What is a weir and how is it used?
Weirs can be used to measure flow rates in open channels and rivers – common for water supply and sewage plants Weirs are structures consisting of an obstruction such as a dam or bulkhead placed across the open channel with a specially shaped opening or notch. The flow rate over a weir is a function of the head on the weir.
What is the flow rate of a triangular weir?
The triangular or V-notch, thin-plate weir is an accurate flow measuring device particularly suited for small flows. For a triangular or v-notch weir the flow rate can be expressed as: q = 8/15 cd (2 g)1/2 tan (θ/2) h5/2 (2)
What is head measurement Zero reference elevation for weirs?
For standard weirs – c d – is well defined or constant for measuring within specified head ranges. The lowest elevation (h = 0) of the overflow opening of the sharp-crested weirs or the control channel of broad-crested weirs is the head measurement zero reference elevation.
How do you find the flow over a weir?
The relationships of flow over weirs can be obtained by applying the energy equation from a point well upstream of the weir to a point just above the weir crest. This approach requires a number of assumptions, and it yields the following results: for a triangular weir (Figure 9.2a):
How do you fill a weir with water?
Turn on the pump, and slightly adjust the flow control to fill the channel upstream of the weir with water. Turn off the pump when the water starts to flow over the weir. Wait a few minutes to allow the water to settle. Level the point gauge with the water level in the channel.
How do you calculate the flow rate of a broad crest Weir?
Broad-Crested Weir. For the broad-crested weir the flow rate can be expressed as: q = c d h 2 b ( 2 g (h 1 – h 2) ) 1/2 (3) Measuring the Levels. For measuring the flow rate it’s obviously necessary to measure the flow levels, then use the equations above for calculating. It’s common to measure the levels with:
Can water level-discharge relationships be applied to sharp-crested weirs?
Water level-discharge relationships can be applied and meet accuracy requirements for sharp-crested weirs if the installation is designed and installed consistent with established ASTM and ISO standards. Rectangular weirs and triangular or v-notch weirs are often used in water supply, wastewater and sewage systems.
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What is the difference between ogee weir and rectangular weir?
The discharge over narrow crested weir is similar to discharge over rectangular weir. Generally ogee shaped weirs are provided for the spillway of a storage dam. The crest of the ogee weir is slightly rises and falls into parabolic form. Flow over ogee weir is also similar to flow over rectangular weir.
What is a standard shape of Weir?
It is a standard shape of weir. The top edge of weir may be sharp crested or narrow crested. It is generally suitable for larger flowing channels. Flow over rectangular weir:
What are the characteristics of a sharp-crested weir?
The weir plate is bevelled at the crest edges to obtain necessary thickness. And weir plate should be made of smooth metal which is free from rust and nicks. Flow over sharp-crested weir is similar as rectangular weir. These are constructed only in rectangular shape and are suitable for the larger flows.
What is the Francis formula for flow through a rectangular weir?
Flow through a rectangular weir can be expressed in imperial units with the Francis formula. q = 3.33 (b – 0.2 h) h3/2 (1b) where. q = flow rate (ft3/s) h = head on the weir (ft) b = width of the weir (ft) Alternative with height in inches and flow in gpm: