8/18/2019 Proportional Weir and Parsall Flume

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PROPORTIONAL WEIR AND PARSHALL FLUME

A proportional weir and a Parshall flume are velocity control devices. Velocity control devices

are also referred to as flow control devices. They control the fluctuations in the wastewater

flows and hence provide a uniform flow through velocity (horizontal velocity) in the different

units of the wastewater treatment plant. It is important to maintain a constant flow through

velocity in a grit chamber in order to ensure that only the organic solids but not the grit are

scoured from the bottom of the grit chamber. The horizontal velocity of flow should be in a

recommended range of 0.2 m/s to 0.4 m/s in a grit chamber.

When a proportional weir is to be used as a velocity control device, then the grit chamber should

have a rectangular cross-section and if a Parshall flume is to be used, a parabolic cross-section is

required for the grit chamber.