Stationary Industrial Exhaust Product Solutions
Selecting a Silencing Solution
Selecting a silencing solution for your application is simple.
There are two methods used to make the selection:
• Use Method 1 when the pressure drop requirement is greater than 1.0 inches Hg (approximately 13.62 inches H₂O).
• Use Method 2 when the Pressure Drop requirement is less than 1.0 inches Hg (approximately 13.62 inches H₂O).
Determining the Exhaust Flow Rate
Regardless of the method you choose, you will need to know the Exhaust Flow Rate. If this value is not
known, use the following equation to estimate the Exhaust Flow Rate, then proceed with Method 1 or 2
to select a silencing solution.
Estimated Exhaust Flow Rate:
D = Displacement in in³
E = 0.85 efficiency for naturally aspirated engines
= 1.2 for engines with scavenging blower
= 1.4 for turbo-charged engines
T = Exhaust temperature (if unknown, use 900 °F (482 °C) for diesel and 1,200 °F (649 °C) for
C = 1.0 (one-cycle engine) or 2.0 (two-cycle engine)
Selecting a Silencing Solution
You must know the following information:
• Exhaust Flow Rate (ft3/min (m3/min))
• Silencer Inlet Area (ft2(m2))
• Level of Silencing Required
1. Calculate the Exhaust Gas Velocity
2. Find the Estimated Pressure Drop
Using the Exhaust Gas Velocity you just calculated, find the corresponding Estimated Pressure Drop in
the “Typical Pressure Drop Curves” column on pages 1-6 and 1-7.
3. Select a Silencer
Select a silencer that achieves your silencing level requirements at an acceptable Pressure Drop level.
1. Given: Exhaust Flow Rate is 2352 ft3/min (66.60 m3/min )
Silencer Inlet Area is 6″ (152 mm) diameter which equals 0.196 ft2 (0.018 m2)
Level of Silencing Required is Critical Grade
2. Using the Typical Pressure Drop Curve, find the Estimated Pressure Drop using the Exhaust Gas Velocity. For this example it is approximately 20 inches H2O (1.49 inches Hg).
3. If this Pressure Drop is acceptable, select any 6″ (152 mm) Critical Grade silencer.
Using the Exhaust Flow Rate, select the correct silencing solution from the Quick Selection Table
shown below. Find the lowest flow rate greater than or equal to the engine flow rate at the required
What Else Should I Know?
Nelson Global Products exhaust silencers provide optimum performance for all applications by offering
silencers crafted for four different attenuation grades. Due to the variability of different applications,
performance levels are most accurately shown as broad range “expected attenuation bands,” which
are based upon typical conditions. These bands will not define the exact insertion loss for a specific
application, since insertion loss is influenced by engine size, type, speed, and unsilenced noise levels
(see product spec sheets for attenuation, back pressure, and design details).
Note: Keep in mind that silencers are not designed to support their weight from the inlet or outlet tube, or
support other components of the exhaust system, such as stacks. For the most efficient operation of all
silencing units, proper mounting attachments are required.
Drains are standard on all models with a 9″ (229 mm) O.D. or larger. Models with a 26″ (660 mm) O.D. or smaller have a coat of high heat-resistant paint. Models larger than 26″ (660 mm) O.D. have a rust-inhibiting primer under high heat-resistant paint. Maximum operating temperature is 1,250°F (677 °C) for aluminized units. Heat-resistant paint maintains its properties up to 900°F (482 °C) on aluminized steel and 1,100°F (593 °C) on mild steel.