Laserfiche WebLink
<br />OOlG'/7 <br /> <br />An actual emergency closure test was not conducted due to the risk of damage to the gate and <br />gate frame structure. The tests verified that the gate could not be raised under a full differential <br />head. The gate's hydraulic system simply could not develop the pressures necessary to move the <br />gate leaf off of its seat [21]. . <br /> <br />fI <br /> <br />; <br />I <br /> <br />The 6- by 13-foot fixed-wheel gate was not designed to regulate flow. If the gate was to become <br />locked in the flow, damaging cavitation would be expected on the leafand in the downstream <br />tunnel. The area that would be damaged is accessible only when there is no flow. Air admission <br />to this gate is designed for draining the pipeline only, and not for flow regulation. Attempted long <br />term regulation from the 6- by I3-foot fixed-wheel gate could cause dangerously low pressures in <br />the llO-inch pipe. Iflow enough pressures are reached, the llO-inch pipe could possibly <br />collapse. <br /> <br />2. 72-inch hollow-jet valves. - The hollow-jet valves operate by hydraulically moving a 72-inch- <br />diameter faired needle into the end of the pipe, closing off the flow. Two of these valves are <br />located downstream from a bifurcation in the 11 O-inch pipe and discharge into the stilling basin. L <br />The valves are designed to regulate flow without structural damage, but are not designed to hold ~ <br />water at reservoir pressures for long periods of time, <br /> <br />The faired needle is attached to a hydraulic cylinder which is operated by a hydraulic system <br />located in the valve house. Oil removed from this system in 1996 was found to have extremely <br />high levels of water, dirt, and other contaminants. The contaminants had been present for several <br />years as evidenced by damage found during hydraulic system repairs. These contaminants were <br />not completely removed from the hydraulic cylinders of the hollow-jet valves since the hydraulic <br />cylinders are below tailwater levels. Special provisions would be required for access. <br /> <br />Hollow-jet valve No.1 has performed poorly for several years. During testing in 1996, evidence <br />of hydraulic sealing problems in the valve became apparent. The operating cylinder has an <br />external and an internal seal. Small pieces of external seal were found to be extruded. Some <br />damage is present on the surface of the rod, which slides through the seal under pressure. The <br />interior of the cylinder is very smooth machined steel designed to be submerged in oil. Water and <br />dirt has been present on this surface for some time. The surface has been damaged by corrosion <br />and scratching. Damage to this surface results in internal leakage and reduces the valves' ability <br />to operate. Currently, hollow-jet valve NO.1 fails to operate at about 10 percent open without <br />the force of water on the needle. There is also some risk that the external seal will begin to leak <br />or fail when high pressures are applied. <br /> <br />Since the hollow-jet valves close as the hydraulic cylinder fully extends the rod, a seal failure <br />would have the greatest effect at smaller valve openings. If the seal was to fail, the valve would <br />open rapidly. With the valve closed, approximately 136 gallons of oil could escape from the <br />cylinder. Therefore, hollow-jet valve No. 1 is safest to operate at larger valve openings. There is <br />no reliable method to determine when the seal will fail. Due to the construction of this valve, no <br />rod end amplification testing should be attempted. Setting an upper operating position limit on <br /> <br />20 <br />