Measuring Low Flows with a Palmer Bowlus Flume

The Palmer-Bowlus flume is one of the best flumes available if you’re looking to install it in an existing piping channel or sewer manhole, but there are some things you should be aware of. Piped systems tend to have higher flows, which the Palmer-Bowlus excels at dealing with, but you may run into situations in which you have to deal with a low flow. That’s where the problems can start. Learn all about measuring low flows with a Palmer-Bowlus flume.

Flow Accuracy

Under normal circumstances, the Palmer-Bowlus flume is accurate to about +/- 3-5%. This is the case when the head in the flume is large compared to the length of the throat, which is how normal piped systems operate. If the flow is lower, however, the accuracy can decrease to +/- 5-6%. The way the flume is designed relies on the head being high in comparison to the throat length, so if it’s too low, your accuracy is going to be unreliable.

Typical Flume Operations

In most flume types, you’ll find that their accuracy remains largely unaffected by the head of the flow as long as the flow rate is within the design’s effective range. This is not the case with Palmer-Bowlus flumes, making them more of a specialized option when compared to other, more universally applicable flume types.

Alternative Options

Instead of using a Palmer-Bowlus, you may want to use something like a Trapezoidal flume instead. Not only can Trapezoidal flumes still work nestled within piped systems, but they can deal with a lot more variation in the head of the flow as long as the flow is within their effective rate parameters. The HS/H design is another popular alternative for situations in which the Palmer-Bowlus can’t be as accurate as you deserve.

Accuracy Tweaks

When you have to use a Palmer-Bowlus, there are some tweaks you can do to increase your accuracy. The most common is to simply go down a size. For example, if you have a 10-inch line, you may want to use an 8-inch Palmer-Bowlus flume rather than an accompanying 10-inch. The problem with this approach, however, is that you’ll need to ensure a smooth transition of flow into the flume, which can be difficult when narrowing a stream.

Another option is to utilize a nested flume configuration. This is essentially a flume within a flume. When you try this approach, however, it will increase the amount of standing water upstream of the flume. This can, in turn, lessen the upper range of the inner flume depending on how exactly it was fit inside its larger counterpart.

Flumes From Tracom

Measuring low flows with a Palmer-Bowlus flume can be tricky, but it can be done under the right circumstances. Whether you’re looking for tweaks or a different style altogether, Tracom has got you covered. We offer a wide variety of fiberglass flume designs and a team that can help you design one of your own. Contact us today to learn more about how you can find the perfect flume.

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