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

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

the gates 14 inches for conduit filling with maximum unbalanced pressures on the gate; and in an emergency, to close the gates with full flow to the turbines under a maximum head of 255 feet. The cylinder size for the hoists was determined by the sum of the weights of the gate and stems, plus maximum downpull, minus friction of the coupling hooks sliding on the concrete guide surface, and minus one-half the gate wheel and seal friction. This load would produce a cylinder pressure of approximately 1,200 pounds per square inch during emergency closure; however, normal balanced operations or conduit filling will require a maximum cylinder pressure of less than 600 pounds per square inch. The hoists and stems were designed for a relief valve setting of 1,000 pounds per square inch, using normal factors of safety. The pressure switch setting of 750 pounds per square inch provides a minimum lifting force at the hoists of 437,000 pounds which exceeds the 392,000-pound force required to open the gate for conduit filling. The hoists were

designed to lower the gates, without operating the pumps, by bypassing oil from the underside of the piston directly to the top of the cylinder. The design time selected for opening the gates balanced was about 20 minutes, and for closing unbalanced less than 2 minutes, based on normal oil temperatures. The closing time will increase slightly as the oil temperature drops, and decrease slightly when the gate is subjected to downpull forces during emergency closure. A hanger stud is provided in the upper cylinder head of each hoist to engage the piston stem and support the weight of the stems and gate in the open position during gate installation or removal. During normal operation the hanger stud will not be engaged, as the piston was designed to support the gate and stems on oil confined under the piston.

Two constant-delivery pumps, having a combined delivery of 49 gallons per minute at a pressure of 1,000 pounds per square inch and a pump speed of 1,800

revolutions per minute were selected for each cabinet to open the gate within the predetermined design time. Two 15-horsepower motors, using 440-volt, 3-phase, 60-cycle current were required to drive the pumps. The two independent pump units were used to provide protection against failure of a single pump unit. A 110-volt transformer was used to provide power for most of the control circuits and the cabinet heater; however, the control was designed to use a separate source of direct-current power from the powerplant to operate the emergency close circuit and the solenoid-operated, four-way valve which directs the flow of oil to open, close, or stop the gate.

The control was designed for gravity closure of the gate with the closing speed controlled by a throttle valve in the bypass piping from the bottom to the top

of the cylinder. A restoring cycle was incorporated in the controls to maintain the gate automatically within close limits of the open position. A penstock pressure switch was included to prevent opening the gate until the penstock is full and the pressures on either side of the gate are essentially balanced. Gate position indication was provided in the cabinet using a vertical scale with a pointer driven by a stainless steel cable connected to the piston stem.

The control was designed for normal gate operation by pushbutton from the control cabinet and for emergency gate closure by selector switch or automatic protective devices from the powerplant. The emergency close circuit was designed to override all opposing signals initiated from the control cabinet.