Author
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Replogle, John |
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Wahlin, Brian |
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Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/1/2003 Publication Date: 7/1/2003 Citation: Replogle, J.A., Wahlin, B.T. 2003. Characteristics of flap gates at the end of drain pipes. Transactions of the American Society of Agricultural Engineers. 46(4):1077-1084. Interpretive Summary: In the current climate of competition for water, improved management is seen as a means of stretching water resources benefits. Protecting low lands and drain outlets from back flooding extends this concern in another dimension. Flap gates are commonly used at the end of pipe drains and pump outlets to prevent back flows of water and entry of small animals. In larger sizes in urban areas, they offer a response to child safety concerns. Flap gates are relatively inexpensive, with low maintenance costs, but can trap debris in their hinge systems and require regular maintenance. The flap-gate back pressure effect on a gate with free outfall is small. However, under certain submerged conditions, a flap gate will slightly increase the upstream backwater levels. This may be critical in sewerage situations and some surface land drainage cases. Recently, at least one manufacturer sells a rubber-coated steel gate cover with a flexure hinge made of the same rubber material. Users have questioned whether this arrangement introduces significant back pressure. While it reduces the opportunity for trash to catch as it may on a standard pinned-hinge type of pivot, this rubber hinge arrangement essentially becomes a spring-loaded gate, with the force of closure due to both the weight of the gate and the elastic properties of the hinge. The rubber hinge resulted in a slight deviation towards more head loss at large gate openings. Updated design information for both pin-hinged flap gates and the new rubber-flexure flap gates are presented for convenient design use by drainage engineers in municipalities, irrigation districts, drainage districts, and Federal agencies, such as Natural Resources Conservation Service (NRCS), U.S. Bureau of Reclamation (USBR), and the Army Corps of Engineers(COE). Technical Abstract: Flap gates are commonly used at the end of pipe drains and pump outlets to prevent back flows of water and entry of small animals. Flap gates are relatively inexpensive, with low maintenance costs, but can trap debris in their hinge systems. Many texts refer to studies performed on flap gates at the University of Iowa in 1936, which may be limited in value because they are for specific ¿light weight¿ gates. More recent studies in England have attempted to generalize the characteristics for pin-hinged flap gates and place the Iowa studies into a broader perspective. The flap-gate back pressure effect on a gate with free outfall appears to be small. However, under certain submerged conditions, a flap gate will increase the upstream backwater levels. This may be critical in seweage situations and some surface land drainage cases. Recently, at least one manufacturer sells a rubber-coated steel gate cover with a flexure hinge made of the same rubber material. While it reduces the opportunity for trash to catch as it may on a pinned-hinge type of pivot, this rubber hinge arrangement essentially becomes a spring-loaded gate, with the force of closure due to both the weight of the gate and the elastic properties of the hinge. Users have questioned whether this arrangement introduces significant back pressure. To this end we tested a rubber-hinged flap gate to verify whether these gates fit into the general pattern of the limited previous studies on pin-hinged gates, which is to exhibit lower backpressure with increasing flow rate, and hence gate opening. The rubber hinge resulted in a slight deviation towards more head loss at larger gate openings attributed to the flexure strength of the rubber hinge. We then summarized and updated the design information for pin-hinged flap gates to make it more readily available for design uses. |
