Blower Silencers - Technical Literature - Universal: Acoustic Silencers

Silencer RecommendationsAs mentioned on page 2 pitch line velocity (PLV) isthe speed of the timing gear in feet per minute (ft/min). For purposes of silencer application. PLV isconsidered “critical” at 3,300 ft/min for intake and2,700 ft/min for discharge.Table 1 gives transition speeds in RPM. Blowersrunning at these speeds or greater will have criticalPLV. Operating speeds below transition will be inthe sub-critical range. Blowers operating in thesub-critical speed range usually require only simplechamber-type silencers while those in the criticalrange require combination chamber-absorptivetype silencers. If there is doubt, it is best to usethe combination-type silencers. When gear sizeand operating speeds are known, the proper typesilencer is easily selected.Silencer Size Selection, CapacityTable 3 gives the nominal capacity of the varioussize silencers. “Size” in this table refers to thesilencer “nominal size,” or its “inlet size.” Capacitiesare expressed in inlet CFM (ICFM), thus, dischargesilencers are rated at higher capacities than inletsilencers since the air is compressed to reducedvolume at the discharge operating pressure.3Size11.522.533.545681012141618202224262830Est Temp.Silencer CapacityInlet Silencer30701201902703704807501,0801,9203,0004,3005,9007,7009,70012,00014,50017,30020,30023,50027,00070˚FA From Table 1 determine whether blower RPM isabove or below the transition speed forcritical PLV.B Consult Table 2 for recommendedsilencer models.Pressure DropThe following formulas may be used to calculatepressure drop through the silencers covered in thiscatalog.VP = Inlet:4005(assumes silencer inletis open to atmosphere)Application,Capacity,Pressure Drop DataBlower Silencers1 Blower Transition SpeedBlower Transition Speed-RPMGear Size Inlet DischargeDischarge:2P V c P 5302 6,300 5,1552.54005 14.75,040 4,125T3 4,200 3,435P = pressure drop through silencer, inchesof waterV = air velocity through silencer, ft/min*c = individual silencer restrictioncoefficient—empirical constant (seeTable 4)P = discharge pressure, PSIA (operatingpressure in PSIG + 14.7)T = discharge temperature, ˚R absolute(operating temperature in ˚F + 460)* To calculate velocity through silencer, divide flow in ACFM bycross-sectional area of silencer inlet diameter in square feet.45678101214161820223,1502,5202,1001,8001,5751,2601,0509007857006305702,5752,0601,7201,4701,2901,03086073564557051547024525 430Capacity (Inlet CFM 14.7 PSIA at 70˚F)Discharge Silencer4 PSIG 6 PSIG 8 PSIG 10 PSIG 15 PSIG 2 Silencer Model Specifications35 40 40 40 45Pitch Line Inlet DischargeVelocity Silencer Silencer80 85 90 95 1052c140 150 160 165 185BelowTransition220 235 245 255 285UCI, URB URB, UCD, URD320 335 355 370 415AboveTransition430 455 480 505 560RIS SD, RD560 600 630 660 735880 935 985 1,030 1,1501,260 1,340 1,410 1,480 1,6504 Pressure Drop Coefficients2,250 2,390 2,510 2,630 2,940ModelPressure DropCoefficient (C)3,520 3,730 3,930 4,110 4,590URB, URBY4.25,070 5,370 5,660 5,920 6,600UCI, UCIY, UCIH4.26,890 7,310 7,700 8,060 8,990RIS, RISY, RISH4.29,000 9,550 10,000 10,500 11,800UCD, UCDY4.211,400 12,100 12,700 13,300 14,900URD, URDY, URDH 4.214,000 14,900 15,700 16,400 18,400SD, SDY, SDH4.217,000 18,100 19,000 19,900 22,200RD, RDY, RDH4.220,200 21,500 22,600 23,700 26,400RDS, SDS, URDS7.023,800 25,200 26,600 27,800 31,00027,600 29,300 30,800 32,200 36,00031,700 33,600 35,400 37,000 41,300115˚F 140˚F 165˚F 190˚F 240˚F© 2011 Universal Acoustic & Emission Technologies, Inc. All rights reserved.Toll-Free: 1-888-300-4272www.universalAET.com94-1547 Rev 03