Brochure

Control Valve Noise Technologies
6 | The Silent Treatment
Two primary challenges face the control valve supplier:
1) effectively control unwanted noise and 2) accurately predict
the noise levels associated with a specific control valve in a
given set of operating conditions. Both of these challenges
require a deep understanding of the foregoing fundamentals.
Effective control of noise arising from mechanical sources has
been accomplished by improving control valve design and
implementing good maintenance protocols.
Controlling fluid-generated noise requires a number of
different strategies dependent on control valve style and
degree of attenuation.
Source Treatments
A principle aerodynamic strategy is to break the flow stream
into many small, parallel flow passages. Not only does this
reduce the strength of the noise source, but also shifts the
frequencies to a higher, non-problematic range. These and
other techniques are known as source treatments.
Source treatments prevent noise at its source, which can
involve the control valve. Common source treatments include
noise-attenuation control valve trims, inline diffusers, and vent
diffusers that minimize turbulence.
Emerson utilizes unique flow passage shapes and multi-stage
pressure reduction in noise-attenuation control valve trims
as source treatments. These unique flow passage shapes
reduce turbulence to minimize shock-associated noise and
place turbulent shear layers away from solid boundaries to
reduce noise. The multi-stage pressure reduction utilized
with sound engineering principles control jet size, formation,
interaction, and accommodates fluid expansion. It is important
to control these aspects of the exiting jets to reduce the noise
and vibration. Emerson has developed a variety of noise-
attenuation control valve trims that offer attenuation levels of
up to 40 dBA.
Path Treatments
In addition to eliminating noise at its source, noise levels can
be attenuated by impeding the propagation and transmission
of the sound waves. Solutions of this type are referred
to as
path treatments. Path treatments help eliminate noise heard
outside of the pipe wall by increasing the resistance of the
noise path. Typical path treatments include increasing the pipe
thickness, adding acoustical or thermal insulation, or adding
inline pipe silencers. Noise levels can be decreased by as much
as 45 dBA depending on treatment and application.
The weakness of path treatments is that both the fluid stream
and the piping itself are very effective at transmitting noise;
therefore complete noise attenuation is difficult. This means
that attenuation is only effective for the area where the
treatment is applied.
Noise-Attenuation Technologies
Fisher noise-attenuation technologies, listed below, are
compatible with many Fisher control valve types.
n Whisper Trim I Cage
n Whisper Trim III Cage
n WhisperFlo Cage
n Vee-Ball Control Valve with Rotary Attenuator
n V260A Control Valve with Aerodome Attenuator
n Vent Diffusers
n Inline Diffusers
Emerson maintains application guidelines specifically for
Fisher technologies. We would never recommend using our
proprietary application guidelines for non-Fisher technologies,
nor using other suppliers’ application guidelines for Fisher
technologies.
Emerson routinely fulfills custom orders for noise solutions
not offered in the standard product line using the dedicated
application engineering team. Emerson is the only custom
control valve provider in the world who can offer the
combination of experience, control valve engineering,
research understanding, and worldwide manufacturing
capabilities. The track record of custom Fisher control valves
is proven many times over. Tens of thousands have been
produced in recent decades.
Computational fluid dynamics show jet independence from three
properly spaced holes (left). The same three holes spaced too closely
(right) show jet interaction, which leads to additional noise. Being
able to predict and control jet interaction can reduce the noise
produced by up to 40 dBA.