Noise generated by industrial processes is often more than just a nuisance. It frequently creates an environmental health and safety hazard to workers that can pose a substantial risk, including permanent hearing damage. In the industry, silencers are used to reduce noise from machines and other sources and are generally installed to meet EPA, OSHA or other occupational health and safety organization noise level standards.
There are many types of silencers, and each is designed to effectively and economically reduce the noise for a specific application.
For machines, the acoustic source is either a pulsation or continuous-steady type noise mechanism. A positive displacement device, such as a piston pump, low-speed rotary pump or reciprocating engine, produces pulsation type energy. A blower, fan or turbine fall into the continuous/steady type category. However, some machines have both characteristics, and these require a combination silencer.
The selection of a blower silencer is based on two primary considerations: The silencer must be the correct size with sufficient capacity for the volume flow, and it must be the proper type for the application. The nominal silencer size need only be based on the gas volume (CFM of the gas or air at the operating conditions). However, the silencer design must also consider the blower size and operating speed.
There are three basic types of silencers commonly used on positive blowers:
- Reactive type silencer, consisting of a series of expansion chambers having interconnecting tubes
- Combination chamber-absorptive type silencer, similar to the reactive type but with an acoustically-packed, sound absorbing section added to the connection closest to the blower
- Simple, straight-through packed type, used on small, high-speed machines which characteristically produce significant high-frequency noise and relatively mild pulsations
The Pitch Line Velocity (PLV) is usually the criterion for silencer type selection. PLV is the peripheral velocity of the timing gear, equal to the product of the gear circumference and the rotation speed of the blower, usually expressed in feet per minute (FPM).
When a blower operates in the critical PLV range, it usually generates an objectionable high-frequency noise which may cause shell ring or tank hammer in the piping and the silencer. Critical PLV conditions always require a combination chamber-absorptive silencer for satisfactory results.
Universal AET Blower Silencers
Blowers operating at or above 3,300 ft./min are generally considered critical for an inlet silencer application. These will invariably require the Universal RIS Series combination chamber-absorptive type silencer.
Blowers operating at less than 3,300 ft./min are considered sub-critical and can be silenced adequately with a chamber-type silencer, such as Universal URB or UCI Series. Inlet Filters or Filter Silencers are commonly used on blower inlets, either individually or in series with a separate inlet silencer.
RIS Series Inlet Silencer
The Universal AET catalog provides detailed information for each silencer type. The following is an example of the RIS series:
The RIS Series Inlet Silencer is a heavy-duty, all-welded unit constructed of carbon steel sheet and plate. It includes an acoustically-treated outlet and will provide pulse control and silencing suitable for critical PLV applications.
For sizes 4″ and larger, the silencer is equipped with flanged connections drilled to 125/150 lb. ANSI specifications. Smaller sizes are standard with male threaded pipe nipples. Units sized 4″ and 5″ are available in either flanged or male pipe threads. Exterior surfaces receive a shop coat of rust-inhibitive primer and may be finish painted in the field if desired.
The RIS Series is the basic model, having conventional end-in, end-out configuration. A low side outlet version is designated RISY Series and a high side outlet configuration is designated RISH Series. The performance is identical for three types.
For the more severe discharge conditions of typical blower installations, a PLV of 2,700 ft./min is generally accepted as the critical transition speed. Blowers operating below 2,700 ft./min are considered subcritical and can usually be adequately silenced on the discharge side by use of a chamber-type silencer Universal UCD or URD Series. Blowers operating above the 2,700 ft./min transition speed will require combination chamber-absorptive silencers, such as the SD or RD Series.
Universal AET provides blower silencer models for every application as follows:
- UCI Series Inlet Silencer: Chamber-type for use on sub-critical PLV applications
- RIS Series Inlet Silencer: Combustion chamber-absorptive type for critical PLV applications
- UCD, URB/URD Series Discharge Silencers: Chamber-type for use on sub-critical PLV applications
- SD, RD Series Discharge Silencers: Combination chamber-absorptive type for critical PLV applications
Universal AET will also custom design a silencer to meet special noise abatement requirements. Design characteristics for all Universal AET blower silencers can be found in their catalog.
Universal AET provides custom-engineered acoustic, emission and filtration solutions to the natural gas power generation, midstream natural gas pipeline, locomotive and general industrial end-markets. Their product offering includes gas turbine inlet and exhaust systems, custom silencers, filters and custom enclosures. Babcock & Wilcox Enterprises, Inc. (B&W) acquired Universal Acoustic & Emission Technologies, Inc. (Universal AET), in January 2017. The new company name is Babcock & Wilcox Universal.