wheelgates as well as on crest-type radial gates. For radial gatesprovided on orifice spillways, the bottom seal may be bar-typeor a flat seal attached to the sill as shown in Fig. 2 (detail B).Because of high heads associated with the orifice spillway, aflat seal is usually better than the bar seal for flow efficiency.If the bar type seal is not present, the gate bottom presents asharp, well-defined surface for flow. J-type seals should not beused as bottom seals for spillway gates because they tend toinitiate gate vibration. For large spillway gates, locating thebottom seal downstream of the skinplate is desirable to reduceflow induced vibrations.
Radial gates for orifice spillways require top seals. Two topseals are usually provided, one attached to the embedded lintelbeam to prevent leakage at the top while the gate is partiallyopen and the other attached to the gate skinplate to ensuretight sealing while the gate is fully closed. The top seal attached to the embedded lintel beam should preferably be adouble-stem type. A J-type is not suitable in this case becausethe bulb of the J-type seal is subject to rolling and damage asthe skinplate moves against it. The second top seal may be J-
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ELEVATION OF ANCHOR BLOCK
FIG. 9. Type I Trunnion Support and Anchorage System
For hoisting capacities above 50 t, spillway gates (exceptvertical lift gates) are nonnally equipped with hydraulic hoists.Hydraulic hoists are advantageous because of their design simplicity, ease and flexibility of control, and economics. Wirerope hoists can be designed with reasonable costs for capacities up to about 30 t. Chain hoists, previously used extensivelyfor large gates, are not used because of maintenance problems.Hydraulic hoists raise environmental concerns due to the fearof accidental spills of the hydraulic fluid. In general, the hydraulic system is quite reliable and spills do not occur. In critical installations, a fluid containment arrangement can be provided. In warmer climates, nontoxic vegetable-based fluids oreven water can be used. The use of nonpetroleum based fluids,however, requires special materials for seals and other items.
A hydraulic hoist comprises one or more oil hydraulic cylinders, a hydraulic power unit (including an electric motor,pump or pumps, a fluid reservoir, filters, necessary valves andpiping), and piping interconnecting the hydraulic cylinder(s)and the power unit. The cylinder(s) can be conveniently trunnion-mounted to suit the angular movement of the radial orflap gates. Any hoisting capacity can be obtained by selectinga suitable cylinder bore size and/or pump pressure output.
Typically, a hydraulic system is designed to operate at apressure between 14 and 20 MPa. Higher pressures result inmore economical size of the equipment but leakage problemsare more likely. Pressure and return filters (10 j.Lm) must beused in a hydraulic system to keep it clean. Use of suctionstrainers or suction filters is discouraged. The large mesh size(100 j.Lm) nonnally provided to protect pump suction fromdebris is not useful. However, pump damage could occur ifthe screen becomes clogged. Although the spillway gates normally close by gravity, the pump should run during loweringof the gate so that each cylinder's upper chamber remains full.A suction or gravity flow line may be relied on to fill thecylinder upper chamber only during emergency lowering without power. The maximum pressure on the top of the pistonshould be limited by provision of relief valves connected tothe upper chamber, and the piston rod must be designed towithstand buckling due to this limited pressure. The reliefvalve connected to the cylinder top chamber will also serve toprotect the cylinder against pressure rise due to heat expansion.A relief valve must also be connected to the cylinder bottomchamber to safeguard against the pressure rise due to heatexpansion in the bottom chamber.
Each hydraulic hoist is usually provided with a drift controlsystem that restores the gate to its set position if the gate driftsfrom that position due to system leakage. The system constantly compares the gate position with the set position andraises the gate back to the set position if the drift exceeds apremeasured amount (50-75 mm). When the gate is operatedby the use of open or close commands, the set position lockis automatically canceled.
A typical wire rope hoist system comprises two wire ropedrums, one connected to each end of the gate width, an electricdrive motor, a solenoid brake, and the necessary reductiongearing. The drive motor and solenoid brake, which is coupledto the drive motor, may be located at one end only or at themidway point between the two drums on the top of a hoisting
JOURNAL OF HYDRAULIC ENGINEERING / MARCH 1996/163
HOISTS AND CONTROLS
ferred to the support and anchorage must consider the loadcontributed by the hoisting forces (in the direction of the hydrostatic loading) in addition to the hydrostatic and hydrodynamic loads. As a rule of thumb, the hydrostatic loading isincreased 20% to account for the hoisting forces and the hydrodynamic loading that is difficult to compute. The worstloading condition usually occurs with the gate opened slightlyfrom the fully closed position.
....
t:.:::::=:::Y- Steel girder
FIG. 10. Type II Posttensioned Gate Anchorage System
FIG. 11. Type III Posttensioned Gate Anchorage System
;~.~"i~~~:i5~~i: ~ .. .. .: . .-. . .. '. '.. '.'
{;:iM~~~~[i"
the gate is transferred to the trunnion and anchorage. Fig. 9(type 1), Fig. 10 (type 2), and Fig. 11 (type 3) show threetypes of anchorage systems generally in use. Types 2 and 3are the posttensioned type and are generally considered moreeconomical for larger than 10m X 10m crest type radialgates. The size limitation for high-head orifice spillway radialgates would depend on the head on the gate.
Because of larger hydrostatic loads associated with largergates, the anchor girder to be embedded in concrete in a type1 design is long, which complicates the pier design. Type 2has a concrete girder similar to the steel girder of type 1 butuses a posttensioned anchoring system. Type 3 also uses aposttensioned anchoring system but a massive reinforced concrete block integral with the pier is provided instead of a separate steel or concrete girder, and the pier is narrowed to athin neck that enables the gate load to be located closer to thecenterline of the pier. This reduces the moment of the loadabout the pier which is critical especially when only one ofthe two adjacent gates is open. While the narrowing of thepier reduces the load moment, the shape of the pier becomescomplicated and must be carefully analyzed. The load trans-
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bridge. The two drums are usually connected, through necessary reduction gearing, by a connection shaft. In some cases,a separate drive motor is provided for each side and the twomotors are synchronized electrically. The drums may be eitherregular or spiral type. Regular drums permit the wire rope towind in a single layer, whereas in the case of spiral type, thewire rope winds on the drum in multiple layers. Regular drumsare provided with up to two wire ropes per drum, whereas thespiral types can have several ropes, each rope winding beingseparated from the next by plates bolted or welded to thedrum.
To lower the gate without power in an emergency (by releasing the solenoid brake), a wire rope hoist must be equippedwith a system such as a fan brake or a hydraulic device toabsorb the energy of a free falling gate. In addition, a directcurrent brake should be provided to stop the hoist, after thegate is fully closed, to prevent reverse winding of the rope onthe drum.
Advantages of wire rope hoists include a resulting simple,easily understandable system, the requiring of less headroomfor vertical lift gates, a lower hoisting capacity for radial gates(if attached on the upstream face of the gate), easy provisionof a reliable mechanical position indicator, and no problemsassociated with gate drifting and oil spillage. Advantages ofhydraulic hoists include, besides design simplicity, economicsand versatility in meeting changes in loading and speed, asstated earlier, easy provision of end of stroke cushioning, possibility of operating several gates using only one power unit,ease of manual lowering without power, high mechanical efficiency, and low maintenance costs due to very few movingparts.
Wire rope hoists can be readily fitted with a reliable mechanical indication system through reduction gearing. Hydraulic cylinders, for which mechanical indication systems wouldbe more cumbersome, are usually provided with an electronicmagnetic linear displacement transducer (MLDT) fitted intothe cylinder head. A MLDT combines ultrasonic and magneticeffects to measure movement of the piston rod. An electroniccounter-type position indicator may be used for hydraulic cylinders where the stroke exceeds the range of an MLDT, whichis usually under 10 m; this requires use of a ceramic (or othernonmetallic material) coated steel piston rod with serrationsmachined on the surface.
The raising and lowering speed for vertical and radial gatesis usually about 0.6 m1min. The speed for flap gates is usuallyabout 0.6 m/min. The speed for flap gates is usually muchslower at about 0.1 m/min. Hydraulically operated gates areequipped with cylinders with end cushioning devices so thatin case of hose rupture at the cylinder, which would result inthe gate lowering at high speed, the gate does not get damagedwhen it hits the sill.
The radial and vertical gates should normally not be maintained for long periods at small openings, otherwise cavitationand erosion damage to the gate and the spillway crest canoccur. The minimum opening is a function of the specific siteconditions. However, as a rule of thumb, the minimum opening is restricted to about 75 mm for smaller gates (up to 3 mwide) to about 1 m for larger gates (15 m wide and above).
To prevent unintentional spilling, the spillway gates shouldbe controlled such that they cannot be opened more than apredetermined opening (1 to 2 m) upon receiving an opencommand; additional opening must require an additional opencommand. Gates for flood control should not be automatedunless they are constantly monitored remotely and can be controlled from the remote location.
ICE PROBLEMSBoth vertical lift and radial-type spillway gates present op
erational difficulties under icy conditions. They may be unable
164/JOURNAL OF HYDRAULIC ENGINEERING / MARCH 1996
to operate because of increased hydrostatic loading and increased operation friction caused by the ice. In extreme cases,the gate could be overwhelmed by the ice and frozen in place.To keep a gate operable in the winter, choose among the following options:
• Provide heaters for the gate embedded parts and, if necessary, for the gate skinplate. Heating piping should beinsulated on the exposed areas to minimize heat loss.
• Design the hoist with generous capacity sufficient to overcome, to a reasonable extent, the increased ice loading.Hydraulic hoists are preferable because of their push capability. Besides having no push capability, wire ropesconnected to the gate on the upstream side could get frozen in ice.
• Select material to suit site conditions. Structural materialsshould resist embrittlement at cold temperatures. Greaseor hydraulic fluid should retain their properties at the lowest expected temperatures.
• Provide adequate drainage to prevent ice buildup on thedownstream face of the gate to minimize addition of iceweight to the gate.
• Do not open the gate to too small of an opening (say lessthan 75 mm); small flow will result in faster ice formation.
• Provide an ice boom upstream of the gates to preventfloating ice from reaching the gate.
Gate design and gate hoisting capacity should consider aconservative hydrostatic ice load. A common value used forice load is 75,000 N per meter run of gate width acting approximately down to 0.6 m below the maximum water level.
The most common methods of combating ice on the gatesare as follows:
1. Use of heaters for gates and embedded parts2. Use of bubbler system3. Installation of flow mixers
Methods 2 and 3 are less common than method I because theyare relatively slow and inefficient. Direct heating presents themost effective means of combating ice because of fast action.The heating system may be operated on a cyclical basis, controlled by timers and/or thermostats. The heat must be appliedeither by electric heaters such as nichrome strip heaters, mineral insulated heating cables, radiant heaters or tubular heaters,or by circulating heated fluids such as a 50%-50% water glycolsolution or hot air through piping or ducts attached to the gatesand embedded parts. The fluid system requires greater initialinvestment than the electric heater system. Most electric heaters, however, have to be frequently replaced because their lifeis limited by high wattage concentrated in a narrow band. Inaddition, the heaters are affected by the humid conditions andby gate vibrations. Frequent replacement of heating elementscan be expensive and may offset their initial cost superiority.
LEAKAGE RATES
A permissible leakage rate of 0.05 LIs per meter of sealperimeter is usually assumed when the gate installation is complete. The leakage tends to reduce somewhat as the seals settlein.
ACKNOWLEDGMENTThe writer of this paper worked as a member of the ASCE Hydrogates
Task Committee.
APPENDIX. BIBLIOGRAPHY"Design of hydraulic steel structures." (1993). Engineering Manual
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Erbiste, P. C. F. (1994). "Developments in hydraulic gates." Int. J. onHydropower and Dams, Aqua-Media International, Ltd., Sutton Surrey,U.K., 51-56.
Grishin, M. M. (1982). Hydraulic structures, Vol. 2, Mir Publishers, Moscow, Russia.
Sehgal, C. K. (1987). "Selection of spillway gates for cold regions."
CENEPR1/Hydro-Quebec lee Problems Workshop, Montreal, Canada.Sehgal, C. K., Fischer, S. H., and Sabri, R. G. (1992). "Cushman spillway
modification." USCOWAnnu. Meeting, Forth Worth, Tex.Sehgal, C. K., and Wirzberger, E. (1991). "Position indicator arrange
ments for gates." Proc., Watelpower '91 Conf., Denver, Colo.Yeh, C. H., Paul, W. J., and Witnik, J. A. (1982). "Design of prestressed
anchorage for large tainter gates using the finite element method."Proc., Int. Cont on Finite Elements, Shanghai, China.
Zipparro, V. J., and Hasen, H. (1993). Davis' handbook of applied hydraulics, 4th Ed., McGraw Hill, New York, N.Y.
