Flow sensors are used by Wessex Water, a regional water and sewage treatment company, for confirmation of wash-water flow to plant and equipment. The thermal dispersion flow switch and the wash-water in the systems used either final effluent from the plant or partially treated water from some other point in the treatment process.
The water content and increase in temperature on the probe, however, was resulting in algae, which affected the thermal dispersion from the probes to the point where they no longer detected flow. Removal from the pipeline would traditionally involve the isolation and draining of the wash-water lines.
As a solution, Trant Construction identified that a non-intrusive, cost-effective and simple to operate sensor that would not be subject to fouling was required. Dave Rich from the company then discovered the Micronics DFS-ll Doppler Flow Switch, which is designed for ‘dirty liquids’, and agreed with the client to trial one unit for pipelines ranging from 32mm to 300mm, dependant on the velocity of flow through the pipe-work.
With the DFS-II, the sensing is non-invasive, working by injecting high frequency sound through the pipe wall into the flowing liquid. Acoustic pulses are continuously reflected back to the sensor and the device measures a frequency shift to calculate flow velocity. It controls flow without any drop in pressure, no sensor fouling and minimal maintenance. Installation takes just a few minutes because there is no need to cut into pipes.
As a result of the trial, Wessex Water is now using the Micronics clamp-on flow switches for most applications, including not only wash-water but also pump discharge monitoring where some non-return valves had proved to be unreliable.