The SPEL Storm-Brake attenuation tank is a two compartment unit with a weir overflow to storage. The first compartment incorporates the inlet and flow controller and, being small in capacity, quickly attains the head for optimum performance of the flow controller.

During storm conditions level will rise and pass over the weir into the storage compartment and as the storm abates and the level falls in the first chamber, non-return valves operate to allow the stored stormwater to pass back into the first chamber and through the flow controller.

The most common systems are on-line where the tank forms part of the drainage system with all flows passing through the tank or interconnected tanks. However, the SPEL Storm-Brake can also be designed for off-line attenuation.