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Montana Flume Dimensions

The dimensions for the Montana flume are based upon those of the Parshall flume from which it's derived. 

The dimensions, and tolerances, of Parshall flumes have been standardized in a number of national / international standards and authoritative publications:

The Montana flume is defined in:

It's critically important to note that although Montana flumes share a common layout, they are NOT scale models of each other – they are empirical devices for which investigations have been made to determine their specific flow rates.

The use of non-standard flume sizes is HIGHLY discouraged and the dimensions and flow accuracies of such devices should be considered suspect.

Dimensional Tolerances

ASTM D1941 requires that Parshall (Montana) flumes have dimensions within +/-2% of nominal, while JIS B7553 requires tolerance of +/- 1-1.5% depending upon flume size.  

Parshall (Montana) flumes with dimensions outside of these ranges should be considered to be non-conforming and should be either replaced for field rates.