Galvanized Steel Parshall Flumes

In the right applications, galvanized steel Parshall flumes can be a good choice to measuring the flow of water. Irrigation and water rights applications (generally in the Intermountain Region of CO, UT, WY, MT, ID) were abrasive grit, stones, or debris are not present are common. Galvanized steel is rugged and, with care, can provide a decent service life.

Advantages of Galvanized Construction

Cost is the primary draw for galvanized steel Parshall flumes. In mid-range sizes, galvanized steel construction is about 3/4 the cost of fiberglass construction. For small flumes, labor is more of a deciding factor between galvanized steel and fiberglass – more so than material cost. On large sized flumes fiberglass can have lower capital costs when molds for the flume exist.

Galvanized steel flumes will always bet cheaper than stainless steel flumes. Here the labor is similar, so the primary difference is the cost of the raw material input.

Galvanized steel excels versus fiberglass when fire is used to burn back or clear plants and weeds around the watercourse.

The Need for Inspection and Maintenance

It is important to understand that to achieve maximum life from a galvanized steel flume, that the flume in general and the weld seams in particular should be periodically inspected for rust. This inspection can take place as part of a general inspection that should occur anyway to verify the flume is in good operating order. has not settled, flow conditions have not changed, area is free of encroaching vegetation, etc. Cold galvanization is not generally as durable as hot dipped galvanization so those areas were cold galvanization has been spot applied (usually seams and bends) should be given particular attention.

Once the protective zinc coating is breached, the oxidation process begins to attract the underlying steel. Unchecked, this rusting can lead to a failure of a flume's walls or floor, which not only affects the flow reading but also potentially lead to flow bypass or under cut as water erodes the surrounding channel.

cold galvanization of welds and seams on a 12-inch Parshall Flume

All welded seams should have cold galvanization thoroughly applied, extending well beyond the weld line. Smaller flumes can be hot dipped in their entirety after construction. Make sure that in moving the flume prior to installation that care is taken not to abrade the zinc coating. If the coating is penetrated, spot application of a cold galvanization product should occur.

The Case for Other Materials

Galvanized steel is not for marine, industrial discharge, leachate, or sanitary flows. Here the corrosion resistance of fiberglass or stainless steel is superior for the application.

Fiberglass construction can be lighter and easier to install than galvanized steel. Make sure that in moving a galvanized flume that care is taken not to abrade the zinc coating. If the coating is penetrated, spot application of a cold galvanization product should occur.

Attention to the zinc coating should continue after the flume in installed. As during installation and shipment, galvanized Parshall flumes should be inspect on a regular basis for signs of coating deterioration or rust.

As with any one-off construction, careful checking and rechecking of the flumes dimensions is required during the flume's construction. Unlike fiberglass where dimensions are set by the quality of the mold and are highly repeatable from part to part, galvanized steel flumes are not stock products where standardized precut pieces are available for welding. Each piece is cut as needed, introducing a greater potential for error.

fiberglass Parshall flume mold

What to Look for in a Galvanized Flume Manufacturer

In selecting a fabricator for a galvanized steel flume it is important to consider not only the fabrication expertise of the flume manufacturer, but also their support for the product. The dimensions of the Parshall flume are standardized and available in a variety of publications, but what is important here is that the manufacturer is well founded in the proper application of Parshall flumes. A dimensionally correct but poorly applied flume reads no better than poorly dimensioned one.

Look for:

Heavy gauge construction
External ribbing on larger Parshall flumes
Anchor clips to aid in installation
Application expertise
A variety of customer service options that fit the way YOU work
Warranty support

It is important that the manufacturer be able to provide both pre-sale application and post sales support for the installation. Questions commonly arise as a flume is being installed or after operation is underway. Many who use flume are not experienced in their use, so it is important that the manufacturer be thoroughly grounded in the use of the product and its proper application.

Customer service and the ability to get questions answered through multiple channels can be key!