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Hydro Vortex Drop Shaft

A compact flow control solution that is safer and less expensive than simple vortex drops shafts.

The Hydro Vortex Drop™ Shaft is a compact, single shaft system used for controlling flows from high level sewers into deep tunnels. The system dissipates the energy of dropping water in order to protect infrastructure from noise, vibration and damage.


  • Controlled drop of water into deep tunnels
  • Energy dissipation of dropping water
  • Flood control
  • CSO systems
  • Stormwater systems


  • No auxiliary air and/or maintenance shafts needed
  • No requirements to keep an air core within the drop pipes so pipe sizes are significantly reduced
  • Safe, controlled, efficient
  • Self-activating with no moving parts
  • A multiple pipe arrangement can accommodate higher flow rates
  • Easy, safe and low maintenance

Vortex Mode

During low flow conditions, when the Hydro Vortex Drop™ Shaft is operating in the air-entrained mode, water flows into the inlet of the vertical drop barrel. Air enters the vertical pipe through the open air switch, located at a higher elevation than the inlet pipe. Water flows down through the vertical pipe barrel and into the cylindrically shaped Energy Dissipation Unit (EDU), where the geometry of the device causes water to flow in a horizontal vortex flow path through the cylinder and out to the outlet. The air core at the center of the vortex in the EDU throttles back and dissipates the energy of the flow that is conveyed down the vertical drop pipe.

Pipe Full Mode

The combination of the vertical pipe and vortex in the EDU continues to throttle the effluent discharge as flows into the upstream chamber increase. As a result, the water level in the upstream chamber rises. As water levels rise, the Air Switch controls the amount of air that is allowed into the Vertical Drop Pipe. When the water level finally reaches the height of the Air Switch the air is switched off and the flow in the vertical drop pipe transitions into a pipe full mode of operation. The design of the air switch ensures a smooth transition preventing glugging noises and vibrations that can be caused by other drop shaft systems.

Hydro Vortex Drop Shaft - Flow Control Device cutaway in vortex mode
Vortex Mode


Hydro Vortex Drop Shaft - Flow Control Device cutaway in Full Pipe mode
Pipe Full Mode

What is a drop shaft?

Drop shafts are used in water conveyance tunnels to transfer flows from a higher elevation to a lower elevation. Such drop shafts are typically used for flood control, CSO systems and deep tunnel systems.

Why are drop shafts needed?

Drop shafts are needed to dissipate the increase in energy of falling water. A drop shaft is also needed to remove any air that mixes with or is entrained in the water as it descends to eliminate cavitation and hydraulic instability that falling water would cause and to minimize hydraulic head losses when drainage tunnels are surcharged with storm flows.

What kinds of drop shafts exist?

Present drop technologies include conventional technologies such as weirs, cascades, flumes, backdrops and vortex drops. Innovative technologies include advanced vortex drops.

Aren’t drop shafts unsafe and dangerous?

It is true that conventional drops can cause flowing water to have a high velocity and turbulence. Improperly designed drop shafts can cause hydraulic shock and glugging (transient and surging flows causing rapid pressure releases of air and water in the opposite direction of the flow, causing dynamic instability and possible tunnel collapse). Additionally, improperly designed drop shafts may accelerate erosion of the pipes if entrained air is not properly removed. Entrained air can cause cavitation, the phenomenon where micro-bubbles form and explosively collapse on the surface of a pipe due to rapid changes in water elevation.

How does a properly designed drop shaft prevent hydraulic shock and cavitation?

In order to prevent the formation of damaging high-pressure air buildups, a properly designed drop shaft will ensure a smooth transition between air-entrained and full-pipe modes of operation.

What are the limitations of conventional drop technologies?

Weirs, cascades, flumes and backdrops are simple to design. However, weirs and backdrops have practical height limits sometimes as low as 8 ft. Cascades are expensive and cause water to gain energy on each “step” down, risking the loss of control and overshooting. Flumes are simple but risky because it is difficult to match energy dissipation with energy gain.

Are vortex drops better than conventional drop technologies?

Vortex drops can offer a more acceptable drop solution because they can be used for very tall drops. However, conventional vortex drop technologies require very large diameter pipe to accommodate the large air core that forms within the vortex. The systems also require elaborate entry structures and a large stilling basin to dissipate energy at the bottom.

Does the Hydro Vortex Drop™ Shaft require very large stilling basins and pipes?

No. The Hydro Vortex Drop™ Shaft has innovative components that allow for a smaller, simpler inlet structure and utilizes a compact energy dissipation unit at the base. The Hydro Vortex Drop™ Shaft also offers a more acceptable drop solution because it enables the use of small diameter pipes as they can run full. The small pipes can be fixed to the tunnel wall allowing for safe man access to the base of the drop. This eliminates the need for auxiliary shafts for maintenance access.

How far can you drop water with a Hydro Vortex Drop™ Shaft?

Depending on the flow rate, up to 350 ft.

What is the difference between a Hydro Vortex Drop™ Shaft and a conventional drop shaft?

Our design is more compact and is a pipe full design (i.e. does not need to maintain an air core).


Compact and effective flow control solution with the Hydro Vortex Drop™ Shaft.


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