Wastewater Treatment Plant Ultrasonic Flow Meter and V-notch Weir
Effluent flow measurement in wastewater treatment plants have traditionally been measured by weirs, flumes, time-transit flowmeters, partially filled pipe flow meters, insertion meters, magmeters and other flowmeter technologies. This wastewater treatment plant uses two 90 degree V-notch weirs along with an Ultrasonic Flow Meter system from Aqua Technology Group and Nivelco to accurately measure the treated waste water as it flows out of the plant into the receiving waters.
But what if you have a flow meter application like this dual 90 Degree V Notch Weir or another primary flow device? Aqua Technology Group and Nivelco have you covered with a best of breed solution for any wastewater flow application.
How Does a Ultrasonic Flowmeter with V-notch Weir Flowmeter Work?
The two v-notch weirs act as the primary flow measurement devices for the system. Primary measuring devices like these weirs provide a reliable way of producing a measurable head (or water level) above the crest elevation. The V-notch weirs are are available in various angles and we typically fabricate them out of 1/4″ or larger aluminum plate. We can even provide them as fabricated fiberglass weirs. The head 0r water level above the crest (or bottom of the V) of this 90 Degree V-notch weir is accurately measured by a Nivelco EasyTREK ultrasonic level transmitter. The integrated ultrasonic level transmitter and flow meter sends a scaled 4-20 mA + HART signal over two wires to the Nivelco MultiCONT multichannel display and process controller. The MultiCONT can act as a fully featured multichannel process controller in many applications but here it simply provides a remote display of the instantaneous level in feet along with flow in GPM (Gallons Per Minute). The MultiCONT process controller also provides the accumulated flow in both resettable and non-resettable totalizers. The 4-20 mA signal is then looped through the wastewater effluent sampler and back to the RTU and SCADA system for analysis and archiving.
What’s the angle of that V-notch weir?
V-notch Weir Angles Range from 22.5 Degrees up to 120 Degrees
22.5 Degree V-notch weir
30 Degree V-notch weir
45 Degree V-notch weir
60 Degree V-notch weir
90 Degree V-notch weir
120 Degree V-notch weir
V-Notch Weir Design Considerations
- Minimum of 2.4 inches or 0.2 feet of head (water level above the crest).
- Maximum of 24 inches or 2.0 feet of head (higher is possible but not recommended for good accuracy).
- The upstream weir face must be vertical – always check with a level.
- The edges of the weir must be cut or machined straight, sharp and crisp – no burs or jagged edges.
- The channel should have a free-fall of 6″ (152.4 mm) downstream of the crest of the weir.
- Ice, debris, corrosion, algae and biological buildup must be removed regularly – keep the edges clean!
- The weir nappe must be adequately aerated so the water does not cling to the outfall face of the weir.
- The pool on the upstream side of the weir must be kept free of weeds and debris.
- The upstream pool must be large enough and properly sized to ensure accuracy.
- The approach velocity of weirs should normally be below 0.5 ft./s (0.1524 m/s). Above this requires calibration.
How to Size Your V-Notch Weir
What is the Minimum and Maximum Head for V-notch Weirs? Download V-notch Weir Min/Max Table
Flow may become very unstable if you regularly have low discharge head (or water level above the notch). If the minimum head of .2′ (2.4″) is not reached, you may see flow inconsistencies or even meter errors. Engineers and flow experts alike agree that heads less than 2.4 inches will not produce reliable flow meter results as the nappe tends to adhere to the crest of the weir and viscous drag is observed.
How Do I Calculate Flow Across a V-notch Weir at a Given Head? Download V-notch Weir Discharge Table
In this 90 degree V-notch weir application, we want to know our flow in GPM (gallons per minute). We have approximately 1.0 feet of head which calculates out to about 112o GPM. We calculate this by taking 1120 times the head in Feet ^2.5 power. (1120 x 1^2.5 = 1120 GPM).
Choosing the Right Ultrasonic Flow Meter for V-notch Weirs and Flumes
Not all flowmeters are created equal. Some consist of cheap components, low accuracy and other shortcuts to keep costs low. The units keep moving out the factory door but later end up in the trash bin!
We prefer the customer centric longer approach by providing the best mixture of price and quality. That leads to industry leading customer satisfaction and the least amount of warranty service calls. The Nivelco EasyTREK and MultiCONT in this application have been in continuous service for nearly a decade. We hope every customer can get that type of life. Nivelco keeps you covered with a industry leading 3 Year Warranty.
No flow meter can be the perfect fit for every V-notch weir or flume flow measurement application. Contact our team save you time and money with a matched system for years of service. Looking for a compact ultrasonic flow meter solution? Check out the EchoTREK compact ultrasonic flow meter. We can also help you meter water and collect meaningful data throughout the entire water cycle – raw water sources, wells, raw water pumping, water treatment plant, water distribution, waste water collection system, metering manholes, lift station flowmeters, wastewater treatment plant flowmeter, plant process flow meters, wastewater treatment plant effluent flow and everything else in between.
Maybe you even have an existing V-notch and ultrasonic flow meter that needs service. Aqua Technology Group provides flow meter calibration, repair and emergency service for your water and waste water plant.