The GNA CSO HYDROSWITCH is a proven technique for transferring by gravity, highly polluted base flows and wet weather floatables from a sewer at a higher elevation to a receptor system, without hydraulic or electrical controls.

Operating Characteristics

During dry weather, base flows and pollutants are continuously deflected to the "receptor" sewer. During a wet weather event, an initial portion (based on additional flow that the "receptor " sewer can accept) of the " first flush" is diverted to the " receptor" sewer. If the event is low intensity and short duration all collected materials are deflected to the "receptor" sewer. During a major flow event, floatable materials are retained by a floating baffle which does not impede the overflow weir capacity. Once the event has abated the connection to the "receptor" sewer is re- established and all collected materials are once again diverted to it.

Typical Intsallation



  • Low cost & easy to install or retrofit 
  • Useful in transferring pollutants to sanitary sewer 
  • Useful for cso areas undergoing load separation 
  • Useful for separate systems 
  • Provides positive control 
  • All stainless steel materials

Testing has shown that the GNA CSO HYDROSWITCH, has the ability to reduce 40-50 % of the tss and 30- 35% of the cod pollutants when as little as 23% of run-off volume is transferred to the "receptor" sewer.

Top of page