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Hach Area Velocity Flow Meter Sizing: Submerged AV Sensors for Stormwater Sewer Inspections
Quick Answer: Sizing a Hach area velocity flow meter for stormwater sewer inspections starts with pipe diameter, velocity range, and water depth. A submerged AV sensor with 0.02 to 6.00 m/s velocity range and 0 to 5 m level range covers most DN200 to DN2000 stormwater sewers. Send Silver Automation Instruments your pipe size, flow range, and output signal for a direct model and price.
What a Submerged AV Sensor Actually Measures in a Stormwater Sewer
Stormwater sewers rarely run full. That is why area velocity flow meters use a submerged pressure transducer for level and a Doppler sensor for velocity. The flow rate comes from the continuity equation. Flow equals cross sectional area multiplied by mean velocity.
A Hach submerged AV sensor works well for short term stormwater inspections. It handles solids, grit, and changing water levels. In practice, most engineers skip the full channel theory and focus on three inputs. Pipe diameter, expected peak velocity, and maximum water depth.
Start With Pipe Diameter and Velocity Range
Hach area velocity flow meter sizing for stormwater sewers depends on pipe diameter more than anything else. For DN150 to DN300 drains, low flow accuracy matters. For DN1000 to DN2000 trunk sewers, the sensor must read velocity across a wide area without losing signal.
We have seen this on customer sites many times. A contractor in Vietnam measured stormwater outfalls in Da Nang. The pipes ranged from DN300 to DN1200. The peak velocity during rain events reached 4.2 m/s. A sensor rated for 0 to 5 m/s worked, but the low end needed to stay at 0.03 m/s or better because dry weather flow was very small.
For most stormwater sewer inspections, specify a submerged AV sensor with velocity range of 0.02 to 6.00 m/s. Level range should be 0 to 5 m. This covers temporary flooding and normal dry weather depth. Temperature rating of 0 to 60 °C is enough for tropical and desert sites.
Hach Area Velocity Flow Meter Sizing for Different Pipe Conditions
Concrete, HDPE, and corrugated metal pipes all affect Doppler signal quality. The Hach type submerged AV sensor can handle these materials, but the mounting location matters. The sensor needs a clear position at the pipe invert. Avoid mounting behind silt bars, roots, or lateral inflows that create turbulence.
For a stormwater sewer inspection, portable meters are common. A utility in the Philippines tested 12 outfalls in Manila with a portable area velocity flow meter. The key sizing parameter was cable length. Some access points were 8 m below street level. A 10 m sensor cable was enough, but a 15 m cable gave more flexibility.
So before you order a Hach compatible submerged AV sensor, check your manhole depth. Standard cable length is 10 m. If your site has deep access chambers, specify 15 m or 20 m. This small decision prevents extra site visits.
Silver Instruments Alternative for Hach AV Sensors
Silver Automation Instruments supplies a direct alternative for stormwater sewer flow measurement. The Silver Instruments SA-AV100 submerged area velocity flow meter matches many Hach AV sensor sites. It includes a Doppler velocity sensor and a level transmitter in one IP68 body.
The SA-AV100 covers 0.02 to 6.00 m/s velocity and 0 to 5 m level. Output is 4-20 mA HART plus RS485 Modbus. Power is 12 to 24 VDC, which fits battery powered telemetry systems. The sensor works in raw sewage, s
Because Silver Instruments is a flow meter manufacturer, the price is lower than brand name Hach sensors. A distributor in Peru replaced a Hach AV sensor on a municipal stormwater project in Lima. The pipe was DN900 concrete with silt and sand. The SA-AV100 gave stable readings at 0.15 m/s dry weather flow and 3.8 m/s during storm peaks.
Common Sizing Mistakes in Stormwater Sewer Inspections
One mistake is selecting a level range that is too small. Stormwater pipes can surcharge during heavy rain. If the level sensor tops out at 2 m and the pipe diameter is 2.4 m, the flow calculation becomes wrong. Select a level range above the pipe diameter. For a DN2000 pipe, use a 0 to 5 m level sensor, not 0 to 3 m.
Another mistake is ignoring minimum velocity. Many stormwater sewers have dry weather flow below 0.05 m/s. A standard area velocity flow meter may read zero. Specify a low velocity cutoff around 0.02 to 0.03 m/s. This matters for regulatory monitoring and pollution load estimates.
Do not mount the AV sensor near drop structures or energy dissipators. Air bubbles and hydraulic jumps cause unstable Doppler readings. The best position is 3 to 5 times the pipe diameter downstream of any junction or drop. This is a practical rule used by field crews in Australia and Southeast Asia.
What to Send for a Quote
If you need a Hach area velocity flow meter sizing check or a Silver Instruments substitute, send us the following data. Pipe diameter in DN or inches, pipe material, expected minimum and maximum velocity, maximum water depth, cable length from access point to invert, power supply, and output signal.
We will reply with a specific model, price, and lead time. Do not send only the flow rate. Stormwater sewers are not full pipes, so the area velocity formula changes with depth. A full pipe electromagnetic flow meter will not work in the same application.
FAQ: Hach Area Velocity Flow Meter Sizing for Stormwater Sewers
What pipe sizes can a submerged AV sensor handle?
Most submerged AV sensors work from DN150 to DN3000. For very small drains below DN150, a portable Doppler sensor or a weir box may be more accurate.
Can a Hach AV sensor measure surcharged stormwater pipes?
Yes, it can measure level and velocity during surcharge. But if the pipe runs completely full for long periods, a full bore electromagnetic flow meter gives better accuracy. Area velocity sensors are best for open channel and partly full pipe conditions.
What is the minimum velocity for a submerged AV flow meter?
Typical minimum velocity is 0.02 to 0.03 m/s. Below this, sediment movement and signal noise can cause zero readings or unstable data.
What output signal should I specify for stormwater sewer telemetry?
4-20 mA HART is standard for local SCADA. RS485 Modbus RTU is better for long distance data logging. Battery powered remote sites often need pulse or SDI-12 output. Confirm with your telemetry provider before ordering.
Can Silver Instruments supply a direct replacement for Hach AV sensors?
Yes. The Silver Instruments SA-AV100 has similar mechanical mounting and signal output. Send us your existing sensor photos, pipe size, and output signal. We will check the replacement fit.
Contact Silver Automation Instruments
Tel: +86-25-68650347
Whatsapp: +86-25-52155837
WeChat: +86 15365082610
Website: flow-meter.com.au
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