Modifications to accommodate different inlet geometry, custom sidewall heights, or molded-in accessories are essentially impossible with out a complete (and expensive) rebuild of the form for each specific application.įiberglass on the other hand is extremely adaptable. With the metal forms required to make concrete flumes there is a lack of design flexibility. At 144-inches (the point at which concrete is occasionally used), the ASTM throat tolerance is 2 7/8-inches - more than achievable in concrete construction.
For a 3-inch Parshall this means that the throat width should deviate no more than 1/16th of an inch - a level of accuracy extremely difficult to achieve with field formed concrete.Īs Parshall flumes get larger, though, this level of accuracy becomes more attainable. Hydrogen sulfide attacks concrete with such efficiency that it is standard practice in many parts of the United States to coat concrete channels at treatment plant headworks to increase their longevity. The isophthalic polyester resins used in their construction are highly resistant to hydrogen sulfide. In wastewater / sewage treatment plants Parshall flumes are almost exclusively made from fiberglass. Competition, therefore, tends to be very localized - with fabricators usually (but not always) owning their local markets. The 144-inch Parshall flume, in fiberglass, ships in three pieces and takes one and a half flat bed trailers. Transport of large fiberglass flumes is also an issue. * Galvanized steel Parshall flumes have a strong presence in water rights / irrigation applications. Applications requiring Parshall flumes 180-inches and larger are rarer still – with almost no fiberglass Parshall flume manufacturers having even temporary molds. In given any year (or sometimes years) there are few applications across the industry requiring Parshall flumes 144-inches in size - not even enough to support each fiberglass flume manufacturer having a 144-inch Parshall flume mold (a mold which takes considerable time and money to fabricate). At 144-inches a new mold is required as these dimensions change - as they do again for the 180-inch size. A single adjustable mold can be made from which a wide range of Parshall flume sizes can be made. Part of the reason is this: Parshall flumes from 12-inches to 120-inches share the same throat, discharge, and sidewall geometry. Above 180-inches concrete is always used. At 180-inches concrete is almost always used. At the 144-inch size, flumes are formed either in fiberglass or concrete, with fiberglass still the norm. Metal forms are expensive and unless there are a large number of identical flumes, the cost associated with making the forms is prohibitive unless spread out over a number of units.įor Parshall flumes from 1-inch to 120-inch in size, fiberglass is the predominant material of construction for most applications*.
Water concrete flume install#
Parshall was involved with the install of a large number of sites (130) so he developed metal forms with which he constructed his concrete Parshall flumes. Parshall used a variety of materials, including: sheet metal, wood, and concrete to from his flumes. In his investigation of what would become the Parshall flume, Dr. Ready availability of fiberglass and galvanized steel Parshall flumes.The use of concrete in makiing Parshall flumes is limited by a number of factors: Periodically we are asked the question: Can Parshall flumes be made out of concrete? The answer is: yes, they can (but they usually aren’t)!
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