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.

Size	CAPACITY (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