Blower Silencers

Silencers

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.

  • Chamber Type
  • Chamber Absorptive Type
  • Absorptive Type

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 flow rating for the inlet flow to the blower.

The flows under the "CAPACITY (Inlet CFM 14.7 psia & 68°F)" and "DISCHARGE SILENCER" heading are calculated back to an inlet flow. Therefore, if you have a blower with an inlet flow of 500 CFM (Cubic Feet per Minute) at 6 psig, a 5" inlet silencer would be required (rated for 639 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.

SizeCAPACITY (Inlet CFM 14.7 psia & 68°F)

INLET

SILENCER

DISCHARGE SILENCER
2 psig 4 psig 6 psig 8 psig 10 psig 15 psig
1
28
30
32
34
36
38
40
1.5
65
71
76
81
84
89
95
2
107
118
126
133
139
147
156
2.5
153
168
180
190
199
210
222
3
236
259
277
293
307
324
343
3.5
316
347
371
392
410
433
459
4
407
447
478
506
529
558
592
5
639
701
751
794
829
876
929
6
923
1013
1084
1146
1198
1265
1342
8
1598
1754
1877
1985
2074
2191
2324
10
2519
1764
2959
3129
3269
3454
3663
12
3576
3924
4201
4442
4641
4903
5199
14
4323
4743
5078
5369
5611
5927
6285
16
5645
6194
6632
7012
7327
7740
8208
18
7145
7841
8394
8876
9274
9797
10390
20
8880
9745
10433
11031
11527
12176
12913
22
11329
12432
13310
14073
14705
15534
16473
24
12844
14094
15089
15954
16671
17610
18676
26
15680
17206
18422
19478
20353
21500
22800
28
18290
20070
21487
22719
23740
25077
26594
30
21099
23153
24789
26210
27387
28930
30680
Est. Temp.
68°F
103°F
127°F
153°F
182°F
208°F
286°F
?P(“H2O)
5.5
5.5
5.5
5.5
5.5
5.5
5.5
Inlet losses of 0.3 psi and discharge loss of 0.2 psi assumed