Brochure

Factors and Effects of Control Valve Noise
The Silent Treatment | 5
Noise doesn’t always cause damage. The potential for noise
damage and vibration are dependent on the following factors:
n Pressure Drop and Pressure Drop Ratio – Greater drops
in pressure and higher pressure drop ratios increase the
potential for noise. The pressure drop ratio—the change in
pressure divided by the inlet pressure—is an indicator used
to determine the performance level required of the control
valve trim.
n Valve/Trim Geometry – Tortuous flow paths can increase
turbulence and noise, which can cause damage to the
control valve trim, body, and pipeline. Other factors
affecting noise include flow path size, shape, and location.
n Valve Outlet Area – High fluid velocity at Mach numbers
at or above 0.3 through the control valve outlet or pipe can
result in increased turbulence and noise. Valve outlet area
must be accounted for to obtain the most accurate noise
prediction.
n Flow Rate – Higher flow rates have a potential to increase
turbulence and noise.
n Time of Exposure – The longer an area is subject to high
vibration, the more likely it is to be damaged.
n Project Noise Assessment – Factors external to the control
valve can affect the overall noise being generated in the
plant. These factors include:
•
Flow Path – Orifice plates, elbows, manifolds, and
other downstream equipment can obstruct and/or
disrupt the flow. These changes generate acoustic
pressure fluctuations that can alter the intensity of
the noise.
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•
Combined Noise Sources – Two similar noise sources
in close proximity can be up to 3 dB higher than the
greater of the two original sources.
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Material, Thickness, and Diameter – Thicker and
larger diameter pipelines reduce the ability of noise to
radiate through the pipe wall and create sound waves
that people can hear.
Most regulatory agencies have placed restrictions on workplace noise
exposure. For instance, allowable sound pressure levels in the U.S. are
shown above.
Vibration Damage
Noise can cause vibration in control valves, pipe, and other
system elements. This vibration can shorten the life of your
equipment.
Environmental Noise
Noise frequencies between 20 and 20,000 Hz are audible and
can be a nuisance to plant operators, maintenance personnel,
and others who come into contact with the noise. At high
levels, noise can cause damage to human hearing and radiate
to surrounding environments where it may result in further
problems such as fines and restrictions on operations.
Control valve stem/shaft breakage is a common fatigue failure due to
heavy vibrations within the system.