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(f) Painting_. --Shop painting of the outlet pipe was not required except for those surfaces that will be inaccessible after assembly. These include the inner surfaces of the outer sleeves of the expansion joint and the packing gland, and the outer surfaces of the inner sleeve. These surfaces were cleaned and given three shop coats of CA-50 coal-tar paint.
25. 4- by 5-Foot High-Pressure Gate. - As previously noted, the valve chamber near the axis of Platoro Dam houses a 4- by 5-foot high-pressure gate (fig. 10). This gate is used only for emergency closure or to permit unwatering and necessary inspection and maintenance of the outlet pipe and butterfly valves. A semi-automatic gate hanger is suspended above the hydraulic cylinder of the emergency gate and is used to hold the gate in the wide open position.
The frames and bonnets of the gate and the sections of conduit lining and transitions are embedded in concrete, and the concrete is reinforced sufficiently to carry the water load. The top flange of the bonnet, the bonnet cover, and the circular end of the transitions were designed for a 200-foot head, as these parts are not embedded. Stresses and factors of safety for the various metals were allowed as follows:
Cast iron, class 25
Cast iron, class 40
Cast steel, class 2
Tin-base babbitt-bearing 3, 500
The gate leaf was designed as a beam with a uniformly distributed load, for a maximum head of 250 feet. It is made of cast steel, class 2. The seats of the gate leaf are cast bronze, class C, of the following chemical composition:
Copper 82.00 to 83.00 percent
Tin 6. 75 to 7. 50 percent
Lead 4. 50 to 5.00 percent
Zinc 5.00 to 6.00 percent
The seats on the downstream frame are cast bronze conforming to Federal specification QQ-B-691b, composition 6. The difference in the composition of the seats permits the use of bearing pressures up to 3,000 pounds per square inch without seizing, although the design stress was limited to 1, 100 pounds per square inch as previously noted.
There are air inlet connections on the downstream frame of the gate to which pipes are connected and extend above the floor of the gate chamber. A flanged bypass opening is provided for the gate on the right side of both the upstream and downstream frames. The bypass is for filling the outlet pipe when the emergency gate is closed, and prior to opening.
The gate stem was designed to withstand the tensile load imposed when the gate leaf is raised and the compressive load when the leaf is lowered. For lowering and seating the gate leaf, the stem was designed as a column.
The gate is operated by a hydraulic cylinder hoist mounted on the bonnet cover. Ordinary motor lubricating oil, SAE 10 or Navy specification 2110, is used. The lifting capacity of the hoist is 110, 000 pounds. The size of the hoist was selected to provide the required lifting capacity with the oil pressure at 900 pounds per square inch.
The hydraulic system consists of an oil pump, motor, supply tank, four-way valve, regulating valve, pressure gage, and the necessary interconnecting piping. Typical operation consists of setting the four-way valve for "Raise" or "Lower" and starting the oil
pump. Oil will circulate at no head through the regulating valve back to the supply tank. Upon closing the regulating valve, pressure is built up in the system and oil passes through the four-way valve to the gate, causing it to move in the direction selected. The oil on the other side of the piston returns to the four-way valve and is directed into the supply tank. When the gate reaches the desired position at the end of its travel, the regulating valve is opened, the four-way valve is set on the "Stop" position, and the motor is turned off.
Before closing the emergency gate, the chain from the semi-automatic gate hanger must be fastened to a hook on the hydraulic hoist and the gate raised slightly to disengage the hooks in the semi-automatic hanger.
26. 48-Inch Butterfly Valves. - As previously noted, the downstream end of the 56inch outlet pipe is divided into two 48-inch-diameter branches, with a 48-inch butterfly valve controlling the flow in each branch.
(a) Design Rec^ir_ernents_. --In selecting the valves it was considered that a regulating valve was required at the downstream end of each of the two branches. The valves would control all releases from the reservoir, except those discharged over the spillway. They were required to withstand a maximum static head of 150 feet plus 36 feet due to water-hammer, or a total head of 186 feet, and they must provide an estimated combined discharge of 875 cubic feet per second with the maximum reservoir surface at elevation 10,042.0.
It'was considered that two 48-inch butterfly valves installed at the downstream ends of the branches would meet all the requirements for regulating valves in an economical and satisfactory manner, and these valves were therefore selected.
(b) Gen£ral_De£criptiqn. --The general arrangement and details of the butterfly valves as initially installed are shown on figure 11. (The valves are being replaced in 1954 because of inadequate operating mechanism, see section 85.) The nominal size of the valve is 48 inches, which is the diameter of the pipe at the valve inlet; the inside diameter of the valve liner is 47 inches. The valve is bolted by its upstream flange to the downstream end of the outlet pipe and discharges horizontally into the river. A base on the bottom of the valve is bolted to a concrete pedestal directly beneath it.
The butterfly valve consists of a body and a leaf bulkhead. Rotating the leaf within the valve body, from a position parallel to the water flow to one across the flow, closes the valve. The leaf rotates about a horizontal shaft through an angle of about 80°, with the bottom half of the leaf moving downstream when opening. A right-angle gear reducer is mounted on the butterfly valve body with the output shaft of the gear reducer coupled directly to one end of the valve shaft. Noncorrosive metallic seals are placed in the valve body and contact the leaf in the closed position. The shaft ends are packed to prevent leakage.
(c) Contr£l_Unit. --Each valve has an individual control unit which is located above the valve on the floor of the operating chamber. The unit consists of a stand supporting a limit-torque reversible electric motor and a handwheel, either of which can be operated independently of the other. The unit is connected through shafting to the input shaft of the gear reducer mounted on the butterfly valve body. The limit-torque mechanism of the motor contains adjustable switches to stop the motor when its torque reaches the desired amount and so stop the valve leaf at the ends of its travel. A pushbutton station to operate the motor and a cabinet for its electrical equipment are placed near each unit.
(d) Va_lve_and_Contrql Um^Desigru--The valve is a commercial 125-pound butterfly valve manufactured by R. S. Products Corporation. The axial thrust of the water on the valve is transferred through the body!to the outlet pipe upstream from the valve. The weight of the valve and its contained water is considered to be supported by the concrete pedestal. It may be operated with full reservoir head at any desired opening.
The motor and gear-reduction units provide ample torque to operate the valve for all reservoir elevations and discharges. Both are standard commercial items and were assembled by the valve manufacturer. The motor requires about 4 minutes to open or close the valve. The handwheel need only be used for emergency operation.
A bulkhead is provided for closing either branch when it becomes necessary to remove a butterfly valve for maintenance. The estimated weight of each valve and its operating unit is 9, 750 pounds.
(e) Modification of the_Valve_Hquse_Wall. -- After the award for purchase and delivery of"th~e butterfly valve had been made it was learned that the valves and operating mechanism could not be placed in the space provided. It was necessary to remove part of a wall between the two valves and to reposition the valves from their planned location. When part of the dividing wall was removed special care and steel placement were required to insure adequate load sustaining ability of the concrete left in place.