Throttle shaft for constant discharge in case of heavy rainfall

New tube throttle AquaLimit tube by FRÄNKISCHE

FRÄNKISCHE’s new AquaLimit tube throttle shaft for the controlled discharge of stormwater from storage/infiltration systems and reservoirs is ideally suited for small feed quantities. The active flow control convinces in particular with its steep throttle characteristics, simple modular structure, and small throttle discharge values.

According to the German Federal Statistical Office (Statistisches Bundesamt), surfaces of a total size of 50 football fields are paved every day. This interrupts the natural water cycle: The accumulating stormwater drains quickly via the surfaces, and the existing sewers and nearby waterbodies are overburdened by the approaching water masses. This results in damage to the waterbodies and the infrastructure. For this reason, local communities such as Berlin have increasingly been defining discharge limitations of less than two litres per second per connected hectare. In addition, the proof of overflow stipulates that the stormwater of at least a 30-year rainfall event must be completely retained on the plot of land. Rigofill storage/infiltration modules are the ideal solution – as universal components for basins with a modular structure.

The retained stormwater can be used, infiltrated and/or discharged in a controlled manner. If no or only incomplete infiltration of stormwater is possible due to the composition of the soil, a throttle element normally controls discharge in the stormwater storage systems. This ensures the maximal permissible discharge for all filling levels in storage/infiltration systems or reservoirs – even in case of excess backwater over the top edge of terrain. This helps to reduce the discharge duration, and the storage volume is again available for the next rainfall event. Moreover, the smallest possible stormwater retention volume can be implemented due to the constant discharge.

Tube throttle for small discharge values

In construction projects with limited stormwater inflow, only small volumes of water can be discharged into the sewer or receiving waters – depending on the size of the plot and on-site conditions. This is why FRÄNKISCHE has now designed the new AquaLimit tube throttle shaft with its development partner Umwelt- und Fluid-Technik Dr. H. Brombach GmbH (UFT). “Thanks to our new tube throttle, we are perfectly prepared for the current and future requirements of stormwater management: Because of the climate change, heavy rains and urban flash floods occur more often, which makes solutions for retention and controlled discharge for premises of all sizes increasingly more important. With AquaLimit tube, we now offer a variant for medium to very little discharge volumes depending on the filling levels,“ explains Christoph Huth, FRÄNKISCHE Product Manager Drainage Systems.

Constant discharge through all operating stages

To discharge the stormwater from storage/infiltration systems or retention facilities with a delay but continuously, as well as to improve the natural stormwater balance, the compact throttle shaft ready for connection is integrated into the drainage system. The function of AquaLimit tube is based on the so-called Bernoulli’s principle. This principle states the following: An increase in the speed of flowing fluid occurs simultaneously with a decrease in static pressure. The pressure differences lead to the deformation of the membrane, due to which the discharge remains constant. In the tube throttle, an elastic rubber membrane is fitted onto the plastic pipe with two lateral, rounded cut-outs. Due to pressure differences, it bulges in to a greater or lesser extent depending on the water level – this reduces the throttle section and subsequently the discharge.

Thanks to the steep throttle characteristics as compared to a simple orifice, the tube throttle can achieve an almost constant discharge even with water levels over the top edge of terrain. Since our partner UFT manufactures the flow control project-specifically, discharge values of 1-10 l/s can be realised. Therefore, the new corrosion-resistant shaft with small discharge values is ideally suited for both smaller and larger connected areas, and especially in case of excess backwater events. Since AquaLimit tube operates without mechanically moving parts and external power supply, virtually no maintenance is required.

Modular system for flexibility and quick delivery

AquaLimit tube is available in three different total heights. Since the system is based on a modular structure, the shaft can be individually adjusted to the installation depth on site. The users benefit from fast delivery times, since the base shaft is pre-manufactured to stock and can be supplied with the required throttle at short notice. The UFT manufactures the throttle project-specifically considering the greatest head and the maximum permissible throttle outlet range. If legal requirements or the connected areas change, you can adjust the limited discharge volume by simply exchanging the throttle element. Since FRÄNKISCHE’s AquaLimit tube is delivered ready to connect, it is installed easily and in no time at all.

Huge range of throttle products from the drainage expert

To ensure controlled discharge of stormwater from reservoirs and storage/infiltration systems, FRÄNKISCHE offers throttle variants for nearly any application: AquaLimit is furnished with a vertical stainless steel vortex valve that works according to the hydraulic operating principle without external power supply. The QuadroLimit system shaft with a lying vortex valve that can be integrated into the layout can be arranged same level at the edge of the Rigofill inspect system. Depending on the head, discharge volumes from four to 80 litres are possible. The compact RigoLimit V vortex throttle shaft in turn is based on the operation principle of the vortex technology, and can be easily adjusted to changed discharge conditions thanks to its exchangeable orifice.

AquaLimit tube supplements FRÄNKISCHE’s range of throttle products with a model for very small discharge volumes. The new flow control convinces in particular with its constant discharge – even in case of excess backwater over the top edge of terrain.


AquaLimit tube