24,000 pounds, and of the gate frame is 35,000 pounds.

(b) Design.-The gate was designed for a static head of 362 feet, assumed to be uniformly applied over the skinplate. Bending stresses in the horizontal and vertical beams were limited to 20,000 pounds per square inch tension and compression, with the web shear limited to 13,000 pounds per square inch. Combined stress in the skinplate, due to beam bending and skinplate bending, was limited to 20,000 pounds per square inch. The bending stress in the web of the horizontal beam at the hoist connection was limited to 25,000 pounds per square inch, and the tension in the gate stem was limited to 25,000 pounds per square inch. A portion of the skinplate was considered to act as the downstream beam flanges. The skinplate was also assumed to act as a continuous beam with the support on the centerline of the webs.

67. OUTLET PIPES. (a) Description.-An irrigation outlet pipe is used in conjunction with the penstocks to assure an adequate flow of irrigation water to the downstream river channel and the Bighorn Canal. An evacuation outlet pipe is provided to draw the reservoir down to its minimum level. The irrigation and evacuation outlet pipes also serve as an emergency spillway. Fabrication and installation requirements are described in specifications No. DC-5525.

Two 84-inch-diameter steel outlet pipes (figs. 82 and 121) with bellmouth transitions in the upstream face of the dam extend through the dam to ringfollower gates at the downstream side of the dam, and from the ring-follower gates for a short distance to 84-inch hollow-jet valves. The irrigation outlet pipe, at inlet elevation 3400 and a length of approximately 300 feet, slopes to elevation 3191 at hollow-jet valve No. 1. The evacuation outlet pipe, at inlet elevation 3300 and a length of approximately 220 feet, slopes to elevation 3191 at hollow-jet valve No. 2.

One bulkhead gate normally stored at the top of the dam serves as an emergency shutoff for either inlet. Manholes provide assess to the outlet pipes from the the 7-foot 6-inch access adits.

Six-inch air vents (fig. 129) extend upward from the outlet pipe bellmouth transitions to two 8-inchdiameter, wire-cloth-covered intake assemblies located at elevation 3658.50 on the upstream face of the dam. When filling or unwatering either outlet pipe, the six-inch air vents allow air to escape or enter.

Eight-inch filling lines (fig. 83) are connected to the outlet pipes just upstream from the ring-follower

gates. The filling line valves are located in room 502 in the powerplant.

Six-inch drains (fig. 83) provide for drainage of the bellmouth transitions and discharge into sumps in the access adits. Six-inch flushing pipes also extend from the bottom of the ring-follower gates and discharge into the stilling basin. The drain valves are located beside the hollow-jet valves.

The interior surfaces of the outlet pipes were lined with coal-tar primer and coal-tar enamel. The exterior surfaces exposed to the atmosphere or public view were coated with one coat of red lead priming paint and two coats of phenolic-resin aluminum paint. Unpainted exterior surfaces of the outlet pipes were whitewashed to protect the linings during field storage.

(b) Design and Testing.-The outlet pipes were designed for a maximum static head of 460 feet and to withstand external loads caused from embedment and the placement of concrete. The 84-inch-inside-diameter irrigation outlet has a plate thickness which varies from 7/16 to 9/16 inch. The 84-inch-inside-diameter evacuation outlet has a plate thickness which varies from 1/2 to 9/16 inch. Plate thickness was based on the larger of two values which were calculated from a formula for minimum plate and a formula for internal pressure. Each outlet pipe is reinforced by stiffener rings and encased in concrete.

68. 84-INCH RING-FOLLOWER GATES. Two ring-follower gates, one for each outlet, are required for normal closure of the river outlets when the hollow-jet valves are not in use, and for emergency closure under full flow if the hollow-jet valves should become inoperable. Ring-follower gates are used because they provide a smooth, unobstructed fluidway for the high-velocity flow during normal dischrages. The ring-follower gates were manufactured by GoslinBirmingham Manufacturing Co. under invitation No. DS-5730.

(a) Description.-The ring-follower gates are located upstream from the hollow-jet valves in the outlet structure, as shown on figure 84. The ringfollower gates and hollow-jet valves are operated from a common control cabinet (sec. 70) located in the outlet structure, as shown on figure 91. Remote controls are not provided.

Each ring-follower gate is made of cast and welded steel construction, and consists basically of a body, leaf, and a hydraulic hoist which is an integral part of the gate. The gate is of the slide type with a leaf made to include a follower ring having a circular opening equal to the diameter of the pipe to provide an unobstructed water passage when the leaf is in the open position, as shown on figure 85 and 86. The hoist has a 24-inch-diameter cylinder and a travel of 7 feet 8 inches. A direct reading position indicator is located adjacent to the hoist cylinder. The estimated weight of each ring-follower gate is 117,000 pounds. Figures 87 and 88 show shop views of one of the ring-follower gates.

(b) Design.-Each ring-follower gate was designed to operate under a maximum reservoir head of 465 feet and a hoist oil pressure of 2,000 pounds per square inch. The hoist capacity was based on the weight of the leaf plus the sliding friction of the gate seals using a friction coefficient of 0.6. Stainless steel seats were used on the gate body and bronze seats on the leaf to provide a low friction and rust-resistant sliding surface. The maximum waterload on the gate produces a bearing pressure between the sliding surface of the leaf and body seats of 800 pounds per square inch. The steel piston stem was clad with nickel-copper alloy to prevent corrosion. A hand-operated mechanical latching device was provided on the upper cylinder head to hold the gate in the open position.

The maximum stresses used for design were based, in general, on the following criteria:

(1) Tensile.-The allowable design stresses in tension used for the following materials were the

Each hollow-jet valve is made of cast and welded steel construction and consists basically of a circular body and movable concentric needle which forms an annular passage and seals in the entrance throat. The hollow-jet valve is operated hydraulically by a cylinder within the annular passage which is positioned concentrically by six radial splitters, as shown on figure 89. The cylinder is 48 inches in diameter, and the needle has a travel of 29-1/2 inches from fully open to fully closed position. As the valve is opened, water

Figure 84.-84-inch ring-follower gate and 84-inch hollow-jet valve installation for the river outlets.

Before operating Ring-Follower gates, thoroughly clean body
and leaf seats and guides Apply o uniform coat of
Teroco 'All-Temp, or other grease meeting Specification
NO MIL-G-109244

REFERENCE DRAWINGS

RIVER OUTLETS

84RING-FOLLOWER GATE -

459-0-488 459-0-993

ASSEMBLY-LIST OF DRAWINGS.

84" HOLLOW-JET VALVE -

ASSEMBLY-LIST OF DRAWINGS.

CONTROLS FOR 84 RING FOLLOWER GATE AND

BE HOLLOW JET VALVE INSTALLATION

PLANS, PROFILES, AND SECTIONS.

YELLOWTAIL POWER PLANT

GENERAL ARRANGEMENT-TRAVERSE SECTIONS

OF UNITS AND OUTLET STRUCTURE.

UNITED STATES

DEPARTMENT OF THE INTERIOR
BUREAU OF RECLAMATION

MISSOURI RIVER BASIN PROJECT

LOWER BIG HORN DIV-YELLOWTAIL UNIT-MONT

YELLOWTAIL DAM

RIVER OUTLETS