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encountered in some western watersheds made evident the desirability of providing a superabundance of operating force in needle valve control mechanism. This made it particularly desirable to find some practicable means whereby inward or outward leakage through the clearance space between the exterior of the needle body and the bore of the needle cylinder, prevalent in the first internal differential needle valves, would be prevented, thereby making available the closing force which could be produced in chamber A, without the attendant disadvantages manifest in those valves.

Much study was devoted to the problem, with only discouraging results, until finally a workable solution was found in a quite marked modification of the internal differential needle valves. This led to the development of a type of valve known as an "interior differential needle valve."

INTERIOR DIFFERENTIAL NEEDLE VALVES

In this valve the needle cylinder, formed in the body and nozzle of its predecessor, has been eliminated, and the equivalent has been provided by forming the cylinder inside of the needle, as shown in figure 9. By this arrangement, the needle, instead of telescoping inside the cylinder as previously occurred, now telescopes over a member fixed to the valve body known as the body extension. The exterior diameter of the needle body forms the inner boundary of the annular water passage through the valve. This permits the use of a smaller diameter than before, and in consequence reduces the over-all diameter and length of the valve. The change resulted in a saving of about 25 percent in valve weight.

By this arrangement of needle mounting, the entrance of the circumferential operating clearance space, between the bore of the needle and the cooperating diameter of the supporting body extension, is now placed at the upstream end, instead of at the downstream end where the higher velocity of flow tended to produce a strong suction when the previous valve was discharging. This rearrangement also made possible the installation of an expanding piston ring, found so effective in preventing leakage between chambers B and C in the previous valves, in the valve body extension to prevent leakage through that clearance space in either direction, thus making practicable the employment of cavity A as a pressure chamber under all conditions of operation.

The changed construction and rearrangement of the parts results in chamber A being a complete chamber instead of an annular chamber; chamber B remains unchanged as an annular chamber; and chamber C is changed from a complete chamber to an annular chamber, due to the diaphragm tube being fastened to the needle.

In this valve, the problems of drainage and air venting of the chambers are made simple and more efficient, as the presence of the valve body extension makes possible the installation of a direct drainage port from chambers C to A, at a

location low enough to remove practically all water by gravity flow. A similar port on the upper side allows all the air in A to escape. Chamber B is likewise served by a port in its lowest portion, insuring complete drainage, and by a complimentary port in its high side, for venting. This makes possible the elimination of the intercommunicating bleeder ports between chambers C and B and from B into A, formerly required, as the ports from chambers A and G and from chamber B to the paradox control now serve as gravity drains as well.

The paradox controls used with these valves are essentially the same as those used with the internal differential valves, except that they do not include the separate cylindrical screw actuated drain valve. This member is not required since the former cavity A is now made into a pressure chamber and no longer requires a separate drain outlet through the control.

Interior differential needle valves have been, or are being, installed in the outlet works of the following dams: Two 36-inch valves at Moon Lake Dam, two 36-inch valves at Agency Valley Dam, two 42-inch valves at Boca Dam, two 48-inch valves at Taylor Park Dam, two 54-inch valves at Alamogordo Dam, two 60-inch valves at Seminoe Dam, and two 66-inch valves at Bartlett Dam.

NEEDLE-VALVE OUTLETS

Needle-valve outlets may be divided into four general classes, as follows:

1. On the water face of the dam, as at Arrowrock and Belle Fourche Dams, and in the South Tunnel Outlet at Pathfinder Dam. Installations of this character were discontinued after the balanced needle valve was developed for installation at the outlet ends of closed conduits.

2. On the downstream face of the dam, as at Owyhee and Gibson Dams.

2a. At the outlet ends of the diversion tunnels, as at Tieton and McKay Dams.

3. Inside of diversion tunnels as at Alcova and Boulder Dams.

4. At the outlet ends of tunnels or galleries provided for the sole purpose of releasing water from a reservoir under lesser head than that prevalent at the diversion tunnel level, as the Canyon Wall Outlets at Boulder Dam.

These four main divisions are susceptible of further subdivision in accordance with the arrangement, type, and location of the service or emergency gates guarding the valves. For example, under class 2, the 4- by 4-foot highpressure gates that guard the 48-inch needle valves at Owyhee Dam, figure 10, are in a separate gallery near the upstream face of the dam, while the 5- by 5-foot highpressure emergency gates guarding the 60-inch needle valves at Gibson Dam, figure 11, have the outlet flanges of the gate frame transitions bolted directly to the inlet flanges of the needle valves.

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At dams where the river is diverted through a tunnel around the site, the tunnel can usually be later employed as an outlet for releasing water by placing a plug, containing a high-pressure gate chamber in the upstream portion of the tunnel. One or more plate-steel pipes are provided from the gate chamber to the tunnel outlet portal, where suitable needle valves are installed in an outlet valve house, and arranged to discharge into the river channel or into a stilling pool below the dam. Tieton and McKay Dams, figure 12, are typical examples of this type.

If the dam and outlet works are of more than average size and importance, a vertical shaft, extending from the emergency gate chambers to the ground surface at an elevation higher than maximum reservoir level, is provided for remote-control purposes. A second high-pressure oil pump, motor, and interconnecting oil lines to the highpressure gates below are arranged to permit the closure of the gates by remote control from a house at the top of the shaft. The outlet works at Tieton and Echo Dams are arranged in this way.

CLASS 2 NEEDLE-VALVE OUTLETS

The outlet works at Gibson Dam, figure 11, are typical of this class. They consist of two 72-inch diameter conduits formed of 5-foot lengths of semisteel castings, designed to take full reservoir pressure. The conduits are provided

with bellmouth inlets 8 feet in diameter, protected by trashracks. The conduits are bolted to transitions, 10 feet long, near the downstream face of the dam; and the outlet flanges of the transitions are bolted to the upstream flange faces of two 5- by 5-foot high-pressure emergency gates. The downstream gate frames are formed into transitions from the square to the circular sections and receive the inlet flanges of short body 60-inch internal differential needle valves, which protrude through and have the body castings embedded in the downstream wall of the needle-valve house. The emergency gates are embedded in heavily reinforced concrete that merges into the downstream face of the dam.

The emergency gates and needle valves are subjected to a maximum operating head of 163.5 feet. The leaves of the emergency gates are of cast steel, and are provided with 21inch diameter hoist cylinders, operated by a gasolineengine-driven triplex pump in the valve house. A mast-type jib crane serves both the high-pressure gates and the needle valves. A 6-inch bypass is provided around each highpressure gate, so that the needle valve can be closed, the bypass valves opened, and the pressure balanced on both sides of each gate before it is opened.

At Owyhee Dam, figure 10, the needle-valve outlet consists of one semicircular trashrack on the upstream face of the dam, serving three 4- by 4-foot square semisteel conduits with 5-foot square bell mouths formed in the concrete. Three 4-foot lengths of conduit liners, immediately downstream from each bellmouth, are bolted to the inlet flanges of the respective 4- by 4-foot high-pressure gate frames. To the outlet flanges of these high-pressure gates are bolted 4by 4-foot to 57-inch diameter transitions, each made up of two sections 4 feet long. These are connected at the outlet flanges to 57-inch, inside diameter, semisteel conduit liners that extend through the dam and connect to the entrance flanges of 48-inch balanced needle valves of the split-body type.

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The center lines of the 4- by 4-foot high-pressure gates are located 19 feet from the upstream face of the dam, in a gate chamber common to all three gates, having a recess midway of its length on the downstream side, in which the highpressure oil pump, motor, and control equipment are located.

Hoops, 7 feet 6 inches in diameter, of 1-inch square bars on 5-inch centers, were placed around the square bellmouths and all the square conduit from the upstream face of the dam to the downstream flanges of the transitions.

The high-pressure gates are provided with automatic hydraulic gate hangers of the stem-extension type. This needle-valve outlet is subjected to a maximum head of 200 feet. The high-pressure gates are designed for a 250-foot head, are provided with cast-steel leaves, and are operated by 18-inch diameter hydraulic hoist cylinders. The 57inch inside diameter conduit liners, connecting the transitions to the needle valves, are designed to take the maximum working pressure with a liberal allowance for corrosion.

The needle valves are located wholly within the heavily reinforced concrete valve house, to facilitate handling by means of a 5-ton, low headroom, hand-operated crane just beneath the ceiling. The jets pass through removable plate-steel discharge guides that are bolted to the steel orifice liners embedded in the valve-house wall.

A good example of class 2 outlets as applied to a reinforced concrete slab and buttress dam is found in the needlevalve outlet at Stony Gorge Dam, shown in figure 13. A recess was formed between the buttress walls on the water face of the dam, and covered by by 6-inch trashrack bars, with their upper edges flush with the upstream face of the dam. Two 3-foot 6-inch by 3-foot 6-inch square conduits, with bellmouth inlets, lead to high-pressure gates, operated by 12-inch diameter hoist cylinders. The gates are housed in a reinforced concrete enclosure, the upstream wall of which is formed by the outlet side of the trashrack structure. They were designed for 98 feet of head and are operated by a direct motor-driven triplex pump.

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Bolted to the outlet flanges of the gates are semisteel transitions that connect to 50-inch, inside dameter, riveted plate-steel outlet pipes, supported on concrete saddles. The pipes extend downstream to 42-inch balanced needle valves, enclosed in a reinforced concrete valve house where the pipes are provided with expansion joints. A concrete walkway, supported by cross beams between the buttresses, extends from the operating floor of the emergency gate chamber to the operating floor of the valve house. A small hydraulic turbine drives a 25-kilowatt generator that supplies power for operating the oil pump and lights, and also charges a 125-volt storage battery for stand-by service.

The two 42-inch balanced needle valves, designated as nos. 1 and 2, are identical insofar as their general construction is concerned; but each valve has a differing control. No. 1 valve has the sleeve type of control, wherein the needle actuated sleeve is operated by a lever attached to the rear end of the needle; so that vertical axial or end

wise movement is imparted to the sleeve. No. 2 valve has the cylinder type of control, wherein the needle actuated member is rotated through a rack, attached to the needle, driving a pinion on a vertical shaft, to the upper portion of which a pinion is attached that meshes with and drives an internal gear integrally formed with the cylinder member so rotated by movement of the needle. Both of these controls have been found to work equally well and have proved to be reliable and satisfactory.

The needle-valve outlet at Bartlett Dam is analogous in some respects to the Stony Gorge installation just described, yet in many ways it is distinctly different. Here two 66-inch needle valves are installed inside a reinforced concrete valve house, built against the downstream end of a dual hollow buttress which receives the thrust loads of two adjacent arches. A vertical slot, 8 feet wide, is formed between the adjacent buttress walls, within which two 72-inch inside diameter %-inch plate-steel outlet pipes, with inside field welded girth joints, are placed one above the other, with the center line of the lower at elevation 1,633 and the upper 17 feet higher at elevation 1,650. These pipes extend from their inlets, situated in the crotch formed by the converging surfaces of adjacent arches at the water face of the dam, to the needle-valve house. There they are anchored in a heavily reinforced concrete thrust block and are connected to tapered increasers from

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