Reducing the speed of rotating and moving parts in machines and mechanical systems results in smoother operation and lower noise output. Likewise, reducing pressure and flow velocities in air, gas, and liquid circulation systems lessens turbulence, resulting in decreased noise radiation. The following suggestions can be incorporated in design:
Operate fans, impellers, rotors, turbines, and blowers at the lowest bladetip speeds that still meet job needs. Use large-diameter, low-speed fans rather than small-diameter, high-speed units for quiet operation. In short, maximize diameter and minimize tip speed. All other factors being equal, centrifugal squirrel-cage type fans are less noisy than vane axial or propeller type fans. Figure 6.6.2 shows these two types of fans. In air ventilation systems, reducing the speed of the air flow by 50% can lower the noise output by 10 to 20
Lubricate at points A. Align between points 'A' - 'A'. Polish surfaces at Points B. Counterbalance at points C.
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