Once, visiting a plant equipped with scrapers, we realized that these were not operating continuously and that the owners decided to stop them every once and a while. When we asked them why, they were not able to give us any technical reason that justified the stopping.
From our experience, we can say that the answer to the question is yes. Scrapers need to be constantly in operation and the example below will leave no doubts as to why it is so.
We recently participated in a lamella clarification project. The project had to integrate circular central-axle scrapers, i.e. 4 units of 18 meters of diameter each.
Before making an offer, TecnoConverting Engineering always studies the technical feasibility of the project. This is why we request a variety of information such as flow, suspended solids, clarifiers height, clarifiers measures, type of water to be treated, etc. In this particular case the total flow rate was 6.030 m3/h with a concentration of SS of 10,000 ppm.
From this data, we determined that each scraper would have to extract 18,090 kg/hour of sludge. And that, if the scraper stopped working for two hours, it would have 36 tons of accumulated sludge, which was obviously impossible to handle.
When a scraper restarts after being on hold for a while, the torque limiter could activate. This is normal because of the amount of accumulated sludge. That is why we recommended cleaning it before restarting the equipment.