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GATE HOISTS (Continued)
. Hoists are operated by means of a motor and oil pump with the directional
flow of oil controlled by valves that are actuated by electric contacts from any desired position.
. The lifting capacity of the hoist will be the sum of the following:
Weight of gate leaf
The operating pressure in the hydraulic cylinder should be limited to about 750 psi and the cylinder should be designed for 1,000 psi.
. The cylinder is made of rolled plate or pierced forging with forged flanges
welded to the ends of the cylinder. The heads are made of cast steel. The piston stem if of monel metal and the intermediate and gate stems are low-carbon or alloy-steel forgings.
The working stress in steel castings should be limited to about one-third of the yield point of the material.
The stress in the cylinder wall and stems should be limited to about one-third of the yield point of the material when loaded to the capacity of the oil-pump relief valve.
D. A typical design of a hydraulic hoist is illustrated in the following drawing:
15’ x 19.05’ Penstock Coaster Gate Hoist--
MISCELLANEOUS METAL WORK
LIFTING .34 Lifting frames or lifting beams are used as grappling devices for placing or
FRAMES & BEAMS
removing bulkhead gates, trashracks, and stop logs, and are designed to operate below the water surface, utilizing the guides or slots provided for the equipment being handled. Trashracks are generally left in place after the initial installation, for periods of 10 years or more; therefore, lifting frames :oldered maintenance equipment and are designed at the project if needlecl.
A. Wherever possible, large stop logs and bulkhead gates should be picked up
from a single point, with a single hook. Where two hooks are used, the
1.34B MISCELLANEOUS METALWORK (Continued) B. Typical designs of lifting frames or beams are illustrated by the following Reference drawings: - Drawings Bulkhead Gate Lifting Frame--Shasta Power Plant 214-D-6407 Bulkhead Gate Lifting Beam--Hungry Horse Power Plant 447-D-411 Bulkhead Gate Lifting Beam--Marys Lake POWer Plant 245-D-4330 Bulkhead Gate Lifting Frames (Specifications No. 1717–D)-- 214-D-10203 and Friant Dam 214-D-10376 Stop-log Lifting Beam--Enders Dam 328-D-397 Stop-log Lifting Beam--South Coulee Dam 222-D-10556
.35 Trashracks are used to protect turbines, pumps, and valves from objectionably TRASHRACKS large debris. The usual practice is to provide as large a clear opening between trashbars as is consistent with the features to be protected, to consider hydraulic head loss through the rack only when this loss is important, and to consider the ease of replacement in proportioning the rack so as to build long life into those racks which may not be readily replaced.
A. The details and general construction of trashrack installations vary with Types & the service required, depth of water, and accessibility for replacement. Reference Trashracks may be divided into types according to their constructional Drawings
features and the methods required for their installation. The types are
(1) Type 1.--Removable-section racks which are installed by . the Type 1
Grand Coulee Pumping Plant 222-D-3814
Davis Power Plant 351-D-2014
Granby Pumping Plant 245-D-2692 (2) Type 2--Removable-section racks in which the individual sections are Type 2
not installed between guides in the trashrack structure, but are placed
Yakima Project--Pumping Plants 33-D-3402
MISCELLANEOUS METALWORK (Continued)
(3) Type 3--Trashrack sections which are bolted in place below water line in locations which may be readily unwatered, or are accessible Seasonally. Reference drawings are:
Trashrack, Drop No. 4 Power Plant--
Drum Gate Chamber Supply Inlet
Penstock Intake Trashrack--Cove
. The appropriate type of rack for an installation is dependent upon its
accessibility for painting or replacement, the size and quantity of trash expected, and the requirement for raking. The type of rack selected must be suitable for the trashrack structure, and the design of the rack, including spacing of the bars, should be discussed with the engineers responsible for the design of the structure and the equipment being protected. Trends in trashrack-type selections are indicated in the following:
(1) All major trashrack installations where at least a portion of the racks are deeply submerged have been Type 1 side-bearing racks, installed in a vertical position.
(2) Type 2 racks have been used for canal headworks, and for pumping
. In small installations of deeply submerged outlet works, racks should be
designed to fail at approximately 40 feet differential hydraulic head. Racks which are submerged 20 feet or less are usually designed to fail at a hydraulic head equal to two-thirds of the maximum depth of submergence; however, if these racks are intended to serve as Supports for flashboards, they should be designed for safe stresses under maximum loading conditions.
. Trashrack bar sections are usually rectangular, but if considerable
tonnage of racks is purchased at one time bars having rounded edges o
of the bar. Similarly, safe working stresses for trashrack bars used to support flashboards should not exceed the following value:
1.35E MISCELLANEOUS METALWORK (Continued)
E. Members used as horizontal beams in Type 1 side-bearing rack sections Design of do not require stress reduction to compensate for lack of lateral support. Horizontal These members are assumed to fail at yield point stress; but calculations Members should include stress due to the dead weight of the beam members and trashrack bars. To insure rigidity during handling, the lateral deflection of the beam members due to dead load should not exceed one three-hundreths of their span.
F. Several large trashrack installations, notably at Friant and Marshall Ford Materials
Dams, have racks fabricated from a low-alloy steel. However, whether
The thickness of metal to be used in trashracks is to some extent dependent
G. In proportioning welds for trashracks it should be recognized that the Proportions corrosion of the weld is a factor of greater importance than the strength of Welds of the weld, also that a fillet weld will corrode from one side only, whereas a trashrack bar will corrode on two sides. It is recommended that the minimum size of fillet weld be the same as the thickness of metal in the trashrack bars where these bars are three-eighths inch or less in thickness and that 3/8-inch fillet welds be used for connections of heavier trashrack bars. It is also recommended that the horizontal beam members of Type 1 side-bearing rack sections have 1/2-inch welds at their end connections.
H. Type 1 side-bearing racks are usually installed between guides formed in Economies of the concrete of the trashrack structure, thus eliminating the necessity for Trashrack embedded metalwork, except for small bearing plates at the base of high Installations tiers of racks. Type 1 side-bearing racks are more economical than Type 1 end-bearing racks, the economy being more pronounced in racks having the closer bar spacings. For power intakes, the actual economy of a trashrack may depend upon low hydraulic head loss rather than upon the initial cost of the rack. In these racks it is usual to use Streamlined supports, and to use bar sections instead of structural shapes for horizontal beams of Type 1 side-bearing racks. However, streamlining of trashbars is quite expensive and the added expense is generally not justified with prevailing power sales rates.
I. Structural details, connections, etc., should at least provide for failure Structural loads on the rack. Also, care should be exercised to avoid heavy loadings Details
MISCELLANEOUS METAL WORK (Continued)
near the exposed edges on corners of concrete construction. Thus it is
Shop fabrication specifications have been developed for Type 1 side-bearing racks (see Specifications No. 2537).
STAIRWAYS .36 Stairways and ladders constitute an important means of access to different
elevations in powerhouses and dams. The types in common use are inclined straight stairways and spiral Stairways. Ladders are usually vertical or Slightly inclined.
A. The preferred slope for gallery stairways is 9 inches vertical to 12 inches
B. Stairways may be typified by the following reference drawings:
Keswick Dam 214-D-10010-13
DaViS Dam 351-D-2039–40
Friant Dam 214-D-11881-84 and
C. Spiral stairways should preferably be 6-foot 0-inch diameter; however, lack of sufficient space may justify the use of a smaller size, in which case a 5-foot stairway is used. The direction of the stairway should be clockwise going down, with 12 treads constituting a complete turn. The desired distance between platforms is 1-1/2 turns; this may be increased when necessary, but the maximum should not exceed 2-1/2 turns. The landing platforms may be 60, 90, or 120 degrees, but 90-degree platforms are preferred.
(1) When spiral stairways are used between the galleries of dams, it is