weir type flow meter

It depends on the flow variability. A V-notch weir—usually 90 degrees—provides good accuracy at low flows because a small change in head produces a measurable flow change. For larger, relatively steady flows, a rectangular weir with full width or end contractions is easier to construct and less sensitive to slight level errors. If you have very wide flow ranges, a compound weir combining sections can help, but it complicates installation. Kingmach typically helps size the weir based on your expected minimum and maximum flows, making sure the crest height and channel dimensions avoid submergence and approach velocity issues.

Not always, but it’s recommended when the surface is choppy or wave action affects the reading. A stilling well is a separate column connected to the channel via a small inlet; the water inside remains calm, so the level sensor gets a stable surface. Ultrasonic sensors can sometimes work without one if you use a damping pipe, but submersible pressure sensors almost always need a stilling well to filter out waves. It’s one of those details that makes a big difference in data consistency, especially in outdoor sites exposed to wind.

The main task is keeping the weir crest clean and checking for damage. In clean water, you might just inspect it quarterly; in wastewater or sediment-heavy flows, weekly cleaning could be necessary to prevent buildup that changes the crest profile. The level sensor—whether ultrasonic or pressure—should have its calibration verified every few months. Kingmach’s setup guides include a simple dip test using a known reference point to confirm the zero offset hasn’t drifted.

It’s not common because normal weirs need a well-formed approach channel with uniform velocity. In a pipe, the flow pattern at the discharge can be asymmetric, which affects the head-flow relationship. Sometimes a short flume or transition section is added at the pipe outlet to create a channel before the weir. If space is tight, a flume-style meter might work better, but weirs can be adapted with proper entrance conditioning if there’s room.

Under good conditions—properly built weir, accurate level sensor, and minimal approach velocity—it’s reasonable to expect ±2% to ±5% of actual flow. The weir formula itself is fairly precise, so the main error sources are level measurement uncertainty, crest deformation over time, and not accounting for submergence or debris. Kingmach’s documentation walks through these factors and suggests ways to estimate total uncertainty based on your installation.