Studies have shown that the complete absence of sound can drive a person insane, causing them to experience hallucinations. Likewise, loud and overwhelming sound
can have the same effect. This especially holds true in manufacturing and plant environments where loud noises are the norm.
A NJ-based food processing plant began experiencing this
issue firsthand after building a new manufacturing space. Some
of the plant’s equipment is powered by a series of hydraulic
systems in a central pump room that contains a number of dual-stage hydraulic pumps. These 3,000-5,000 psi pumps push fluid
through steel pipes that run under a conference room and up the
side of a wall next to offices before moving out into the plant.
Unfortunately, out of sight out of mind isn’t always the case
with hydraulic machinery. The pipes connected to the pump
were hard-clamped to the building structure to prevent them
from moving around. This setup created a severe noise issue as
the hydraulic pump went on stroke and pushed hydraulic fluid
through the pipes, rendering the office space and a conference
room almost unusable.
The unbearable and disorienting noise wasn’t coming from
the pump itself. The pulsations, produced by the pump, created vibrations that radiated noise through the pipes and off of
Norm Dotti, Consulting Acoustical Engineer, Russell
Acoustics, diagnosed the source of the noise problem.
“The pipes were singing as fluid was pumped through them,”
Dotti said. “They would shake the steel walls and cause them
to radiate sound. The entire building structure around the office
space was essentially acting as a loudspeaker to convey that
A simple house fan can be used to provide a layman’s view
of the pump sound effect. If you take the number of blades on
a fan (or the number of pistons in a pump) times its rotational
speed, that fan (or pump) is going to put out a tone at the rota-
tional speed called blade passage frequency. A helicopter does
the same thing. Take the number of blades times the speed at
which the rotor turns and you get a component sound or vibra-
tion at that frequency.
In our food processing plant scenario, even detaching the
piping from the structure wouldn’t completely resolve the
issue. The force and sound was coming from pulsations in the
hydraulic fluid running down the pipeline. These pressure pulsations flowing through the lines are difficult to absorb since
hydraulic fluid is hard to compress. Dotti determined that the
best, most efficient solution would be to utilize a muffler.
The muffler needed for this application is very different from
the commonly known car muffler used in exhaust systems.
Rather than stifling the force of airborne sound, the muffler
needed to reduce the pressure pulsations in the hydraulic fluid.
Sound can travel through air, water or even hydraulic fluid, but
properties such as viscosity and speed at which sound travels
varies for each medium.
The major difference is that air is a compressible medium,
while hydraulic fluid isn’t nearly as compressible. That makes
The Sound Beneath