Pump action screen, type PASRobust cleaning system without moving parts

Combined sewer systems carry both rain water and sewage. During periods of increased flow the capacity of the system can be considerably exceeded and the flow is discharged to a watercourse via a combined storm overflow (CSO). In order to prevent the discharge of unsightly sewage related debris (condoms, panty liners, cotton buds etc.) and gross solids the CSO is required to be screened.

Operational description

The Pump Action Screen is a simple robust CSO screen. It is designed to prevent the discharge of floating, suspended, non-biodegradable, solid material; greater than 6mm in two directions, from the incoming flow without disturbing the discharge process. The screenings and solids are retained within the flow for later removal at the wastewater treatment plant inlet works.

The screening basket is manufactured from 6 mm perforated stainless steel plate and is located beneath and immediately in front of the overflow weir of the chamber. The submersible pump, which can be removed and serviced without entry into the chamber, can be located either in the main flow or in the storm outfall. The pump is connected to the ejector section by pipework that in turn is connected to the screenbasket. Pump operation is controlled via a level control device.

During storm conditions the level in the CSO chamber or storm tank rises. Once the level has reached the top of the screen the level control device (float switch or ultrasonic) sends a signal to the control panel and the pump starts. Water is drawn through the pump, as it passes the ejector it draws air into the flow, the combined air and water mixture passes into the underside of the screening basket and scours the screen removing the screenings from the screen face and returning them directly into the pass forward flow. A timer controls the pump running time.

  • No moving parts
  • Wear-resistant operation of the screen
  • High cleaning performance
  • Easy retrofitting
  • Variable cleaning period and frequency
  • Fully automatic operation
  • Low maintenance