Hydro-Brake Drop
Flow control and flood protection

Hydro-Brake Drop

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Safely convey water or sewage while protecting infrastructure from damage, vibration and noise.

Hydro-Brake® Drop is a compact, self-activating conveyance and flow control system that dissipates the energy of dropping water, enabling engineers to convey clean or foul water from height while preventing the erosion, corrosion and nuisance effects associated with uncontrolled falling fluids.

Benefiting from vortex technology proven over 40 years, Hydro-Brake® Drop enables engineers to safely convey up to 10,500 ft3 / min (5,000 L/s) of clean or foul water from heights of up to 330 ft (100 m) in a fraction of the space needed for alternative technologies.

Hydro-Brake® Drop is a compact, self-activating conveyance and flow control system that enables engineers to safely convey water or sewage from height while protecting infrastructure from damage, vibration, smell and noise.

Using the same advanced vortex technology that enables the Hydro-Brake® Optimum to deliver precision flow control, Hydro-Brake® Drop's vortex technology dissipates the energy of dropping water, enabling engineers to drop water from heights of up to 330 ft (100 m) while preventing the damage and nuisance effects that conveying water from these heights would otherwise cause when using a conventional solution such as a drop manhole or equivalent drop shaft structure. 


  • Flood control
  • Sanitary and combined sewer (CSO) systems
  • Stormwater conveyance
  • Deep tunnel drainage and sewerage systems
  • Industrial water conveyance

Only Hydro-Brake® Drop:

  • Enables you to convey water safely through vertical drops of up to 330 ft (100 m)
  • Incorporates an air switch to manage flow and control nuisance and corrosive gases such as hydrogen sulfide
  • Leverages our unmatched legacy of vortex flow control expertise

Drop large amounts of water safely

With Hydro-Brake® Drop flows of up to 10,500 ft3 / min (5,000 L/s) can be transferred safely through drop heights of up to 330 ft (100 m). The use of multiple pipes can accommodate even higher flow rates.

Prevent erosion damage

Hydro-Brake® Drop has been designed using the latest computational fluid dynamics to mitigate erosion and other kinetic damage to expensive or important structures. Rigorous real-world testing has confirmed that the destructive forces associated with cavitation and water hammer have been eliminated. 

Control corrosion

Hydro-Brake® Drop incorporates a specially designed air switch that draws air through the pipe continuously as water flows through the system. This entrains air in the water, oxidizing odorous gases such as hydrogen sulfide and preventing the release of noxious gases that could otherwise cause corrosion problems.

Install and retrofit easily and cost effectively

Hydro-Brake® Drop is a self-activating conveyance and flow control system with no moving parts and no requirement to keep an air core within the drop pipes, so it can be installed easily and cheaply either as part of a new construction project or as a retrofit to an existing system. Its integrated access and small pipe sizes cut excavation costs, shaft diameters and prevent the need for a separate access shaft. The system also benefits from a compact and simple-to-construct inlet chamber with no complicated curves or benching required.

Air Entrainment mode

At low flow water passes through the inlet pipe and drops as a film, maintaining contact with the inside surface of the Drop Pipe. This results in the formation of a central air core through the pipe. Water then enters the top of the Energy Dissipation Unit and exits the system through the sides into the bottom of the drop chamber. A weir at the bottom of the chamber creates a stilling area to absorb the release of energy from the water exiting the Energy Dissipation Unit - this ensures a smooth operation with minimal turbulence.

At increased flows, the water level in the inlet chamber submerges the inlet pipe. At this stage, air is fed in via the Air Switch, maintaining the stability of the air core and a smooth flow regime.

Pipe Full mode

If the flow rate continues to increase then the water in the upstream inlet chamber rises until it reaches the Air Switch, whereupon the system begins to enter the transition to Pipe Full mode. At this stage any increase in flow has a much lower impact on the upstream water level due to the high flow capacity. The Air Switch is designed to smoothly and efficiently regulate the transition phase, eliminating any 'glugging' or vibrations, until Pipe Full mode is reached completely and there is no more air flow through the system.

The Energy Dissipation Unit

During Air Entrainment mode air is carried down the shaft and released in the outlet chamber to ensure that damaging water hammer cannot occur. During Pipe Full mode no air is carried and therefore the drop pipe can operate at full capacity, pulling water from the inlet chamber until once again air is introduced.

Video file



Performance characteristics

Maximum flow: 10,500 ft3 / min (5,000 L/s) (in a single unit)

Maximum drop height: 330 ft (100 m)


The system is constructed from stainless steel. 

Key Components

Air switch

Controls the amount of air entering into the falling flow from the Drop Pipe, eliminating 'glugging' and therefore the damaging effects of water hammer or hydraulic shock.

Top bend

Safely transitions the flow into the vertical section of the pipe. A taper may be required depending on site circumstances.

Drop structure

A full-depth chamber housing the Drop Pipe, a control weir, maintenance access and the Outlet Structure.

Energy Dissipation Unit

Developed using the latest vortex flow control techniques, this component is designed to disperse the energy created by the falling water, in addition to effectively preventing erosion and controlling the onward flow.


Why are conveyance and control systems needed when dropping water from height?


Dropping water from height without some form of control can result in noise, vibration and damage to the network infrastructure. A conveyance and control system is needed to dissipate the increase in energy of falling water, to eliminate cavitation and hydraulic instability that falling water would cause, and to reduce hydraulic head losses when drainage tunnels are surcharged with additional flows, as might be the case during a storm event.


Does the Hydro-Brake® Drop require large stilling basins and pipes?


The Hydro-Brake® Drop allows for a smaller, simpler inlet structure and uses a compact Energy Dissipation Unit at the base. It also enables the use of small diameter pipes, as the technology allows them to run full. The small pipes can be fixed to the tunnel wall allowing for safe access to the base of the drop. This eliminates the need for auxiliary shafts for maintenance access.


What are the limitations of conventional drop technologies?


Conventional technologies such as weirs and backdrops have practical height limits sometimes as low as 8 ft (2.4 m), cascades are expensive and cause water to gain energy on each downward 'step', increasing the risk of loss of control and overshooting, and flumes are difficult to design to match energy dissipation with energy gain. Conventional vortex-type drop technologies require very large diameter pipe to accommodate the large air core that forms, and the systems also require elaborate entry structures and a large stilling basin to dissipate energy at the bottom.


Is dropping water from height dangerous?


Conventional drops can cause flowing water to have a high velocity and turbulence, and improperly designed shafts can also cause hydraulic shock and glugging. Additionally, improperly designed drop shafts may accelerate erosion of the pipes if entrained air is not properly removed. Entrained air can also cause cavitation, a phenomenon in which micro-bubbles form and explosively collapse on the surface of a pipe due to rapid changes in water elevation. Hydro-Brake® Drop has been designed to prevent these factors.


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