While a weir can be a convenient solution for flow channel measurement, there are problems that can arise. For the most part, these problems are due to improper installation. They can manifest in several different ways, so it’s always best to be wary of them beforehand to ensure that your installation goes as smoothly as possible. Here are the most common errors to be aware of in weir installations.
Poor Approach Velocity
In order for a weir to provide accurate flow measurements, the approach velocity must not be more than 0.5 feet per second. That’s just the beginning, however, as the upstream channel itself has to be straight, with room for 20 times the maximum anticipated head, or the Hmax measurement. Additionally, the channel itself must be as wide as 2Hmax. If these conditions are not met, the weir’s accuracy will be severely impacted by the poor approach velocity.
Bad Crest Condition
In order to measure flow channels properly, a weir will need to have a crest in good condition. For the most part, that means the crest is free of any damage that could alter its shape, like chipped pieces or abrasions. Cleaning the weir plate regularly is essential for maintaining a quality crest condition. Additionally, the crest must be kept sharp, though it’s not necessary to keep it as sharp as a knife. The main goal here is preventing the crest from being rounded.
Just as the upstream conditions are important, the downstream conditions must meet certain requirements as well. The primary factor to consider in this regard is the water level after the weir. It must be beneath the nappe in order for the weir to function properly. The nappe is the height of the water flowing over the crest of the weir. Should the downstream water level be higher than the nappe, the weir will be submerged. This will drastically change the indicated flow rate, rendering measurement efforts fruitless.
The physical installation of the weir must be completely uniform in order for flow rate measurements to be accurate. Specifically, the crest needs to be centered in the channel. That’s the only way for it to provide accurate measurements of the flow rate. Additionally, it must be level from side to side and vertically plumb. If the installation renders the weir off in any of these ways, your measurements will be thrown off, making your efforts useless.
Fiberglass Weirs From Tracom
If you’re looking for a quality weir specifically tailored to your flow channel conditions, Tracom has got you covered. You can work with our expert design team to craft a weir that’s perfectly fitted for your unique flow channel to ensure accurate measurements. We can even provide installation support and a two-year warranty to ensure quality measurements without having to worry about common errors in weir installation.
All you have to do to get started is reach out to our team. Contact us today to take the first step toward crafting the ultimate weir solution for your flow rate measurement needs.