72-inch inside diameter to 79-inch inside diameter, whose downstream 79-inch inside diameter outlet flanges are bolted to the inlet flanges of their respective needle valves. The nozzle flanges of the needle valves are bolted to platesteel discharge guides that extend through the downstream wall of the valve house.

An overhead traveling crane of 15-ton capacity serves both valves, this being made possible by arranging the relative positions of the two valves so that the upper valve is set back upstream from the lower valve. By removing the plate-steel discharge guide of the upper valve, the crane can readily serve the lower valve from above.

A cable-operated, 8- by 16-foot structural-steel bulkhead gate, operated from a hoist on top of the dam, is provided so that if a flash flood were to occur while either needle valve was rendered inoperative by dismantling for maintenance work, the gate can be lowered over the conduit inlet leading to the valve.

Another form of class 2 installation which has been found to be most advantageous where power plants are built

against the downstream faces of the dam, is to place the needle valves inside the power plant, with the emergency gates either in galleries adjacent to the upstream face of the dam, or preferably inside the power plant and behind the valves, where the powerhouse crane can serve the entire installation. This was done at Coolidge Dam, Madden Dam, and at Seminoe Dam.

At Seminoe Dam two 60-inch interior differential needle valves will be installed in the powerhouse. Each of these valves will be protected by a 72-inch ring-follower emergency gate, which will likewise be inside the powerhouse, and so arranged that by removing steel floor plates, they may be made accessible to the powerhouse crane. The control stands for these valves are to be located upon the turbine floor immediately above their respective valves.

CLASS 2A OUTLETS

At McKay Dam, the tunnel used for diversion during construction was later converted for use as the reservoir outlet. The geological formations were of a nature that

made it desirable to line the entire 705-foot length of tunnel with concrete. The entrance to the tunnel was extended about 40 feet from the portal by a reinforced. concrete transition, as shown in figure 12, connected to a rectangular reinforced concrete trashrack structure 16 feet 6 inches wide by 9 feet 9 inches high, extending 24 feet 9 inches into the reservoir.

The reinforced concrete plug, containing the two 4- by 4-foot high-pressure emergency gates and the operating chamber, is located 155 feet upstream from the outlet portal. From these two gates, 54-inch inside diameter riveted %-inch plate-steel outlet pipes, with inside countersunk rivets and outside strap joints, made vitally necessary by velocities of 35 to 45 feet per second, extend along the concrete-lined horseshoe tunnel on concrete saddle supports with a plank walkway between, to the two 48-inch balanced needle valves located in the reinforced concrete needle-valve house. The needle-valve body castings are embedded in the downstream wall, and the nozzles protrude beyond.

The maximum outlet capacity required is 800 secondfeet, a demand that either one of the 48-inch needle valves can readily satisfy when the reservoir water surface is near maximum elevation. The maximum static head on the outlets, measured from the center-line elevation of the needle valves to the maximum reservoir water surface, is 138.6 feet. One of the valves, when tested with a net head of 90 feet at its inlet flange, discharged 640 secondfeet.

The needle valves are installed in a reinforced concrete valve house, located a short distance beyond the outlet portal of the tunnel. They are arranged to provide ready escape of water from the tunnel without damage to the valve house and its enclosed machinery in the event that a major break should occur in either or both of the outlet conduits within the tunnel. An operating floor, 7 feet 5 inches above the center line of the valves, carries the control stands which are located immediately above their respective valves and by shaft extensions operate the cylinder sleeve controls that are bolted to the upper side of each valve body. These controls have worked well, it being found that regulation of discharge can be held within less than 10 second-foot increments.

A motor-operated triplex pump and the high-pressure oil-pipe control system for the operation of the highpressure gates in the tunnel plug emergency gate chamber are located on the same floor as the needle-valve control stands. A 6-ton, hand-operated, structural-steel gantry crane runs along the downstream wall face of the valve house, on elevated reinforced concrete runway beams that span the diaphragm walls on either side of each needlevalve nozzle. These walls are provided with stop-log grooves and are so arranged as to permit enclosure along

their tops and in front with planking to prevent the valves from freezing during the winter seasons.

The 4 by 4-foot high-pressure emergency gates in the tunnel plug are designed for a 140-foot head and are operated by 15-inch hydraulic hoist cylinders. The gates are equipped with automatic gate hangers with signal lights for remote control from the valve house. Flap-type air valves with screened intakes, located at the downstream face of the tunnel plug, admit air to the downstream side of each gate leaf. When air is being admitted, or whenever there is no pressure in the conduits, these metal valve flaps hang down, leaving the valves open, but whenever water under pressure comes up into the valves from the conduits, it forces the flaps upward against their seats, and thus closes them.

CLASS 3 OUTLETS

A representative example of class 3 outlets is found at Alcova Dam, figure 14, where two 84-inch interior differential needle valves are to be installed in a concrete tunnel plug about midway of the diversion tunnel. The valves are to be arranged so that in plan view they "toe in", with their jets converging as they discharge through platesteel discharge guides into the tunnel beyond.

A large duct will admit air from a shaft extending to the surface above to the roof of the tunnel just over the location where the jets from the needle valves emerge from the discharge guides through the wall of the valve chamber. A 102-inch ring-follower, hydraulically operated emergency gate will be installed in the chamber close behind each needle valve. A 20-ton low head-room type, handoperated crane will serve both needle valves and emergency gates, and can lift any of the parts to a car traveling on rails embedded in the concrete floor of the operating gallery running to the elevator shaft.

The most notable tunnel-plug installations are at Boulder Dam, where twelve 72-inch needle valves are installed in two diversion tunnels. Six were installed in the Arizona tunnel plug, and six in the Nevada tunnel plug, with center lines at elevation 657.95 and elevation 658.89, respectively; so that the valves operate under maximum heads of 571 and 570 feet.

Both tunnel-plug outlets are essentially alike in their main features. Each consists of an operating gallery, 34 feet 6 inches wide by 114 feet 6 inches long, containing six 72-inch needle valves with 86-inch paradox emergency gates, a 16-inch deep-well tunnel drainage pump, all the operating and control equipment, and an overhead, 20-ton capacity, electric traveling crane.

The maximum pressure to which the valves will be subjected, including water-hammer, is 265 pounds per square inch; but they are designed for 300 pounds per square inch maximum working pressure. When all valves are discharging at maximum capacity, they will release in excess

of 42,200 second-feet. At such times each valve will be releasing about 230,000 horsepower, making the total for each group of six equal to 1,400,000 horsepower. This energy is all released into a converging oval, on the downstream side of each tunnel-plug outlet, measuring 50 feet high by 82 feet wide, tapering into the 50-foot diameter diversion tunnel beyond. Much study was devoted to the problem of getting the jets from the valves directed so as to pass out through the tunnel with the least possible. disturbance.

The valves are provided with special control stands, electrically operated and interconnected in symmetrical pairs, whereby pairs of valves may be set at any desired opening from the operating chamber of each tunnel-plug outlet, or from the central control room in the power plant by remote control. The control systems of the valves are likewise electrically interlocked with the Stoney gates at the exits of the tunnels; so that it is impossible to open any of the needle valves if the Stoney gate at the outlet portal of the tunnel is closed.

Access to both tunnel-plug outlets is by tile-lined adits in the canyon walls, extending from the tunnel plugs to the downstream ends of the power house wings. Rails are laid in the floors and a roller-bearing car is employed to transport heavy parts. Communication with the canyon wall valve houses is provided by vertical shafts in which automatic electric passenger elevators operate.

Water is supplied to the six valves of each outlet by a 25-foot inside diameter, welded plate-steel header, whose lower end terminates in a three-way branch manifold, each branch bifurcating into wyes whose outlets thus form the six conduits required for the six valves. The 25-foot header extends upstream in the diversion tunnel to a point just below the entrance to the last 13-foot diameter penstock, leading to the power house. A tapered increaser enlarges the header from 25 to 30 feet in diameter, and the header then continues upstream in the diversion tunnel until it reaches the incline tunnel leading to the base of the intake tower. Here it curves upward through the tunnel and is made fast to the throat liner of the lower cylinder gate in the base of the intake tower at elevation 895, as shown in figure 15.

The manner in which the upper end of the header connects into the throat liner of the lower cylinder gate is illustrated in figure 16, which likewise shows a vertical section through the lower cylinder gate in the closed position, with the water passageways through the intake tower walls. In this figure, the half sectional plan shows the 12 radially converging water passages with the semisteel conduit linings.

A similar cylinder gate is placed 150 feet higher in each tower as shown in figure 15. The two gates in each tower are operated by an electrically driven hoist, located on the

operating floor as shown in figure 17. The hoist consists of a central dual drive unit, from which three vertically aligned pairs of drive shafts extend radially in a horizontal plane to three dual hoisting units spaced 120° apart circumferentially. Each of the three radially extending pairs of drive shafts is coupled to two worms in each hoisting unit, which engage and drive worm gears provided with vertically disposed hollow hub members to whose extremities threaded lifting nuts are affixed. The lifting nut on the upwardly extending hub, attached to the upper worm gear, engages and supports a solid threaded stem which extends downward to the bottom cylinder gate at the base of the tower below. The lower worm gear hub extension lifting nut engages and supports a tubular threaded stem which extends downward, concentrically enclosing the solid stem previously described, this tubular stem being connected to the upper cylinder gate. The center-drive unit has two independent vertically aligned gear motors, the upper motor driving through the upper three radial shafts that are connected with the upper worms and gears in the three hoist units, and so operate the lower cylinder gate. The lower gear motor similarly drives the lower radial shafts and worm gears, and so operates the upper cylinder gate. The upper cylinder gates, which are alike in all four intake towers, will have a maximum operating head of 184 feet on the bottom sills, while the lower cylinder gates will have a maximum of 334 feet on the lower sills.

Both the upper and lower gates have a normal travel of approximately 9 feet; but the hoists are arranged so that when inspection or maintenance is required, the gates may be raised an additional 2 feet to provide access to the top seals and seats. The upper or lower gate in each tower may be operated independently or simultaneously, the time required for opening being 52 minutes.

Two of the four intake towers at Boulder Dam control the batteries of 72-inch needle valves in the tunnel-plug outlets as described before. The other two towers control batteries of 84-inch needle valves which constitute the canyon wall outlet works.

CLASS 4 OUTLETS

The canyon wall needle valve outlets at Boulder Dam consist of two batteries of six 84-inch valves, one on each side of the canyon. The valves will normally operate under heads of from 160 to 320 feet, but are designed for a maximum head of 430 feet. The center lines are placed at elevation 820, and discharge curves show that the combined capacity for all 12 valves will be 47,500 second-feet, with the reservoir water surface at elevation 1,225. When this occurs, each valve will be controlling in excess of 190,000 horsepower, making a total for the 12 valves in excess of 2,000,000 horsepower. The valves are connected to the cylinder gate towers by plate-steel header pipes, similar to those used in the tunnel plug outlets.