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Venturi Flume vs Weir | Difference between Venturi Flume and Weir

This page compares Venturi Flume vs Weir and mentions difference between Venturi Flume and Weir.

Venturi Flume

Venturi Flume

• It is critical flow open flume with constricted flow. This causes drop in hydraulic grade line which creates critical depth.
• Venturi flume is used for very large flow rate measurements, usually in units of millions of cube.
• Venturi Flume measures in meters unlike venturi meter which measures in millimeters.
• Measurement of discharge with venturi flume requires two measurements viz. one at upstream and the other at throat (i.e. at narrowest cross-section).


Weir working

• It is a barrier across flowing fluid which is designed to alter flow characteristics.
• It is used to prevent flooding, to measure discharge and to render river navigable.
• It takes forms of obstructions which are smaller compare to conventional dams.
• Geometry of top of weir as well as water flows over it are known. Hence depth of water behind weir can be converted into rate of the flow.
• Discharge can be summarized as follows.
Q = C*L*Hn
• Weir crest should be free of rust or impurities to have accurate flow measurement.
• Types of weirs include Labyrinth weir, Broad crested weir, Sharp crested weir, Compound weir and V-Notch Weir.

Following table summarizes core difference between Venturi Flume and Weir.

Features Venturi Flume Weir
Hydraulic Head Loss Less More
Dead Zone Does not exist (where debris/sediment accumulate) Exists (upstream of the weirs)
potential energy difference Does not exist Exist
Suitability for unclean waste water It can be used. It can not be used.

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