How Energy Absorbing Manholes Control High Velocity Flows

Flumes are among the best ways to properly measure flow rate. In order for them to function correctly, however, the approaching flow needs to be at a certain velocity. If it’s too fast or too slow, the measurement will be thrown off, leading to inaccurate results that make the entire process a waste. Fortunately, there is a way to help control and condition the approaching flow. Learn how energy absorbing manholes control high velocity flows.

How Do Energy Absorbing Manholes Work?

An energy absorbing manhole does exactly what its name would suggest: It absorbs energy from incoming flows to decrease their overall velocity. By doing this, it creates the conditions in which the flow can achieve critical velocity as it’s going through the flume for maximum accuracy with measurements. Remember, if a flow is going too fast when it enters the flume, it will reach a supercritical velocity, throwing off the measurements.

These manholes absorb energy using something called a dissipating baffle. This is the component that specifically functions to slow down the flow. The flow will pass on either side of the baffle to be met by curved wing walls on both sides of the outlet pipe. Navigating these obstacles will slow down the flow, making it easier to reach critical velocity.

What Are They Made From?

Given the essential nature of energy absorbing manholes, they need to be made from sturdy and long-lasting materials. While you’ll find several options available, fiberglass manholes tend to be the most reliable. The material is resistant to wear and tear, along with the natural erosion that occurs due to the constant flow going through the area.

Additionally, fiberglass energy absorbing manholes don’t require much maintenance. In fact, it’s not uncommon for one to operate for years without needing any maintenance at all. You just have to make sure the initial installation goes well. As long as all the components are secure, with baffles slightly larger than the incoming pipe, they should last for quite a while.

Where Should They Be Placed?

To ensure that an energy absorbing manhole is working at peak efficiency, it’s typically placed just upstream behind a packaged metering manhole. This ensures not only an efficient measurement but an easy measurement as well when it comes to high velocity lines. Specifically, there should just be a few feet between the energy absorbing manhole and flume. The exact figure will vary based on the flow rate you’re dealing with.

Energy absorbing manholes are more versatile than you might think, and they’re compatible with several different configurations, provided they meet the requirement that they be upstream from the meter. For example, they can work with a drop manhole configuration as long as the dissipation baffle and flow rate account for the velocity shifts from the flow dropping down into the lower area.

Finding an Energy Absorbing Manhole

If you think an energy absorbing manhole might be exactly what your flow measurement system needs, Tracom is happy to help. We offer customizable energy absorbing manholes along with just about every other kind of manhole you can imagine, from packaged metering options to manholes with grinders. Contact our experts today to start designing your ultimate manhole solution.