POWER July 2021 - 12

O&M
Mechanical Seals and
Bearing Isolator Solutions
for Tidal Energy Equipment
Protection
As clean power technologies become
more mainstream, offshore and riverbased
energy generating systems are
beginning to come into their own in
terms of proven performance. While
the sea and rivers are a widely available
resource, they do come with a unique
set of equipment protection and sealing
challenges. The sealing solutions should
be robust, safe, and effective, and able
to handle the difficulties of the environment,
lifecycle requirements, and inaccessibility
for maintenance.
Turbine Gearbox Sealing and
Protection
Effective equipment sealing is necessary
for successful deployment of tidal
turbines, such as the turbines shown in
Figure 1. Within the turbine, the gearbox
lubrication must be retained while
moisture and contaminants must be
excluded. Traditionally, such rotational
sealing applications would utilize lip
seals at the gearbox boundaries, which
are a reasonable solution in many pieces
of equipment.
However, oil seals must contact the
rotating shaft to provide an effective
seal, and even when operated in a welllubricated
environment, the lip seal will
have a finite life. Oil seals require eventual
replacement, and when used in a
submerged marine environment, an oil
seal replacement could come with a
hefty price tag.
Bearing isolator technology offers a
non-contact seal that will provide both
ingress and egress protection for the
life of the equipment, with zero wear
to the seal or the shaft. Bearing isolators
feature a labyrinth path to exclude
dust and moisture, providing Ingress
Protection (IP), a rating system used
to define levels of sealing effectiveness
of electrical enclosures against
intrusion from foreign bodies and
moisture. This bearing isolator design
also eliminates a contacting wear surface
on the rotating shaft. The Garlock
Guardian bearing isolator is an example
of this technology, and includes
three components: the stator, rotor,
and unitizing element.
The rotor uses an incorporated Oring
to create the static seal on the
shaft. The rotor and O-ring both turn
with the shaft, removing any relative
movement between them and, most
importantly, eliminating shaft wear. The
rotor and the stator are separated by
a unitizing element, which is unique to
this type of bearing isolator. The unitizing
element is made from polytetrafluoroethylene
(PTFE), known for its
low friction and chemical inertness.
The unitizing element maintains the
spacing between the rotor and stator
during installation, and prevents met2.
Bearing isolator technology offers a noncontact
seal that will provide both ingress
and egress protection for the life of the
equipment, with zero wear to the seal or the
shaft. The Garlock Guardian bearing isolator
shown here is an example of this technology.
It includes three components: the stator, rotor,
and unitizing element. Courtesy: Garlock
Sealing Technologies
al-to-metal contact between the two
parts during operation (Figure 2).
Keeping the rotor and stator from
interacting with each other eliminates
the potential for the seal to generate
contamination through internal metalto-metal
contact. The stator is retained
within the equipment bore by patented
Cam-Lock O-ring grooves, which allow
for installation by hand while providing
excellent seal retention without damaging
or galling the mating equipment.
This non-contact seal technology
allows the bearing isolator to have a
truly infinite life. There are no wear
components within the seal design,
removing the need for costly routine
maintenance.
Bearing isolator technology is scalable
in size, with applications ranging
from 1/2-inch thru 24-inch diameter
shafts. Bearing isolators are rated for
surface speeds of up to 12,000 feet per
minute and can absorb radial misalignment
of up to 1/5 inch. Bearing isolators
are available in several materials
including bronze, stainless steel, and
Hastelloy for compatibility in challenging
environments.
1. Tidal turbines come in many configurations. They are similar to wind turbines in that they
have blades that turn a rotor to power a generator, and can be placed on the sea floor where
there is strong tidal flow. These turbines are part of Verdant Power's RITE Project on the East
River in New York City. Courtesy: Verdant Power
12
www.powermag.com
When using a traditional bearing isolator
design, the fluid level within the
gearbox must be maintained below the
bottom of the shaft as noted in Figure
3. Within some gearbox designs the oil
level or behavior of the oil under running
conditions can result in high splash or
even a flooded seal condition. In such
applications, an advanced design of
bearing isolator can meet the need. The
Flood-Gard bearing isolator is an example
of such technology.
POWER | July 2021

http://www.powermag.com

POWER July 2021

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