How do you size a Parshall flume?

Parshall flume sizes are designated by the throat width, W, and dimensions are available for flumes from the 1-in size for free flow of 0.03 ft3/s at 0.2 ft of measuring head up to the 50-ft size with 3,000 ft3/s at a head of 5.7 ft.

How accurate is a Parshall flume?

Parshall Flume Accuracy Under laboratory conditions, Parshall Flumes can be to be accurate to within +/-2%. However, practical considerations such as approach flow, installation, and dimensional tolerances result in free-flow accuracies of +/-5% (per ASTM D1941).

Why are Parshall flumes the most common flow measuring devices?

Parshall Flumes are commonly used for a number of reasons: Most municipal operators are exposed to them during their initial training. The flat bottom makes determining the water level simple and straightforward. The Parshall Flume has a single point of measurement.

What is a Parshall flume explain how do you measure water discharge using a Parshall flume?

A Parshall Flume is a fixed, hydraulic structure used to measure water flow in an open channel or non-full pipe. The flume accelerates flow by both a contraction of the parallel sidewalls and a drop in the throat’s floor elevation.

How do you calculate flume flow rate?

Parshall flume discharge values For free flow, the equation to determine the flow rate is simply Q = CHan where: Q is flow rate (ft3/s) C is the free-flow coefficient for the flume (see Table 1 below) Ha is the head at the primary point of measurement (ft)

What is the slope of a throat for metering flumes?

What is the slope of a throat? Explanation: By using the masonry walls the normal section of the channel is narrowed with a slope of 1:1 to 2:1 to a rectangular section known as the throat. 3. After the throat the channel is diverged to avoid the loss of head in the flume.

How does Parshall flume work?

The Parshall flume is a fixed hydraulic structure. The Parshall flume accelerates flow through a contraction of both the parallel sidewalls and a drop in the floor at the flume throat. Under free-flow conditions the depth of water at specified location upstream of the flume throat can be converted to a rate of flow.

What is the advantage of cut throat flume over Parshall flume?

Available Sizes The range of 16 sizes does not cover flow rates as large as the middle to upper end Parshall flumes. A distinct advantage of the Cutthroat flume is the ability to interpolate between throat widths for a given flume length to obtain intermediat size flumes.

What does a Parshall flume measure?

The Parshall flume is an open channel flow metering device that was developed to measure the flow of surface waters and irrigation flows. It is used to measure volumetric flow rate in industrial discharges, municipal sewer lines, and influent/effluent flows in wastewater treatment plants.

What are the advantages and disadvantages of Parshall flume?

The advantages of the Parshall flume are: (1) it passes sediment and small trash easily, (2) it requires only a small head loss, and (3) it allows accurate flow measurements even when partially submerged. A disadvantage of the Parshall flume is that it is not accurate at low flow rates.

What is flume width?

Flumes are used to measure flow rate (discharge) in open channels. They typically have widths from a few cm to 15 m or so. The water depth in the approach section of flumes typically can be between a few cm and about 2 m.

What is slope of a throat?

Explanation: By using the masonry walls the normal section of the channel is narrowed with a slope of 1:1 to 2:1 to a rectangular section known as the throat. 3. After the throat the channel is diverged to avoid the loss of head in the flume.

How big is the head of a Parshall flume?

Parshall flume sizes are designated by the throat width, W, and dimensions are available for flumes from the 1-in size for free flow of 0.03 ft3/s at 0.2 ft of measuring head up to the 50-ft size with 3,000 ft3/s at a head of 5.7 ft. The free-flow discharge

What are the dimensional tolerances for Parshall flumes?

DIMENSIONAL TOLERANCES ASTM D1941 requires that Parshall flume dimensions be within 2% of nominal, while JIS B7553 requires tolerance of +/- 1 to 1.5%, depending upon flume size. Parshall flumes with dimensions outside of these ranges should be considered to be non-conforming and should be either replaced or field rated.

How to calculate the flow rate of Parshall flume?

For free flow, the equation to determine the flow rate is simply Q = CH an where: 1 Q is flow rate (ft 3 /s) 2 C is the free-flow coefficient for the flume (see Table 1 below) 3 H a is the head at the primary point of measurement (ft)

When did dr.parshall make his first flume?

Starting in 1915 with the sub-critical Venturi flume, Dr. Parshall made a series of modifications which lead, six years later, to his filing of a patent for his new “Parshall Flume”. Over the years Dr. Parshall’s work has been extended to flumes both larger and smaller than his original investigations.