The 12-inch Parshall flume is the most popular size of Parshall flume - whether the application be treated effluent or water rights apportionment.

Flow Rates

The 12-inch Parshall flume has a measurement flow range of 0.1202 cfs [3.405 l/s] to 16.13 cfs [456.9 l/s], for heads from 1.2-inches [3.05 cm] to 30-inches [76.2 cm].  Freeboard for the flume is 6-inches 15.24 cm] at the maximum flow rate - allowing some room for wave action or turbulence without the flume overtopping.

The free flow discharge equation for the 12-Inch Parshall flume is:

Q (cfs, h=ft) = 4 * H^1.522

Q (l/s, h=m) = 690.9 * H^1.522

Dimensions

The flume is 9-feet 4 7/8-inches [286.7 cm] long, 2-feet 9 1/4-inches [84.46 cm] wide (at the inlet), with a sidewall height (at the primary point of measurement) of 3-feet [91.44 cm].  The outlet of the flume is 3-inches [7.62 cm] lower than the flat converging floor, with a maximum drop in the the throat of 9-inches [22.86 cm].

Uses

For wastewater treatment plants, the 12-inch Parshall flume is commonly seen at the head works of he plant as well as the discharge point out of the plant.

For agricultural flow, the 12-inch Parshall flume is on the smaller size of the flumes used for this application.  Agriculture flumes usually start with the 9-inch Parshall and go as large as the 48-inch Parshall - although larger and smaller flumes are possible.

End Connections

Both end adapters and wing walls are available for the 12-inch Parshall.  

The end adapters are capable of comfortably accommodating pipe stubs up to 36-inches [91.44 cm] in diameter (although 24-inches [60.96 cm is more common).   

While the wing walls, with a standard 20-inch [50.8 cm] radius, span channels up to 5-feet 6-inches [167.64 cm] wide.

Shipping

The size of the 12-inch Parshall is such that the flume has to ship palleted via LTL carrier.  For a shorter length installation, where free-spilling discharge is present under all flow rates, a Montana (short Parshall) or USGS Portable Parshall can be used.  The Montana flume deletes the throat and discharge sections, while the USGS Portable Parshall flume deletes just the discharge / diverging section.  

Materials

The 12-inch Parshall flume is available in:

• Galvanized steel
• Fiberglass
• Aluminum
• Stainless steel (304 and 316)

Documents

12-Inch Parshall Flume

• Drawings
  • Plain 12-inch Parshall flume
  • 12-Inch Parshall flume with 36-inch pipe stubs
• Discharge table