Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
This -Lnvention relates to rotary end ~ace seals and
particularly to such seals which are used in high pressllre,
large diameter applications.
End ~ace seals depend upon the constant ~latness and
parallelity o~ their cooperating radially disposed faces for
the e~fectiveness of the seal produced by these facesO Inl-
tially, the faces are lapped ~lat and smooth so that when
placed together, there is no space through which the ~luid to
be sealed can escape. In use, however, these faces are sub-
jected to uneven wear because of (1) di~ering linear speedso~ the faces produced by the di~fering'radii o~ the ~aces;
(2) lack of homogeneity o~ the material of the faces; ~3) dis-
tortion of the faces by the pressure of the fluid on the rings
on which the faces are formed; and (4) poor lubricatlon.
The ~irst factor cannot be eliminated since it is
inherent in the operation of two flat surfaces rubbing to-
gether with a rotating movement.
The second ~actor can be controlled to some extent,
but since the material o~ the rings is determined by the na-
ture of the ~luid to be sealed, the choice o~ material islimited. In high pressure? large diameter water ~pplications,
one o~ the sealing rings is made o~ carbon. Thls material is
di~:ficult to mold i.n such manner that it is per~ectly homo-
geneous in the large diameters and masses required to with-
stand the pressures encounteredO
The third factor has lead to various balancing ar-
rangements and to increases in the amount o~ material in the
ring, the latter bo provide greater stiffness to resist the
pressure of the ~luid. However, balancing is e~fective in an
axial direction and has little or no e~fect upon radial pres-
sure differences which are largely responsible for pressure
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dlstortion in the ring. Increasing the mass of the ring ag-
gravates the dlfflculty in assuring homogeneity ln the material
of the ring.
The fourth factor is more difficult to detect than
t~ remedy.
Over the years, seal designers have evolved certain
design principles whi~l serve to assist them in solving seal
design problems~ These are (a) increased seal balancing to
reduce axial pressure on the seal faces and, hence, wear of
said faces, (b) increased face width to reduce unit pressure
on the faces, (c) zero turning moment o~ the ring and seat
about the centroid of their axlal sections at operating pres-
sures to assure parallelity of t'he seal faces and, henceJ even
'~ wear thereacross~ and (d) the use of relieved areas (hydro-
'pads) on at least one seal face to draw lubricant between khe
the faces when they move relative to one anotherO
However, seals are desired ~or devices producing the
following operating condition~:
- 1. Di~ferential pressures ~rom 0 to 2)500 PSIG.
2. 8 Inches to 9~ inches outside di.ameter of the
sealing ~aces.
3. 2,750 Feet per minute surface' velocity.
4. Temperature transients of 20F. in 7 5 minutes.
~' 5. Pressure changes in increments of 500 PSIG./min-
ute, both increasing and decreasing the pressure, in the o~er-
all range of 0 to 2,500 PSIG.
6. Leakage rates o~ 15 cc/minute under extreme con-
ditions.
It has been ~ound that following the classical de-
sign principles outlined above does not produce a satis~actory
seal for such operating conditions. It is~ accordingly, an
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object of this invention to provide a seal which is satis~ac-
tory under the operating conditions given above.
We have found that a seal having the following three
properties will operate satisfactorily under the above operat-
ing conditions:
1. An aspect ratio in the range of 0.0~5 to 0.30.
The term "aspect ratio" is defined as the ratio of the radial
sealing face width to the inner radius of the :Eace~
2. Hydrodynamic lift-off pads incorpo~ated into the
desi.gn to allow the seal to operate on a thicker interfacial
film.
3. Controlled negative rotation of the sealing
rings~ "Negative rotation" of a sealing ring is defined as
that direction o rotation o the seal ring about its centroid
which will pinch off face l.eakage at the outer diameter or
pressure side o~ the ring.
Accordingly, this invention provides a rotary end
~,
ace seal comprising relatively rotatable primary and seat
rings having abutting radially disposed sealing faces~ a
~ 20 support or the seat ring~ means sealing a radially outer per-
iphery o the seat ring with respect to the support, means
limiting contact between the seat ring and the support in an
aKial direction to a radially outer region o the seat ring,
the centroid o an axial section taken through a quadrant of
the seat ring being located radially inward o the means limit-
ing contact between the seat ring and support~ the ratio o~ the
radial sealing face width of each of said rings to its inner
; radius being in the range of 0.085 to 0O3~ and at least one of
said sealing aces being relieved radially inwardly from the
pressure side o the seal at peripherally spaced intervals
to orm
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hydro-pads.
The invention will now be described wikh reference
to the accompanying drawings, in whlch:
Figure l is a radial section through the seal; and
Figure 2 i5 an elevational vi~w of one ring, the
face of which has been modified in accordance with this inven-
tion.
In Figure l, a shaft lO is shown on which is mountea
a sleeve ll havlng a step 12 into which a radially inner por-
tion 13 o~ a primary sealing ring 14 projects to ef~ect a par-
tial balance of the axial ~orces acting upon said ring. The
latter may be made of molded carbon in washer form to surround
sleeve ll~ the ring beipg machined to have a raised portion or
nose 15 extending axially from the body thereof. Raised por-
tion 15 has a flat-lapped sur~ace 16 which functions as the
sealing ~ace ~ the primary sealing ring.
Immedlately axia].ly adjacent primary sealing ring 14
is a mating ring 17 or seat made of appropriate material and
held in a recess 18 in a gland plate l9 or other fixed part of
the device to be sealed. An l~o11 ring 20 o~ elastomeric materi-
al seals the radially outer cyli.ndrical sur~ace o~ mating ring
17 with respect to gland plate l9, and an "O~ ri~g 21 operating
in a counterbore 22 in primary ring 14 s0als said primary ring
with respect to the outer sur~ace 27 o~ sleeve ll. One or
more pins 23 secured to gland plate L9 and extending axially
into recesses 24 in the rear radial face of mating ring 17
hold said seat ring against rotation relative to gland plate
19.
Primary ring 14 is ~ormed with axially extending
, 30 slots 25 (Figures l and 2) disposed preferably at 90 inter-
-~ vals in the outer periphery o~ a radially ext0nding ~lange 26
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located at the rear o~ ring 14.
A portion of sealing ~ace 16 has a smaller radius
than the outer surface 27 of sleeve 11 on whlch "0" ring 21
rests. Ring 14 is exposed at bokh ends to the ~luid under
pressure to be sealed and, hence, the axial pressure o~ the
fluid acting upon one end opposes the flui.d pressure acting
upon the other end of said ring. Th~ latter pressure, however,
-~ is designed to be slightly greater ~h~ the fluid pressure on
the said one end so that a closing pr~ure is still exerted by
the fluid upon ring 140
Balancing a primary sealing ring to a predetermined
degree is a ba~ic requirement of all hi~h pressure seals. It
is understood that the combination of thr~e properties of this
invention are to be applied to an appropriatel~ balanced seal.
Considering now the first prop~rty mentioned above,
viz., the particular aspect ratio found essential, it may be
noted that in the example shown, the inner radius of ~ace 16
i9 4.150 inche~ (10.541 centimeters) and the radial dim0nsion `
oP face 16 i8 0.443 inch (1.125 centimeters) so that the aspect
ratio o~ face 16 as de~ined above is ~ or 0.107, which ls
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within the required range o~ aspect ratios given above. `
Next, in the same example, and as shown in Figure 2,
the radially outer portion o~ the face 16 is formed with es~
sentially semi~circular shallow recesses 28 whlch serve, when
the seal is operating~ to force ~luid between face 16 and the
.,
radial ~ace 29 on seat ring 17 to reduce friction between said
f'aces. Such recesses are generally known as hydro-pads.
Taking up now the third property, negative moment,
each ring 14 and 17 has in radial sect~on a center o~ gravity
or centroid shown at 30 and 31, respectively. Fluid pressures
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upon selected portions of the rings will develop moments of
force around the centroid of each ring tending to twlst it
about its centroid in the direction of the algebraic sum of
such moments. Thus, the contour o~ the primary and mating
xings in radial cross section, when each ring is exposed to
fluid pressure between its seal face and secondary seal, will
determine whether there will be a twisting force ~n the rings,
and if so, whether it will be clockwise or counterclockwise
around the centroid o~ each ring.
- 10 It has been proposed previously to use a contourfor the radial cross section o~ a primary sealing ring which
will result in a zero moment of force around the centroid of
the ring s~ that the sealing faces will remain flat for all
expected pressures of the fluidu Such zero moment, however,
is not satisfactory in the environment for which the seal of
this invention i~ intended. It is known, for example~ that
during operation of a seal under the conditions Df this inven-
tion, the friction developed between faces 16 and 29 will pro-
duce a downward temperature gr~dient on ring 14 away ~rom the
contacting faces, and that this gradient will produce maximum
radial expansion at the face, with progressively less expan-
sion away from the faces. Such differential expansion is the
equivalent o~ a turning moment in a primary ring about its
centraid in a clockwise direction when ring 14 in Figure 1 is
considered. A zero moment based solely upon the geometry o~
the radial cross section of the primary ring would, there~ore~ `
allow the distortion produced by the temperature gradient to
develop unhindered.
~y designing the net moment around centroid 30 to be
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in a counterclockwise negative dlrection as viewed in Figure 1,
the thermal distortion is counteracted and the flatness o~ face
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~ ~5 ~ O ~ ~16 i9 preserved. Assumlng that seat ring 17 i~ relatively un-
distorted by pressure and temperature gradients, a negative
moment ln primary ring 14 will be sufficient to maintain ~ace
16 thereof flat and in sealing engagement with ~ace 29 of seat
ring 17. Should ring 17, however, be ~ected by temperature,
then the pressure of the fluld being sealed upon seat ring 17
is controlled in such manner as to result ln a negative moment
o~ force about centroid 31 o~ said ~eat ring 17
In khe example shown in Figure 1, a negative moment
10 is produced in seat ring 17 by .relieving the bottom sur~ace 32 :
- o~ recess 18 radially outwardly to leave a land 33 which is
- radially beyond centroid 31. Thus, axial pressuxe on seat
ring face 29 will result in a turning moment about centroid
31 in a clockwise direction as vlewed in Figure 1 which, ac-
cording to the definition given above is negative, i.e., in a
direction to pinch o~ fluld acting upon the exterior or ring
17.
It is understood that the surface o~ land~33 in con-
tact wi~h seat ring 17 as well as the surface of seat ring 17
contacted thereby are lapped ~lat 80 that no dlstortion is in-
troduced into rin~ 17 by land 33. To ~acilitate lappingl land
33 may be formed as part o~ a separate ring (not shown) placed
against the flat bottom of reces~ 18, either d~ ectly, or ..
through the intermediar~ o~ a de~ormable washer to allow the .
separate ring to assume a positlon parallel with the contact-
ing su.r~ace o~ ring 17.
Heating o~ seat ring 17 and the adjacent portions o~
primary sealing ring 14 and particularly o~ the contacting
faces 16 and 29 is minimized by passing cooling ~luid there-
over through a passage 34 encl~sing ring 17 in close proximitythereto and ~ormed in gland plate 19. The cooling fluid in
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the form ~f seal illustrated herein ls the fluid being ~ealed.
It is contemplated, however, that the cooling fluid will not
be used until the temperature of the primary and seat rings is
high enough to cause thermal distortion in said rings. Upon
start-ups) the maximum operating fluid pressure may be reached
before any thermal distortion takes place~ In khis event, the
negative moment will cause the outer edge of the primary seal
~ace 16 to bind against face 29 of seat ring 17, but this is a
temporary condition which is "corrected" by thermal distortion
as the faces heat up. In a seal wherein the primary sealing
washer has one inner diameter of 8-5/8 inches the distortion
caused by the negative moment at 2,500 PSIG. may be 4.5 minutes
of arc ~rom the vertical, which, if allowed to remain would
cause the seal to fail prematurely, but, because of the heat
generated by such dlstortion, is soon removed by the thermal
distortion.
I~ any one of the three properties, correct aspect
ratio, hydro-pads and negative momentJ is omitted from the de-
sign of a high pressure balanced end face seal, the seal will
fail. For example, if the hydro-pads are omitted, the seal
will burnjup because of poor lubrication of the contacting
faces. I~ the negative moment is omitted, the seal faces will
separate and an unsatisfactorlly high leakage rate will result.
I~ one incorrect aspect ratio is used, the seal will
have an unstable operation, with recurring popping open of the
faces accompanied by spirts of fluld and high fluctuations in
the power required to drive the seal.
The total area o~ the hydro-pads is a factor in de-
termining the design of the primary sealing ring from the
; 30 standpoint of balance. Thus, in a typical seal wherein khe
actual balance desired is 63-~ percent of the tone balance, the
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balancing effect of the pads will comprise,a part of the 63
percent balance. Obviously, the balance to be produced by the
pad cannot be concentrated in one pad 9 ince lt would lead to
dynamic unbalance o~ the rotating primary sealing ring. Con-
sequently~ once the required pad area is known, tha number,
configuration and spacing of each pad is then determinedO
The ideal aspect ratlo ~or high pressure seals for
relatively large diameter sha~ts (6 - 8 inches) is 0.107 and
this ratio may be ~aried up to 10 percent. For smaller sized
10 shafts the aspect ratio may approach the upper limit of the ~ ~'
range speci~ied above7 viz., 0.3.
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