Flumes come in many different shapes and sizes, but one of the most important factors is the size of the throat section. Both long-throated and short-throated flumes have plenty to offer, along with advantages and disadvantages to consider, but only one kind can be the right fit for your flow channel conditions. Learn about the most important differences between short-throated and long-throated flumes.
Points of Measurement
The point where you take measurements is different in long-throated flumes compared with short-throated flumes. This is largely due to how each controls flow. Long-throated flumes control flow by creating parallel flow lines, which allows fluid flow concepts alone to be able to rate certain flows. Meanwhile, short-throated flumes have to be rated through empirical methods.
Because empirical methods are necessary for short-throated flumes, you’ll have a singular defined point of measurement with no room for alternatives. If you go upstream of that point, you will overestimate the flow, while measuring downstream will underestimate the flow. With long-throated flumes, on the other hand, you can measure virtually anywhere in the flume that’s upstream of the throat drawdown, granting plenty of flexibility.
Flume sizes are different depending on whether you’re working with long- or short-throated flumes. Long-throated flumes don’t really have standard sizes with plenty of variance, but that can be an advantage because they’re easier to integrate into a variety of flow channel configurations. This degree of customization is especially useful when you’re dealing with an uncommon flow channel configuration.
Short-throated flumes, on the other hand, are much more standardized with dimensions that are specific for each available class of flume. While many sizes are available, with the Parshall and Montana in particular having 22 different options, they don’t always fit your flow channel conditions. With standardization comes operator familiarity, so short-throated flumes do have that advantage.
When downstream flow doesn’t have the conditions necessary to keep moving past the flume, it will back up into the flume, which leads to submergence. Both throat types can suffer submergence, of course, but long-throated flumes tend to be more resistant to it. In fact, you’ll find submergence transitions for long-throated flumes up to 90%.
Short-throated flumes aren’t typically built to withstand submergence to any significant degree. You’ll find some that can handle it quite well with submergence transitions of up to 80%, but most are closer to around 50%. In some cases, like with the Montana flume, the submergence transition is 0%, meaning it can’t handle submergence at all.
Flumes From Tracom
With the differences between short-throated and long-throated flumes in mind, it’s time to get a flume of your own. No matter what kind of style you’re looking for, Tracom has the flume for you. You can even work with our design team for something more uniquely built for your flow channel conditions. Contact us today to get started!