transitions may be reached by temporary ladders brought inside the penstocks through the manholes and laid on inverts. A 20-inch-inside-diameter manhole is installed in each penstock immediately upstream from the first expansion joint.

Two piezometer orifice stations 50 feet apart are located on each penstock in its level portion near the power plant. Individual 3/4-inch pipes lead from each piezometer connection into the powerplant.

(c) Installation and Coating.-Penstock sections were installed under the prime contract, excepting makeup sections, which were installed under the completion contract, specifications No. DC-5750.

Interior surfaces of penstocks were coated with coal-tar primer and coal-tar enamel. Exterior surfaces in backfill, except the sleeve-type couplings, were coated with coal-tar primer, coal-tar enamel, bonded-asbestos felt, and kraft paper wrap. Exterior surfaces of sleeve-type couplings in backfill were coated with coal-tar primer and coal-tar enamel, and surrounded by sand shields. The penstock exterior embedded surfaces were not coated. Exterior surfaces of penstocks, makeup pieces, and sleeve-type couplings exposed to view in the powerplant were coated with phenolic-resin aluminum paint.

59. PENSTOCK TRASHRACKS. A total of 280 trashracks are provided for the penstock trashrack structures to protect the turbines from oversize trash. The 280 trashrack sections, approximately 9.33 feet wide by 12.5 feet high, as shown on figure 143 were furnished under invitation No. DS-5512.

The trashracks are installed in vertical slots in the penstock trashrack structures. The racks consist of 2by 5/8-inch trash bars supported by 9- by 1-inch horizontal load carrying plates which transmit the load to the side members. The 4-3/8-inch clear opening between the trash bars conforms with the recommendations of the turbine manufacturer. The estimated weight of the 280 trashracks is 980,000 pounds.

The trashracks were designed for a differential head of 20 feet at a stress of 33,000 pounds per square inch.

60. PENSTOCK STOPLOGS. Twenty-three stoplog sections were required for the penstock intakes

*Not included.

to provide a bulkhead for inspection and maintenance of the fixed-wheel gates and appurtenances. One set of stoplogs, sufficient for one unit, is provided for the penstock intakes.

The following log sections were furnished for stacking in accordance with drawing No. 557-D-2080*: 9 lower log sections, approximately 24.5 feet wide by 4.80 feet high, weighing 24,700 pounds each; 7 intermediate log sections, approximately 24.5 feet wide by 5.30 feet high, weighing 25,100 pounds each; and 7 top log sections, approximately 24.5 feet wide by 6.79 feet high, weighing 27,200 pounds each. A lifting frame was also furnished for grappling purposes. All material was furnished under invitation No. DS-5354.

The stoplogs are installed in vertical guides on the face of the dam and in the trashrack structures. The stoplogs are placed in the guides in one stack. Effective sealing is obtained by means of music-note-type rubber seals bolted to the log sections.

The stoplogs were designed for a maximum head of 250 feet at safe stress.

61. 165-TON GANTRY CRANE. (a) Description.-A 165-ton gantry crane (fig. 274) is installed on rails on top of the dam for the installation and maintenance of penstock gates and hoists and river outlet gates and stop logs. The crane was manufactured under invitation No. DS-5521 and is an outdoor, cab-operated, electric gantry crane with a trolley supporting a 165-ton main hoist and a 25-ton auxiliary hoist.

The main hoist is reeved 6 parts double with 1-1/2-inch-diameter, 6 by 37, improved plow steel, fiber-core wire rope. The block has a lifting eye in lieu of a hook. The hoist has a lift of 53 feet, is powered by a 40-horsepower, 1,200-r.p.m., direct-current motor, and operates at incremental speeds up to 3.7 feet per minute hoisting and 4.3 feet per minute lowering with a 165-ton load.

The auxiliary hoist is reeved 2 parts double with 1-inch-diameter, 6 by 37, improved plow steel, fiber-core wire rope. The block has a sister-type hook bored for a horizontal lifting pin. The hoist has a lift of 380 feet, is powered by a 40-horsepower, 1,200-r.p.m., direct-current motor and operates at incremental speeds up to 24 feet per minute hoisting and 28 feet per minute lowering with a 25-ton load.

The trolley is driven by a 15-horsepower, 1,200-r.p.m., alternating-current motor at 4.8 feet per minute in either direction, through a rack and pinion drive. The gantry is driven by four 5-horsepower, 1,150-r.p.m., alternating-current motors at incremental speeds up to 48 feet per minute in either direction.

A single motor-generator set installed in the control enclosure supplies direct-current power for both hoist motors, the hoist motor controls being electrically interlocked so that only one hoist may be energized at a given time. Full magnetic controllers for each motion of the crane are located in the operator's cab. Five-point-speed control is provided for each direction of the main hoist, auxiliary hoist, and gantry drive, and single-speed control for the trolley drive.

Each hoist motor is equipped with two alternating-current magnetic brakes, one on each side of the motor, which are released when the hoist motor circuit is energized. Each of these brakes is capable of overcoming the full-load torque of the motor with which it operates. The trolley drive is equipped with a similar brake which is capable of overcoming at least three-fourths of the full-load torque of the drive

motor.

Each of the gantry drive motors is equipped with a hydraulic brake, all of which are actuated by a single foot pedal located in the operator's cab. Each brake is capable of overcoming the full-load torque of the motor with which it is associated, simultaneously with the other gantry drive brakes, with no more than 50 pounds of operating force on the foot pedal. Each brake is equipped with an automatic, spring-applied, parking feature.

Block-actuated limit switches on each hoist limit the upward travel of the hook. A two-contact-geared limit switch on the auxiliary hoist limits the lower travel of the hook and lights a red light in the operator's cab. Each contact is individually adjustable within the last 30 feet of travel.

operator's cab, in the control room, and on the trolley access walkway. One 100-watt lamp is installed in the operator's cab and one in the control room, each with conveniently located wall switches. Two 100-watt lamps are located on the trolley access walkway. One 750-watt narrow-beam floodlight is mounted under the trolley access walkway. Two 500-watt medium-beam floodlights are mounted on the upstream side of the crane and two 500-watt wide-beam floodlights are mounted to illuminate the roadway under the crane. There is a 240-volt, 3-kilowatt heater installed in the operator's cab.

Spring bumpers are mounted on the gantry legs at one end of the crane only. Double-acting spring bumpers are provided on the trolley. Ladders and walkways provide access to the trolley, control room, and operator's cab.

(b) Design.-The crane was designed according to the Navy Department's standard of design for structural steel using a base stress of 16,000 pounds per square inch. Computations of stress took into account wind loads, all dead and live loads, and loads due to acceleration and deceleration. Allowable stresses due to combinations of these stresses were increased according to the Navy standard noted. A factor of safety of not less than five, based on the ultimate strength of the material and rated capacity of the crane, was used in the design of all mechanical parts.

62. 13.96- BY 22.45-FOOT FIXED-WHEEL GATES FOR PENSTOCK INTAKES. (a) Description.-Eight fixed-wheel gates are provided in the penstock intakes for emergency closure of the penstocks in case of damage to the penstocks or the powerplant equipment, and also to permit unwatering of the penstocks for inspection and maintenance. Normally, the gates will close only after flow through the penstocks has been stopped by closing the wicket gates. However, in an emergency the gate may be closed with water at full reservoir head flowing through the penstock. The gates were manufactured by Voest Co. of Linz/Donau, Austria, under invitation No. DS-5577. The frames were manufactured by Rockwell Engineering Co. of Blue Island, III., under invitation No. DS-5469. The general arrangement and some details of the 13.96- by 22.48-foot fixed-wheel gate installation are shown on figure 144.

Each gate is made in four units, fabricated from welded shapes and plate connected by rivets and rib bolts. Six wheels on each side of the gates carry the waterload to the tracks embedded in the downstream side of the gate slots. Rubber seals are mounted like a

Figure 144.-13.96- by 22.45-foot fixed-wheel gate installation for penstock intakes.

DRAWN

SUBMITTED.

ONECHED blo

DENVER,

COLORADO. SEPT.22, 1900"

SNEET OF 10

557-D-975

The stresses in the tracks and wheels were investigated by a method of calculating stresses due to the pressure of one elastic solid on another. The bushings in the wheels have self-lubricating inserts and may be greased when assembled. Friction forces of the loaded wheels, busings, seals, etc., were investigated to be certain that the gate would have sufficient weight to close without the aid of an externally applied force. Bearing pressure on the projected area of the bushing was limited to 4,000 pounds per square inch.

Figure 145 shows the downstream face of the gate as fabricated in the manufacturer's shop.

63. HOISTS AND CONTROLS FOR THE 13.96BY 22.45-FOOT FIXED-WHEEL GATES. (a) Description.-A hydraulic hoist and control are provided to operate each of the eight 13.96- by 22.45-foot fixed-wheel gates. Normally, a hoist will be required to close the gate under balanced pressure to unwater the penstock for maintenance purposes, but may be required to close the gate under flow conditions in an emergency. Eight hydraulic hoists were furnished by the Pacific Coast Engineering Co., Alameda, Calif., under invitation No. DS-5601. The controls were manufactured by Auto-Control Laboratories, Inc., Los Angeles, Calif., under invitation No. (D) 90,638-A.

Figure 145.-Downstream elevation of shop assembly of 13.96by 22.45-foot fixed-wheel penstock gate. P557-D-46362NA.

Some installation and assembly details are shown on figure 146. The hydraulic hoists are installed on the slope of the intake structure (0.170:1) at the upstream face of the dam and are supported by steel beams at elevation 3713.00. Each hoist is connected to the gate by a series of intermediate stems with an assembled length of 172 feet 9-3/4 inches. Each hoist piston has both packing and piston rings, is 30 inches in diameter, and has a stroke of 26 feet 5 inches. An individual control cabinet is located adjacent to each hoist in the control house, and contains all the hydraulic and electrical equipment for operating the hoist, and a gate position indicator.

The estimated weight of the eight complete hoists is 800,000 pounds and of the eight complete control systems is 42,000 pounds. Figures 147 and 148 show the shop assembly of the hoist and stems.

(b) Design.-The hoists were designed to open and close the gates normally with the water pressure balanced on both sides of the gates; to open any one of