C. The largest gate of this type for which standard drawings are available is 6.4 feet by 8 feet 0 inches, and the smallest 2 feet 0 inches by 2 feet 0 inches. Typical examples of a cast-iron gate and a hand-operated hoist are shown on Drawings Nos. 100-C-85 and 100-C-68, respectively. A complete list of sizes and drawing numbers can be obtained from the Drawing and Data Files, Denver. Standard gates are generally available in the open market as stock items from manufacturers of irrigation equipment.
.28 Screw-lift turnout gates are for use along canals and laterals to control the
distribution of irrigation water. The gates are made in two types, one of
which operates vertically and the other on a slope of approximately 45 degrees.
Standard gates are made in groups, namely, for heads of 0 to 3 feet, 3 to 6 feet,
6 to 9 feet, 0 to 10 feet, and 10 to 15 feet. All of these gates except the very
small sizes and those for low heads are operated by hand by means of a hand-
wheel rotating on a threaded stem. The gate opening is circular or rectangular
for a vertical gate and elliptical or rectangular for a sloping gate. The gate
leaf was formerly made of steel plate and the leakage through the gate was
sometimes objectionable. It has been found that a cast-iron gate leaf, with a
machined surface and wedging device for holding the leaf on the seat, insures
a watertight gate which is very satisfactory.
A. A complete list of sizes and drawing numbers for screw-lift gates can be obtained from the Drawing and Data Files, Denver. A typical example of a gate with cast-iron leaf is shown in Figure 43. Standard gates are generally available in the open market as stock items from manufacturers of irrigation equipment.
.29 The roller gate or rolling wier, although a European development, has been
used extensively in this country over a period of more than 35 years. One of
the earliest American installations was for the diversion dam across the
Colorado River near Grand Junction, Colorado, which was built by the Bureau
of Reclamation. These gates have given satisfactory service in continuous
operation since 1915. Recent installations consisting of four gates for the
All-American Canal headworks on the lower Colorado River (1937) and two
gates for the Roza Diversion Dam, Roza Division, Yakima Project, Washington
(1939) were installed by the Bureau of Reclamation.
A. Roller gates are more generally used on extremely low head dams and in
installations where a wide unobstructed opening between piers is desired
for the passage of ice or debris. There are often serious objections to
the great wastage of water and loss of head attendant to opening gates for
sluicing out ice or debris. Submergible roller gates are so designed that
they may be lowered 1 to 4 feet below the pond level, which allows ice
and other floating matter to pass over the gates. For normal operation
the gate is raised to give full required opening underneath.
Discharge Characteristics
HYDRAULIC GATES (Continued)
MISCELLANEOUS GATES (Continued)
B. The roller gate consists of a horizontal, hollow, steel-plate cylinder
which extends into a vertical or steeply inclined recess in each end pier.
An apron, extending along the length of the cylinder, effects a seal with
the bottom of the waterway when the gate is at the lowest point of its
travel. In case the gate is not designed for passing ice or trash over the
top, it is generally provided with a flash weir, similar to the apron, but
extending upward when the gate is in the closed position. The purpose of
the flash weir is to prevent overtopping of the gate by waves and to provide
freeboard above the highest longitudinal element of the cylindrical shell.
Around each end of the cylinder is a rim consisting of a gear and a smooth
circular rim. The rim rolls on a corresponding track placed in the recess
in the pier and the teeth of the gear engage with the teeth of a rack also
placed in the recess. A guide ring fastened to the gate and a counterguide
supported on the pier in the recess opposite the track prevent the teeth
of the racks from becoming disengaged in case trash should accumulate
on the track or between the teeth.
C. Watertightness along the sill, in case of a nonsubmergible gate, is usually effected by means of an oak beam bolted to the apron and resting on an adjustable I-beam sill. To obtain watertightness along the sides, the gate is provided with flexible shields attached to the upstream face of the gate and extending from the bottom seal on the apron to the top of the flash wier. To the upstream edge of each shield is bolted an oak or rubber sealing strip. The sealing strips travel on and bear against steel or machined cast-iron armature plates set in the piers. In the case of submergible gates, a well is provided in the crest of the dam. When the gate is submerged to allow ice and trash to pass, the apron extends into the well and a special rubber seal usually maintains contact between the apron and the upstream wall of the well.
D. The rotation of the gate to effect raising is accomplished by means of a
sprocket chain around the end of the cylinder and attached to a chain
anchor at one end of the gate and actuated by a motor-driven sprocket-chain
hoist. The hoist is usually located in a hoist house on top of one of the end
piers. In the case of several gates in a group, two hoists are usually placed
together in one hoist house. Only alternate piers will thus have hoist
houses. A locking link is usually provided, which may be latched to the
gate in its fully raised position, thus securely holding the gate and
permitting the sprocket chain to be removed.
Roller gates have been installed in this country and in Europe that vary
in length from about 25 feet to 147 feet. Although installations with more
than 150 feet clear opening are rare at the present time, it would doubt-
less be feasible to design gates of considerably greater length. Two
submergible-type gates installed at Rosa Diversion Dam are each 110
feet long. The drums are 14 feet in diameter and have curved aprons
attached to the upstream side which form the lower part of the gates, and
by means of wooden sealing strips make contact with the metal sill castings
set in the concrete weir crests. (See Figure 44.)
The 110-foot roller gates which were installed at Roza Diversion Dam
weigh 233 tons each and are raised and lowered through chains and
sprockets by means of compound herringbone-geared hoists located in
the control tower on the center pier. (See Figure 45.) The chain sprocket
is made the minimum size consistent with the load and chain size in order
to minimize the torque on the sprocket shaft and the tooth load on the
sprocket drive gear. The use of roller chain and sprocket compared with
the use of a wire rope and drum, greatly reduces the diameter and tooth
load of the drive gear and results in a more compact hoist. The difference
HYDRAULIC GATES (Continued)
MISCELLANEOUS GATES (Continued)
is especially significant for the larger sized roller gates. The gears and
their bearings are supported on a machined bearing plate, which is a part
of the plate-steel girders. These girders span the open recesses in the
gate piers at both ends of the gate.
E. The hoist frame, which supports the gear bearings, is composed of two
parallel plate-steel girders tied together at the ends by means of angle
web stiffeners. One end of the hoist frame rests on fixed base plates.
The other rests on sliding plates to accommodate temperature variations
in the main girders. Care should be exercised in the design of the hoist
girders so that, when the maximum hoist load is applied, the resultant
deflections will be the same in each girder. This produces uniform tooth
pressures between the pinion and gear for the full face width, and is
especially necessary when straight-toothed spur gears are used. The
maximum tensile and compressive stresses should not exceed 75 percent
of minimum yield point of the material used at breakdown of the motor.
The hoist chain should be of the roller type. Due to high bearing pressures
between the link and the pin, care must be exercised in the selection of
materials. The pin is usually made of high-tensile-strength bronze and
the link and rollers of alloy steel. The use of collodial graphite as a
lubricant between the link and pin is recommended to reduce the tendency
to galling of the pressure surfaces and to reduce friction.
.30 Power-operated gate hoists are usually used for operating low-head slide
gates. They are built in sizes ranging from 7,000- to 40,000-pound capacity.
A typical gate hoist consists of a cast-iron pedestal on which is mounted a
commercial vertical gear-motor. The motor, through gearing, drives an
Acme-threaded, bronze stem nut which rotates on and raises a threaded steel
gate stem. The control unit consists of a rotating-type limit switch to limit
the upper and lower gate travel, and a pointer to indicate the gate opening.
A selsyn transmitter for remote position indication may be furnished if
required.
A. The thrust load on the stem is carried on ball thrust bearings. The
pedestal covers, with the exception of those for the smallest hoist, are
made of cast steel and are designed to take any upward thrust due to
seating the gate with the limit switch inoperative. The hoist is so designed
that the maximum stress under the breakdown torque of the motor will not
exceed 80 percent of the yield point of the materials used. The unsupported
length of stem is limited to an 1/r of 200, based on the root diameter of the
threaded portion or on the outside diameter of the unthreaded portion of the
stem.
B. A complete list of hoist capacities and drawing numbers can be obtained from the Drawing and Date Files, Denver. Examples of power-operated gate hoists and the control unit are shown on the following drawings:
POWEROPERATED
GATE HOISTS
Power-Operated
Gate Hoists
.31 Radial gates are normally hoisted by a two-drum, manually or power-operated wire-rope hoist. The hoisting ropes are usually connected to lugs near the bottom of the upstream face of the gate. In the case of top seal gates the connection is made at the top of the gate.
A. Manually operated hoists are used for capacities up to and including 5,000 pounds. Such a hoist consists of a 50 to 1 commercial worm-gear reducer with a 3 to 1 helical gear attachment, and the drums are directly connected to the worm-gear shaft. Ungrooved rope drums having a minimum diameter of 18 times the diameter of the rope are used.
B. Power-operated hoists are used for capacities greater than 5,000 pounds.
The 5,000-pound and 7,500-pound-capacity hoists are the same as the
manually operated hoists, except that the 3 to 1 helical gear attachment is
replaced by a gear motor. The 10,000-pound-capacity and larger hoists
have a centrally located drive unit and a spur-gear drum unit at either
end of the hoist. The drive unit for all motor-operated hoists consists
of a commercial gear motor with disc brake, direct-connected to a com-
mercial worm-gear reducer on a common base plate. The 5,000-pound
to 15,000-pound hoists have an extended reducer worm shaft with a squared
end for ratchet-wrench operation in case of power failure. The rope drums
are grooved and have a minimum diameter of 20 times the diameter of the
rope. On the 15,000-pound and larger hoists, two parts of rope are used on
each drum to permit small drum diameters; this reduces the torque and
allows the use of small worm and spur-gear reducers. A rotating-type
limit switch is used to limit the extremes of gate travel for all
power-operated gate hoists.
C. The 3,000-pound and 5,000-pound-capacity manually operated hoists and
the 5,000-pound power-operated hoists are of two types. One type has the
drive unit centrally located, and the other has the drive unit located at one
end of the hoist which allows a narrower concrete deck to be used.
Hoisting speeds for power-operated hoists vary from 1-1/3 to 2-1/4 feet
per minute. The rope pull on each drum is assumed to be 60 percent of
the rated hoist capacity, since inequalities may exist due to greater
friction or sticking of the gate seals on one side of the gate and produce
a greater load on one drum than on the other. The hoist drum gearing and
all related parts are accordingly designed on the above basis. The rope
used is extra-flexible steel hoisting rope of 6 strands, 37 wires, with fiber
core and a factor of safety of 5 to 6. A turnbuckle is provided at one gate
connection for adjustment in order to equalize the length of the ropes. In
case of highly corrosive water, stainless-steel ropes may be used. All
parts of the equipment have sufficient strength to resist the forces produced
by a 250-percent breakdown torque of the motor without exceeding 80
percent of the yield point of the materials.
Ball or roller self-alining bearings or ball-bearing self-alining pillow blocks are used for all hoists except those operated manually. Plain, babbitted, flat box bearings are used on the manually operated hoists. Flexible couplings are of the all-metallic, dustproof, and fully enclosed type.
D. A complete list of hoist capacities and drawing numbers can be obtained from the Drawing and Data Files, Denver. Examples of standard radial gate hoists are shown on the following drawings:
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.32 Chain-and-sprocket hoists are used to raise and lower large gates which
regulate the discharge of water over spillways and are operated only at
infrequent intervals. A complete assembly drawing of a 50- by 50-foot
gate hoist of this type is shown in Figure 54. The hoists are powered with
electric motors. Each hoist, as shown in Figure 54, consists of a motor-
driven reduction unit having two output shafts each of which is connected to
a gear-reduction hoist unit. Each hoist unit is equipped with a drive sprocket,
an idler sprocket, and a sprocket chain. One end of each sprocket chain is
attached to the regulating gate and the other end of the chain is attached to a
counterweight.
A. The hoisting speed depends largely upon the operating requirements of
the spillway. In cases where flood control is the primary purpose of the
gates, faster hoisting speeds are required, but where regulation only is
to be considered slower speeds may be used. The size of the gate also
influences the hoist speed and in cases where large gates of the 50- by
50-foot class are to be moved, speeds ranging from 0.3 to 1.0 foot per
minute are most frequently used. Smaller gates of the 30- by 30-foot
class are hoisted at speeds ranging from 0.5 to 1.5 feet per minute.
B. For stresses in the hoist chain links, refer to Technical Memorandum No. 558. The maximum stress in the chain link should not exceed 75 percent of the yield point of the material used when the pull-out torque of the motor occurs. Particular attention should be given to providing adequate pin clearances in the links.
C. Typical designs of mechanical hoists are illustrated in the following
drawings:
50- by 50-foot Regulating Gate Hoist,
Complete Assembly--Keswick Dam
Main Hoist and Spur Gear Assembly
.33 The hydraulic type of hoist is usually placed on the upstream face of a dam, with the top of the hoist just below the road or walkway, and is used for raising or lowering the fixed-wheel or roller-mounted gate that closes the upstream end of a penstock or outlet conduit. A hydraulic hoist consists of a vertical cylinder, piston, and stem, with the stem passing through a packing in the lower cylinder head. The upper cylinder head contains latches that hold the piston and stem in the raised position without maintaining oil pressure below the piston. The piston stem is connected to the gate stem for low-head installations, or has intermediate sections of stem between the piston and gate for high-head installations. The entire assembly is supported on a bracket resting on the concrete. An assembly drawing of a hoist of this type is shown. in Figure 53.
MECHANICAL HOISTS FOR FIXED-WHEEL
HYDRAULIC HOISTS FOR FIXED-WHEEL OR ROLLERMOUNTED GATES
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