The 24-inch Parshall Flume is a popular size of Parshall Flume for measuring surface water flows, water rights, and sanitary flows at treatment plants.   

Applications

The 24-inch Parshall Flume can be useful in a number of applications, including:

• Mine dewatering
• Surface waters
  • Creeks
  • Canals
  • Streams
• Wastewater treatment plants
  • Headworks - influent
  • Treated effluent
  • Interplant flows
  • Lagoons
• Water rights / apportionment

Configurations

Openchannelflow offers the 24-inch Parshall in four primary configurations:

• Plain (for field formed inlet / outlet transitions)
• End adapters (allowing the flume to be connected to pipes / flanges)
  • Stubs and flanges up to 36-inches [91.44 cm]. 
• Metering manholes (factory integration into a fiberglass manhole)
  • A 24-inch Parshall Flume requires a 72-inches [1.83 m] manhole barrel

  • Two-piece manhole construction is needed when burial depths are greater than 8-feet [2.44 m]

• Wing Walls
  • Radius / flat inlet wing walls
  • Flat / flared outlet wing walls

Flume Accuracy

Although laboratory investigations have shown that Parshall Flumes can be accurate to within +/-2% (under free-flow conditions), once approach conditions, installation errors, and construction tolerances are accounted for, it is more practical to expect the free-flow accuracy to be +/-5% (ASTM D1941).

Should the flume submerge, either a dedicated submerged flow or a universal flow equation should be used.

The accuracy of a Parshall Flume can be affected if the flume settles out of position.  Corrections to the flow equations have been developed to account for this.

Flume Dimensions

Parshall Flumes are not scale models of each other.  The flumes are similar in layout, but they do differ in section lengths and convergence / divergence angles.  

Free-Flow Equation

The general free-flow equation for Parshall Flumes is:

For the 24-inch Parshall Flume:

Minimum Head (ft)	0.10	Minimum Head (m)	0.0305
Minimum Flow Rate (cfs)	0.4227	Minimum Flow Rate (l/s)	11.97
Maximum Head (ft)	2.50	Maximum Head (m)	0.7620
Maximum Flow Rate (cfs)	33.11	Maximum Flow Rate (l/s)	937.5
Equation (cfs, ft)	8*H1.55	Equation (l/s, m)	1429*H1.55

Discharge Table

Openchannelflow's discharge table for the 24-inch Parshall Flume is available for download. 

The table provides:

• Plan view of the flume showing the free-flow point of measurement (H_a) 
• Discharge equations in CFS, GPM, MGD, L/S, and M3/HR units
• Typical flume accuracy
• Submergence transition (S_t)
• Source for the flow table

Materials

The 24-inch Parshall Flume from Openchannelflow are available in a range of materials:

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

Fiberglass provides the greatest flexibility out of the four materials when it comes to customization.

Submergence Transition

A flume is said to be submerged when the downstream conditions are such that they restrict the flow out of the flume.  The submergence transition (S_t) is point at which the impact of submergence is large enough that the indicated flow rate needs to be correct to match the actual flow rate.

The submergence transition for a 24-inch Parshall Flume is 70%.  If the submergence ratio is above this, the discharge needs to be corrected.