Blow Off Silencers
During free blowing off / venting of pressurised steam or gas, kinetic energy in terms of waves with high pressure amplitudes is released.
At minor amounts of venting media (500 – 1000 m³/h) and relatively low expansion pressures (1 – 2 bar), this effect causes a quite high sound pressure level – depending on application – of 115 to 125 dB(A) in 1m distance from blow off opening (e.g. piping, etc.). At bigger blow off flow and higher expansion, e.g. blowing of safety valves, the sound pressure level SPL can increase up to 150 dB(A). This radiation of noise can be reduced effectively with blow off silencers, preferably with expansion stages (orifice).
The effectiveness of noise reduction of such blow off silencers is caused by the expansion orifice right after the nozzle inlet (multi hole expansion stage), followed by an attenuating absorbing splitter system analogous to baffle type silencer. At the expansion orifice the media is streaming through several cylindrical stages. The multi-hole cylinders are designed in dependence with the individual application of the blow off case (hole-diameter, distance of stages, etc.). Using special design of the multi hole cylinders and the absorbing splitters, a noise reduction (sound transmission loss) of up to 60 dB(A) can be achieved.
For the design of a silencer, following information is needed:
- Gas- or steam flow
- Temperature and pressure upstream (before) valve
- Permissible sound pressure level at emission point (in defined distance), e.g. 85 dB(A) in 1m distance
- Diameter of inlet nozzle (if defined)
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