This year marks the 50th anniversary of an idea that changed concepts and practices in flood control, while leading to the creation of one of the surface-water and wastewater industry’s most important devices – the “vortex water brake,” also known as the flow regulator.

The year was 1959 and Joergen Mosbaek Johannessen was an engineering student in Denmark. He was assigned to design a flood control solution for a local villa, and as he tried to unravel the difficult puzzle he remembered how his mother would collect and hold rainwater in a tub for rinsing the family’s clothes. He thought, “What if the rainwater runoff at the villa could be controlled by directing it to a small storage tank?” It could then be discharged at a safe, steady rate into the main sewer lines. The villa would have a cost-effective solution because it could use smaller, less expensive pipes and there would be no more property damage.

But the system for discharging the water into the sewer lines in a steady, regulated manner did not exist. So in 1969 Joergen invented the device he called the vortex water brake and launched a new, never-seen-before approach to managing stormwater runoff in sewer systems.

In 1971, Joergen submitted his designs and ideas in his first patent application. By 1975, Mosbaek was licensing flow regulators under the brand name HYDRO-BRAKE through a series of international agreements. In 1993 he began managing his own manufacturing facility in Denmark, marketing Mosbaek (www.mosbaek.com) products and services throughout the world.



Today, Mosbaek produces approximately 1,600 units each year and can increase its capacity to 3,000-3,500 units annually as sales grow. It has market share of 25 percent or more in many countries, and has sold 16,500 regulators designed and built to customer specifications. The production system has also evolved over time to be highly efficient and streamlined: it typically takes three to four weeks from initial contact with Mosbaek’s technical consultants through completion of manufacturing and shipping.

In its latest growth move, Mosbaek last year launched a North American division based in Atlanta, Georgia – Mosbaek North America, Inc. – and is actively marketing its products and consulting services to customers across the United States and Canada.

How the Cyclone Flow Regulator Works


During low and dry weather flows, the water surface elevation is well below the top of the regulator inlet opening and there is virtually no resistance to the flow or increase in head (Figure 1).

As the rainfall intensity increases, the flowrate upstream of the regulator also increases, as does the head on the regulator. When the water surface elevation is above the top of the regulator’s intake opening, but is still below the top of the vortex chamber, air is trapped inside the vortex chamber and the flow’s cross section is reduced. This increased resistance limits the flowrate through the regulator (Figure 2).

When the water surface elevation in front of the flow regulator rises above the top of the vortex chamber, the head will induce vortex flow inside the regulator. The trapped air forms a core in the vortex chamber and the flow’s cross-section is heavily reduced at the outlet. The result is a considerable intentional pressure loss through the regulator (Figure 3).