E-mail jerry@freeflowinc.com Phone 800-933-4818 or 402-332-4818 Fax 402-332-3036
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Parshall flumes are designed for flow measurement in open channels. When setting the flume in concrete, pay attention to the following points: 1. The flume must be installed at the elevation specified by the engineer. Very small Parshall flumes can be set in place as follows: All-thread rods can be embedded in the concrete below the flume, with the rods aligning with the anchor clips on the flume's exterior. Either grout the rods in place below the flume or drill holes and epoxy them in place. After the all-thread rods are firmly anchored in place, the flume can then be locked in place and leveled by using a nut and washer on both sides of the anchor clips. The flume can then be grouted in place. The first pour of grout should just cover the bottom of the flume and allowed to set before additional pours are made. The finished surface should be sloped toward the flume so that any water will drain back into the flume. Installation procedure for larger Parshall flumes: The positioning procedure described above can also be used to secure larger flumes in
the correct position. Large flumes must also be weighted and lined on the interior to
prevent floating or distortion due to the grout's hydrostatic pressure. The sidewalls of flumes that are 2 ft. or taller must be lined and braced to prevent distortion Line the flume's interior with plywood sheeting and weight with sandbags or other weight. In small flumes additional weight can be positioned by placing a board across the top of the flume and using a 5 gal. bucket filled with sand or other heavy items. If there is any doubt as to the weight required, calculate the interior volume of the flume, from the bottom of the flume to the top of the first pour of grout. The weight required must be equal to the weight of the grout that is displaced by this volume. Grout is 2.5 times heavier than water. Water is 62 lbs./cu.ft., grout can be estimated at 155 lbs./cu.ft. If all-thread is not used a piece of "U" bent rebar can be placed through the anchor clip holes to insure that the flume is firmly locked into the grout. Weighting must be done if the all-thread is not used. The flume sidewalls must be lined and braced to prevent deformation due to grout pressure. A maximum lift of 6" of grout, with delay until grout is firm, on flumes with sidewalls 2 ft and taller.
Large Flume Installation Large flumes have large flat bottoms which require particular attention during installation. The buoyant forces of grout can cause a flume to float during installation. This usually results in less than optimum dimensional accuracy at the metering station. The anchor clips on the flume exterior are designed to secure the flume against the grout once it is cured. They will not prevent a flume from floating during installation. Consideration should be given to the following suggestions concerning flume installation. Channel or vault should be designed with adequate clearance at the sides to allow grout
placement and worker access for chaining during installation. This usually requires at
least 18" on each side.
Figure 1. Vault walls for approach section same width as flume inlet. Pour piers (perpendicular to flow) under area where flume is to be located. Top surface
of piers under crest of flume should be level, such that when flume is resting on them, it
will be at the correct elevation. Piers to be located so the floor of the flume rests on
piers, not the ribs. Set flume in place & check that flume crest is level in both directions. Shim where required.
Wire anchor clips on flume's underside to vault floor or place rebar bent into a "U" shape through the anchor clip. Check that flume's crest is still level. Run two chains from side to side on underside of flume for "chaining" during grouting. Chains should extend above to of flume, with enough additional length to allow a 2 man, side to side, "tug of war" for agitation. Vibrator sticks can be used in lieu of chaining. Line interior floor with plywood and adequately weight inside floor of flume to prevent floating during grouting. Weight must be adequate to resist buoyant forces of the grout. The density of grout results in a buoyancy 2.5X than of water. Pallets with 55 gal drums of water are a typical weight source. Only grout one section between piers at a time. The use a grout hose may be required.
Flow grout in from one side of flume only. Use vibrator sticks or agitate with chains against underside of flume to be sure all air pockets are removed & grout is in place along entire underside of section being grouted. Remove chains & let grout cure before proceeding to next section. Good concrete and grout techniques should be observed. Non-shrink grout is not
required. The use of plasticizers and too much water in grout can result in the excess
water coming out of the grout & pooling between the exterior of the flume floor and
the grout. It may result in an unwanted void after curing. Wire anchor clips on flume exterior walls, rebar, or place bent rebar through anchor clips. Line interior sidewalls of flume with plywood & 2x4's to prevent distortion. Grout sidewalls in 6" lifts, letting each lift cure before proceeding. The finished surface even with the top of the flume should be sloped toward the flume so that any water will drain back into the flume.
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