Description
 
Industrial silencers and mufflers absorb and attenuate noise levels from machinery and other sources for environmental amelioration and regulatory compliance. They use several basic designs.

• Absorptive silencers and mufflers incorporate sound-deadening materials, fabric and compounds to absorb the noise energy from the flow of gas or air.
• Reactive silencers and mufflers use complex passages and/or chambers to optimize noise attenuation while maintaining application requirements such as pressure drop, airflow and size.
• Hybrid designs use both absorptive and reactive design elements, combining airflow path management and acoustical materials to reduce noise.

By contrast, active noise cancellation devices use sound sensors to characterize the sound profile and noise-cancelling speakers to produce sound 180° out of phase with the airflow noise. Industrial silencers and mufflers vary in terms of port type, inlet placement, outlet placement, and special features.
 
Types
There are two basic types of ports: inlet silencers and exhaust silencers.

• Inlet silencers mount on the intake side of the device to be silenced.
• Exhaust silencers mount on the outlet or exhaust of the muffled device.

Inlet Placement 
In terms of placement, both inlets and outlets can be located either in-line or on the side.

Special Features
Special features for industrial silencers and mufflers include filter silencers, separator silencers, and spark arrestors.

• Filter silencers consist of filters, traps, or screens for removing dust, grit, water or other impurities from the flow of gas or air.
• Separator silencers include components that physically separate water from the flow.
• Spark arrestors are designed to trap hot carbon and soot particles. They usually feature a chamber design and are used in combustion exhaust applications to minimize danger and maintain air quality.

How to Select
Selecting industrial silencers and mufflers requires an analysis of physical specifications, performance specifications, and mounting attachments.
 
Physical Specifications
Physical specifications include inlet size and outlet size. Some industrial silencers and mufflers have a round, circular, or oval-shaped cross section. Others are square or rectangular.
 
Performance Specifications
Performance specifications include noise attenuation, maximum pressure rating, and maximum flow rating.

• Noise attenuation is measured in decibels (dB) and expressed as a performance curve across the audible frequency range.
• Pressure is measured in pounds per square inch (psi).
• Flow is measured in standard cubic feet per minute (SCFM).

Mounting Attachments
Mounting attachments include male threads, female threads, flanges, and pipe clamps. Products that are welded in-line or that use adhesive compounds or industrial adhesive tape are also available.
 
Applications
There are many applications for industrial silencers and mufflers. Some products are designed to silence industrial engines, air or gas compressors, vacuum pumps, or turbines. Others fit the exhaust ports of air cylinders, solenoid valves, or other pneumatic components.

• Blowdown silencers are used for rapid exhaust or venting applications.
• Pressure relief valve silencers are also used to attenuate the noise associated with relief blowoffs.
• Chimney silencers are used in the exhaust systems of industrial boilers, ovens, and furnaces.
• Automotive filters are used on cars, trucks, motorcycles, and industrial vehicles.

Standards
The American Society for Testing and Materials (ASTM) specifies standard ASTM E477, which describes procedures for the measurement of acoustical insertion loss, the airflow generated noise, and pressure drop as a function of airflow for sound attenuating devices including duct liner materials, integral ducts, and in-duct absorptive straight and elbow silencers used in the ventilation systems of buildings.