Parshall Flumes and Pipe Stubs

Unlike the Palmer Bowlus flume which was specifically designed to be used in-line with sewer pipes and conduits, Parshall flumes were originally developed to measure flows in irrigation channels and natural streams / rivers. Over the years, though, Parshall flumes have been successfully adapted to measuring pipe flows.

End Adapters

To transition the flow from a round pipe into a rectangular shaped Parshall flume, end adapters have been specifically engineered to minimize transition turbulence and condition the flow before it enters the flume.

12-inch fiberglass Parshall flume with end adapters and pipet stubs

On the inlet, the end adapter forces the flow to rise vertically up into the flume at a 1:4 slope. Horizontally, the flow is abruptly expanded out from the round pipe into the rectangular adapter and is then smoothly directed into the entrance to the flume through the use of radius wing walls. Radius wing walls allow a much smoother transition into the flume and help to eliminate the wave-trough phenomena that can develop when flat wing walls are used.

Pipe and Flume Throat Sizing

It is important to remember that, unlike the Palmer Bowlus flume, Parshall flumes VERY RARELY have throat sizes the same as the pipe that they are connecting to.

Usually the flume has a throat size that is 1/2 to 1/3 the size of the pipe.

Watertight Connections

To make the connection between the end adapter pipe stubs and the upstream / downstream piping, flexible Fernco couplings are used. Stainless steel band clamps help to make the connection watertight and mounted in groves on the outside of the coupling.

inlet end adapter on a parshall flume with pipe stubs

If an installation needs extra strength or rigidity, coupling shields can be used. Coupling shields are stainless steel covers that go around the outside of the flexible coupling.