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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 Requirements. --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) General Description. --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) Control 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) Valve and Control Unit Design. --The valve is a commercial 125-pound butterfly valve manufactured by Ř. 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.

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Figure 11. --48-inch butterfly control valves as initially installed.

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 House Wall. -- After the award for purchase and delivery of the 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.

CHAPTER. III--CONTRACT ADMINISTRATION 11/

,ĄThe Prime Contract

27. Specifications No. 2594. - The construction of Platoro Dam was accomplished in accordance with specifications No. 2594, Seven bids were received and were opened at Monte Vista, Colo., April 12, 1949. Contract No. 12r-18514 was awarded on May 5, 1949. to the Hinman Brothers Construction Company of Denver, Colo., the low bidder.. The three lowest bids were as follows:

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Notice to proceed was received by the contractor on June 16, 1949, fixing the completion date as January 6, 1953, a period of 1,300 days being allowed for the completion of the contract. The contractor moved in and began building roads and the camp on May 16, 1949, 31 days before the effective date of the notice to proceed. Except for the winter shutdowns in 1949-50 and 1950-51. there were no appreciable delays, and work proceeded rapidly; the contractor finished work September 26, 1951, 468 days ahead of schedule.

28. Orders for Changes. - Order for changes No. 1, issued September 24, 1949, provided for the placement of all concrete in the gate chamber below the floor between stations 7+24 and 7+54 in one stage instead of two separate stages. This resulted in a saving to the contractor, and a price adjustment was therefore made.

Order for changes No. 2, issued June 12, 1950, provided for placement of secondstage concrete and substructure concrete in the center wall before placement of substructure concrete in the outside wall. This change was requested by the contractor for convenience in concrete placement. A reduction was made in the price of concrete in the center wall. .

Order for changes No. 3, issued July 12, 1950, designated two additional rock borrow areas from which riprap could be obtained. The original area was close to the valve house and it was feared that heavy blasting might damage the structure. There was no increase or decrease in the amount of the contract as a result of this order.

Order for changes No. 4, issued March 8, 1951, involved several changes, most important of which was the reduction of zone 1 and zone 3 and an increase in the crosssectional area of zone 2. This permitted faster placement because zone 1 material was very moist and required excessive drying on the fill. Other changes involved increasing the screen openings of the separation plant from 3 to 5 inches; extending borrow area 6 to include an area southeast which contained drier material; providing for use of salvaged materials from rock borrow area 2 in zone 3 of the dam and dike; and providing for quarrying additional zone 3 material from rock borrow area 4. The last two items were for making up the shortage of zone 3 material from the slide rock borrow areas. The only price adjustment was a slight increase in cost of the zone 3 material obtained from rock borrow area 4.

* Order for changes No. 5, issued August 7, 1951, provided for the construction of approximately 600 feet of access road connecting the existing haul road with the top of the dam and eliminating the requirement for the construction of a small dike for protection of Mix Lake. The small amount of interconnecting roadway was necessary to provide an access road to the top of the dam. By leaving a fill section of the contractor's haul road, ample protection of Mix Lake was provided without constructing the dike originally planned. A lump sum of $3,000.00 was allowed for payment for the interconnecting road.

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