The installation of a Palmer-Bowlus flume is a straight forward and can be accomplished with a minimum of effort. The straight-through, u-channel design means that there are no changes in elevation to accommodate and that the flume is well suited for installation in manhole U-channels and on piped flows.
The installation itself can be broken down into four parts:
Setting the Flume
The Palmer-Bowlus flume should be set so that the ramp in the throat of the flume is level from side-to-side and from front-to-back. While true of flumes in general, this is particularly true of Palmer-Bowlus flumes as studies have not been published on the effects of flume slope on measurement accuracy (as there have been for Parshall and Cutthroat flumes).
On Permanent style Palmer-Bowlus flumes anchor clips are bonded to the outside of the flume to assist in level / securing the flume. Wire or threaded rod can be run through the holes in the anchor clips to ensure that flume is level and does not shift out of place.
For applications where the flume is to be free-standing (not encased in grout / concrete), small to medium sized Palmer-Bowlus flumes can be secured solely through the use of threaded rod through the anchor clips.
Cribbing the Flume
With the flume in place and its level verified, cribbing should be placed inside the flume. Cribbing ensures that the flume does not distort during installation (fiberglass retains some plasticity even after cured and on larger flumes it is possible to distort the sidewalls). The rounded cross-section of the Palmer-Bowlus, combined with the geometry of the throat ramp, make it less likely that the flume will distort during installation, but that shouldn’t imply that it is a step that should be overlooked.
Palmer-Bowlus flumes require 25 diameters of straight run pipe/channel upstream of the flume. In the upstream pipe, there should be no bends, dips, elbows, or change in slope. Other flumes may have shorter rule-of-thumb upstream requirements (3-5 for HS / H Type flumes) (15 for Parshall / Montana, Trapezoidal, and Cutthroat flumes), but the Palmer-Bowlus should not be shorted.
There are five ways of directing flow into / out of Palmer-Bowlus flume: grout/concrete formed transition, nesting the flume in an existing pipe/U-channel, pipe stubs (with flexible couplings), flanges, and caulking collars.
In the formed transition the flume is placed in its desired location and then u-channel is formed upstream / downstream of the flume in grout or concrete. Although low cost, this method does require that some care be taken – particularly on the upstream side – in make a smooth transition into the flume. Where the pipe is smaller / larger than the width of the flume, a gradual transition must be formed. Formed transitions are suitable for 4D+1-inch Permanent style Palmer-Bowlus flumes.
Nesting the flume in an existing pipe or u-channel can be cost effective – so long at the channel is sufficiently straight an uniform upstream of the flume itself. With nesting installation, the upstream pipe / channel effectively forms part of the flume. The point of measurement for the flume will be in the upstream pipe / channel, D/2 upstream of the flume ramp (where D = flume size). With the point of measurement upstream of the flume itself, molded-in accessories such as bubbler tubes and staff gauges cannot be used as there is no way to factory mount therm. Nested installation is only for 2D+2-inch length Insert and Cuttback style Palmer-Bowlus flumes.
Pipe stubs with flexible couplings are the most common connection method for Palmer-Bowlus flumes. Here a pipe stub is laminated to the inlet / outlet of the flume to mate up to the line piping. A flexible coupling is provided with stainless steel clamps to seal the connection between the two pipes and make it watertight.
As the pipe connection is made upstream of the point of measurement, upstream pipe stub connections are only possible with Palmer-Bowlus flumes from 3D+1-inch to 4D+1-inch (the standard lay length) long. Shorter permanent style 2D+2-inch Palmer-Bowlus flumes can only have outlet pipe stubs, as there is no place on the flume inlet to mount the pipe stub to.
Alternatively, flanges may be provided where a rigid connection is required or where the materials of construction available for the standard flexible coupling are not suitable with the process conditions. Like pipe stub connections, inlet flanges can only be supplied with 4D+1-inch Permanent style Palmer-Bowlus flumes. Outlet flanges can be supplied for both 2D+2-inch and 4D+1-inch Permanent style flumes.
On very rare occasions caulking collars may be provided. Here oversized pipe stubs are provided into which the line piping is slid. The annular space between the two pipes is then packed with a watertight compound or material (i.e. oakum). Inlet / outlet connection availability is the same as for pipe stubs and flanges.
Exiting a Palmer-Bowlus flume, the pipe should continue for an additional 5-20 pipe diameters. The downstream slope should be as great or greater than in the inlet slope. The idea here is to ensure that flow does not back up into the flume. Although Palmer-Bowlus flumes have a relatively high resistance to submergence, there are no corrections available should the flume become submerged.
Pouring a Bench
With the flume set and connections to the upstream / downstream channel made, the last step is to pour a bench around the flume. A bench around the flume serves two purposes:
- It provides a convenient place from which maintenance personnel can service the flume
- Should there be any back-up of flow due to a downstream blockage, a bench allows for the flow to be directed back into the flume and down the discharge line once the blockage had been cleared
When pouring the bench around the flume, make sure to keep the flume free of grout / concrete. Any debris that accidently gets into the flume during the pouring of the bench should be immediately cleaned out before it sets.
With the wide variety of styles availabe for the Palmer-Bowlus flume, not all of the steps above may apply to any given applcation. There are, however, certain universal considerations: the flume must be level, the flow approach the flume should be tranquil and well conditioned, and flow should not be allowed to back up into the flume. With these in mind, your installation should be successfull.