Tech Briefs Magazine - June 2022 - MD-10

vibrations produced by
sound waves, which
can also have a negative
impact on nearby
equipment and processes.
For
environments
where reducing sound
is
important,
variTraditional
HPU (left) and a modern, self-contained HPU from Bosch Rexroth (right) designed with a sand-casted manifold, " J-shaped "
reservoir, liquid-cooled variable-speed pump drive and polymer-concrete material.
systems provide more efficient options
to consider before choosing where to
invest.
When replacing or retrofitting an
HPU, manufacturing engineers are advised
to consider some key metrics that
differentiate modern hydraulic system
design from conventional systems: size,
noise, energy efficiency, connectivity,
and total cost of ownership.
1. Size: The overall size of an HPU is
determined largely by the size of its hydraulic
fluid reservoir. For traditional
HPUs, the generally accepted rule is to
size the reservoir a minimum of three to
five times the maximum pump flow, to
allow for degassing (time enough for the
oil to sit in the reservoir and air bubbles
to rise to the surface). For example, to
achieve a max flow of 150 L using this
old rule requires an approximately
600-L reservoir, which occupies a considerable
amount of space within the unit's
footprint.
Conversely, some modern HPUs use
alternative methods of degassing that
reduce the required amount of reservoir
oil to a 1:1 ratio. More efficient manifold
block designs, along with optimized reservoir
shapes, allow for smaller tanks.
That technique improves flow characteristics
and better integrates component
functions. The resulting manifold is
more compact and lighter than a con10
ventional
manifold and can be manufactured
in a variety of shapes to fit into
tight spaces.
This is combined with a special
" J-shaped " reservoir that allows for passive
degassing of any bubbles in the oil.
As a result, a unit that produces a max
flow of 150 liters per minute only needs
a reservoir capacity of 150 liters, or 75
percent less reservoir capacity than a
traditional HPU. In terms of space on
the plant floor, that can translate into a
0.5 m2
able-speed hydraulics is
making notable headway,
operating at around
10 dB quieter than conventional
HPUs in the
7.5 kW to 30 kW range.
Considering every three
decibels equals a twofold
increase in noise
volume, this represents
a significant improvement
in noise reduction.
Lowering the system
noise to 75 dB is
considered conversation
level, which means
two co-workers could stand next to the
HPU and communicate with each other
without wearing earplugs.
How is this noise reduction accomplished?
First, by operating at variable
footprint, versus a typical 2 m2
footprint, and an 80 percent reduction
in weight. The manufacturing plant
would only need to supply and maintain
one-fourth as much hydraulic oil in this
example.
2. Noise: By nature, manufacturing
facilities are considered noisy and usually
require special personal protective
equipment to block out that noise. But
what is considered an acceptable amount
of noise is not universally defined. In a
steel manufacturing plant, for example,
an HPU could operate in total silence
and still not reduce the overall noise on
the plant floor. But in other types of facilities,
such as automotive manufacturing
or rubber molding with assembly
lines and long machine run times, quiet
operation is desirable to maintain a
pleasant working environment. Noise
can also be a consideration due to the
speeds, modern units are naturally quieter,
as they are not demanding their full
power 100 percent of the time but instead
only delivering the power needed
at the moment. Second, modern systems
can be constructed of materials that
dampen sound and minimize vibrations
by using design strategies like a liquid-cooled
motor, compact arrangement
of components, unitary housing, and
built-in sound-insulating mats that are
not features in conventional power
units. For example, to eliminate the
damping bearings that transmit noise to
the reservoir tank, Bosch Rexroth attached
its CytroBox motor pump group
to a polymer-concrete foundation that
absorbs vibrations.
Takeaway: Recent advances in HPU designs
have resulted in noise levels as low as 75
dB (conversation level), which is a significant
leap in sound reduction.
3. Energy Efficiency: A fixed-speed
HPU operates at 100 percent motor
speed, 100 percent of the time, regardless
of whether the application requires
it or not. Any energy that is not being
used to do work is converted to heat,
and simply turning a motor and pump at
Motion Design, June 2022
MD Fluid Power Feature 0622_1.indd 10
Cov
ToC
5/18/22 10:01 AM

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Tech Briefs Magazine - June 2022

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