The 36-inch Parshall Flume is equally at home measuring water rights, sanitary flows, and surface waters.   

Applications

The 36-inch Parshall Flume is useful in a number of applications:

• Dewatering of mines
• Measuring surface waters
  • Creeks
  • Canals
  • Streams
• WWTP
  • Influent
  • Effluent
  • Lagoons
• Water rights 

Configurations

Three standard configurations of the 36-inch Parshall Flume are available:

• Plain (for field formed inlet / outlet transitions)
• End adapters (allowing the flume to be connected to pipes / flanges)
  • Stubs / flanges up to 36-inches [91.44 cm] 
• Wing Walls
  • Inlet / outlet wing walls for rectangular channels

Flume Accuracy

Research has shown that the Parshall Flume be accurate to within +/-2% under controlled, laboratory conditions.  Field conditions differ however and the free-flow accuracy shouldn't be expected to be better than +/-5% (ASTM D1941).

Should the flume submerge or shift out of position, corrections for submergence and settling have been developed.

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:

36-inch Parshall flume:

Minimum Head (ft)	0.15	Minimum Head (m)	0.0457
Minimum Flow Rate (cfs)	0.6151	Minimum Flow Rate (l/s)	17.42
Maximum Head (ft)	2.50	Maximum Head (m)	0.7620
Maximum Flow Rate (cfs)	50.39	Maximum Flow Rate (l/s)	1427
Equation (cfs, ft)	12*H1.566	Equation (l/s, m)	2184*H1.566

Discharge Table

Openchannelflow's head vs flow table for the 36-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 M3/HR, L/S, MGD, CFS, GPM
• Free flow flume accuracy
• Submergence transition (S_t)
• Flow table source 

Materials

Openchannelflow offers the 36-inch Parshall Flume in four different materials:

• Aluminum
  • Lightweight and abrasion resistant
• Fiberglass (FRP)
  • Lightweight and easily customized
• Galvanized steel
  • Most economical
• Stainless steel
  • Greatest resistance to abrasion and corrosion

Submergence Transition

Submergence in a flume is when the downstream conditions are such that they restrict the flow out of the flume.  As submergence increases, a point is reached where the impact on the flow rate is large enough that the discharge equation overstates the flow out of the flume.  This point is termed the submergence transition (S_t).

The submergence transition (S_t) for the 36-inch Parshall Flume is 70%.  At 70% or above and the indicated discharge needs to be corrected to reflect the actual discharge.