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Storm King

An advanced vortex separator with a self-cleansing, non powered screen designed to effectively capture a wide range of sewer solids.

The Storm King® is a vortex separation chamber with the option to incorporate unique, non-powered, self-cleansing swirl cleanse screening technology. The Storm King® is ideal for satellite treatment at overflow sites and has been shown to save municipalities up to 50% on overall project costs when compared to conventional solutions.


  • Floatables control, sedimentation and disinfection of CSOs
  • Upgrades to existing CSO facilities
  • New satellite CSO facilities
  • Treatment of excess wet-weather flows at WWTPs
  • Stormwater treatment at centralized stormwater treatment plants

Storm King - An advanced vortex separator with a self-cleansing, non powered screen designed to effectively capture a wide range of sewer solids.

View a video produced by Gannett Fleming for their CSO project at Mon Valley Pennsylvania featuring the Storm King®


  • Effluent meets primary treatment equivalency for BOD & TSS removal
  • Vortex chamber can be used for disinfection
  • Screening down to 4mm for debris, floatables, gross solids & neutrally buoyant material
  • Save up to 50% on CSO project costs
  • No moving parts
  • No external power source needed
  • Minimal maintenance needed
  • Low system headloss

Flow is introduced tangentially into the side of the Storm King® causing the contents to rotate slowly about the vertical axis.

The flow spirals down the perimeter allowing the solids to settle out. This process is aided by rotary forces, shear forces and drag forces at the boundary layer on the wall and base of the vessel.

The internal components direct the main flow away from the perimeter and back up the middle of the vessel as a broad spiralling column, rotating at a slower velocity than the outer downward flow. By the time the flow reaches the top of the vessel, it is virtually free of settleable solids and is discharged to the outlet channel. Prior to discharge, the overflow passes through the swirl cleanse screen.

The swirl cleanse screen captures all floatables and neutrally buoyant material greater than 4mm. The air regulated siphon provides an effective backwash mechanism to prevent the screen from blinding.

The collected solids and floatables are then discharged by gravity or pumped out from the base of the unit to the sanitary sewer. 

Q. What is a Storm King®?

A. The Storm King® Overflow is a hydrodynamic separator used for removing settleable solids from wastewater. As the flow within the unit is dynamic (moving) the unit requires far less volume than a conventional passive device to obtain the same removal performance. This is because of drag forces set up within the unit due to the flow patterns which are dictated by the unit geometry.

Q. Does a Storm King® control the flow rate as well as providing solids removal?

A. No, it doesn't. Reg-U-Flo® Vortex Valves are typically used to control the pass-on flow rate to treatment. If a gravitational system is unobtainable then a pump can be used to control the pass-on flow to treatment as an alternative to the Reg-U-Flo®.

Q. What performance can a hydrodynamic separator achieve?

A. The performance efficiency of a hydrodynamic separator depends on the physical size of the unit itself (and consequently retention time) and on the settleability of the incoming sewage. Neutrally buoyant material cannot be removed by gravitational forces alone. A hydrodynamic separator typically achieves the same removal performance as a primary sedimentation tank in a quarter of the plan area. Higher loading rates can be used when less efficient performance is required, e.g. at a treatment works where grit and silts are desired to be removed but where it is beneficial for finer fecal material to pass forward to further downstream treatment processes. Conversely, chemicals can be added to enhance solids separation. The system provides floatables control, primary treatment equivalency and disinfection of CSOs and SSOs. 

Q. What dictates the size of a Storm King®?

A. The required diameter of a Storm King® is a function of the peak design inflow rate, design removal performance and the available depth. Within defined design limits, unit diameter can be increased to counteract the effect of limited available depth.

Download Case Study

This case study discusses how the Town of Bucksport, ME found the solution to their CSO flooding project with Hydro's Storm King System. 


Wet weather sedimentation, screening, and disinfection in a single device.


Trials conducted at Columbus and Saco have shown that because of the flow characteristics of the Storm King®, both solids removal and disinfection can be achieved in the same vessel. This bulletin outlines the theory of how this is achieved; along with practical examples from active fullscale sites, and cites where independent studies have been undertaken on this application, together with what was observed.


An overview of Hydro's high performance CSO / Wet Weather Solutions.