How It Works - TD Series
The TD Series of BFD's maintains constant head by suspending a horizontal orifice inside a buoyant body. The body is able to float while maintaining a connection to the outfall by the use of an expanding pipe, called the bellows. The bellows, made of welded polyurethane and reinforced with stainless steel rings, ensures the body returns to its rest position when pond water level lowers below the minimum discharge elevation. The buoyant body also acts as a skimmer for the orifice, since it is always partially submerged, water always enters from below the body. The TD Series of BFD's achieves constant flow once the body begins floating. Click here to see a typical TD Series rating curve.
The TD Series of BFD's can be installed in three seperate configurations.
These are shown below as Case A, Case B, and Case C.
In Case A, the TD Series BFD is installed in the open, with no housing box. The orifice inside the buoyant body is set at the minimum discharge elevation. Please note that there is no specific design tool for Case A. If generating a rating curve for a Case A installation, you may use either the Case B or Case C design tool. Enter the proposed submergence as 0.00, and enter a very large number (100,000+) in the housing box information cells.
In Case B, the BFD is installed inside a housing box, and flow to the BFD is over the rim of the housing box. The rim of the housing box is at the minimum discharge elevation, while the orifice of the TD Series BFD is set below this elevation. This allows the buoyant body of the BFD to begin floating, and therefore discharging at the design rate, soon after the pond reaches the minimum discharge elevation.
In Case C, the BFD is installed inside a housing box, and flow to the BFD is through weirs or orifices in the housing box. The inverts of these structures is at the minimum discharge elevation, while the orifice of the TD Series BFD is set below this elevation. As in Case B, constant flow starts soon after the pond reaches minimum discharge elevation, and the housing box can have baffles installed to provide an additional level of skimming for the device.