Note: Descriptions are shown in the official language in which they were submitted.
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MEC ISM FOR SEALI~1G A ROTATING S FROM LOAD END
LEAKAGE
Field of Invention
This invention relates to a sealing methodology for rotating machinery. More
particularly, this invention relates to a sealing mechanism far sealing a
rotating shaft
against passage of a fluid along a central axis defined by the shaft.
Background of the Invention
Environmentally hazardous media such as acids, oils, and toxins, in both
liquid and
gaseous form, that can cause serious harm to the environme~~t, often need to
be processed
within systems consisting of pipes and vessels. These systems often utilize
rotating shaft
driven equipment such as compressors, blowers, pumps and mixers to transfer or
agitate
the fluid or gaseous media within the process system. When handling such
dangerous
media, it is important that the media does not escape to the atmosphere.
Heretofore, conventional mechanical seals were developed to overcome rotating
shaft
sealing problems. When functioning properly these prior art mechanical seals
can be
configured to allow for a fairly secure seal against the fluids and gaseous
media so as to
limit leakage along the shaft to detection levels that are compliant with
current federal
and state environmental guidelines. Mechanical seals are available in numerous
configurations, usually involving a combination of staging of flat seal faces
and various
ports that allow for flushing, draining, or venting. A number of these priar
art
configurations are shown by reference herein. Regardless of the configuration
the
objective is to prevent leakage of hazardous media to the atmosphere.
Predicting the amount of staging or the complexity required can only be
broadly
approximated based on the type of media being handled. The more hazardous the
liquid
or gas, the more secure the seal construction need be.
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One problem with the aforesaid conventional mechanical seals is that gasses by
themselves, or gases produced by liquids that are being sealed against, often
escape.
Conventional mechanical seals are often permeated by these vapors. One
solution to this
problem was the creation of a seal configuration known as a double seal 'with
a barner
fluid, or gas, protection. In this arrangement, two seals form a cavity that
is filled with a
clean or environmentally safe fluid, or inert gas, referred to herein as the
barrier, at a
higher pressure than the liquid or gasses being sealed against. Because of
this higher
pressure, flow is from the barrier side of the seal to the hazardous process
side,
preventing any atmospheric contamination.
A drawback associated with conventional double seal systems is that any
failure by the
first seal can defeat the entire double seal arrangement. If the first of the
two seals breaks
down, the barrier is permitted to escape from the cavity, in effect allowing
the harmful
liquid or gases to reach the second seal at a higher than atmospheric
pressure. 'The
hazardous liquid or gas then penetrates the second seal due to its higher
pressure thus
creating harmful leakage that can injure people and pollute tl~e surrounding
environment.
Therefore there exists a need for a reliable seal system that will not leak to
the outside
environment in the event of failure of a conventional mechanical seal.
The breaking of the aforesaid conventional double seals is a problem of
longstanding
concern due to the sometimes high differential pressures that they operate
under. These
high pressures often result in a break or Leak in one of the two seals. Often
conventional
double seals share common internal parts. When one seal fails, damage to the 1
st seal can
often adversely affect shared components failing the second seal. Therefore,
there exists
a need for a seal arrangement that would be relatively unaffected by the
failure, or
leakage, of an adjacent seal.
Another problem with conventional mechanical seals of this type is that they
utilize
springs, bellows, or other forms of mechanical means to energize sealing
surfaces and
assist them in maintaining a close proximity with each other for proper seal
operation.
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This adds to the complexity, cost, and the overall shaft length required to
accommodate
the seal arrangement. Increased seal length increases the a:~ial distance
between the
supporting bearings and the driven load. Those familiar with the art of
rotating
equipment design recognize that this in turn causes an increase in bending or
deflection
of the shaft that in itself is a known contributing factor to failure of
mechanical seals.
Therefore there exits a need for a seal system of simple design that shortens
the shaft
overhang required for a multiple stage sealing arrangement.
Some equipment, such as that described by Rockwood U.S. Pat. No. 5,261,676,
attempt
to eliminate the possibility of sealing leakage to atmosphere; by enclosing
the bearing
frame and the sealed media within a common housing sealed from the external
environment. Rockwood teaches the use of multiple barrier sealing devices
including an
expeller, multiple stage seal arrangement, and piston seal arrangement, al.l
arranged
axially between the motor and pump assembly adding complexity and cost to that
assembly.
Another common alternative is to use what is known as a close coupled motor. A
close
couple motor eliminates a bearing housing, driving the load directly with an
extended
shaft supported by the motor bearings. Close coupled motors either rely on
conventional
mechanical seals, with all of the size, complexity, and cost associated
therewith, such as
described by Gogwer U.S. Patent 566012, or they rely on elastomeric seals such
as
Ramthum U.S. Patent 6008556 that rub on the rotating shaft, expellers such as
Thompson U.S. patent 633453 that use a pumping device, either attached to, or
integral
with the rotating shaft, various labyrinth designs such as Orlowski U.S.
Patent 6311984
that use a torturous path with a combination vents and drains. Elastomeric
Seals,
expellers, and labyrinth designs are effective at keeping grease or oil in a
bearing, and are
somewhat effective in dealing with incidental weepage from an adjacent
mechanical seal.
However none of these designs can seal completely against a positive pressure,
such as
from a failed mechanical seal, on a continuous basis, both when the machine is
idle and
when it is in operation.
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All rotating equipment that incorporate shaft seals in conjunction with an
overhung shaft
use a certain amount axial distance between the driven load and the closest
bearing to
accommodate housings, covers, and the sealing arrangement. Paul E. Griggs'
pending
U.S. application ser. no. 10/093,99, incorporated herein by reference, teaches
that
applying L3/D4 of less than 50 to a canned motor seal design greatly improves
the shaft
stiffness and thus the operating environment for the mechanical seal. The
L3/D4 ratio is
defined as the overhung shaft length (L) measured between the axial centerline
of the
bearing closest to the impeller (inboard bearing) and the axial centerline of
impeller
cubed (L3) divided by the shaft diameter (D), defined as the diameter of the
smallest cross
section within length L, exclusive of the impeller mounting surface, raised to
the fourth
power (Da)
A larger the L3/D4 ratio results in more shaft deflection. Such shaft
deflection may be
generated by any unexpected operating conditions such as pump cavitations,
closed
suction or discharge valves, or improper operating conditions i.e. improper
equipment
selection. Greater shaft deflection results in greater wear on seals and
bearings in the
system. Close coupled motors are particularly susceptible to deflection
problems because
the shaft extension is usually applied by the motor manufacturer without
changing the
motor frame or bearing design. This results in close coupled motors having a
poor
reputation for maintaining seal reliability. It would be desirable to reduce;
the L3/D4 to
less than 50 on new designs and to reduce it on retrofits where the existing
bearing frame
or close coupled motor is used in a conversion to this innovative sealing
system thereby
increasing the seal reliability. It would further be desirable to achieve the
improved
decreased L31D4 while at the same time lowering the manufacturing cost.
Canned motors are an excellent choice for handling hazardous media. The
problem with
canned motors is that they are expensive to build due to the extra containment
housings
(or cans) and they typically rely on a liquid filled cavity for lubrication.
The extra drag
associated with rotating the cans through a viscous fluid decreases the motor
efficiency
and increases the cost of operation due to the increased power draw. Therefore
it would
be desirous to have a design that will not leak process liquids or gasses to
atmosphere and
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that eliminates the additional costs associated with containment cans and that
does not
rewire a liquid filled housing for bearing lubrication.
Summary of the Invention
The principle object of this invention is to provide a sealing arrangement
which enables
the user to efficiently and safely handle fluids and gasses.
Another object of this invention is to provide a sealing arrangement that will
not leak to
the outside environment in the event of failure of a conventional mechanical
seal.
Another object of the invention is to provide a sealing arrangement with .at
least one
sealing member that is relatively unaffected by the failure of adjacent seals.
1 S It is still a further object of this invention to provide a simple seal
design that shortens the
shaft overhang required of a multiple stage sealing arrangement.
It is still a further object of this invention to provide a close-couple motor
arrangement
that can effectively seal against positive pressure, such as from a failed
mechanical seal,
on a continuous basis, both when the machine is idle, and when it is in
operation, without
the use of mechanically energized seal faces.
It is still a further object of this invention to provide and enable the use
of a L3/D4 of less
than 50 at a reduced cost relative to similar machines using mechanically
energized seal
faces to achieve the same Ievel of sealing protection.
It is still a further object of this invention to enable the reduction of
L3/Dø on retrofit units
thereby increasing their seal reliability while simultaneously providing a
design that
prevents leakage of harmful liquids or gasses to the environment.
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It is still a further object of this invention to provide a close-coupled
configuration
whereby the motor is protected from cantamination from the process media.
It is still a further object of this invention to provide protection against
leakage of
hazardous liquids and gasses to the environment, without utilizing
mechanically
energized seal faces to seal bearing frames or motor housings, and to do so
without the
cost associated with motor cans, or the viscous drag associated with liquid
filled
housings.
According to the invention, the arrangement of construction, preferably, has a
shaft
driven load rnernber such as an impeller, mixer, or fan, mounted on rotatable
drive shaft
cantilevered some axial distance from a supporting bearing such that the load
member is
exposed to a process liquid or gas that is desirable to seal from the external
environment.
The process is sealed by a first mechanical shaft seal of a conventional type
whereby flat
seating faces are held in extremely close proximity each other by a
combination of
mechanical energization means, such as bellows and springs, and any pressure
differential that exists between the upstream (process) side, and the
downstream (non-
process) side of the seal. This seal can be in a single or mufti-stage
configuration and can
be designed to seal either gas or liquid. This seal will herein. be referred
to as the primary
seal. For the purpose of clarification herein the side of any component that
is closest in
the axial direction to the driven load will be referred to as the inboard side
and the side of
any component that is located axially furthest away from the driven load will
be referred
to as the outboard side. A second seal activated by a radially displaced
source of sealing
force, such as by a radially adjacent magnetic force applied between the
sealing
surfaces, and capable of withstanding a sufficient differential pressure from
either liquid
or gas without leakage, while either running or idle, is positioned
indeper.~dently, in that it
has no shared components with the first seal, axially along the shaft on the
outboard side
of the primary seal. This second seal, referred to herein as the secondary
seal, is mounted
in an adapter housing that mates to either a motor or bearing frame such that
the
secondary seal is positioned between the primary seal and the most inboard
bearing
within the bearing ar motor housing. The axial space required by the secondary
seal is
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less than the axial length of an equivalent conventional mechanically
energized face seal.
The adapter housing axially separates the bearing or motor housing from the
process
housing forming a chamber between the fist mechanical seal and the second
mechanical
seal. The adapter housing's purpose is to rigidly connect and axisymetrically
align the
S bearing frame or motor housing, the primary seal and the secondary seal, to
serve as a
leak free adapter between the bearing frame, or motor housing, and the process
containing housing such that a single bearing frame or motor housing could be
adapted to
multiple process housings without re-machining the process housing, or the
bearing
frame or motor housing, and to house a connection means for a conduit to
redirect any
leakage from the first mechanical seal away from the bearing frame in such a
way that the
pressure in the adapter housing separating the primary seal and the secondary
seal does
not pressurize beyond the sealable limits of the secondary mechanical seal.
The adapter
housing can also serve as a location for instruments that might monitor for
leakage from
the first mechanical seal and activate an appropriate alarm.
An outlet connection in the wall of the adapter housing, with a cross
sectional area of
some magnitude greater than the cross sectional area of the largest a.nnulu~s
that could
serve as a leak path in the event of failure of the primary seal, leads to a
safe location
such as a environmental containment vessel, or scrubber system which is at or
near
atmospheric pressure. Those skilled in the art know that the differential area
between the
outlet connection and the largest annulus that could serve as a leak path,
serves to
breakdown pressure leaking by the primary seal, such that should the leakage
fill the
chamber, the maximum pressure in the chamber would be equal to the inverse of
the ratio
between the area of the larger outlet connection and the smaller seal leak
path. ~y way of
example an outlet connection of ten tines the cross sectional area of the
annulus formed
by the largest leak path at the primary seal would limit the accumulation of
pressure in
the chamber to 1/l0th the process pressure. This would mean that a 200 psi
process could
be reliably contained by a secondary seal that would only see 20 psi pressure,
which is
within the capabilities of current non-mechanical face seals such as those of
magnetic
type.
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Brief Description of the Drawings
Fig. 1 is a cross section view of a rotating shaft with load end process
fl~zid sealed from
leakage along the shaft by a primary mechanical seat and a secondary magnetic
seal
devided by a chamber having a leak path to a containment vessel.
Detailed Description of the Preferred Embodiment
While the invention is susceptible to various modifications and alternative
forms, certain
specific embodiments thereof have been shown by way of .example in the
drawings and
will be described in detail. It should be understood, however, that the
intention is not to
limit the invention to the particular forms described. Dn the contrary, the
intention is to
cover all modifications, equivalents, and alternatives falling within the
spirit and scope of
the invention as defined by the appended claims.
l2efernng now to Fig. I, there is shown a preferred embodiment with the
following parts:
A load member, such as an impeller, mixer, or fan, 1, coaxially mounted on a
drive shaft
2, such that the load member 1 extends into a process containment housing 3,
such as a
pump casing or vessel. A cover 4 facilitates the removal of the load member 1
from the
process containment housing 3. Primary seal 5, is sealingly mounted to cover
4. Adapter
housing 6 is seallably mounted to bearing frame or motor housing '7 and to
cover 4.
Primary seal 5 consists of a rotating portion 8 that is driven by shaft 2
through lCey, o-
rings, setscrews, or other suitable means, and a stationary portion 9, both
installed in
accordance with the manufacturer's instructions. Conventional mechanically
energized
mechanical seals are available in many configurations, but in practice use an
axially
stacked mechanism of springs or bellows to energize one closely toleranced
flat sealing
surface or face against another, with one seal face rotating and the other
stationary. The
energization mechanism can be on either the rotating or the stationary member,
but is
preferred to be on the pressure side of the seal so that the process pressure
is additive to
the sealing force of the energization mechanism. The configuration shown in
Fig. 1 one
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is by way of illustration only. tether seal configurations could be applied
without
detracting from the invention described and claimed herein.
Secondary seal IO is positioned inboard of bearing 11, with rotating portion
12 mounted
on shaft 2 , and stationary portion 13 mounted onto adapter housing 6. Magnet
17,
radially adjacent to rotating seal face component 19, attracts target 18 which
is likewise
radially adjacent to stationary seal face component 20 in st<~tionary portion
13, thereby
providing sealing pressure to secondary seal 10, irrespective of shaft
rotation.
The operation of the secondary seal is fully independent of the operation of
the primary
seal; in particular it is not operationally affected by any failure mode of
the primary seal.
The two seals are preferrabiy distinctly separate assemblies, sharing only a
common fixed
mechancial reference in the form of the common housing, frame or structure to
which
their stationary components are attached. However, a common assembly
incorporating
the primary and secondary seals is within the scope ofthe claimed invention,
so long as
the seals operate independently, and a failure of the primary seal does not
adversely
affect the operation of the secondary seal.
The axial length of primary seal S is denoted by the letter A. The axial
length of
secondary seal 10 is denoted by the letter C. Length C is less than length A.
Length B
represents the gap between primary seal 5 and secondary face seal 10.
Connection 14 penetrates the outer wall of adapter housing 6 in a plane normal
to the
shaft axis. The cross sectional area of connection 14 is greater than the
cross sectional
area of the annulus formed by the rotating portion 8 and stationary portion 9
of
mechanical seal 5 at the largest radial cross sectional area that could forms
a leak path to
adapter housing 6 denoted by t6 in the typical arrangement shown in Fig. 1.
The inside
diameter of connection 14 is approximately tangent to wall of adapter housing
6 at its
lowest elevation, and approximately tangent to cover 4, such that any leakage
from
primary seal 5 will drain from adapter housing 6 regardless of whether the
assembly is
oriented horizontally or vertically with the load end downward. A sealed
conduit such as
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piping leads from connection 14 is connected to a hazardous waste atmospheric
collection tank or to the plant's sub-atmospheric processing system such as a
flare or
scrubber that collects and processes hazardous vapor from various plant-site
areas.
In operation, fluid or gas from the process 3 which is at a higher pressure
than the
environment within adapter housing 6 will try to pass between the rotating
portion 8 and
the stationary portion 9 of primary seal 5. Due to the extremely close
proximity of these
parts only minute amounts of liquid or gas normally cross the seal faces into
adapter
housing 6. The pressure within adapter housing ~ is at atmospheric, or sub
atmospheric
pressure depending on the configuration of the waste collection system. .Any
liquid or
vapor passing into the adapter housing from primary seal 5 leaves adapter
housing 6
through connection 14 to the atmospheric or sub-atmospheric collection system.
Adapter
housing 6 does not pressurize and no gas or liquid passes secondary seal 10 to
the bearing
housing or motor frame 7.
In the event of a failure of primary seal 5, the fluid or gas from the process
3 which is at a
higher pressure than the environment within adapter housing 6 will try to pass
through
the largest opening available to it which is a annulus ~6 formed by rotating
portion 8 and
stationary portion 9 at the point where the two parts enter adapter housing 6.
The
differential area between the outlet connection 14 and the largest annulus
that could serve
as a leak path 16, serves to break down or relieve the pressure caused by
fluid or gas
leaking by the conventional first mechanical face seal 5 such that should the
leakage fill
the adapter housing 6, the maximum pressure in the adapter housing 6 would be
no more
than equal to the inverse of the ratio between the area of the larger outlet
connection 14
and the smaller seal leak path 16. By way of example an outlet connection of
ten times
the cross sectional area of the annulus formed by the smallest leak path at
the first
mechanical seal would limit the pressure build up on the adapter housing to
lJlOth the
process pressure. This example demonstrates that a 200 psi process with a
failed primary
seal could be reliably contained by a secondary seal that would only see a
maximum of
20 psi pressure, which is within the capabilities of current non-mechanical
face seals
such as those of magnetic type.
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Because secondary seal 10 would not leak into bearing frame or motor housing 7
under
these circumstances, it would have zero leakage to the environment, and
sealing would
be accomplished without the extra expense and loss of efficiency associated
with liquid
filled motors or complex bearing frame seal arrangements.
Referring again to fig. 1, the axial length C of secondary seal 10 is less
than the axial
length A of primary seal S. Distance B is some minimum distance required
solely to
prevent contact between primary seal 5 arid secondary seal 10 that is a
insignificant
percentage of the total axial length of the sealing system described by the
sum of lengths
A, ~, and C. ~f primary importance is the fact that due to its radially
displaced
energization mechanism for providing sealing pressure rather than an axially
stacked
mechanical means of energizing the sealing surfaces in order to maintain the
close
operating proximity with each other necessary for sealing, secondary seal 10
will always
have an overall length less than that required by a similar sized seal that
employs an
axially stacked means to energize the sealing surfaces. Therefore the overhung
shaft
length (L) measured between the axial centerline of the bearing closest to the
load
member (inboard bearing) and the axial centerline of load member will be
shorter for this
sealing arrangement than for any machinery using two axially stacked
mechanically
energized seals to provide an emissions free system that seals bearing frame
or motor
housing 7. For any give diameter shaft a lower L3/D4 will be obtainable as a
result of this
lower L value, providing an environment that facilitates a greater reliability
for the seals.
The benefits of a small shaft overhang ratio are readily apparent. A new piece
of
machinery can be provided with a L3IDø ratio of less than 50 with a smaller
diameter
shaft, and thus a lower cost due to the shorter axial length L. Existing
pieces of
machinery can be retrofitted with this design by machining adapter Housing 6
to mate
with exiting cover 4 and existing bearing frame or motor Housing 7. Adapter
housing 7
can be designed to minimize distance B, allowing the existing shaft 2 to be
shortened,
again decreasing the L3/D~ ratio while, simultaneously, eliminating the risk
if
environmental contamination due to the release of hazardous liquids or gasses.
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Among the many examples within the scope of the invention as claimed, there is
a
sealing mechanism for sealing a rotary shaft from leakage along the shaf from
a high
pressure zone through a bulkhead to a low pressure zone, consisting of a
sealing chamber
incorporated with the bulkhead such that the chamber is disposed between the
high
pressure zone and the low pressure zone with the shaft extending theretlwough.
A
primary seal around the shaft is sealingly engaged with the high pressure end
of the
chamber/bulkhead structure, with the primary seal haring a rotating seal face
component
contacting a stationary seal face component and an energization source for
applying
sealing pressure between the seal face components. A secondary seal around the
shaft is
sealingly engaged with the low pressure end of the chambe:r/bulkhead
structure, with the
secondary seal having a rotating seal face component contacting a stationary
seal face
component and an energization source that is radially displaced from the seal
face
components for applying sealing pressure between said seal face components.
The
sealing chamber is configured with an outlet for conducting leakage away from
the
chamber. The outlet has a low pressure connection to a suii:able leakage
material disposal
system which might simply contain or otherwise process tlve leakage material.
The outlet
has a cross sectional area greater than the cross sectional area of the leak:
path annulus of
the primary seal. The secondary seal has a pressure rating at Least equal to
the maximum
working pressure of the primary seal multiplied by the ratio of the cross
section areas of
the annulus to the outlet.
'The low pressure zone and the low pressure connection may be substantially at
or less
than ambient or atmospheric pressure. The secondary seal rnay ha s a maximum
working
pressure rating of at least 5 psi.
There may be a rotatable load mounted to the shaft external to the chamber
proximate the
primary seal, with a shaft bearing assembly configured external of the chamber
proximate
the secondary seal so as to be supporting the shaft; and a duive motor
incorporated with
the shaft proximate or just outboard of the shaft bearing assembly. The load
may be
~12~
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confined within a housing, where the housing is incorporated with or forms the
bulkhead
structure.
The chamber incorporated with the bulkhead may be in the form of an adaptor
housing
which sealingly connects a motor frame to a pump housing with the intent that
there be
no leakage from the pump housing through the adaptor housing into the motor.
The energization source of the primary seal may be a spring or bellows
assembly axially
stacked with one of the sealing face components in the usual manner such that
the axial
length of the primary seal is extended by about the axial length of the spring
or bellows
assembly. Other axially stacked mechanisms would likewi se be additive in
length to the
sealing face components.
The outlet is preferrably tangential to at least one of a sidewall and an end
of the chamber
or adaptor housing such that any leakage into the chamber drains by gravity
from the
chamber through the outlet when the shaft and chamber are oriented so as to
have the
outlet at the lowest point within the chamber.
The drive motor may be a close coupled motor. 'The drive xnator, shaft, load,
and sealing
mechanism in combination may have a shaft overhang L3/~4 ratio of les;> than
50.
The invention is inclusive of methods as well. For example, there is according
to the
invention a method for sealing a rotary shaft from leakage along the shaft
from a higher
pressure zone through a bulkhead to a lower pressure zone consisting of
several steps:
incorporating with the bulkhead a sealing chamber through which the shaft
extends such
that the chamber is exposed to the higher pressure zone at one end and the
lower pressure
zone at the other end; sealingly engaging a primary seal around the shaft with
the higher
pressure end of the chamber, where the primary seal has a rotating seal face
component
contacting a stationary seal face component and an energization source for
applying
sealing pressure between the seal face components; sealingly engaging a
secondary seal
around the shaft with the lower pressure end of the chamber, where the
secondary seal
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has a rotating seal face component co~atacting a stationary seal face
component and an
energization source radially displaced from the seal face components for
applying sealing
pressure between the seal face components; configuring the sealing chamber
with an
outlet having a cross sectional area greater than the cross sectional area of
the leak path
annulus of the primary seal; and connecting the outlet at or below the
pressure of the
lower pressure zone to a leakage matez~ials disposal system.
The pressure at this connection to the leakage materials disposal system may
controlled
by the same source as the lower pressure zone, such as atmospheric or ambient
pressure,
or have a separate control device maintaining the pressure at or even slightly
lower than
the lower pressure zone. Also, the secondary seal may have a pressure rating
at least
equal to the maximum working pressure of the primary seal times the ratio of
the cross
section areas of said annulus to said outlet, providing redundant sealing
protection to the
motor and/or lower pressure zone. Alternatively, secondary seals having .a
maximum
working pressure rating of at least S psi (pounds per square inch) may be
employed for
use in systems requiring Spsi or lower secondary seal pressures.
According to this method, there may also be a rotatable load mounted to the
shaft
external to the chamber proximate the primary seal. There may be a shaft
bearing
assembly configured external of the chamber proximate the secondary seal
supporting the
shaft. There may also be a drive motor incorporated with the shaft proximate
the shaft
bearing assembly. Also, the load may be confined within a housing, and the
housing
incorporated with the bulkhead. Turthermore, the sizing and spacing of the
shaft, bearing
assembly, seals, and load may be such that the shaft overhand L3JD4 ratio is
less than 50.
In both apparatus and method aspects of the invention, there is a secondary
seal on the
shaft sealingly engaged on one end of the chamber or housing. 'The secondary
seal has a
rotating seal face component contacting a stationary seal face component and
an
energization source, such as a magnet or electromagnetic device, displaced
radially
outward somewhat from one of the seal face components so as to apply a
magnetic force
on a correspondingly configured magnetic or EIvIIF (electromagnetic force)
responsive
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target relating to the other sealing face component for applying sealing
pressure between
the seal face components. The length of such a seal is able t:o be less than
the sum of the
lengths of the seal face components and the energization sources due to the
radial
displacement of the energization mechanism from the sealing faces.
In another aspect, while the invention contemplates the more typical case
where the load
end of the shaft extends into a higher pressure environment from which leakage
may be
expected; the invention is equally applicable to the case where the load end
is intended to
be at sub-ambient or relatively lower pressure than the drive end, and leakage
into the
dividing chamber is more likely to occur at the drive end or motor end of the
shaft. The
primary seal in this case is understood to be on the motor or drive end of the
shaft, and
the secondary seal on the load or driven end, with the adaptor housing or
central chamber
outlet functioning in the same manner, being held normally at or near the
lower of the
two pressures so as to transport material leaked through the primary seal away
from the
zone between the two seals while limiting the maximum pressure to which the
secondary
seal might be subjected in the event of total primary seal failure.
Other and various examples within the scope of the claims that follow will be
apparent to
those skilled in the art, from the specification and drawings provided.
_ l~ _
