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<br />OOlG'76 <br /> <br />steel shafts connect the operating cylinder to the gate leaf This design allows the gate to be <br />removed for maintenance purposes without the difficulty and expense of installing a bulkhead gate <br />in the reservoir intake structure. The design is more mechanically complex and requires more <br />maintenance than other outlets where removal of the emergency gate requires the installation of <br />an upstream bulkhead. <br /> <br />To operate the fixed-wheel gate for maintenance, the 72-inch and 30-inch hollow-jet valves must <br />first be closed. The hollow-jet valves are designed to withstand hydraulic forces and cavitation <br />pressures developed during flow regulation. Once the flow is stopped, the 72-inch and 30-inch <br />ring-follower gates should be closed. The main inlet butterfly valves to the City ofFannington <br />Power Plant should also be closed according to their procedures. Under these conditions, there <br />are no forces on the fixed-wheel gate's wheels, so the fixed-wheel gate can be operated. Normal <br />operation of the gate would be for maintenance of the downstream pipe, valves, gates, and the <br />City ofFannington Power Plant. <br /> <br />The fixed-wheel gate was designed to close against flowing water by gravity in emergency <br />conditions. Emergency conditions would include failure of the 110-inch pipe, failure of either the <br />72-inch hollow-jet valves or the 72-inch ring-follower gates, or a failure of the City ofFannington <br />Power Plant penstock. The gate controls have a feature that would allow emergency control from <br />the outlet works valve house. <br /> <br />Currently, the 6- by 13-foot fixed-wheel gate has nine ofthe twelve wheels unable to rotate due <br />to corrosion. The frozen wheels damage the steel rails upon which the gate rides whenever the <br />gate is moved. As the rails lose material, the gate seal compression is reduced and leakage <br />increases. The steel rails cannot be repaired without the installation of the upstream bulkhead. In <br />addition, the gate hoist and hydraulic system currently cannot hold the gate leaf in position <br />without frequent cycling. The cycling has lead to wear on the piston stem at the bottom seal of <br />the hydraulic cylinder. To alleviate the rate of wear on the system, the fixed-wheel gate is usually <br />set on dogs in the maintenance chamber, and usage of the gate is kept to an absolute minimum <br />[20]. <br /> <br />If the fixed-wheel gate was to be released for closure in an emergency, large forces would be <br />developed by the flowing water on the gate leaf, which is the reason for the gate having wheels. <br />Since 75 percent of the wheels are locked, the leaf would be forced against the r~s and cause <br />friction greater than the hoist could resist and the gate would become locked in position. It would <br />not close further, since gravity alone cannot overcome the friction of the locked wheels against <br />the rails. This locked-in-position problem was accidentally confirmed when the gate closed due to <br />leakage in the operating cylinder. The fixed-wheel gate could not be operated in either the close <br />or open direction. The hollow-jet valves had to be closed first, for the fixed-wheel gate to be <br />raised. <br /> <br />Emergency gate tests were performed at Navajo Dam under the Safety of Dams prograin in 1993, <br />to test the ability of the gate hoist system to lift the fixed-wheel gate leaf under a differential head. <br /> <br />19 <br />