Note: Descriptions are shown in the official language in which they were submitted.
~73t3'7~
PLURAL FLUID MAGNETIC/CENTRIFUGAL SEAL
.
BACKGROUND_OF THE IN~ENTION
Field of Invention
. _
This invention relates to a novel plural fluid
combined magnetic/centrifual seal.
More particularly, this invention relates to a
novel combined centrifugal and magnetic seal structure
which employs separate, different viscosity fluids
for use during separate magnetic seal and centrifugal
seal operating modes of the structure whereby each
seal complements the other at different rotational
speeds. The plural fluid/magnetic/centrifugal seal
makes it possible for the design parameters of each
sPal stage, though coacting over a complete speed
range, to be substantially independent one from the
other and optimilzed design criteria can be employed
in the construction of the two cooperating seals.
Background of Invention
. .
A combined magnetic/centrifugal seal is described
and claimed in United States Patent 4,304,411 issued
December 8, 1981 for a "Magnetic/Centrifugal-Fluid Seal"
in the name of Donald F~ Wilcock et al and assigned to
Mechanical Technologyr Inc. I'he combined magnetic/
centrifugal seal disclosed said patent employs a
ferromagnetic fluid which in conjunction with a
magnetic seal gap region of the structure, provides
~173~37~
magnetic sealing for speed ranges from zero to rota-
tional speeds of about 2000 revolutions per minute
(rpm). At higher rotational speeds above about
2,000 rpm the same ferromagnetic fluid provides
through centrifugal effects on the fluid a centrifugal
sealing action for speed ranges from about 2000 rpm
to 20,000 rpm~ At the higher rotational speeds,
however, cooling of the ferromagnetic sealing fluid
is required in order that its magnetic sealing
capabilities not be adversely affected by the high
temperatures encountered at higher rotational speeds.
It will be appreciated therefore that the upper
rotational speeds at which the combined magnetic/
centrifugal seals of the type described in the
aforementioned patent can be driven, in effect is
limited by the temperature characteristicsof the
ferro-magnetic fluid and the ability to design into
the seal structure effective cooling for the
ferro-magnetic fluid. To overcome these limitations,
the present lnvention was devised.
SUMMARY OF INVENTION
... . _ , . _ .
It is therefore a primary object of the invention
to provide a new and improved plural fluid combined
magnetic/centrifugal hermetic seal which employs
separate sealing fluids to effect both magnetic and
centrific hermet:ic sealing at different rotational
speed ranges.
A feature of the invention is the provision of a
new and improved plural fluid, combined magnetic/
centrifugal hermetic seal capable of operation over
a speed range e~tending from zero to over 100,000
rpm.
Another feature of the invention made possible
by the plural fluid combined magnetic/centrifugal
seal is that it produces less heat at higher rota-
~L1';~3~37~
tional speeds thereby avoiding the need for the
installation of water cooling jacekts and the like
for those applications where the installation of
such cooling capability is not feasible.
Still another feature of the invention is the
provision of a seal having much lower power loss
at higher rotational speeds due to the lower viscosity
of the centrifugal sealing fluid.
Still another feature of the invention is the
pro~ision of a plural fluid, combined magnetic/centrifugal seal which provides a 100~ hermetic
seal over the entire speed range at which it is
designed to operate and which is double acting,
that is, the high pressure atmosphere PH acting
on the seal can be on either side of the seal at
any time during operation.
A furthe~ feature of the invention is the
provision of a plural fluid combined magnetic/
centrifugal seal which does not leak during the
transition from magnetic to centrifugal sealing
and vice versa due to the diff~rences in viscosity
of the high viscosity ferromagnetic sealing fluid
and the low viscosity centri~ugal sealing fluid.
Because of the differences in viscosity, density and
shearing forces, the low viscosity centrifugal sealing
fluid separates and is flung centrifugally outward
at lower rotational speeds than the higher viscosity
ferromagnetic sealing fluid while going through
the transition from low rotational speeds to high
rotational speeds. Conversely, during slow down
from higher rotational speeds to ~ower rotational
speeds~ the higher viscosity ferromagnetic fluid
and lower shearing force acting thereon, causes it
to break off and reform the magnetic seal well in
advance of the break-up of the lowex viscosity
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centrifugal sealing fluid. .Thus, there is an o~erlap
transition period during which hermetic sealing
is provided by both the magnetic sealing fluid and
the centrifugal sealing fluid during the critical
transitional speeds.
A.still further feature of the invention i5 the
ability to optimally design the magnetic seal arrange-
ment to withstand high pressure differentials by
reason of the fact that the design of the magnetic.,
seal stage is not restricted by volume/ratio considera-
ti-ons dictated by an associated centrifugal seal
stage. The same observation is true of the design
~ of the centrifugal seal stage whereby flexibility of
design of both the magnetic seal and the centrifugal
seal is made.possible due to the fact that each
operates independently of the other.'
. As a consequence of the advantages listed in
; - the preceding paragraphs, the problem of leakage
during transition from magneti~,to centrifugal sealing
! .20 and vice versa can be readily overcome in any seal
configuration.since e~ch sealing stage operates
ind,ependently of the other and the viscosities,
de~sities and shearing forces acting on the respective
ferromagnetic'and centrifugal sealing fluids can be
appropriately tailored to provide any desired over~
lapping sealing period during transition under
conditions where the load capacity (~P2) is propor-
tional to the'density of:the centrifugal fl~id,
rotor speed ~, and the $1uid leveI dif~er;ence ~etwee'n the '
low p~essu~e side, and the high pressuXe 'side.
In pract'icing the invention a plural fluid
magnetic/centrifugal seal is provided for hermeti-
cally sealing the space between a rotating shaft
member in a close'fitting spaced-apart stationary
3~ housing mem~er. The seal comprises means formed
~:173~
on members defining at least one magnetic pole-like
close clearance magnetic seal gap region between
opposed surfaces of ~wo members. A high viscosity
magnetically permeable, ferromagnetic fluid normally
is disposed in the magnetic seal gap region with the
rotating shaft member at rest or at low rotational
speeds. Magnetic field producing means are mag-
netically coupled to at least portions of the ro-
tating shaft and stationary housing members so as
to include the magnetic seal gap region and the high
viscosity magnetically permeable ferromagnetic
fluid in a closed magnetic circuit. A circumferen-
tially arranged centrifugal seal forming region is
radially disposed outwardly from the magnetic seal
gap region and is located between the rotating shaft
and stationary housing members. Means are provided
in communication with the centri~ugal seal forming
region for receiving and pooling a low viscosity
centrifugal sealing fluid with the centrifugal
sealing fluid being centrifugally thrown outwardly
during rotation of the rotating shaft member into
the centrifugal seal forming region so as to form
a centri~ugal hermetic seal through the medium
of the fluid pooled between the rotating shaft and
stationary housing member by centrifugal force at
higher rotational speeds of the rotating shaft
member.
In preferred embodiments of the invention, a
reservoir is provided for receiving the magnetically
permeable ferromagnetic sealing fluid in a space
intermediate the rotating shaft member and the
stationary housing member. The reservoir serves
to collect and pool the ferromagnetic sealing
fluid during high speed rotation of the rotating
shaft member so as to isolate the two different
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fluids one from the other in separate but communicating
spaces.
In another preferred embodiment of the invention,
the low viscosity centri'fugal sealing fluid is comprised
by the lubricating oil of an apparatus or m~chine on
which the plural fluid combined magnetic~centrifugal
seal is installed. In such installation, the centri-
fugal sealing stage is included in and comprises a
part of the lubricating oil cooling and supply system
of the machine or other apparatus and the centrifugal
seal serves as an auxiliary lubricating oil pump
used in conjunction with the main lubricating oil
circulating pump for pumping the lubricating oil from
'the centrifugal seal region to a lubricating oil
reservoir comprising a part of the lubricating oil
supply system for the machine, for cooling the seal
system or other apparatus. In such an arrangement,
the installation may further include a pressurized
labyrinth'buffer seal positioned on the rotating
shaft member adjacent the plural fluid magneticj
centrifugal seal and a hostile high pressure atmos-
phere so as to form a combined two-stage labyrinth
and magnetic/centrifugal seal against ~he high
pressure hostile'atmosphere.
BRIEF DESCRIPTION OF DRAWINGS
These and other objects, features and many of
the attendant advantages of this invention will become
better understood upon a reading of the following
detailed description when considered in conjunction
with the accompanying drawings, wherein similar
elements in the several figures are identified by
the same ref~rence character, and wherein:
Figure 1 is a partial sectional view of a new
ana improved double acting plural fluid magnetic/
centrifugal hermetic seal constructed according to
31~7~
--7--
the present invention;
Figure 2 is a partial sectional view of a second
form of the invention different from that of Figure 1
in that it employs an axially arrayed magnetic seal and
S includes a cooling jacket for maintaining the temperature
of both the magnetic sealing fluid and the centrifugal
sealing fluid within prescribed limits;
Figure 3 is a partial schematic view of still a
third embodiment of the invention somewhat similar to that
of Figure 2 wherein the magnetic seal region is formed on
a tapered portion of the shaft;
Figure 4 is a partial sectional view of still a
different form of the invention wherein the lubricating
oil of a machine or other apparatus is used as the
centrifugal sealing fluid, and illustrates how pumping
action for the lubricating oil is obtained with the vane;
Figure 5 is an operating characteristic curve for a
novel plural fluid combined magnetic/centrifugal seal
according to the invention, showing the speed versus
differential pressure sealing capability of the structure
wherein the speed of a shaft being sealed is plotted as
the abscissa and the differential pressure sealing
capability in pounds per s~uare inch is plotted as the
ordinate;
Figure 6 is a plot of the change in viscosity
versus temperature of two different ferromagnetic sealing
fluids wherein the temperature is plotted as the abscissa
and the changes in viscosity are plotted as the ordinate;
Figures 7 and 7A are partial schema~ic sketches
showing the rotary vane of the seal structure in the at-
rest condition;
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Figure 8 is a partial, explode~ sectional view
of the ferromagnetic fluid reservoir showing the
details of the shoulder design of the vane.whereby
slinger action is achieved; and
Figure 9 is a partial schematic view of the
~igure 8 structure and illustrates certain critical
dimensions.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figur.e 1 is a partial sectional view of a novel
plural fluid combined magnetic/centrifugal seal
constructed according to the invention for sealing
out a higher pressure exterior atmosphere indicated
at P~ from the interior of a machine or other area
having a somewhat lower pressure or the same pressure
PL, ox vice-versa. The seal shown in Figure 1 is
for a shaft indicated at 11 which is rotatably
journaled in bearings (not shown) in a housing or
other stationary member part of which is shown at
12. The shaft 11 includes an annular-shaped
collar vane 13 keyed or otherwise secured to sh~t
11 and located within a cavity or other open space
formed within housing 12~ The a~nular collar vane
13 is comprised by a larger thickness inner portion
13A having a thin vane like portion 13B secured
around its outer periphery or integral therewith.
The inner thick portion 13A of collar vane 13
has its flat side surfaces opposing a plurality
of magnetic pole-like teeth shown at 14A and 14B
on respective opposite sides of the thick-dimension
portion 13A of the collar vane. The magnetic
pole-like teeth 14A and 14B are disposed opposite
the opposing flat surfaces of portion 13A so as
to define a plurality of close clearance magnetic
gap spaces in which are disposed a plurality of
droplets of a magnetically permeable ferromagnetic
~1731~7~
fluid 15. The ferromagnetic fluid 15 preferably
comprises a Diester fluid in which are suspended
ferromagnetic particles and may be commercially
available ferromagnetic fluid sold by Ferromagnetic
Fluids, Inc., and others preferably, the ferro-
magnetic fluid should be immiscible with respect
to the centrifugal fluid 17 (described hereafter)
and the atmospheres PH and PL. The Diester base
ferromagnetic fluid is preferred because of its
better temperature characteristics. The ferromag-
netic fluid in the magnetic gap spaces between the
ends of the pole piece teeth 14A and 14B and the
opposing surfacesof:the collar vane portion 13A
are exposed to and have access to enlarged reser~oir
cavities 16 having the shape of a light bulb in
cross-sectional configuration but which extend
around the entire periphery of the interior of the
housing member 12 which surrounds the outer vane-
li~e portion 13B of the collax vane. The purpose
ZO of the reservoirs 16 ~ill be described more fully
hereinafter with relation to the operation of the
. . .
seal.
The interior portion 12A of housing member 12
is fabricated from a non-magnetic material such as
copper, aluminum or alloys thereof or could eve~
compris~ a plastic material of appropriate physical
strength and temperature characteristics. Besides
the reservoirs 16 for the magnetic fluid 15, the
interior portion 12A of the housing member includes
a centrally disposed open area or casing in which
the vane-like portion 13B of the annular-shap~d
collar vane secured to shaft 11 rides. A finite
space is provided between the vane 13B and the oppo-
sing interior surfaces of the housing portion 12A
so as to form a chamber in which a centrifugal
~173~7~
sealing fluid indicated at 17 is trapped.
The centrifugal sealing fluid 17 with the shaft
11 at rest would be disposed in the lower portion
of the open area or casing in which vane 13B rides
as best shown in Figures 7 and 7A of the drawings.
From this condition, as shaft 11 rotates and speeds
up to higher rotational speeds, centrifugal effects
will force the centrifugal fluid from the position
shown at 17A out to the position at 17 if there is a
aP across the seal, thereby effecting a centrifugal
seal within the region. As readily determined from
an examination of Figure 1, the centrifugal seal
region 17 is radially disposed outwardly from the
magnetic seal region defined by the close clearance
magnetic gap spacing between the ends of the pole
pieces 14A and 14B which oppose the flat side
; surfaces of the larger thickness porti~n 13A of the
collar vane.
The exterior peripheral portions 12 of the
stationary housing member 12 that surround the inter-
nal non-magnetic portion 12A is fabricated from a
magnetically susceptible material such as stainless
steel, iron or the like. This magnetically sus-
cepti~le portion 12B of housing member 12 is generally
in the shape of an automobile tire which surrounds
the rotatable shaft 11 and is horseshoe-shaped in -
cross section with the inner ends thereof being
turned inwardly towards each other so as to form
the pole pieces 14A and 14B opposing the flat side
surfaces of the enlarged thickness portion 14A
of the annular-shaped collar vane 13. A permanent
magnet shown at 18 is mounted as an insert in the rim
or outer peripheral surface of this magnetically
permeable housing portion 12B. By this construction,
a closed magnetic path is formed via the permanent
11'73~
magnet 18, the outer side portions 12B of the housing
structure 12, the pole piece teeth 14A and 14B, the
ferromagnetic fluid 15 and the enlarged thickness
portion 13A of collar vane 13 which is formed ~rom
magnetically susceptible material. Vane portion 13B
preferably is non-magnetic and is not included in
this closed magnetic path.
As mentioned earlier, during high speed rotation
of the shaft 11 (and accordingly the vane 13B of
annular collar vane 13 which is secured to shaft 11)
the centrifugal sealing fluid 17 is thrown out-
wardly by centrifugal force into the space between
vane 13B and the space or casing defined by the
sides of the interior non-magnetic portion 12A of
the housing. While operating in this manner, fric-
tional forces produce a substantial amount of heat
and it may be necessary to proviae in the interior
portion 12A a cooling jacket as shown by the cooling
fluid passages l9A and l9B which are supplied from
a source of cooling fluid via the conduit 19.
In operation, the novel plural fluid magnetic~
centrifugal seal ~f Figure 1 operates in the following
manner. At standstill and at low rotational speeds
up to about 2,000 rpm, the ferromagnetic fluid 15
will be retained in the close clearance magnetic
gap space between the ends of the pole pieces 14B or
14A and the opposing side surfaces of the enlarged
thickness collar portion 13A of collar vane 13.
While retained in this position, the ferromagnetic
fluid 15 forms a multiple stage magnetic seal that
hermetically seals the higher pressure region P~ to
the right of the structure from the lower or e~ual
pressure region PL on the left hand side of the
structure. Under these operation conditions, the
centrifugal fluid 17 will be in the at-rest condition
11~3
12
as shown in Figures 7 and 7A.
Thereafter, as the rotational speed of the
shaft 11 increases, at some poi~ centrifugal force
effects will cause the centrifugal sealing fluid to
move outwardly through centrifugal force so that
it surrounds the outer peripheral edge of the vane
13B as shown at 17. At this operating point, it is
conceivable that both the magnetic seal 15 and the
centrifugal seal 17 will be coexistent for hermeti-
cally sealing the space between the shaft 11 andhousing 12 from the two different pressure atmospheres-
P~ and PL. If thereafter the rotational speed
of shaft 11 is increased further up to a speed of
say about 10,000 rpm, the centrifugal effects at
this speed will be so great that the ferromagnetic
fluid 15 will be forced by centrifugal effect up
to the position 15A in the reservoir cavities 1
as the centrifugal force overcomes the magnetic
force. During operation in this manner, hermetic
sealing is provided primarily by the ce~trifugal
seal formed by the fluid 17 and somewhat by a
slinger seal formed by 14C and 14D. It will be
appreciated therefore that by appropriate tailoring
of the relative sealing capacities of the magnetic
seal and the c,entrifugal seal, a distinct overlap
can be designed into the seal thereby as~uring
that hermetic sealing in the space between the shaft
11 and housing 12 is always provided. If necessary
during the high speed operation, cooling fluid can
be supplied through the conduit 19 to the cooling
jacket 19A and l9B to maintain the temperature o~
the seal within prescribed limits. However, in-
clusion of such a cooling scheme is not essential
in the embodiment of the invention shown in Figure 1
and can be done away with due to the fact that the
~1~ 3~
low ~iscosaty centri~ug~l :sealing fluid can be
comprised of water, lubricating oil, or other low
viscosity fluid which does not heat up at the higher
speeds of the speed range over which the seal is
designed to operate.
From the above description, it will be appre-
ciated that.the-invention makes it possible to opti-
mally design both the centrifugal seal and the magne-
tic seal to take advantage ~.the strongest features
of each. By employing light oils or water as the
centrifugal fluid for use in high speed operationO
power loss and efficiency is significantly improved
and may eliminate the need for a water-jacketed
cooling arrangement. As a result, the seal produces
less power loss and is more efficient than previously
known magnetic/centrifugal seal designs.
At standstill, ~he sealed pressure different ~P
is maintained by the multi-stage magnetic seal formed
by the several sets of teeth of the opposed pole
20 pieces 14A and 14B by the magnetic sealing fluid 15.
The magnetic energy is supplied from the permanent
magnet or electrical magnet and with the shaft at
rest this pressure differential ~P is given by the
following expression: M ~ .
2~ ~P1 =IM (H) d~ = 45~ 10 6 (atmospheres) (l)
Ms = Magnetization saturation of magnetic fluid
(ferromagnetic fluid 15)
H = Field density in air gap (Oersteds)
~p = Seal capacity/(atmospheres) per stage
~O = Permeability of air equal to (4~ x 10 7 ~t m)
At - ampere turns
M - meter
W - Webers
As the shaft ll starts to rotate, the centrifugal
sealing fluid 17 maintained between the vane 13B and
~73~
14
housinq portion 12A generates a centrifugal pressure
which is augmented by the magnetic fluid seal as
defined above. The sum of the differential pressure
carried by the plural fluid combined m~gnetic/cent~i-
fugal seal at this point is given by the expression:Pl ~ P2 where:
~P2 8 (r 2 _ ri2) (2)
rO is the fluid level on the high pressure
side as indicated in Fig. 2;
ri is the fluid level on the low pressure side
as indicated in Fig. 2;
p is the density of the fluid (17);
is shaft speed (11) rad/sec (angular speed)
~Pl is the pressure differential across the magnetic
1~ seal; and
aP2 is the pressure differential across the
centrifugal seal.
At high speed the magnetic sealing fluid 15 is
eventually ejected from between the magnetic pole
piece teeth 14A and 14B by centrifugal force and
eventually will be trapped in the magnetic fluid
reservoirs 16 as shown at 15A, where it rotates
due to the slinger action provided by the slinge~
shoulders 14C and 14~ as best shown in Fig. ~
The slinger design at the shoulders of-the collar
vane portion 13A prevents the magnetic sealing fluid
15 from moving into the centrifugal seal region and
hence keeps the two fluids from mixing. The geo-
metrical configuration of the magnetic fluid reser-
voirs 16 also assists in preventing mixing of the twosealing fluids by preventing the magnetic seal fluid
15 from beooming mixed with the rotating mass of
centrifugal sealing fluid 17 at the outer rim of
vane portion 13B of the collar vane. Consequently,
the magnetic sealing fluid 15 at high speed will be
li7387~
.
retained in the reser~oir 16 as shown at 15A because
of the slinger action as described earlier. At the
higher speeds, the differential pressure carried by
the plural fluid combined magnetic/centrifugal
seal will be provided primarily by the centrifugal
sealing region and is given by the expression:
P2~ ~ 2
. ~P2 = ~ (xo ri ~ (3)
In addition, any slinger sealing capacity ~P3 provided
by the slinger action described above is added to
that of the centrifugal seal.
As the rotational speed o~ shaft 11 decreases,
the magnetic-gravitational forces again wili dominate
the centrifugal forces acting on the magnetic sealing ~ -
fluid 15 so that the magnetic sealing fluid 15 flows
from the reservoir 16 back in between the magnetic
teeth 14B (or 14A). Upon this occasion, the pressure
difference again will be carried by both the magnetic
seal region and the centrifugal seal region as
explained with relation to e~uation (2). Thereafter
as the rotational speed of shaft ll decreases fur~her
to approach zero and at standstill, the pressure
difference then will be transferred to the multiple
magnetic stages alone and the pressure differential
will be carried only by the magnetic seal region as
set forth in equation (1).
Figure 5 is a characteristic curve showing
rotational speed N of shaft 11 in revolution~ per
minute plotted against the differential pressure ~
in pounds per square inch for the plural fluid com-
bined magnetic/centrifugal fluid seal of the typeshown in the drawings. In this plot, the rotational
speed of the shaft is plotted as the abscissa and
the differential pressure which the seal can with-
-stand is plctted as the ordinate. ~rom Figure
it will be seen that the differential pressure
:L173~7~
16
withstood by the multiple stage magnetic seal ~Pi
remains substantially constant as might be expected
since the terms of equation (1) are not effected by
the speed of shaft 11. It will be noted, however,
that at the transition point ~Pl drops speed
from its constant value to some non-zero but very
small value at the operating speed where the magnetic
fluid 15 is thrown from the magnetic sealing region
up into reservoir 16. In contrast to the magnetic
~O seal, the centrifugal seal provides essentially zero
sealing at standstill and low rotational speeds and
increases exponentially with increases in speed in
accordance with e~uation (3~. -
Figure 2 of the drawings illustrates a modified
form of plural fluid combined magnetic/centrifugalfluid seal according to the invention wherein the
plurality of magnetic sealing stages are axially
arrayed in concentric rings along the rotating shaft
21. In contrast to the Figure 1 structure, shaft
21 is f~rmed from magnetically permeable materials
such as stainless steel, iron, etc., and has a
plurality of concentric ring-like pole piece teeth
21A and 21B formed thereon on each side of a collar
~ane 13 comprised by a magnetically susceptible
enlarged diameter portion 13 integral with or other-
wise secured to shaft 21 and an outer vane portion 13B
preferably formed of non-magnetic material. The
concentric rings of magnetic pole teeth 21A and 21B
oppose the end surfaces of the outer stationary
housing portion 12B which is horseshoe-shaped in
cross-sectional configuration.and is fabricated from
magnetically permesble material such as stainless
steel, iron and the like. The ends of the stationary
housing portion 12B are spaced apart a short distance
from the circumferential ends of the pole piece teeth
3~
17
21~ and 21B formed on shaft 21 so as to define close
clearance, magnetic gap spaces in which a ferro-
magnetic fluid 15 is disposed with the shaft 21 at
standstill or at low rotating speeds. The magne-
tically permeable stationary portion 12B surroundsan inner stationary portion 12A formed from non-
magnetic material which surrounds and is spaced apart
a small distance from the rim or circumferential
end as well as the sides of the vane portion 13B
of the collar vane 13. Disposed in this space is
a low viscosity centrifugal sealing fluid 17 which
may comprise water, a light hydrocarbon oil, a
vegetable oil or the like which is not immiscible
in the ferromagnetic sealing fluid 15 or vice versa
or in the atmosphere being sealed out by the sealing
structure. If desired, a suitable cooling ja~ket
which is connected with a cooling fluid shown at
l9A via conduit 19 to a source of cooling flui~ may
be formed in the housing portion l~for providing
cooling to the structure. ~owever, the inclusion
of such a cooling jacket is not necessary for
applications where the centrifugal sealing fluid
may comprise water or some other light oil having
low friction~1 losses at high rotational speeds of
vane 13B. Reservoirs 16 are provided on each side
of housing portion 12B which coacts with slingex
surfaces 14C ~nd 14D in the same manner as described
with relation to Fig. 8.
In operation, the seal structure of Figure 2
functions in substantially the same manner as ae-
scribed with relation to the structure of Figure 1.
Both the Fig. 2 and Fig. 1 embodiment~ of the
invention are symmetrical in design in that both
designs ha~e equal numbers of ferromagnetic sealing
stages on both sides of the centrifugal vane 13B.
~L173~37~
18
For this reason it does not matter to which side of
the seal the high pressure atmosphere PH is applied.
For installations where it is known to which side of
~ the seal the high pressure-~ is to be applied, it may
be possible to reduce the number of ferromagnetic
sealing stages on the opposite side in much the same
manner as shown in Fig. 4 of the drawings and as
will be described more fully hereinafter in connection
with Fig. 4.
10Figure 3 of the drawings illustrates a modified
form of the plural fluid, combined magnetic/centrifugal
seal shown in Figure 2 wherein a tapered centrifugal
vane regi~on is provided on shaft 11. The plural
fluid, combined magnetic/centrifugal sealing struc-
ture of Figure 3 differs from the structure of Figure
2 in that a plurality of magnetic sealing stages
- are formed by magnetic pole piece teeth 14A and 14B
which oppose tapered side sur~aces of an increased
thickness, tapered magnetically permeable portion
13A of the collar vane 13. Opposite tapered collar
portion 13A, the magnetic pole piece teeth 14A and
14B are formed in complementary, diagonally taperea
end surfaces on the exterior stationary housing
portions 12B.- The stationary housing portions
12B including pole piece teeth 14A and 14B are
fabricated from magnetically permeable material such
as stainless steel, iron, etc., and are included in
a series magnetic circuit with permanent magnet 18.
With the shaft 31, which may be of a non-magnetic
mat~erial, at standstill or at low rotational speeds,
the ferromagnetic sealing fluid 15 will be dispersed
in the close clearance gap spaces between the ends
of the pole piece teeth 14A and 14B and the tapered
side surfaces of the magnetically permeable vane
portion 13A. As a consequence, a closed magnetic
~173~72
19
.
circuit will be formed which includes the vane portion
13A, the.ferromagnetic sealing fluid 15, the pole
pieces 14A and 14B, the magnetically susceptible
portions 12B of housing member 12 and permanent
magnet 18. The vane portion 13B of collar vane i3
preferably is fabricated from non-magnetic material
and is disposed in a centrifugal sealing region
defined by the inner non-magnetic portion 12A of
stationary housing member 12.
o In operation, the embodiment of the invention
sh~wn in Figure 3 functions in a manner that is
similar to the Figure 1 em~odiment of the invention
and includes the isolating reservoirs 16 for assuring
isolation between the ferromagnetic sealing fluid
15 and the centrifugal sealing fluid 17. An a~-
vantage of the embodiment of the invention shown in
Figure 3 over Figure 1 is that it provides longer
transition time. The ferromagnetic sealing fluid
15 in this design (Fig. 3) take~ greater centrifugal
2~ force in order to transfer magnetic fluid 15 into
.. the reservoir 16 because of tapered path of magnetic
stages ~14B or 14A). Because the projected component
of centrifugal force acts on the fluid~ only, in
order to transfer fluid 15 into reservoir 17 at a
certain speed, the freedom of design for controlling
transition time of fluid 15 is greater in this con-
figuration.
Figure 4 of the drawings illustrates still
another embodiment of the invention wherein the
lubricating oil of a machine or other apparatus
with which the no~el plural fluid, combined mag-
netic/centrifugal fluid seal is installed is used
as the centrifugal sealing fluid. In Figure 4
shaft 11 which may be fabricated from a non-magnetic
material has secured thereto an annular collar
~173~37~
vane 13 having an increased thickness inner annular
portion 13A and an outer vane portion 13B. The inner
annular increased thickness portion 13A is fabricated
: from a magnetically permeable material such as stain-
less steel, iron or the like and rotates in a space
defined by the spaced apart ends of a generally
invexted U-shaped cross-sectional stationary housing
portion 12B of stationary housing 12. Similar to
the Figure 1 seal configuration, the ends of at
least one of the legs of the inverted U-shaped
housing portion 12B, which is fabricated from
magnetically permeable material, have too~h-shaped
magnetic pole pieces 14B formed therein. If it is
not known which side of the seal must sustain the
high pressure atmosphere PH, or if during operation
switches from one side of the seal to the other,
corresponding magnetic p~le piece teeth such as
14A in the Pigure 1 arrangement can be formed in
the remaining end of hcusing portion 12B depending
upon the particular application for which the seal
- is designed. The purpose of h~ving magnetic pole
piece teeth on both sides of the runner or stationary~
part is to seal a system where the high pressure
side is not knvwn, or the seal has to operate
under conditions where the high pressure side,
relative to the speed of the rotor 11 such as in
~ig. 1, is switching from one side to another.
As mentioned earlier, this is one of the advantages
of the double-acting seal. Conventionally, seals
operate unidirectionally. ~or example, most face
seals t mechanical seals, pumping seals or tight
clearance convexgent seals operate unidirectionally~
Therefore, it is not necessary to have the magnetic
seal portion of this invention on both sides of the
runner in all configurations unless it is required.
- 1~73~7;~
21
With reference to Fig. 1 and the condition which is .
shown, (i.e., PH at right.hand side and PL at lef~ -
hand side of the seal), if this arrangément of high
and low pressure s`ides is true, throughout the systcm
operation, then the right hand side of the magnetic
sealing arrangement (.14A, 15, 17A, 15A, 16) does not
function and should be omitted from the design.
While the PH on only one side, after the first start
up, magnetic fluid 15A cannot be returned to 15
.10 unless some positive pressure acts on the fluid l5A.
Thus, sealing capacity is based on one side and only
one side of the magnetic sealing arrangement.. In
.those seal configurations herein disclosed, the
parts have been shown symmetrically for the sake
of broad applications where it is not known that PX
will act from one side.only.
A ferromagnetic sealing-fluid ~ is dis.posed ..
in the close clearance magnetic seal gap region
disposed between the ends of the pole piece teeth
. 20 14B and opposing side surfaces of collar ~ane
- portion 13A. An electromagnet shown at 30 is cen-
trally positioned with respect to the housing p~r-
tions 12B so às to pro~ide a magnetic field indicated
by the dotted line arrow which threads a closed
circuit magnetic path formed by the housing portions
12B, the pole pieces 14B, the ferromagnetic fluid
15 and the collar vane portion.13A. The electro-
magnet 30 is supplied from a suitable source of
excitation current which may comprise a battery 32
through an on/off control switch 33 and a current
controlling variable resistor 34 for controlling
the strength of the magnetc field produced by
coil 30.
The outer ~ane portion 13B of annular collar
3~ vane 13 rotates within a centrifugal sealing space
~173~
. ~2
or region defined by an interior housing portion 12A
formed on non-magnetic material so that during high
speed rotation ofvane portion 13B, a centrifugal
seal is formed by fluid 17 between the confronting
surfaces of the interior housing portion 12A and the
rim and outer peripheral portion o~ vane 13B.
SLmilar to the seal structure of Figure 1, the
ferromagnetic sealing fluid reservoir 16 is formed
in the interior stationary housing portion 12A at
i0 the lower end thereof which communicates with the
close clearance magnetic sealing gap spaces of the
multiple stage magnetic seal comprised by pole
pieces 14B~ By this construction, during hig~
speed rotation of shaft 11, the high viscosity,
ferromagnetic sealing fluid 15 is p~oled in the
reservoir 16 by slinger action as described with
relation to ~ig. 8; and is thereby isolated and
prevented from intermixing with the centrifugal
sealing fluid 17.
. 20 .The centrifugal sealing fluid 17 is supplied
to the centrifugal sealing region from a lubricating
oil reservoir shown at 41 via an oil supply line 42,
lubricating oil cooler 43 and lubricating oil pump 44.
This lubricating oil supply system constitutes the
normal lubricating oil supply and cooling system
used for the bearings and seals of many different
kinds of machines and apparatus wherei~ the lubri-
cating oil is supplied via conduit 42 to the bearing
shown generally at 45. This oil is leaked off
around shaft 11 to a lubricating oil supply con~uit
47 formed in the stationary housing structure 12
that leads to the centrifugal sealing region in
the close clearance spaces between the rim and outer
peripheral portions of vane 13R. From the centri- .
fugal seal region, the lubricating oil then is bled
:L~73~7~
23
off through a discharge conduit 48 and check valve
49~ back to the inlet side of the lubricating oil
reservoir 44. It should be noted a~ this.point,
~ that this may not be the only return conduit providing
for the flow of lubricating oil reservoir 41. The
parameters of the supply conduit 47 and discharge
conduit 48 are tailored to supply and discharge
lubricating oil for use as the centrifugal seahing
fluid for the entire peripheral extent of the cen-
trifugal sealing region:.surrounding the rim andouter peripheral portion of ~ane 13B. Accordingly,
these parameters must be dimensioned to assure
sufficient flow to keep the centrifugal sealing
oil cooled within its specifications. While
operating in this mode at the high rotational speeds,
the vane 13B serves not only to create and maintain
the centrifugal seal but also functions as a pump
for pumping heated lubricated oil through the
outlet conduit 48 and check valve 49 back to the
intake of the lubricating oil reservoir 41. Fig.
.. 4A of the dra~ings.best illustrates the parameters
whereby pumping action is obtained from vane 13B.
In addition to the above features, the sealing
structure of Figure 4 may further include a buf~er
labyrinth seal shown at 12C o~ the outer exterior
end of stationary housing member 12 which rota-
tionally supports shaft 11. A suitable conduit
shown at 51 is formed in the housing portion 12B
to supply pressurized air or other gaseous fluid for
discharge into the space between the labyrinth
seal rings 12C and shaft 11 as indicated by the
solid line arrows. This pressurized air not only
will serv.~ to prevent fluid from a hostile atmos-
phere which may be at a very high pressure as
indicated at PH from entering into the sealing
.
~173~37~
24
structure but also tends to pressurize the side o~
vane portion 13A and vane 13B where no magnetic seal
stages are formed. This then prevents loss of
lubricating oil ~rom the centrifugal sealing region
in addition to preventing seepage of the very high
hostile atmosphere indicated at P~ .
~ rom the foregoing description it will be
appreciated that the plural fluid combined magnetic/
centrifugal seal of this invention makes available
i0 to a designer of seal structures the following
important advantageous featuxes. It provides a
stable and high differ~ntial pressure QP across the
seal at both high and low rotational speeds as well
as at standstill and produces a 100~ hermetic seal
under all conditions of operation. The high dif-
ferential pressure ~P provided at 0 rotation and
at low rotativnal speeds by the magnetic seal
stages are not governed by volume ratio considerations
dictated by a coacting centrifugal seal region and
therefore optimized magnetic seal configurations
can be devised. There is a much less power loss
due to the low viscosity of the centrifugal sealing
fluid. Because of the independence of the centri-
fugal seal configuration from the magnetic seal
stages, it too is susceptible to flexible design
criteria. The 100% hermetic sealing provided by
the structure can be obtainedat relatively low cost
since tight clearance or spacing, precise machining
of components, etc. is not reguired. Pinally,
there is no problem of leakage during transition
from magnetic fluid sealing to centrifugal fluid
sealing and vice versa because of the difference
in viscosity, density and slinger characteristics
of the two fluids. The low viscosity centrifugal
sealing fluid is sheared and centrifugally forced
~'73~37Z
' 25
.
into the centrifugally sealing region at angular
speeds well below the shearing force required to
separate the magnetic sealing fluid from the magnetic
- sealing region ~ecause of the difference ~R in radii
~ 5 and density, etc. The reverse process is true
during slow down so that at all timés 100% hermetic
sealing is assured.
With reference to Pig. 9, it will be seen that
the average radius RA for the centrifugal sealing
region is given by the expression
r3 ~ r4
R
and the average radius RB for the magnetic seal region
is given by
rl r2
It is clear from Fig. 9 that RA is greater thzn ~
(XA ~ ~) and that the difference ~R = RA~ ince
the centrifugal force in each region is proportional
to the average tip speed and the average tip speèd
for the respective sealing region is given by ~A
and ~ where ~ is the angular speed of the shaft,
it follows tha~ at any transitional shaft speed ~,
the centrifugal force developed in the centrifugal
seal region will exceed the centrifugal force de-
veloped in the magnetic seal region.
Having described several embodiments of a new
and ~mproved plural fluid combined magnetic/cen-
trifugal fluid seal constructed according to the
invention, other changes, variations and modifi-
cations of the various embodiments of the invention
disclosed will become apparent to those skilled in
the art in the light of the above teachings. It
is therefore to be understood that any such modi-
fications, variations and changes are believed to
come within the scope of the, invention as defined
by the appended claims.
