The 18-inch Parshall Flume is mainstay at wastewater treatment plants.  It can also be found out in the field helping to measure water rights.

Applications

The 18-inch Parshall Flume is used for:

• Industrial pre-treatment
  • High volume users (i.e. paper mills and large regional breweries)
• Mine dewatering
• Surface waters
  • Creeks
  • Streams
  • Springs
• Wastewater treatment plants (WWTPs)
  • Incoming flows at headworks
  • Treated discharge 
  • Interplant flows
• Water rights allocation

Configurations

Openchannelflow's 18-inch Parshall Flume is available in several configurations:

• Standard (transitions by others)
• End adapters (used to connect to pipes and flanges)
  • Stubs and flanges up to 36-inches [91.44 cm] can be accommodated
• Metering manholes (factory integration of a flume into a fiberglass manhole)
  • A 60-inch [1.53 m] manhole barrel is required to integrate an 18-inch Parshall Flume
  • Two-piece manhole construction is common when burial depths are greater than 8-feet [2.44 m]
• Wing Walls
  • To span rectangular channels

Flume Accuracy

The laboratory accuracy of Parshall Flumes has been found to be +/-2%.  

In the field, variances in approach conditions, minor errors in the installation, and typical construction tolerances mean that the user should more realistically expect an accuracy of +/-5% (ASTM D1941).

Should the flume become submerged due to downstream conditions, a universal flow equation is available to correct the flow rate.  Also, a correction for settling has also been developed.

Flume Dimensions

Always remember that Parshall Flumes are not scale models of each other.  

Free-Flow Equation

The general free-flow equation for the Parshall Flume is:

The values for the 18-inch Parshall Flume are:

Minimum Head (ft)	0.10	Minimum Head (m)	0.0305
Minimum Flow Rate (cfs)	0.1738	Minimum Flow Rate (l/s)	4.923
Maximum Head (ft)	2.50	Maximum Head (m)	0.7620
Maximum Flow Rate (cfs)	24.56	Maximum Flow Rate (l/s)	695.5
Equation (cfs, ft)	6*H1.538	Equation (l/s, m)	1056*H1.538

Discharge Table

A discharge table for the 18-inch Parshall is available for download.  

The table provides:

• A plan view showing the point of measurement (H_a) 
• Discharge equations in CFS, GPM, MGD, L/S, and M3/HR
• Flume accuracy
• Submergence Transition (S_t)
• Source of the table

Materials

Openchannelflow offers the 18-inch Parshall Flume in four different materials:

• Aluminum
• Fiberglass (FRP)
• Galvanized steel
• Stainless steel

Submergence Transition

When downstream conditions are such that they restrict the flow out of a flume, the flume is termed to be submerged and corrections to the indicated flow need to be made.  The point at which submergence is sufficient to require correction is termed the Submergence Transition (S_t).

The Submergence Transition (S_t) for the 18-inch Parshall Flume is 70%.