Mosbaek's range of flow regulators are designed such that they cover almost complete any perceivable control need. The head-discharge curves are considerably steeper than those of e.g. throttle pipes or gates.
This is how the cyclone flow regulator functions:
When the normal, small flow - the dry weather flow - passes in the sewage pipe, the water surface is below the top of the controller inlet opening, and there is virtually no resistance to the flow (figure 1).
When it starts raining the feed flow increases - the water level in front of the regulator increases - and when the water surface is above the top of the regulators inlet opening, but is still below the top of the controller vortex chamber - air is trapped inside the vortex chamber, and the flow cross section is reduced. This increased resistance limits the flow through the regulator (figure 2).
When the water surface in front of the flow regulator rises to above the top of the vortex chamber, the head will make the water in the regulator rotate. The entrapped air forms a core in the cyclone flow regulator and the flow cross section is heavily reduced at the outlet. The result is a considerable pressure loss, as intended (figure 3).
After the rain has stopped the feed flow decreases. The water level in the structure eventually falls below the top of the vortex chamber and due to the dropping pressure the vortex collapses. Air is drawn into the vortex chamber - with some delay - hence the hysteresis in the head-discharge curve, figure 4.
The collapse of the vortex produces a sudden increase in the flow through the regulator whereby any deposited sediment in the upstream pipe system will be flushed out. See the characteristic 'bump' on the head-discharge curve, figure 5.