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1.12H

HYDRAULIC GATES (Continued)

BULKHEAD GATES (Continued)

temper. For gates having metal-bearing surfaces it is usual to arrange the Construction
guides so that the spring pressure will be applied to the gate during only
the last foot of its downward travel.

Frames for gates having metal-to-metal bearings should not be embedded
in the first-stage concrete of the power-plant substructure, but should be
installed in blockouts, carefully alined by the use of embedded anchors,
and the blockouts filled with second-stage concrete after the final adjust-
ment of the frames. The frame should be sufficiently rigid to withstand,
without appreciable deflection, the forces due to the placing of second-stage
concrete.

H. The following drawings show typical examples of draft-tube bulkhead-gate installations, gates, and frames:

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.13 Stop logs are a laminated type of bulkhead to be used as a temporary or
emergency closure on any type of structure. They may be made of wood, steel,
reinforced concrete, or a combination of these, depending on the span and head.
A. The dimensions of the slot in the concrete structure will probably limit the
size of timber, but in general timber greater than 14 inches thick should not
be considered and stresses should not exceed 1,000 psi for bending, 100 psi
for horizontal shear, and 300 psi for bearing perpendicular to the grain.
Embedded steel seats or guides are not essential, but all longitudinal joints
between logs should be either beveled or calked or sheet-rubber nailed in
place to constitute an effective seal. To overcome the buoyancy effect of
individual logs, concrete weights may be used, or a tighter seal can be
effected by drawing the logs together with tie rods into a single bulkhead,
in which case the unit is held down either by wedging or by additional tie
anchors.

B. Steel stop logs are used where excessive head and span prohibit the use of timber; they may have faceplates of either wood or steel as required to withstand the water pressure. In all instances wood seals should be used against an embedded metal guide and should be rubber-sealed longitudinally between logs. Since the wood seals would probably require replacing before each period of use they may be stressed to approximately 1,200 psi perpendicular to the grain, allowing the crushing effect to give a more uniform bearing surface and consequently a tighter seal. One or more steel beams may be used per log, depending on the weight which can be conveniently handled and the economy involved in changing beam section as the head reduces. Consideration should also be given to the use of a corrosionresisting material for embedded guides such as at the Grand Coulee Main Units, where a combination cast-iron and wrought-iron guide was used.

Details (Cont.)

Reference
Drawings

STOP LOGS

Timber Stop Logs

Steel

Stop Logs

1.13C

Reference
Drawings

GATES

COASTER
GATES

HYDRAULIC GATES (Continued)

BULKHEAD GATES (Continued)

C. Typical designs of stop logs are illustrated by the following drawings:

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.14 Spillway-type gates are used to regulate flow in spillways, and are usually
counterweighted to reduce the required hoist capacity. Chains from each
end of the gate pass over sprockets and support the reinforced-concrete
counterweights. The sprockets are driven by geared hoists.

To eliminate drawdown and also trash accumulation, the skin plate is
located upstream. Flexible seals, which are attached to the skin plate, bear
against faceplates which are embedded flush in the side walls of the structure.
The bottom edge of the skin plate, which supports the gate when closed, has a
rubber sealing strip clamped to the upstream face and projecting one-quarter
inch below the skin plate. The general design principles are similar to those
described in Paragraph 1.15. A typical installation of spillway gates is shown
in Figures 18 and 19.

.15 Coaster gate is the name used to identify a roller-mounted, high-head,
structural-steel gate. Such gates are similar to fixed-wheel gates described
in Paragraph 1.16 except that they are mounted on rollers. Coaster gates
are used for closing off flow through penstocks and outlet conduits under
unusually high heads or for large sizes where fixed-wheel gates would be
impractical due to the necessarily greater frictional resistance. They are
usually operated under balanced pressure conditions to permit unwatering
for inspection or servicing of the other equipment such as turbines or valves,
but are designed for emergency closure if required. They are lowered (closed)
by their own weight.

A coaster gate consists primarily of a skin plate supported by horizontal
beams which in turn are supported by vertical girders at the sides. Contin-
uous roller trains are mounted around the vertical girders and transmit the
load to tracks in the face of the structure. Rollers are usually made of the
AISI Type 410 Stainless Iron heat-treated to a minimum of 250 Bhn. Guide
shoes are located near the top and bottom on each side of the gate and operate
over continuous guides embedded in the concrete structure.

Frames consist of tracks and seal seats mounted on structural beams, and guides. These frames are erected in blockouts in the concrete face and are alined by anchor bolts embedded in the original pour. After alinement the blockouts are filled in with concrete.

Stresses are determined on the assumption that 1/32-inch corrosion allowance
is removed from the gross section of all wetted surfaces. The principle
bending stresses in the skin plates and beams are combined in accordance
with Westergaard's "Criteria of failure for materials subjected to two
dimensional stress" with a maximum allowable combined stress of 24,000 psi.
Direct tensile stress is limited to 18,000 psi. A typical coaster gate
installation is shown on Figures 20 and 21.

1.16

HYDRAULIC GATES (Continued)

WHEEL- AND ROLLER-MOUNTED GATES (Continued)

.16 The name "fixed-wheel gate" describes practically any structural-steel gate mounted on wheels but more often it identifies gates with relatively high head used on the inlet end of penstocks and river outlets and at the entrance and within tunnels. General principles of leaf design are similar to those outlined in Paragraph 1.15 for coaster gates.

Wheels are usually mounted between double vertical girders at the sides of the gate. On small low-head gates, double-flanged wheels are used to guide the gate while moving under load. On the larger gates, wheels without flanges are used. In the latter case spring-loaded guides are provided at the sides of the gate in addition to disc (Belleville) springs at both sides of each wheel. This arrangement forces the gate and each wheel to its central position whenever there is no water load on the gate, and allows lateral movement when the gate is moving under load without an excessive amount of friction.

A minimum tread hardness of 255 Bhn is required for the wheels which should
be specified as wrought steel in accordance with ASTM Specifications No.
A-57-46. Bushings for the bearings of the foregoing wheels should be of the
self-lubricating type, on which an average bearing stress of 3,500 psi of pro-
jected area is allowed. The bushings are usually pressed into the wheels.
The journal surface of the wheel pin is eccentrically located with respect to
its end supports. By this arrangement, the downstream face of the wheel tread
can be adjusted, after final assembly, to a true alinement with the treads of the
other wheels so that all wheels will bear uniformly on the track. An installation
drawing of a gate of this type is shown in Figure 22.

Flexible seals of the music-note type, having a relatively thin continuous brass
quadrant vulcanized to the surface of the bulb on the area that covers the gap
to be sealed, are mounted on the skin plate. This arrangement utilizes the
flexibility of a rubber hinge which permits close local adjustment and provides
the rigidity of metal to support the load and prevent extrusion of the rubber.
Fixed-wheel gates, and coaster gates as described in Paragraph 1.15, are
classified with respect to function and location as follows:

Tunnel gates--located inside of penstocks, tunnels, conduits, etc. (Figure
23.)

Submerged gates--located on upstream face of penstocks, conduits, etc.
(Figure 24.)

A. Tunnel gates are used as penstock inlet gates and as regulating or shutoff
gates in tunnels. In the lower-head installations they are operated by
gantry cranes or chain hoists with counterweights and screw-type hoists.
For higher-head installations hydraulic hoists are usually provided.
(1) By locating the skin plate and seals upstream, hydraulic downpull can
be practically eliminated. Adequate venting to the atmosphere is
provided from the downstream side of the gate through the shaft above
the gate.

(2) Flexible seals are located on the upstream side of the skin plate and
bear against faceplates embedded flush with the surface of the slot in
which the gate operates.

(3) Tracks are extended a little more than one gate height above the top
of the water passage.

B. Submerged gates are used on the upstream face of structures where reservoir pressure can act downward on the area represented by the plan of the gate. High-head penstock inlets and inlets to river outlet conduits

FIXED-WHEEL

GATES

Tunnel
Gates

Submerged
Gates

1.16C

ubmerged
Gates
(Cont.)

Reference
Drawings

HYDRAULIC GATES (Continued)

WHEEL AND ROLLER-MOUNTED GATES (Continued)

are typical applications. They are designed to close under full unbalanced
pressure, or so-called emergency conditions. When used as penstock
inlet gates, they are suspended immediately above the inlet and operated
by hydraulic hoists so that closure can be made in a relatively short time.
For river outlets, canal outlets, etc., where regulation is performed by
other equipment, one gate may be used to serve several outlets and is then
usually handled by a gantry crane and stored in a special pit on top of the
dam.

Skin plates and seals are located on the downstream face of the gate. This
permits the dead weight of the gate to assist in lowering and, together with
a special shape of gate bottom, reduces the hydraulic downpull which occurs
when the gate is lowered under unbalanced pressure conditions. The down-
pull varies from a minor force to one several times the weight of the gate,
depending upon the velocity of flow and the head over the top of the gate.
Vents are provided in the top at the inlet just inside the entrance to relieve
negative pressure when closing the gate under unbalanced pressure condi-
tions and to allow escapement of air when backfilling before gate is opened.
Flexible seals are attached to the downstream face of the skin plate and
bear against seal bars fastened to the structural framework embedded in
the concrete face.

Tracks are extended a little more than one gate height above the top of the
water passage.

C. The foregoing types of gates are illustrated in the following drawings:
8' x 14' Bulkhead Gate --Grand Coulee Dam

50' x 50' Regulating Gate--Keswick Dam
(Figure 18)

222-D-1772

214-D-8956

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GATES

HIGH-PRESSURE CONTROL AND EMERGENCY GATES

HIGH- .17 High-pressure gates are used in outlet works of dams. They are generally PRESSURE installed in tandem, with the upstream gate serving as an emergency gate and the downstream gate as a regulating gate. They are often used as emergency gates in combination with needle valves and hollow-jet valves. The gates may be operated as emergency gates under heads up to 250 feet and as regulating gates under heads up to 90 feet.

Frame &
Bonnet

A. The frame and bonnet of a high-pressure gate and the sections of conduit lining are designed to be embedded in concrete, and the concrete is reinforced sufficiently to carry the water load. The top of the bonnet, the bonnet cover, and the circular end of the transition may be designed for heads as high as 250 feet, as these parts are not embedded.

1.17B

HYDRAULIC GATES (Continued)

HIGH-PRESSURE CONTROL AND EMERGENCY GATES (Continued)

B. The gate leaf may be designed for the following heads and materials:
Head, feet

Design
Heads

0 to 90

90 to 140

140 to 250

Material

Cast iron, Class 25

Cast iron, Class 40
Cast steel, Grade 2

C. The seats on the gate leaf are of cast bronze, Federal Specification
QQ-B-691b, Composition 2. The seats in the downstream frame are of
Composition 6. This difference in the composition of the seats permits
the use of bearing pressures up to 3,000 psi without seizing. For design
purposes, the bearing pressure is limited to 1,000 psi.

D. Air inlet connections are provided on all high-pressure gates. On an
emergency gate, the air inlet piping is installed from the gate to the floor
line and terminated with a blind flange. If necessary at a later date to use
the emergency gate for regulation, an air valve can be installed. On
regulating gates, air is taken from the nearest source. The inlet must be
so placed or guarded that no one can be injured by the inflow of air.

E. High-pressure gates are operated by hydraulic cylinder hoists using oil
as a medium. Different size hoists are used with each gate depending on
the water head. The size of hoist should be selected to provide the required
lifting capacity when using oil at a pressure between 500 and 1,000 psi.

F. The capacity of the hoist required is obtained by the formula

Seats

Air Inlets

Hoist

Capacity

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G. The hoist control system consists of an oil pump, four-way valve, oil tank, Hoist Controls and interconnecting pipe. A light machine oil with a viscosity of 90 to 120 SSU at 130° F, and viscosity index of approximately 70, should be used in the system. The control station may be near the gates or at a considerable distance as desired. Two lines of pipe are required for each gate.

H. Each high-pressure gate is equipped with a hanger to hold the gate open. A semiautomatic gate hanger is provided for each emergency gate when used ahead of another high-pressure gate. This type of hanger can hold the gate leaf in the open position only. When a high-pressure gate is used as an emergency gate ahead of a needle or jet valve or as a regulating gate, a hydraulic gate hanger is used to hold the gate leaf. This type of hanger will hold the gate leaf in any position.

I. Some standard sizes of gates, hoists, and hangers are given below:

High-pressure gates:

2 feet 9 inches by 2 feet 9 inches
3 feet 3 inches by 3 feet 3 inches
3 feet 6 inches by 3 feet 6 inches
4 feet 0 inches by 4 feet 0 inches
4 feet 0 inches by 5 feet 0 inches
5 feet 0 inches by 6 feet 0 inches
6 feet 0 inches by 7 feet 6 inches

Gate Hanger

Standard Sizes

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