The Parshall Flume is the most common type of flume used for monitoring industrial discharges. The ubiquity of the Parshall flume means that it is usually well understood by pretreatment inspectors and industrial users alike – not an insignificant consideration – and is well supported by flow meter manufacturers.
Parshall flumes can be installed in concrete channels or connected to piping. They are suitable for both below grade and above grade installations (where sufficient head is available).
The typical installation is below grade in a manhole (fiberglass packaged metering or existing concrete) outside of the plant building but before the municipal sewer line.
Fiberglass (FRP) Parshall Flume Measuring Slaughterhouse Effluent
Common Size
The most common size of Parshall flume used in industrial pretreatment monitoring is the 3-inch Parshall flume. The flume has a good range of flows - 12.55 to 834.7 gpm [0.7918 to 52.67 l/s], is accurate (+/-3-5%), and is versatile in its configuration (being available plain, with wing walls, and with end adapters). The flume is usually supplied with end adapters and pipe stubs to connect to 6 or 8-inch [15.24 or 20.32 cm] pipe.
Flume Cost
Below are prices for the two most common configurations - the 3-inch Parsall flume by itself and the same flume with end adapters and pipe stubs to connect to piping.
| Flume Size / Configuration | Cost |
| 3-inch Parshall | $1,120 |
| 3-inch Parshall flume with inlet / outlet end adapters | $2,800 |
Bakery Effluent Measured by a Parshall Flume in a Concrete Manhole
These prices do not include accessories or mounting options for flow meters, but they are representative of what an industrial customer should expect to pay.
Sanitary Solids
For industrial applications where sanitary solids are in the flow stream, the 3-inch Parshall flume is the smallest size that should be used. If a 1-inch or 2-inch Parshall flume is used on sanitary solids it is simply a matter of when, not if, the flume will clog.
If the flows are expected to be below 12.55 gpm [0.7918 l/s] (the minimum flow rate for the 3-inch Parshall flume) a Trapezoidal flume is usually a better choice.
Fiberglass Metering Manholes
While the 3-inch Parshall is the most common flume used to measure industrial discharges, when provided with end adapters to connect to the usual 6 or 8-inch [15.24 or 20.32 cm] pipe the flume is too large to fit into a 4-foot [1.22 m] diameter manhole. This rules out many of the existing manholes that an industry might otherwise consider installing a flume in.
One solution can be a fiberglass packaged metering manhole. Here the flume is factory integrated into a fiberglass manhole. The resulting unit is single piece, watertight, lightweight, and corrosion resistant.
The all fiberglass construction means that flumes larger than the manhole’s diameter can be integrated in the structure – with any portions of the extending upstream / downstream of the barrel provided with a water tight cover and laminated to the manhole barrel. Fiberglass manholes ensure that the flume is installed correctly and have the added benefit of single source responsibility.
Plant downtime is kept to a minimum. The site can be prepared (area excavated and slab poured) prior to the actual installation. With the site prepped, the only line downtime needed is that required to cut the pipe, move the manhole into place, and secure the flexible couplings. With a well-prepared installer, this can be a little as 30 minutes. Once the couplings are in place, flow can resume – even while the manhole is being secured to the slab and the excavation backfilled!
Metering Manhole Cost
Pricing for flow metering manholes is a little more complicated as there are a wider variety of opptions / factors to consider (including top style, depth, etc.). Below is pricing for a common industrial metering manhole configuration.
| Manhole Configuration | Cost |
|
$9,950 |
While pricing can vary greatly dending upon a variety of factors, including flume size, manhole diameter, manhole depth, pipe size, the price is representative of what an industrial customer should expect to pay.
