The ability to nest flumes inside each other can be use in a variety of applications, including:
- Where a flume is oversized sized for the current flow rates (i.e. process change, I&I reduction)
- Where flows are seasonally variable (i.e. resorts)
- Where flows may start low but are expected to build over time (i.e. subdivision build-out)
When the difference between two Palmer-Bowlus flumes is small enough (usually only one flume size), the inlet flange of the inner flume is trimmed so that the smaller flume fits snugly into the larger flume. In applications where the inner Palmer-Bowlus flume is considerably smaller than the outer Palmer-Bowlus flume, bulkheads may be required to direct all of the flow through the inner flume.
Unlike Parshall, Cutthroat, or Montana flumes, where a full sized flume is used to nest, the inner nested Palmer-Bowlus flume is only a partial flume - the upstream 2D section and half of the trapezoidal throat section. The shortened configuration allows the throat of the inner flume to rest directly on the throat of the outer flume.
The connection between the two flumes is caulked so that the seal is watertight. In applications where the nesting flume won't be removed, stainless steel fasteners may be used to permanently secure the inner flume to the outer flume.
If the Palmer-Bowlus flumes are more than one size apart, there may be a void space between the inner and outer flumes. If a void is present due to a disparity in flume sizes, it can be filled with sand and capped by grout to ensure that water doesn't collect between the flumes - potentially shifting the inner flume out of place.
In nesting Palmer-Bowlus flumes it is important to understand that the design of the Palmer-Bowlus flume is proprietary to each flume manufacturer. While most flume manufacturers offer trapezoidal shaped throat section Palmer-Bowlus flumes, there can be differences in the throat section designs. As a result, extensive field fitting may be required in applications where the outer flume exists.
Openchannelflow has successfully developed nested Palmer-Bowlus flumes for existing sites, new construction, and above grade applications, all in a variety of sizes.