Pneumatic Crest Dams

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Image from the patent for the concept of pneumatic crest gates.(http://www.google.com/patents/US5538360)

Tom Tarpey said that the proposed dam structure for downtown Lebanon, New Hampshire would include a pneumatic crest gate.  Pneumatic crest gates are designed to maintain consistent water flows and levels at the dams they are used in. This feature functions as the spillway of the dam, in other words it is where water flows over the dam. The gates are operated pneumatically, relying upon air pressure to function. The patent for   this crest gate design provides information on how they work. The bottom on these gates are connected to the of a dam by a hinge that acts as a pivot point for the gate to swing. Large air sacks are placed on the side of the gates opposite of impoundment against the bottom of the gate near the hinges. The air sacks function as supports for the crest gate against the natural pressure of the volume of water held back by the dam. The air sacks can be inflated or deflated to change the orientation of the gate. When fully inflated, the air sacks hold the gate in a near vertical position where maximum water levels are reached.  The air sacks are deflated allowing the gate to lower away from the impoundment towards parallel with the waterway’s bottom. Deflation is generally necessary in instances of reduced water flow through the dam or potential flooding of the impoundment. Additionally, pneumatic crest gates make recreational water releases possible in the dams they are used on. The above information was gathered from http://www.google.com/patents/US5538360.

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Images of Obermeyer Hydro Inc. dams equipped with pneumatic crest gates (http://www.obermeyerhydro.com/Hydropower)