Flow meter


Thread Starter

Monah Fakhoury


We have been asked to replace a flow meter that measures the flow rate into an open tank. The tank lets the water in in one direction, and out the other direction through an opening that is V shaped. The flow rate is calculated by measuring the level increase. I have not seen such a device, where would we find a similar device, client wants to replace the existing with a similar device.

This does not sound like a flow meter, it sounds like a level rate-of-change meter. From your description you need something to continuously measure the level of the tank and display the results integrated over time.

The V-notch (or Cipoletti notch which is a trapezoidal-notch) flowmeters, their sizing equations and features are covered in my handbook under "Weirs and Flumes", which is Section 29 in the Flow Measurement chapter (Chapter 2) in the 3rd edition of the Measurement Volume of the Instrument Engineers' Handbook.

Béla G. Lipták, P.E., Consultant and editor
84 Old N. Stamford Rd., Stamford, CT. 06905-3961
Tel: 203-357-7614, Fax: 203-325-3922
E-Mail: [email protected]
What you have there is a v-notch weir. You can find out lots of information about V-notch weirs in several reference books, including one that is online by the United States Bureau of
Reclamation. I don't have the URL though. ISCO publishes an extremely useful book by Douglas Grant that also has all of this information including complete tables. You use an ultrasonic
transducer to measure the height at a point far enough back from the edge of the notch so that the level is flat, and the level is converted to flow by an equation of the form Q=KH^n where Q is
volumetric flow, K is a conversion constant, H is the measured level and n is the power H is raised to, depending on the type of flume or weir (often n =3/2).

Walt Boyes

Walt Boyes -- Director of New Business Development
Branom Instrument Co.-- P. O. Box 80307-- 5500 4th Ave. So.
Seattle, WA 98108-0307
Phone: 1-206-762-6050 ext. 310 -- Fax: 1-206-767-5669
http://www.branom.com -- http://www.branomstore.com
mailto:[email protected]

Arnold Dillon

I think that your existing device is a v-notch flow weir. The notch is cut to a specific geometry and volumetric flow can be calculated based on the level in the weir. I think SAAB and probably some other radar level detectors can be programmed with the calculation required to
convert the direct level reading into flow. Contact your representative for your favorite radar level system and ask them what they can provide.

Arnold Dillon
I.C. Thomasson Associates

Adolfo Jimmy Saldivias Valarezo

There are several manufacturers, specially the ones who manufacture ultrasound level measuring equipment, among them:

Regards jimmy Saldivias TECSIM Bolivia

Al Pawlowski, PE

If outlet flow falls free over the edges of the V shape, the V would probably be what is called a "V-notch" weir. Most open-channel flowmeters should be able to measure/calculate V-notch flow.
Another excellent ultrasonic device is offered by Greyline (www.greyline.com). The SLT32 has internal calculations for most open channel flume and weir applications and has many options including remote capabilities. - Bob Jones, E&I Supervisor, Fox River Paper Co.