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To help you focus on your flow numbers - and not how you got them - Openchannelflow flow has developed a wide range of accessories for our Weir Boxes.

These accessories cover a wide range of installation, site, and monitoring conditions - but keep in mind that we always have the ability to customize our products to meet your specific needs.

For applications where below grade flow monitoring is required, Openchannelflow offers fully integrated fiberglass Weir Metering Manholes.


End Connections

piped flow coming into the side of an Openchannelflow fiberglass weir box

Openchannelflow Weir Boxes can be provided with a variety of end connections, including pipe stubs, flanges, and caulking collars to connect to piping.  

Pipes can enter / exit a Weir Box along the centerline, off-axis, or from the side.  For applications where the pipes enter the Weir Box from the side or off-axis, additional baffling may be necessary.

pipe flow spilling into an Openchannelflow stainless steel weir box measuring dam seepageIn addition to piped connection, Openchannelflow Weir Boxes can be configured so that flow freely spills into or out of the box as necessary.  

For applications where flow spills into the Weir Box, a splash guard may be necessary to minimize turbulence (or potentially foaming ) in the main weir pool.


Flow Conditioning

While each Openchannelflow Weir Box comes standard with an underflow baffle, sometimes additional flow conditions is needed before the flow enters the main weir pool of the box. For those applications, Openchannelflow has developed a range of flow conditioning accessories.

Energy Absorber

An energy absorber is designed to place in the inlet of a Weir Box so that it can break up energetic flows.  The energy absorber is place directly in the flow stream so that the incoming piped flow hits the absorber, the flow is slowed, and then flows around the absorber and then further into the Weir Box.

Energy absorbers develop turbulence and non-uniform velocity profiles and should always used in conjunction with flow straighteners of baffles.  Also, energy absorbers should not be used on flows containing high solids as these will collect on the absorber plate.

Finally, the splashing turbulence generated by an energy absorber may require that a cover be placed over it.


perforated weir box baffles downstream of pipe stubs

Each Openchannelflow Weir Box comes standard with an underflow baffle.  Sometimes, however, additional condition is necessary to develop a more uniform velocity profile.  

In those cases, multiple underflow / overflow / serpentine baffles can be used in series. The baffles may be solid (for underflow / overflow / serpentine) or they can be perforated.


Flow / Level Accessories

Bubbler Tubes

A bubbler tube is a stainless steel assembly that is mounted to the sidewall of the Weir Box to allow an operator to connect the flexible tubing from their bubbler flow meter.

The bubbler tube extends to just below the crest of the weir plate and is secured in place by two nuts.

Staff / Head / Level Gauge

staff - level gauge in a fiberglass weir box manufactured by OpenchannelflowEssentially a ruler attached or molded into the side of a Weir Box that allows for a quick visual measurement of the level.  

With black numbers / gradation printed onto a high visibility yellow-green background, Openchannelflow staff gauges are designed to be easily read from a distance.  

The standard staff gauge is dual scale with centimeters, 1/10-foot, and 1/100-foot increments.  Staff gauges are also available with custom level and flow scales.

Stilling Well

A stilling well is a chamber (round or rectangular) off to the side of a Weir Box where flow measurement or parameter monitoring can be conducted.  Unlike a flume, which may require isolation of the flow from the flow stream, in a Weir Box the weir pool should already dampen surface waves and turbulence.  As a result, a stilling well on a Weir Box is more about providing a convenient point from which to monitor / sample from than it is about flow conditioning.

Stilling wells can be attached to the side of the Weir Box or they can be remote from it (detached) and are available in a range of sizes – from 6-inches [15.24 cm] and up.

The connection between the Weir Box and the stilling well is usually a 2-inch [5.08 cm] connection, although larger / smaller connections are available.

Ultrasonic Transducer Bracket

ultrasonic transducer bracket mounted on an Openchannelflow fiberglass weir box

An adjustable stainless steel bracket designed to hold ultrasonic transducers (and their separate temperature sensors) above a Weir Box or stilling well.  Transducers up to 1-inch [2.54 cm] can be accommodated with the standard bracket – with custom sensor holders available for larger sensors.

Openchannelflow ultrasonic transducer brackets have multiple degrees of freedom and can be mounted in horizontal or vertical positions and on uneven surfaces.


Parameter Monitoring

Probe Holder

prober holder - right - mounted in a fiberglass weir box manufactured by OpenchannelflowA stainless steel assembly mounted to the sidewall of a Weir Box that allows a parameter probe to be held rigidly in place.  

The probe holder is secured to the top flange of the Weir Box with two nuts while the probe is held in place by two stainless steel spring clips welded to the assembly.

Probe Well

A probe well is a small diameter tube on the outside of a Weir Box that allows a parameter probe to be slid into it without the need to unbolt / mount the probe (like a probe holder).  

Simpler and cheaper than a probe holder, a probe well is essentially a smaller version of a stilling well – with all of its advantages and disadvantages.

Sampler Tube

automatic sampler tube mounted in a fiberglass weir boxSimilar to a bubbler tube, a sampler tube is a rigid stainless steel assembly that is mounted to the sidewall of a Weir Box and it allows an operator to sample from the box using their standard flexible suction line. Sampler tubes are held in place by two nuts in the top flange of the Weir Box.  

Unlike a sampler strainer, a sampler tube has only one opening through which a sample can be drawn.  As a result, should the opening ever be clogged, no sample with is taken.




hinged aluminum cover over a fiberglass weir boxAvailable in bolt-down, hinged, and fixed configurations, Weir Box covers are one way of keeping debris, inflow (and prying hands) out .

Covers are available in a variety of materials and can be provided with hinged and fixed observation windows to operator access without the need to remove the cover.  

In applications were more operator access may be required, sections of the cover can be hinged (typically over the point of measurement) while the rest of the cover remains in place.

Dual / Triple Weir Boxes

Openchannelflow stainless steel double weir box For applications where multiple flow stream need to be measured in on location, Openchannelflow offers dual and triple weir boxes – where each flow stream enters / exits a self-contained weir pool.  

These side-by-side configurations can help to minimize the installation footprint. 

Recessed Grating

For installation where foot traffic will be present next to or around a Weir Box, recessed grating may be necessary to ensure operator safety.  Mounted into a recess at the top of the Weir Box, recessed grating is flush with the top of the box – eliminating any trip hazard while ensuring that the operator cannot accidentally fall into the structure.

Note that use of recessed grating may reduce the maximum flow capacity for standard Openchannelflow Weir Boxes as they intrude in the freeboard of the box.