End Adapters for Parshall Flumes

The most common way of transitioning flow into and out of a Parshall flume is to simply form a channel up to and away from the flume. This works in many situations, and was in fact the way that Dr. Parshall himself installed his flumes. But what about when you need to measure flow in a non-full pipe? That’s where end adapters come in.

Fiberglass 6-inch Parshall Flume with Inlet and Outlet End Adapters

End adapters are specially shaped structures that attach to the inlet and / or outlet of a Parshall flume and are designed to:

Provide a convenient method of connecting to piping.
Transition flow into and out of the flume in a controlled manner.
Condition the flow into the flume so that accurate flow measurement can take place.

Done right, end adapters allow Parshall flumes to accurate measure pipe flows. Done wrong and end adapters can adversely affect accurate flow measurement by introducing turbulence, providing a poor velocity profile, or restricting the discharge of flow away from the flume (submerging it).

Although the specific design of end adapters vary from manufacturer to manufacturer, well designed end adapters share certain common characteristics:

The end adapter is deeper than the flume.
- Deeper end adapters allow flow to rise up into the flume (which helps to dissipate turbulence and produce a more uniform velocity profile) as well as allowing large diameter pipe stubs.

1:4 rise in Parshall Flume inlet end adapter

Integrally molded rise into the flume (inlet end adapter).
- Ideally the rise should be at the 1:4 slope (rise:run) suggested by Dr. Parshall during the development of the flume. Sharper rises induce turbulence as the flow separates and begins to roll or boil.

Inlet width greater than the flume width.
- This allows the flow to spread and then be uniformly directed into the entrance of the flume.

Radius transition on 6-inch Parshall Flume inlet end adapter

Radius transition into the flume.
- Again, following the example set by Dr. Parshall, radius wing walls should smoothly direct the flow from the wider width of the inlet end adapter into the entrance of the flume.

End adapters are most common of fiberglass Parshall flumes where a master mold can be developed, but they can also be fabricated for galvanized and stainless steel Parshall flumes as needed.