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 Parshall flumes.
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 meet your specific needs.
For applications where below grade flow monitoring is required, Openchannelflow offers Parshall flumes integrated into our fiberglass Packaged Metering Manholes. For above grade installations, smaller flumes can be integrated into fiberglass enclosures.
The end connections for Parshall flumes revolve around the end adapter. The adapters are rectangular structures that attach to the end of the flume and that allow the flow to be transitioned into / out of the flume in a controlled manner.
End adapters can be provided with pipe stubs, flanges, or caulking collars to connect to piping. Additionally, open-ended end adapters are also available.
In addition to transitioning flow into / out of the flume, end adapters are also convenient locations to mount other accessories that otherwise would not fit in the flume itself.
Taking our standard end adapter, a curved is molded into the piece so that the flume can now be directly connected to a manhole wall – eliminating the need to either form a transition or have a pipe connection to the flume.
Staged transitions are available for select combinations of flume size and manhole diameters. Contact Openchannelflow for additional details.
Wing walls are radiused (or flat) plates that are attached to the end of the flume to direct flow into or out of the flume from the channel its installed in.
Wing walls can be factory attached or shipped loosed for field installation as required.
Inlet wing walls should always be of the radius type. Research has shown that flat 45º inlet wing walls can adversely affect flow in the converging section of the flume.
A key requirement for a Parshall flume to operate correctly is for the flow to sub-critical, tranquil, and well developed (uniform velocity profile) - but many times the space available for the installation doesn’t allow this to happen. For those applications, Openchannelflow has developed a range of flow conditioning accessories.
An energy absorber is designed break up energetic flows from inlet pipes. The energy absorber is place directly in the flow stream so that the incoming pipe flow hits the absorber, the flow is slowed, and then flows into the flume.
Energy absorbers develop turbulence and non-uniform velocity profiles and should always be used in conjunction with flow straighteners. Also, energy absorbers shouldn't 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.
When the flow entering a flume is unbalanced, flow straighteners installed upstream of the flume serve to break up the incoming flow pattern and force it into parallel lines as it enters the flume. These straighteners are usually used in sets of two or more to maximize the flow conditioning.
Like energy absorbers, flow straighteners shouldn't be used on flows containing large or sanitary solids. They also shouldn't be used on flows with floating debris.
Small Parshall flumes present a problem when it comes to conditioning the flow, as there isn't much space available for more traditional control accessories (energy absorbers and flow straighteners) to be installed.
For these applications a series of perforated plates can be installed to first slow down / break up the velocity profile and then straighten out the flow as it enters the flume.
Flow / Level Accessories
A bubbler tube is a stainless steel assembly used in conjunction with a bubbler flow meter that's mounted in a cavity molded into the sidewall of a flume. The tube extends down to the floor of the flume and is secured in place by two nuts in the top flange of the flume.
Rigid and recessed from the main flow stream, a bubbler tube allows the operator to connect the usual vinyl / Teflon tubing from their bubbler flow meter to the flume.
Essentially a ruler attached or molded into the side of a flume 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.
A stilling well is a chamber (round or rectangular) off to the side of a flume where flow measurement or parameter monitoring can be conducted. Isolated from the main flow of the flume, the level in a stilling well is quite – with surface waves and turbulence eliminated.
Stilling wells can be attached to the side of the flume 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 flume and the stilling well is usually a 2-inch [5.08 cm] connection, although larger / smaller connections are available.
The floor of a stilling well is usually recessed below that of the flume so that there's standing water in the well at all times – even when there is no flow in the flume itself. This body of water can help to keep parameter probes wetted.
Stilling wells are not for use on sanitary flows (clogging) or flows with high solids contents (sedimentation). Periodic flushing / maintenance may be required.
An adjustable stainless steel bracket designed to hold ultrasonic transducers (and their separate temperature sensors) above a flume 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.
A stainless steel assembly recessed into the sidewall of a flume that allows a parameter probe to be held rigidly in place. The probe holder is secured to the top flange of the flume with two nuts, while the probe is held by two stainless steel spring clips welded to the assembly.
Probe holders are preferable to probe wells in applications where sedimentation may occur. Probe holders are not, however, recommended in applications where ragging solids are present.
A probe well is a small diameter tube molded on the outside of a flume 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.
Similar to a bubbler tube, a sampler tube is a rigid stainless steel assembly that can be mounted in a cavity molded into the sidewall of a flume. The tube extended down to the floor of the flume and is secured in place by two nuts in the top flange of the flume.
Recessed from the main flow stream, a sampler tube allows an operator to sample from the flume with standard suction line.
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.
Available in bolt-down, hinged, and fixed configurations flume covers are one way of keeping debris, inflow, and prying hands out of a flume.
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 is needed, sections of a flume cover can be hinged (typically over the point of measurement) while the rest of the cover remains in place, or the cover can be segmented to allow specific sections to be removed.
For above grade industrial flow stations, Openchannelflow offers fiberglass enclosures with integrated Parshall flumes. 1-inch or 2-inch Parshall flumes are available factory mounted in a Redstone Equipment Enclosure. The result is a complete turn-key flow measurement package.
As a flume gets larger it gets heavier. This can make it both cumbersome and difficult to transport it to a remote site or to install it in a confined space. For these applications Openchannelflow offers flume sectioning. Sectioning a flume breaks it down into manageable sections that are later field assembled.
For Parshall flumes the converging section is usually one piece, while the throat / diverging sections one or more additional pieces. Should it be necessary, the walls may be sectioned from floor sections and the floor sectioned into multiple pieces.
The hourglass shape of the Parshall flume lends itself to a unique application – the dual range flume. Here a smaller Parshall flume is nested inside a larger, outer Parshall flume.
The result is an installation that can accurately measure lower flow rates and as time goes by and the flow rates increase can accurately measure those as well.
Nested flumes are usually used in applications where the flow will trend one way or the other over time (subdivision build out or water conservation), but they can also be used in applications where there is a defined pattern of widely varying flows (resorts).
When a flume is installed in an area subject to foot traffic, recessed grating may be necessary to ensure operator safety. Mounted into a recess molded in at the top of the flume, the grating is flush with the top of the flume – eliminating any trip hazard and ensuring that the operator cannot accidentally fall into the flume.
Larger Parshall flumes may require the use of multiple sections of grating while smaller Parshall flumes may have the grating as one continuous piece.
For Parshall flumes, replacement floors can consist of just the converging section or the entire flume floor.
On larger flumes, replacement floors may be sectioned to aid in installation.
While ASTM D1941 prescribes standard sidewall heights for Parshall flumes, there are times when a flume needs to be shorter or taller to meet the needs of an installation. For these cases Openchannelflow offers modified sidewall heights.
Irrigation flumes are the most common use of modified sidewalls (usually half height), although other applications may call for them.
While not verified by research, extended height sidewalls are one means of obtaining higher maximum flow rates without increasing an installation's footprint.