Nelson Airport required a reliable semi-circular screening solution at its Combined Sewer Overflow (CSO) site to remove solids from storm overflows before they entered the treatment process. The system needed to remove screenings at the weir, wash them off the screen surface, and retain all debris within the forward flow to the treatment plant.

Brown Brothers Engineers was engaged by BECA Engineering and Consulting Services to design, manufacture, and supply a solution - the Pump Action Screen (PAS), a revolutionary concept in mechanical screenings. The unit included a semi-circular stainless steel basket with 6mm perforations, a submersible pump, venturi system, and distribution pipework.

No Moving Parts

The PAS is a simple and robust solution, designed to prevent non-biodegradable solids greater than 6mm from being discharged in either direction.

According to Niall Fitzsimons, National Sales Manager-Wastewater Screens at Brown Brothers Engineers, "The Pump Action Screen was installed on the flow side of the overflow weir and is inactive during dry weather flow. As stormwater levels rise and reach the underside of the screen, an ultrasonic level sensor detects the head level and signals the control panel to start the pump."

Once activated, the pump forces water through a Venturi, where a drop in pressure draws in air and creates a high-velocity air-water mixture. This mixture is then directed through a mixing section and onto the underside of the screen basket. The turbulent scouring action effectively dislodges accumulated debris, preventing blockages (blinding) and propelling solids past the screen edge. This ensures they remain in the continuation flow and are captured by downstream treatment processes.

"When the water level subsides after the storm, the ultrasonic sensor triggers the system to shut down, completing the cycle."

Unlike traditional mechanical screens, the PAS has no moving parts, simplifying maintenance and increasing the reliability of the product. The submersible pump is mounted on a guide rail system for easy removal and servicing.

An Innovative and Simple Solution

The PAS installation at Nelson Airport has proven to be a robust, low-maintenance solution that effectively prevents debris from entering the environment during overflow events. With no moving parts and minimal operator intervention required, the system supports reliable operation and compliance with stormwater screening requirements.

"After the success with the product at Nelson Airport, we have several more installations currently in progress around the country," Niall said.

Brown Brothers Engineers is the exclusive distributor for the CSO Group Pump Action Screen in New Zealand. Find out more about the Pump Action Screen here.

Key features include:

• 6mm dual-direction screening - captures non-biodegradable solids, improving overflow quality.
• High Solids Retention Value (SRV) of 58% - reduces the amount of debris entering receiving waters.
• Stainless steel construction (304 & 316) - provides long-term durability and corrosion resistance.
• No moving parts - minimises wear, reducing maintenance requirements and cost.
• Servicing from ground level - able to be carried out without man entry into the chamber.
• Modular design - for retrofitting through existing manholes without major civil work.
• Flexible installation - performs reliably in both deep and shallow chambers.
• Low power requirements - reduces operating costs and environmental impact.