The PURAIN Rainwater filter, also known as the hydraulic jump filter, is the innovation for roof areas ranging from 60m² to more than 15.000m².
This hydraulic jump technology cleans itself automatically. The design model for PURAIN Rainwater filters comes from nature: At almost every course in a stream, you can see how the hydraulic jump functions. The water flows over one of the stones, smooth and rounded by the action of the water over time. The water flow is substantially changed by the height drop, from a sub-critical to a super- critical flow. At the bottom of the dip, the waterflow changes again to a subcritical flow in a process now commonly known as hydraulic jump. This resulting increase in water power forces any impurities over the next level and washes them away downstream.