TECHNOLOGY
There are three types of silencers used on generator sets. A traditional reactive design (left) uses pass-through tubes and expansion
chambers. The absorptive type (center) incorporates packing material in the shell of the silencer, while the combination silencer (right)
incorporates both reactive and absorptive technologies.
and/or pass-through tubes to reduce exhaust noise. These
are the most common style of silencer and are also some of
the least expensive.
Absorptive silencers are used to treat high-frequency
sound waves. High-frequency sound waves are more com-
mon in high-speed, low-horsepower engines. The pulsation
of the exhaust stream is treated by using insulating material
such as fiberglass in the shell of the silencer.
The combination silencer incorporates both reactive and
absorptive characteristics. If an engine produces both high
and low frequencies, the combination silencer should be
selected. The drawback of the combo silencer is that it
tends to be more expensive than other types.
In fully enclosed gen-sets, space inside the package is at
a premium. Some sites allow the mounting of the silencer
on the top or farther away from the package. Locations like
RobinsonCustomEnclos.qxp 2/10/09 1:10 PM Page 1
Our best work begins by
thinking outside the box.
Our best ideas go inside.
At Robinson Custom Enclosures, our state of the art design
begins by thinking outside the box. We custom design each
enclosure package to meet the customer’s need in the
most cost-effective way possible.
WHERE CUSTOM IS STANDARD
1740 Eisenhower Drive | P.O. Box 5905
De Pere, WI 54115-5905
hospitals and office buildings generally prefer the silencer
to be mounted internally, as it provides a more stream-
lined and aesthetically pleasing design. As no two gen-set
designs are ever alike, it’s rare to locate the silencer in the
same location. The best option is to place the silencer in a
corner, roof or center location near a point that can provide
some air movement for cooling.
Several pieces of information are needed when selecting
the silencer. They include:
• the engine exhaust flow;
• the engine exhaust
connection size;
• the engine exhaust gas
temperature;
• the maximum allowable engine
backpressure;
• the required attenuation level
reduction;
• the inlet/outlet configuration; and
• the operating environment.
The engine information is usually readily available from
the engine manufacturer or distributor. Historically, engine
manufacturers typically undersize their engine connec-
tion sizes. This produces additional engine backpressure
when applying a silencer. Adapters are available to provide
a larger connection size. If engine exhaust temperatures
approach or exceed 1250°F, a stainless-steel construction
option should be considered.
Some silencer manufacturers offer online programs to
make the sizing process easier. The selection process is
carried out by using the information mentioned earlier or by
selecting the type of gen-set manufacturer.
There are four grades of attenuation levels available:
Industrial Grade ( 12 to 18 dB(A) reduction); Residential Grade
( 18 to 25 dB(A) reduction); Critical Grade ( 25 to 35 dB(A)
reduction); and Hospital Grade ( 35 to 42 dB(A) reduction).
Higher grades of attenuation create higher levels of
backpressure due to increased exhaust flow restriction.
The engine manufacturer can provide the maximum level
of backpressure allowed. The higher the backpressure on
the engine, the less efficient it becomes, so the difficulty for
any package designer is to minimize engine backpressure
while still maintaining allowable attenuation levels.
There are several types of inlet/outlet configurations avail-
able for silencers that allow it to be positioned in various
locations within the gen-set enclosure, depending on space
