Page 121 - Root Cause Failure Analysis

Fans, Blowers, and Fluidizers 109

clean, direct flow path. All ductwork should be airtight and leak free to ensure proper
operation.

Flow-Control Devices

Fans should always have inlet and outlet dampers or other flow-control devices, such
as variable-inlet vanes. Without them, it is extremely difficult to match fan perfor-
mance to actual application demand. The reason for this difficulty is that a number of
variables (e.g., usage, humidity, and temperature) directly affect the input-output
demands for each fan application. Flow-control devices provide the means to adjust
fan operation for actual conditions. Figure 8-5 shows an outlet damper with stream-

Figure 8-5 Outlet damper with streamlined blades and linkage arranged to move adjacenl
bMes in opposite directionsfor even throttling (Higgins and Mobley 1995).