SIZE CAPACITY (Inlet CFM 14.7 psia & 70°F)
INLET SILENCER DISCHARGE SILENCER
4 PSIG 6 PSIG 8 PSIG 10 PSIG 15 PSIG
1 30 35 40 40 40 45
1½ 70 80 85 90 95 105
2 120 140 150 160 165 185
2½ 190 220 235 245 255 285
3 270 320 335 355 370 415
3½ 370 430 455 480 505 560
4 480 560 600 630 660 735
5 750 880 935 985 1,030 1,150
6 1,080 1,260 1,340 1,410 1,480 1,650
8 1,920 2,250 2,390 2,510 2,630 2,940
10 3,000 3,520 3,730 3,930 4,110 4,590
12 4,300 5,070 5,370 5,660 5,920 6,600
14 5,900 6,890 7,310 7,700 8,060 8,990
16 7,700 9,000 9,550 10,000 10,500 11,800
18 9,700 11,400 12,100 12,700 13,300 14,900
20 12,000 14,000 14,900 15,700 16,400 18,400
22 14,500 17,000 18,100 19,000 19,900 22,200
24 17,300 20,200 21,500 22,600 23,700 26,400
26 20,300 23,800 25,200 26,600 27,800 31,000
28 23,500 27,600 29,300 30,800 32,200 36,000
30 27,000 31,700 33,600 35,400 37,000 41,300
EST. TEMP 70°F 115°F 140°F 165°F 190°F 240°F

Silencers should be mounted directly to the blower to avoid standing wave resonances that can develop by extending the connection length.

More about Rotary Positive Blower Silencers
Rotary Positive Blowers are two impeller compressors that function like a high speed reciprocating compressor. Each revolution displaces a large quantity of gas relative to the individual pulse; each revolution produces 4 pulsations. 
Blower applications involve two acoustic problems: 
1) Pulsation (4/Revolution) that causes pipe vibration 
2) High audible noise levels radiating from the blower housing and piping
Pulsation and noise increase proportionately with blower size and the square of the RPM.

SILENCER CAPACITY

PITCH LINE VELOCITY INLET SILENCER MODEL DISCHARGE SILENCER MODEL
BELOW TRANSITION 142 142
ABOVE TRANSITION 122 122

Silencer Selection
Silencer size and type is determined based on allowable pressure drop and flow, noise reduction required (DIL). The nominal nozzle size of the silencer is based on the Inlet Cubic Feet per Minute (ICFM). However, the silencer type is selected based on consideration of blower size gear Pitch Line Velocity (PLV). 

Where PLV = gear circumference x RPM [usually expressed in feet per minute (FPM)].

PITCH LINE VELOCITY (PLV) SELECTION RECOMMENDATIONS:
Inlet: 3300 FPM (PLV)
Discharge: 2700 FPM (PLV) 

Below 3300 FPM reactive silencers are appropriate, over 3300 FPM combination reactive/absorptive are appropriate.

Silencer type will typically be either a reactive chambered design or a combination reactive/absorptive design. Both inlet and discharge connections will require a silencer.


SILENCER MODEL SPECIFICATION:

Model Pressure Drop Factors
122 4.4
131 4.4
141 4.4
141 12" & Larger 5.5
144 5.5

VANEC Rotary Positive Blower Exhaust Silencers are designed for use in suppressing the discharge noise from rotary positive blowers.  They may be used to silence an atmospheric or a pressurized discharge below 15 psig. Available models: 122, 142

Recommended Operating Velocity Limits:
5500 to 6500

Pressure Drop Factors (PDF)

Rotary Positive Blower Silencers 

INDUSTRIAL SILENCERS