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Each turbine in the Boulder Dam power plant is protected by a butterfly valve, located adjacent to the scroll case inlet and arranged so that a 300-ton powerhouse crane can reach down through a removable metal hatchway in the floor and perform all needful servicing operations. When all machinery has been installed there will be fifteen 168inch butterfly valves and two 120-inch butterfly valves in service.
Designs for the valves were developed by the Bureau and the valves purchased on Government specifications, affecting a substantial saving in cost over commercial-type valves and providing more compact self-contained units, making considerably more space available in the power plant. The 120- and 168-inch valves are substantially alike and consequently only the latter will be described. Figure 18 shows one of the completely assembled valves, including the hydraulic rotor which opens and closes the valves by rotating the leaf in the water passage 90 degrees.
The maximum working pressure on the valves, including water-hammer, is 271 pounds per square inch, or 625 feet of head. The valves are designed for 300 pounds per square inch maximum working pressure. Due to the complex penstock head systems within which they are installed, the valves are arranged for opening or closing operating cycles of not faster than 4 minutes, to avoid setting up harmonics leading to srieous pressure rise. They are designed for safe closure under 300 pounds per square inch pressure, when interrupting a flow of 8,000 second-feet. The waterways through the valves are shaped to gradually accelerate the velocity from 14.1 per second at the inlets to 23.2 feet per second at the outlets, when the turbines arc developing full power under normal operating conditions.
The 13-foot-diameter penstocks, leading to the inlets at the valves, have tapered increasers expanding to 165% inches where the terminating flanges bolt to the butterfly-valve body castings. Tapered plate-steel connector pipes of 129-inch inside diameter are boltedjto the outlet flanges of the valves. These tapered connector pipes are reduced to 120 inches in diameter at the outlet ends, where they are bolted to the inlet flanges of the turbine scroll cases.
Two 12-inch, inside diameter, symetrically arranged bypass lines are provided around the leaf of each valve, governed by 12-inch hydraulically operated, electrically controlled needle valves, arranged to automatically open and establish practically equalized pressure upon both sides of the closed butterfly-valve disk prior to the starting of the hydraulic rotor in the opening cycle. These bypass lines have manually operated guard gate valves above the needle valves for protection.
The butterfly-valve bodies have two heavy base feet or flanges which rest upon anchor rails carried upon a heavy
Figure 17.—Electrically driven hoist for operating cylinder gates, Boulder Dam intake towers.
bifurcated concrete pedestal. The gap in the pedestal allows access to the hydraulically jacked thrust bearing that carries the weight of the rotating parts of each valve, amounting to about 120,000 pounds. A high-pressure oil gun is employed to pump oil into the jack, thereby raising the leaf into its correct central position in the valve body, after which a locking collar on the jack shank is pulled tight, the oil pressure released, and the leaf, stems, etc., are then rotated while supported on the self-aligning roller thrust bearing.
The complete valve consists, essentially, of two separable units, the valve proper and the hydraulic rotor. These two units, which are complete, self-contained, operable entities, are readily combined by setting the hydraulic rotor unit, shown in figure 19, on the receiving flange of the valve unit, then tightening the nuts.
Every reasonable precaution has been taken to insure safety in the operation of the units and to protect the maintenance crews against unauthorized movements of the butterfly valves. Removal of the handle and key from a control panel cuts all electric circuits so that the valve cannot be operated either from the panel or by remote control. Removal of the manhole cover from the turbine scroll case automatically cuts the main leads supplying power to the oil pump motor. Furthermore, the handle on the righthand side of the rotor control mechanism can be unlocked by a special key, the handle turned 90°, and the key withdrawn after relocking the handle, leaving two plug valves in the oil circuit closed.
The hydraulic rotor consists of a rotating member having a cylindrical hub with oppositely extending arms, 180° apart, whose extremities are brought into close proximity to the bore of cylinder. By this arrangement the interior of the cylinder, when viewed in typical horizontal section, see figure 20, is divided into four symmetrical pressure chambers. These are interconnected into diametrically opposite pairs by tubular ports through the rotor hub. The ports are arranged so that if pressure is introduced into one of the pairs of pressure chambers, the force so set up on the vertical faces of the opposite arms of the rotor will cause it to rotate in a clockwise direction. If the pressure is introduced into the other pair of pressure chambers, the rotor will be caused to turn in a counterclockwise direction.
The sectional assembly of the hydraulic rotor (fig. 19), shows that the rotor has a splined shank extending upward, engaging the hubs of two oppositely facing brake disks, causing the disks to rotate whenever the rotor rotates. The brake disks are forced apart vertically, the lower one downward and the upper one upward, by a series of powerful helical coil springs, set in pockets in the opposing faces, thus forcing the conically turned peripheries into braking contact with similarly bored conical seats in the brake cylinder and cover. When the disks are so engaged the hydraulic rotor and the valve disk in the water passage below are all rigidly locked against rotative movement.
The rotor unit constitutes a self-contained mechanism which can be assembled and tested prior to installation. Cavities in the cover, cylinder stators, central core of the rotor and base, are all interconnected and arranged to form an oil reservoir of ample capacity, so that no outside oil storage tanks or supplemental oil supply piping is required. All moving parts are submerged in oil. All oil moving from the reservoir to the pumps passes through a large strainer before entering the pumps; and all oil enter
ing the reservoir passes through the same strainer. All oil and grease pumps, motors, hydraulic rotor control mechanism, control panel, etc., are mounted directly upon the rotor assembly so that none of the parts need be removed when the rotor unit is completed, tested, and ready to be installed on the valve assembly.
When installed on the valve the turning torque is applied to the valve stem in practically perfect balance so that no bending moment is put into the valve stem. Since the rotor unit is bolted directly to the top flange of the valve body all rotational reactions are self-contained, and no outside anchorages in the walls or floor of the power plant are required to resist the torsional reactions arising from the closing or opening of the valve.
A high-pressure, electrically operated grease pump is mounted on the rotor base, on the opposite side from that occupied by the oil pumps and motor. This grease pump is used to lubricate the main valve bearings. Bronze seals, carried in the periphery of the valve leaf and adjustable under pressure from the downstream leaf face, contact mating bronze seats in the valve body. The complete valve and rotor assembly has an over-all height of 27 feet 10 inches, a breadth of 15 feet 11^ inches, an over-all length of 10 feet 6 inches, and weighs 380,000 pounds.
TRACTOR GATES FOR HIGH-HEAD INTAKES
For high-head dams, where large quantities of water are passed through turbines requiring penstocks of exceptional size, the providing of suitable intake gates on the water face of the dam has been a difficult problem. Here again, the rapidly increasing demands for larger installations, under higher heads, has necessitated the creation and development of equipment differing in many respects from that previously employed.
The proposed Friant and Shasta Dams of the Central Valley Project, California, and the Grand Coulee Dam of the Columbia Basin Project, Washington, all of which are being designed by the Bureau, require large intake gates on the water faces, for operation under exceptionally high heads. For such service the Bureau has developed a gate design which has been found well qualified to fulfill the exacting requirements.
In preparing plans for Norris Dam, for the Tennessee Valley Authority, it was necessary to design intake gates for the two 20-foot diameter penstocks which have rectangular inlets, 16 feet 6 inches wide by 28 feet 6 inches high, subjected to a maximum head of 184 feet. Since these gates are now in successful service (see fig. 21), their installation will be described.
Double-drum, clcctric-motor-driven hoists of 300,000pound nominal capacity, located in recesses beneath the parapet on the water face of the dam, are used to operate the gates. The gate-leaf assemblies are suspended on steel cables attached to the hoists. The cables pass around
multiple rope sheaves, housed in enclosed cross-head members, to whose outer ends roller carriages are attached. The roller carriages carry and support each side of the gate leaf, through interposed inclined roller trains, in a manner similar to that used in the paradox gates previously described.
The arrangement is such that the gate leaf, cross head, and attached roller carriages, with their wedge roller trains, all travel as a single entity when they are being lowered from the top of the dam, until such time as the leaf comes opposite the penstock inlet opening, whereupon further downward travel of the leaf is arrested by the lower cross beam coming into contact with stops in the gate frame. When this occurs, the leaf remains stationary while the cross head continues its downward descent about 24 inches farther, allowing the inclined roller trains to gradually withdraw their support from the gate leaf and permitting water pressure to gradually move the leaf horizontally until the seal bars come into contact with the mating seat bars on the gate frame.
In opening the gate, this process is reversed. The cross head with its attendant roller trains are drawn upward by the hoist until the cooperating inclined roller trains engage the sides of the gate leaf. They then act as rolling wedges, gradually forcing the leaf horizontally upstream, away from
sealing contact with the frame seats. The stops on the lower portions of the roller carriages then contact the lower beam of the gate leaf on each end, and the cross head, roller carriages, inclined roller trains, and gate leaf move upward as a single entity.
Figure 21 shows that the entrance to each 20-foot-diameter penstock is protected by a trashrack which extends only part way up the face of the dam. A concrete closure, similar to a chimney, just large enough to allow the gate leaf and carriage assembly to pass through, is built against the face of the dam, from the top of each trashrack up to the location of the bottom of the gate leaf when in the normal raised position. By this arrangement no trash can enter tne interior of the trashrack structures.
Many features of the internal differential needle valves, the paradox controls, the interior differential needle valves, the paradox gates, the butterfly valves, and the tractor gates, as described and illustrated herein, are believed to be new, and patent applications have been entered covering these features.
Accompanying photographs have been furnished through the courtesy of the Bartlett-Hayward Co., Baltimore, Md.; Hardie-Tynes Manufacturing Co., Birmingham, Ala.: Joshua Hendy Iron Works, San Francisco, Calif.; and Thomas Spacing Machine Co., Pittsburgh, Pa.