Glossary

  • Buoyant Flow Control Device – A device which suspends a weir or orifice from a float at a fixed depth below the water surface, such that a constant head pressure is maintained over the weir or orifice regardless of water surface elevation. Thirsty Duck ER Series and TD Series devices are classified as buoyant flow control devices.
  • Moving Riser – The buoyant, inner tube of the ER Series device.
  • Moving Riser Assembly – The Moving Riser, float attachment flange, guide rods, outer restrictor ring and inner orifice disk.
  • Stationary Riser – The outer tube of the ER Series device which is not buoyant, does not move and is connected to the outfall.
  • Outer Flow Restrictor (ER 200 Series) – The lower portion of the moving riser which forms the smallest interstitial opening created between its outside edge and the inside perimeter of the stationary riser.
  • Interstitial Opening – The area through which water flows between the outside edge of the outer flow restrictor and the stationary riser.
  • Inner Orifice – The smallest area through which water flows through the inside of the moving riser. The inclusion of an inner orifice defines the difference between a single restriction device and a dual restriction device.
  • Single Restriction Device – A device through which flow rate is restricted solely through the interstitial opening formed by the outside edge of the outer flow restrictor and inner perimeter of the stationary riser. A single restriction device has no inner orifice. Both ER 100 and ER 200 series devices can be configured as a single restriction device.
  • Dual Restriction Device – A device through which flow rate is restricted through an inner orifice and the interstitial opening formed by the outside edge of the outer flow restrictor and the inner perimeter of the stationary riser. ER 200 series devices can be configured as a dual restriction device.
  • ER 200 Series Device – ER Series device where the stationary riser is formed by placing a custom fabricated steel sleeve within a concrete inlet, junction box or manhole and the moving riser is custom fabricated from 6061-T6 aluminum.
  • Housing Box – A structure in which the TD series devices are placed to protect them from tampering or other unauthorized intrusion. Slots are cut through the housing box to to allow flow to pass to the device contained inside. Thirsty Duck recommends baffles be placed over the slots to prevent floating debris from entering the housing box. The slots should be sized to ensure they do not restrict the flow to the device.
  • TD Series Device – A device which uses an expanding tube ( the "bellows") and a buoyant body housing a horizontally oriented orifice to maintain a constant depth of water over the orifice in order to produce a constant discharge. Thirsty Duck recommends all TD series devices be placed in a housing box.
  • Bellows – An expanding tube formed from welded polyurethane and reinforced with stainless steel rings which connects the TD Series' buoyant body to the outfall.
  • Transition Head – The depth of water over a horizontal orifice at which flow transitions from weir flow along the perimeter of the orifice to orifice flow through the area of the orifice.
  • Minimum Discharge Elevation – The lowest elevation at which the peak or maximum allowable flow rate may be discharged. In geographic regions such as Florida where a minimum volume of water must be detained or retained for water quality or pollution abatement purposes prior to discharging the maximum allowable rate, the Minimum Discharge Elevation is the elevation at which the minimum detention volume (water quality volume) has been achieved. Other geographic regions may have their own criteria.
  • Design Peak Stage – The maximum allowable stage the pond may rise to. For ER series devices, the length of the moving riser must be at least as long as the difference between the Design Peak Stage and the Minimum Discharge Elevation. For TD series devices, the length of the bellows must be at least as long as the the difference between the Design Peak Stage and the Minimum Discharge Elevation.
  • Rim Elevation (ER 200 Series) – The elevation of the top of the sleeve.
  • Tailwater Elevation – The elevation of the water surface at the discharge point of the device. Note: The design engineer must determine the amount of system head loss from the outfall to the discharge point of the device.

Contact Us

Thirsty Duck, LP
2154 Duck Slough Blvd.
Bldg. 4, Suite 103
Trinity, FL 34655

(727) 376-2400 telephone

(727) 376-2411 facsimile