Bubbler style flow meters provide the most accurate measurement of level in open channel applications; more accurate than ultrasonic or even pressure transducer flow meters. Using an internal air compressor to push a measured volume of air through a vinyl or Teflon bubbler line, the meter measures the pressure needed to force air out of the line.
In a flume or weir where the bubbler meter is to be used, the vinyl or Teflon bubbler line is too flexible and must be connected to a stainless steel bubbler tube assembly which is rigidly mounted to the flume / weir.
The weak point of bubbler tube designs is the compression coupling used to connect the smaller, 1/8" OD tube to the larger (typically 1/4" OD) main tube.
Unless care is taken in assembling one of these designs, the threads of the compression coupling can cross thread. Even if the coupling is backed off and reinstalled, the damage has usually been done. Given the cost of the couplings, experience has shown that they still end up shipping - even with the potential problem present - as production workers are loath to explain why an expensive coupling is being thrown away.
The slow leak that results from a compression coupling installation failure can be a real headscratcher when trying to troubleshoot a flow meter installation. The slow leak presents itself as an unexplained difference in indicated depth (and subsequently flow rate). Unless the bubbler tube is removed and the compression coupling submerged to check for airtightness, it is unlikely that the leak will be easily found.
Another problem present in many bubbler tube designs is the thin walled tubing used for the main tube. In storm water applications or stream gauging applications where larger debris, solids, or rocks may be present, the thin walled tubing can be deformed - again presenting as a difference in depth in the flume or weir. Damage during transit, handling, or installation can also end up crimping the main tube or deforming the connection where the compression coupling meets the main bubbler tube.
To solve these problems, Openchannelflow has designed a bubbler flow meter tube that is unique in the marketplace. The tube is one continuous piece of thick walled tubing. The top of the bubbler tube - where the traditional compression coupling is found - is swaged to reduce the OD to 1/8". The main body of the tube remains at 1/4".
Eliminating the compression coupling not only eliminates a potential source of air leakage, but the increased wall thickness in the swaged section increases the mechanical strength and stiffness of the most vulnerable portion of the bubbler tube. Bending or deformation due to shipping, handling, or installation problems are essentially eliminated.
Openchannelflow bubbler flow meter tubes are available for all flumes, weir boxes, and weir channels. In addition, freestanding bubbler tubes are also available as are copper bubbler tubes for applicaitons where marine growth is a concern.
