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Openchannelflow offers an ever-expanding series of accessories for our line of Palmer-Bowlus 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 to meet your specific needs.

For applications where below grade flow monitoring is required, Openchannelflow offers Palmer-Bowlus flumes integrated into our fiberglass Packaged Metering Manholes.


End Connections


bulkheads with pipe stubs on an Openchannelflow fiberglass Palmer-Bowlus flumeBulkheads are flat plates bonded to the inlet / outlet of a Palmer-Bowlus flume to allow the flume to mount pipe stubs, flanges, or caulking collars.  Bulkhead can also be drilled to connect to flanges or vertical walls.  

Bulkheads are only available on Permanent Style Palmer-Bowlus flumes.  Inlet bulkheads are only available on Permanent Style flumes with approach sections.  Outlet bulkheads are available on Permanent Style Palmer-Bowlus flumes.  

Bulkheads are not available for Insert or Cutback Style Palmer-Bowlus flumes as there are no end flanges to which they can be bonded.

Staged Manhole Transitions

To mount a Palmer-Bowlus flume to a manhole wall, a curve is molded into the inlet flume so that it be directly bolted to the wall – eliminating the need to either form a transition or have a pipe connection to the flume.  

Staged transitions are available for select sizes of Permanent Style Palmer Bowlus flumes with approach section and manhole diameters.  Contact Openchannelflow for additional details.


Flow Conditioning

Palmer-Bowlus flumes are more sensitive than other flume types to variations in the approaching flow.  To help ensure that the flow is sub-critical, tranquil, and well developed (uniform velocity profile) Openchannelflow has developed a range of flow conditioning accessories.

The flow conditioning accessories below may require channel extensions at the inlet of the flume.

Energy Absorber

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 piped flow hits the absorber, the flow is slowed, flows around the absorber and then 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 should not be used on flows with ragging 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.

Flow Straightener

removable stainless steel flow straighteners in a fiberglass Palmer-Bowlus flumeFor a Palmer-Bowlus to operate correctly, the flow into the flume must be well distributed across the inlet of the flume.  Sometimes, however, upstream channel or pipe configurations mean that the flow entering the flume is unbalanced.  

Flow straighteners (usually used in sets of two or more) installed upstream of the flume serve to break up the incoming flow pattern and force it into parallel lines as it enters the flume.  

Like energy absorbers, flow straighteners should not be used on flow containing large or sanitary solids.  They should also not be used on flows with floating debris.

Perforated Plate

Small Palmer-Bowlus 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 tranquilizing racks).  

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

Bubbler Tubes

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.

Staff / Level / Head Gauge

staff gauge in a 24-inch Palmer-Bowlus flumeEssentially 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 and is corrected for the curve of the flume sidewall.  Custom level and flow scales are available.

Stilling Well

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 is always standing water in the stilling 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.

Ultrasonic Sensor Bracket

ultrasonic bracket over a Palmer-Bowlus flumeAn 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.


Parameter Monitoring

Probe Holder

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.

Probe Well

probe well on a Palmer-Bowlus flumeA 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.

Sampler Tube

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.



Flume Covers

cover over a Palmer-Bowlus flume in a fiberglass packaged metering manholeBolt down covers offer a clean way to ensure that debris or infiltration do not enter a flume in above ground applications.  Bolt down covers can sit flush with the top of the flume or can be provided with neoprene gasketing between the cover and the top of the flume.

Materials available include fiberglass and clear or tinted polycarbonate (Lexan).  All bolt down covers are held in place through a series of free (non-encapsulated) stainless steel hex bolts for quick cover removal. 

As an option, covers may be segmented so that just the section of interest can be removed – leaving the other cover sections in place.

Flume Enclosure

nested Palmer-Bowlus flumes in a Redstone fiberglass flume enclosureAbove ground, small pipe flows can be a particular problem to measure.  For flows containing sanitary or process solids this problem is compounded as weir boxes are not suitable for use on solids laden flows.

To address this need, Openchannelflow offers the integration of small Palmer-Bowlus flumes in a Redstone Equipment Enclosure.  The packaged unit allows for the measurement of flows in a structure that is safe, secure, and away from prying eyes (and fingers).  

Available for 4 to 10-inch Palmer Bowlus flumes.

Multi-Piece Flumes

As Palmer-Bowlus flumes get larger they can be difficult to move to the installation site.  Additionally, flumes for retrofit into existing manholes and vaults may sometimes be too large to pass through the structure's entrance.  For these instances, Openchannelflow offers sectioning.  Sectioning breaks the flume down into smaller, easier to manage sections for assembly in the field.

Exterior flanges are provided for each flume section and pre-drilled at the factory so that they align in the field.  These flanges must be field sealed to ensure watertightness.  Stainless steel connection hardware is provided.

Nested (Dual Range) Flumes

nested palmer-bolwus flumesThe constant profile of the Palmer-Bowlus flume lends itself to a unique application – the dual range flume.  Here a smaller (shortened) Palmer-Bowlus flume is nested inside a larger, outer 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).  

Riser Boxes

Riser boxes add height to a Permanent Style with Approach Section to allow for shallow burial of the flume when the line to be measured in not far below grade.  Riser boxes can add up to 3-feet of additional height to the flume. The use of a Riser Box can eliminate the need to encapsulate the flume in a shallow concrete vault or manhole.

Recessed Grating

When foot traffic will be next to or around a flume, recessed grating may be necessary to ensure operator safety.  Mounted into a recess 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 flumes may require the use of multiple sections of grating while smaller flumes may have the grating as one continuous piece.