Corrosion Resistant FRP Parshall Flumes

Used in monitoring sewage, plant effluent, storm water and irrigation water the Parshall flume is still the best known and most widely used for permanent installations. It is available in throat sizes from 1 inch to 12 feet. Parshall flumes are available with numerous accessories and adaptations to match your flow and installation requirements. Made of fiberglass reinforced polyester (FRP) Plasti-Fab Parshall flumes offer optimum corrosion resistance and are the industry leader in measuring flow. For extremely severe industrial effluents they are also available in Vinyl Ester, stainless steel or other special materials as needed.

Parshall flumes solve a broad range of flow and installation problems:

• Permanent installation in concrete or earthen channels
• "Montana" or short section flumes for certain space critical locations
• Free standing flumes with Wing Wall or End Adapters
• H_a Head Gage - permanently molded into the side of the flume ensures a smooth sidewall
• Nested Flumes for planned future expansion or downsizing due to water conservation
• End Adapters for Piped Installation - From 1" to 36" throat size
• Packaged Metering Manholes for below grade installation - From 1" to 36" throat
• "Magic Bottom" to cure Submergence or Leveling problems
• Tranquilizer Racks or Energy Absorbing units to reduce turbulence or velocity

Other Accessories and Instrument Setups:

• Adjustable stainless steel Support Brackets for all types of ultrasonic transducers
• Molded Side Cavities and Floor Cavities for:
Stainless steel bubble pipes
Stainless steel sample pipes
Pressure transducers
Capacitance probes and s/s grounding plates
pH probes

• Stainless steel Liftout Brackets for pressure and pH probes
• 2" Threaded Tap for remote still well
• 8" and 12" diameter attached Still Wells
• Hb Head Gage for Submerged Flow Monitoring
• Sealed Ultrasonic Mounting Tube
• FRP Grating
• FRP Flume Covers

Head Gages

Supplied on all Plasti-Fab flumes, the head gauge is molded into the side of the flume during the first stage of construction, ensuring a smooth side-wall surface.

Free Flow vs Submerged Flow

In the free flow condition, the downstream water level does not adversly affect the level of the water upstream.

Technically speaking, in free flow the flow of water passes through critical depth, usually near the flume crest (the entrance to the throat).

In the submerged flow condition, the water tail depth is sufficiently high to affect the upstream depth, and it is therefore necessary to measure head at two places in the flume to determine the flow (Ha and Hb).

The point at which the flow changes from free flow to submerged flow is called transition submergence and is expressed as a percentage, which is the ratio Hb/Ha. In the range of sizes from 1 inch to 8 feet, this ratio varies from 55% to 78%. In all sizes above 10 feet, transition submergence is 80%.

Submerged flow calibration curves are available for each of the standard flume sizes. (Source: Utah Water Lab.) While some instrumentation is now available to record submerged flow electronically, Plasti-Fab engineers encourage our clients to design for free flow whenever possible.

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