Vertical Dam Gate and Hoist Mechanism
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Almost every water resources project has a reservoir or diversion work for the control of floods or to store water for irrigation or power generation, domestic or industrial water supply. A spillway with control mechanism is almost invariably provided for release of waters during excess flood inflows. Releases of water may also be carried out by control devices provided in conduits in the body of the dam and tunnels. In order to achieve flow control, a gate or a shutter is provided in which a leaf or a closure member is placed across the waterway from an external position to control the flow of water. Control of flow in closed pipes such as penstocks conveying water for hydropower is also done by valves, which are different from gates in the sense that they come together with the driving equipment, whereas gates require a separate drive or hoisting equipment.
Right selection of gates and their hoisting arrangement is very important to ensure safety of the structure and effective control. A designer has to plan a gate and its hoisting arrangement together. Separate planning of gates or hoists, sometimes results in unsatisfactory installation. Though the choice for the gates and hoists depends on several factors, primarily safety, ease in operation as well as maintenance and economy are the governing requirements in the same order. It is essential for the water resources engineer to be aware of the different factors, which would largely affect the choice of gates and hoists and would help in selection of the same.
The past thirty-first to forty years has been a period of unprecedented water in our country. Besides a large number of small irrigation and hydro-electric scheme, more than 3000 dams have been constructed. All structures or projects harnessing water needs gates for controlling the flow as such large number of gates of different types had to be designed and manufactured. The design of gates consequently undergone considerable development, since the use of wooden (gates) ‘needles’ or ‘curries’ used in ancient time and has enable us to fabricate gate for high heads and situations.
Whatever may be the type of dam, it is absolutely necessary to provide a safe passage for the flood water, so as to avoid the danger of the dam being overtopped. The part of dam which discharges the flood flow to the downstream side is called as spillway. The spillway is an important part of dam complex and is located either as a part of main dam or separately at suitable place near to the dam.