Positive Displacement blowers have two impellers that trap a “pocket” of air each time they sweep by the inlet and discharge connection. A pressure pulse is created each time this occurs. This pressure pulse creates noise and vibration. Blower silencers can be used to reduce this noise and vibration.
Silencers are typically used on the inlet and discharge of a positive displacement blower used for pressure applications. A discharge silencer is typically used on a vacuum application.
There are three basic types of silencers used to reduce the noise and vibration generated by the pressure pulse.
Silencer Capacity based on Standard Air Conditions and Silencer Velocity of 4,600 fpm which is equivalent to a 0.2 psi pressure drop (5.54″H2O). Silencer sizing is based on a “C” (Pressure Drop Coefficient) of 4.2. This covers the following Universal Silencer Models: URB,URBY,UCI,UCIY,UCIH,RIS,RISY,RISH,UCD,UCDY,URD,URDY,URDH,SD,SDY,SDH,
RD,RDY AND RDH.
Interpreting the Table
The flows stated under the “INLET SILENCER” heading would be the nominal flow rating for the inlet flow to the blower.
The flows under the “DISCHARGE SILENCER” headings are calculated back to an inlet flow. Therefore, if you have a blower with a nominal inlet flow of 500 CFM (Cubic Feet per Minute) at 6 psig, a 5″ inlet silencer would be required (rated for 750 CFM) and a 4″ discharge silencer could be used.
The table can be used as a quick guide to blower silencer sizing at a reasonable pressure drop. A smaller silencer may be selected, however, the pressure drop will need to be calculated. A smaller silencer will typically lead to an increased pressure drop through the silencer. Increased pressure drop results in higher horsepower for the blower or vacuum pump.
|Size||INLET SILENCER||DISCHARGE SIL.