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UDC 628.311:532.572

Loitzker Oskar

Hydraulic design of measuring weirs with a triangular profile chute

Summary

The method of designing measuring weirs with triangular profile chute is presented. In the regulatory document MI 2406-97 «GSI (State System for Ensuring Uniform Measurement). Liquid flow rate in water and wastewater gravity channels. Measuring methods with the use of standard weirs and flumes» that regulates the use of flow metering devices for measuring water flow rate in gravity water supply systems and sewers the design aspects have been condensed without actual examples. This article aims at filling this gap. The conditions that provide for the possibility in principle to use the method of measuring liquid flow with the use of standard orifices (weirs and flumes) are considered. Such condition, in particular, is the availability of a straight-line channel section of adequate length with free (without backflow) flow. The design procedure is presented with specific reference to flow measuring in a concrete rectangular channel 3.5 meters wide with a maximum flow rate of 56 250 m³/h. The procedure suggests sequential determination of the maximum weir head and chute height as well as verifying the conformity of the weir with a triangular profile chute to the regulatory requirements including possible weir submergence with calculating the maximum flow level in the channel downstream. The ratios between the chute width and maximum head, maximum head limits and Froude number are also verified. Further in the process of designing and basing on the hydraulic calculations the type of the flow-level meter and its metrological performance are chosen and the geometry of the chute is determined.

Key words

flow rate measurement , gravity flow , weir , triangular profile chute , hydraulic design