weir box

Everything You Need to Know About Weir Boxes

Weir boxes are one of the most popular solutions for flow measurement needs. They function by incorporating a weir plate to measure flow while the box keeps the overall channel controlled with the proper conditions. Typically, they’re used to measure flows that range anywhere from 10 to 500 gallons per minute. That’s just the beginning, however, as there’s much more that goes into these systems. Here’s everything you need to know about weir boxes.

When to Use a Weir Box

There are several instances in which it’s best to implement a weir box to get the flow rate measurement you’re looking for. The most common is when a flow has a lot of solids that need to be captured. Dam seepage would be a suitable example. Similarly, weir boxes are commonly used when a flume wouldn’t be appropriate, such as in instances without friendly upstream conditions.

Weir boxes are also suitable for implementation in complex piping structures. Whether you have multiple pipes coming in or out, a weir box is useful for keeping that kind of scenario organized and offering accurate flow rate measurements. Additionally, weir boxes are used in situations in which the flow stream needs to be specifically controlled or separated after being measured.

How Weir Boxes Condition Flow

While weir boxes are suitable for channels with unfriendly upstream conditions, the flow itself still needs to be managed in order to get accurate measurements. Fortunately, flow conditioning with a weir box is relatively easy. This is thanks to the easy implementation of a baffle or set of baffles. A baffle is essentially an obstruction designed to reduce the flow rate velocity, ensuring that it’s at a subcritical state upon approach. Sometimes there are multiple baffles, while other instances utilize perforated baffles.

How Weir Boxes Measure Flow Rate

Weir boxes differ quite a bit from their flume counterparts when it comes to actual measurement. This is because the measurement itself occurs upstream of the weir plate rather than at the plate itself. This position is typically three to five times the anticipated maximum head. Just keep in mind that the zero elevation needs to be established beforehand, as flow measurements don’t begin at the weir box’s floor. 

Low flows are particularly tricky to measure using traditional means, but V-notch weirs are adept at measuring such flows, provided the flow doesn’t fall below 3.99 gpm. Even so, you’ll still have to use a 22½-degree V-notch weir for proper measurement. Just make sure your equations are properly adjusted for the unique setup for low flows, and you can enjoy accurate measurements with ease.

Weir Boxes From Tracom

If you’re looking for a weir box of your own, Tracom has got you covered. When you work with our team, we can help design a fiberglass weir that works perfectly for your unique flow channel conditions. Everything is custom made to your specifications, so you can always count on individualized service that continues even after installation. Contact us today to get started!