Louver dampers are used for two functions; control and/or isolation. There are four standard types: Parallel, Opposed, Double, and Tandem Louvers. Each louver has a row of blades that are used to control or isolate the gas flow of any process system. The key advantages of the louver damper include its fast operating speed and minimum perimeter clearance requirements. Typical heavy duty applications include: Flue Gas processing, component of CHP (combined Heat and Power) diverter system, pressure relief, airflow control, gas exhaust, and pre-spinning of duct air.
Parallel louvers are primarily used for isolation applications. All of the blades rotate in the same direction. With the addition of blade seals, this damper can achieve better than 99% shut off. Parallel blade louvers are also used on inlet boxes of large industrial fans to promote pre-spin to the in rushing air, thus enhancing fan performance.
Opposed louvers are used for process gas control. The louvers function by rotating adjacent blades in opposite directions. (One clockwise, the next blade counterclockwise) Operating the blades in this manner gradually decreases or increases the cross-sectional area between the blades during operation. This gradual change in area allows this louver to have reasonably good air control features.
Double louvers are designed to achieve zero leakage isolation. Double louvers achieve zero leakage isolation by pressurizing the space between the two sets of louver blades with “seal air”. This “seal air” is supplied at a pressure higher than the pressure in the flue duct, creating a positive pressure environment.
Tandem dampers are designed to perform as a Double Louver Damper except instead of having “seal air” between two sets of louver blades, the “seal air” is between the two skins of the wider tandem blades. The advantage is a more compact design as well as fewer blades, bearings, shafts, etc.