reduction of mechanical noise
To reduce mechanical noise still needed the following activities:
1. In order to avoid transmission of vibrations through the air ducts should include a small soft box of canvas or rubber 50-100 mm in length between the fan and air ducts. No need to be made from an elastic material the entire cone of the fan. Soft Diffuser usually does not fulfill its basic purpose of an irregularly shaped. This is especially important for exhaust systems, where a soft box is recommended to do only on the intake side, if the ventilation removes toxic substances. Box on the discharge duct is recommended that you very carefully from sheet rubber or plastic, but not from the canvas.
2. Apply only to belts.
3. Install fans in special rooms, walled soundproof partitions.
4. With free entry of air in the fan wheel to set the collector or the sleek cone.
Aerodynamic noise depends on the design of the wheel - the number and profile of the blades, of the speed and mode of fan operation. Aerodynamic noise is reduced when the fan with the highest efficiency. Centrifugal fans with curved blades back, less noisy than with radial blades or bent forward.
The value of aerodynamic noise is most dependent on the circumferential wheel speed, ie, the number of its revolutions. Ceteris paribus aerodynamic noise increases proportionally to the fifth power of changing the number of wheel revolutions. Therefore, in all cases where possible, you should reduce speed to a certain optimum limit, in other words, we should not overestimate the resistance of ventilation systems, especially the inlet. In abated systems generally, the resistance should not exceed 100 kg/m2.
Maximum permissible sound pressure levels in octave bands for premises in the territory of industrial plants or outside this territory should be taken according to the SP 245-63.
To reduce aerodynamic noise may recommend some constructive action. For example, the main supply air duct should be performed not metal, but from a porous material, concrete, slag, alabaster slabs, etc., and cover the inside sound-absorbing plaster. This embodiment of the main supply duct (channel] is quite constructively in multi-storey industrial and ancillary buildings. Is useful to use more turns and separation flows. If necessary, significant silencing of aerodynamic noise have resorted to special muffler.