weir flow measurement
weir flow measurement
(OP)
I am trying to specify a flume or weir, plus automatic recorder for measuring water flow in a toe drain. Client is asking for a product that can be installed in a manhole and fiberglass with automatic recorder. Flow rate is limited to gravity flow through a 4 inch drain pipe. I had specified a steel v-notch weir. Would a Palmer-Bowlus or Parshall Flume have any benefits over a v-notch? As far as recording flow, is ultrasonic the recommended choice? What manufacturers would you recommend?





RE: weir flow measurement
Not that familiar with the palmer-bowlus but a Parshall flume is used where you can't have a severe backwater condition. I doubt backwater is much of a concern on such a small pipe.
RE: weir flow measurement
I have never heard of a 'flowrat' but I have often used magflow meters on pipes.
The most common flume I have used is a rectangular throated flume, which is similar to a Parshall Flume. they are very simple and the flow is calculated and logged using an ultrasonic and data logger.
RE: weir flow measurement
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RE: weir flow measurement
RE: weir flow measurement
RE: weir flow measurement
Example: Triangular notch weir, 28.07 deg notch
At head = 0.10 ft, the flow is 1.05 gpm using standard weir equation (Reference: ASTM D5640-95, D5242-92). At head - 0.11 ft, flow estimate is 1.32 gpm. So a depth measurement error of 0.01 ft would lead to about a 25% error in the computed flow.
IMO it is going to be quite difficult to achieve 0.01 ft or better accuracy in a system with moving water.
So if quantifying the 1-2 gpm range of flows is critical you should consider another system (e.g. tipping bucket system). If you are really after the higher flows, say 10 gpm, the flume or weir could be an okay choice. The same calculation for a weir at 10 gpm, with a 0.01 depth measurement error, only throws off the flow estimate about 10%.
RE: weir flow measurement
RE: weir flow measurement
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RE: weir flow measurement
For automatic monitoring I would use a Vibrating wire weir monitor by GeoKon. I have found it gives reliable results without drift unlike a low range pressure transducer or ultrasonic devices.
To resolve BLT's issues on moving water, use a stilling well and stilling chambers inside the well.
Hydrae