A high-speed, self-acting circumferential type shaft seal for use in turbine engines is disclosed. One or more conventional circumferential ring seals having a central aperture are mounted in a housing. In three of the four embodiments of the invention, a helical groove and one or more dam seals are cut in the inner cylindrical surface of the one or more ring seals. In a fourth embodiment, two or more lift pads are disposed in surface contact with the inner cylindrical surface of the seal rings. To the outside of the lift pads, two dam seals are cut in the inner cylindrical surface of two of the ring seals. In each of the embodiments, a net outward radial force was produced during rotation of the turbine causing the ring seals to lift out of contact with the turbine shaft to minimize wear of the ring seals

Hady, W. F.

Ludwig, L. P.

English

NASA Technical Reports Server

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APR 2 8 1975
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Enclosure
https://ntrs.nasa.gov/search.jsp?R=19750013559 2020-03-19T21:10:30+00:00Z
United States Patent
Ludwig et al.
[in 3,874,677
[45] Apr. 1, 1975
[541 HIGH SPEED, SELF-ACTING SHAFT SEAL
[75] Inventors: Lawrence P. Ludwig, Fairview Park;
William F. Hady, Cleveland
Heights, both of Ohio
[73) Assignee: The United States of America as
represented by the National
Aeronautics and Space
Administration, Washington, D.C.
[ 2 2 ] Filed: July 19, 1973
[ 2 I | Appl. No.: 380,630
|52| U.S. Cl 277/27, 277/40, 277/134
[ 5 1 | Int. Cl F16j 15/16
[581 Field of Search 277/27,40, 134,67
15 61 References Cited
UNITED STATES PATENTS
1.32(1.064 12/1919 Kel le r . . 277/27
1.3.11.360 2/1920 Parsons ct al 277/27
1.949.094 4/1935 Godron 277/27
3.119.623 1/1964 Schevchenko 277/27 X
3.259.393 7/1966 Dcga 277/134
3.333.X55 8/1967 Andresen 277/40
3,364,523 1/1968 Schippers 277/134
3,617.068 11/1971 Sprenger 277/134
Primary Examiner—Samuel B. Rothberg
Attorney, Agent, or Firm—N. T. Musial; G. E. Shook;
John R. Manning
[57] ABSTRACT
A high-speed, self-acting circumferential type shaft
seal for use in turbine engines is disclosed. One or
more conventional circumferential ring seals having a
central aperture are mounted in a housing. In three of
the four embodiments of the invention, a helical
groove and one or more dam seals are cut in the inner
cylindrical surface of the one or more ring seals. In a
fourth embodiment, two or more lift pads are disposed
in surface contact with the inner cylindrical surface of
the seal rings. To the outside of the lift pads, two dam
seals are cut in the inner cylindrical surface of two of
the ring seals. In each of the embodiments, a net out-
ward radial force is produced during rotation of the
turbine causing the ring seals to lift out of contact with
the turbine shaft to minimize wear of the ring seals.
9 Claims, 4 Drawing Figures
HIGH PRESSURE
SIDE2
.\1ENTEOAFR UG75 r*.874,677
HIGH PRESSURE
SIDE 22
LOW PRESSURE
SIDE 24
FIG.l
22
20-
\\x\\
18
-12 a
x/6
26
FIG. 2
;£LT a OF 2
FIG.3
1.874,677
FIG.4
r
3,874,6771
HIGH SPEED, SELF-ACTING SHAFT SEAL
, - ORIGIN OF THE INVENTION:
The invention described herein was made by employ-
ees of the United States Government and may be man- 5
ufactured and used by or for the Government for gov-
ernmental purposes without the payment of any royal-
ties thereon or'thercfore.
10BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to low-wear, self-acting circum-
ferential ring seals of the type used in turbine engines
to seal a rotating shaft between high and low pressure
areas. • 15
2. Description of the Prior Art
Prior art ring seals of the circumferential type consist
of a housing containing one or more carbon ring seg-
ments which have an inner cylindrical surface that rides
on the rotating outer cylindrical surface of the turbine 20
primary .disadvantage of the prior art construc-
tion is that high speed contact between the cylindrical
surfaces of the shaft and the ring seal result in high
wear and expensive replacement. Since the cost of the
prior art r ing seals is relatively expensive, it is easy to
see that increased longevity has a distinct advantage.
S U M M A R Y OF THE INVENTION
The disadvantages of the prior art ring seal are solved
hy the instant invention which provides a relatively in-
expensive solution to the problem of ring seal wear.
The longevity of ring seals constructed according to the
invention is up to ten times or longer than prior art ring
seals depending on the operating conditions to which
the ring seal is subjected.
The invention consists of a housing within which is
mounted one or more circumferential type ring seals
having a central aperture. The inner surface of the ap-
erture is cylindrical in shape and is adapted to be dis-
posed around a high-speed rotating shift. Three of the
embodiments of the invention have a helical groove of
constant cross-sectional area cut in the inner cylindri-
cal surface of. the one or more ring seals. One portion
of the helical groove is coupled to a high pressure area
partially surrounding the housing. One or more dam
seals project radially inward from the inner cylindrical
surface of the ring seal and are disposed between a low
pressure area partially surrounding the housing. In the
case where the high pressure area is filled with a com-
pressible fluid such as air, the helical groove produces
an increasing pressure gradient between the high pres-
sure area and the dam seal. This resultant pressure gra-
dient produces a net outward radial force which lifts
the ring seal out of contact with the shaft during rota-
tion thereof. A small amount of air leakage between the
dam seal and the shaft into the low pressure area main-
tains a constant lifting force which is balanced by garter
springs holding the ring seals in place around the shaft.
In a fourth embodiment, the helical groove is replaced
by (ine or more lift pads having a central aperture
therein forming an inner cylindrical surface adapted to
be disposed around the rotating shaft. Each lift pad has
a channel disposed therein. The cross-sectional shape
of the lift pad defined from a radial direction with re-
spect to the aperture is a rectangle with a smaller cut-
out cross-section having one of its edges in common
with the inner cylindrical surface of the lift pad. The
smaller cut-out cross-section does not border on any of
the corners of the rectangular cross-section. The rota-
tion of the shaft causes drag to occur between the air
molecules in the smaller cut-out cavity of the lift pad
and the walls of the cavity. This drag draws air into the
cavity from the high pressure area surrounding the lift
pad to produce a net outward radial force which lifts
the lift pad and ring seal out of contact with the shaft
during rotation thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. l i s a sectional view of a first embodiment of the
invention;
FIG. 2 is a sectional view of a second embodiment of
the invention;
FIG. 3 is a sectional view of a third embodiment of
the invention; and
FIG. 4 is a sectional view of a fourth embodiment of
the invention.
DETAILED DESCRIPTION OF THE INVENTION
In FIGS. I through IV, housing 10 contains one or
more split rings 12 constructed from carbon or other
25 suitable materials. Split rings 12 have an aperture form-
ing an inner cylindrical surface (not shown for the sake
of clarity) adapted to be disposed around rotatable
shaft 14. One or more of the split rings 12 have a radi-
ally inward projecting dam seal 16. While shaft 14 is at
30 rest, each of the split rings 12 is biased against the sur-
face thereof by an associated garter spring 18. A suit-
able spring 20 (FIGS. I through II I ) may be provided to
hold the split rings 12 in positive axial position with re-
spect to shaft 14. Surrounding housing 10 is high pres-
35 sure area 22 (characteristically in the compressor sec-
tion of a turbine) and low pressure area 24.
Referring to FIG. I, disposed on the inner cylindrical
surface of split rings 12 is a helical groove 26 of con-
stant cross-sectional area. The direction of turn of the
*® heiix 26 is such that it causes a compressible fluid
(characteristically air) to be pumped from left to right
toward dam seal 16. The pumping action of helical
groove 26 causes a positive pressure gradient to be pro-
duced between high pressure side 22 and dam seal 16.
Because of the presence of the high pressure area 22 on
the outer cylindrical surface of the split rings 12,
around garter springs 18, etc., a net uniformly-
distributed outward radial lifting force is produced by
the pressure gradient. The net outward radial lifting
force causes split rings 12 to lift out of contact with
shaft 14 during rotation thereof. A small amount of the
compressible fluid present in the high pressure area 22
leaks between the cylindrical faces of the dam seal 16
and shaft 14. This leakage maintains a relatively con-
stant lifting force on the split rings 12.
Referring to FIG. II, slot 28 is coupled to high pres-
sure area 22. A helical groove 26 is provided on the
inner cylindrical surface of split rings 12. The direction
60 of turn of helical groove 26 is such that a positive pres-
sure gradient is established between slot 28 which is
coupled to a source of compressible fluid such as air
and dam seals 16 causing a net uniformly-distributed
outward radial force to lift split rings 12 out of contact
,^ with shaft 14 during rotation thereof.
Referring to FIG. Ill, a helical groove 26 is provided
on the inner cylindrical surface of split rings 12. The
direction of turn of the helical groove 26, which is cou-
3,874,677
pled to high pressure area 22, is such that a positive
pressure gradient is established between the high pres-
sure area 22 and the dam seal 16 disposed on the left
hand side of split ring 12. The direction of turn of the
helical groove 26 which is coupled to low pressure area
24 is such that oil in the low pressure area 24 is pumped
out of the space between the righ hand helical groove
26 and shaft 15 and into the oil reservoir located in low
pressure area 24. The pumping action by the right hand
helical groove 26 produces a uniformly-distributed net
outward radial force which lifts the right hand split ring
12 out of contact with shaft 14 during rotation thereof.
Referring to FIG. IV, it should be noted that those
parts which are the same as FIG. II will not be discussed
as they have been adequately described supra. The dif-
ference between the first three embodiments and this
embodiment is in the substitution of circumferentially
spaced lift pads 30 in place of helical grooves 26. The
lift pads 30 are formed on the inner cylindrical surface
of the split rings 12 disposed around the shaft 14. The
lift pads 30 are separated by axially extending channels.
Each pad has a recess 32 disposed therein. The cross-
sectional shape of the lift pad defined from a radial di-
rection with respect to the aperture is rectangular with
a smaller cut-out recess 32 having one of its edges in
common with the adjacent axially extending channel.
The recess 32 does not border on any of the corners of
the rectangular cross-section of the lift pad. Rotation of
shaft 14 causes the recess 32 and the shaft 14 to func-
tion as a drag pump causing the compressible fluid
(usual ly a i r ) to be drawn into recess 32 from the adja-
cent axially extending channel. This phenomenon is
readily explained by fluid dynamics. The drawing of the
compressible fluid into recess 32 causes net outward
radial force to lift ring seals 12 out of contact with shaft
14 during rotation thereof.
With respect to FIGS. I through III, it should be noted
that grooves 26 are of constant cross-sectional area.
The pitch of the helical groove 25 and the cross-
sectional area is empirically determined. However, the
viscosity of the fluid being pumped is an important fac-
tor in the design. In the case of air, the groove depth is
in the range of one-half to one mil in depth.
While all of the embodiments are shown with two
split rings, it will be apparent to those skilled in the art
that a greater or lesser number of split rings could be
used with equal facility.
To produce a greater lifting force, it is possible to cut
a channel in the inner cylindrical surface of the dam
seals and couple that channel with the high pressure
gradient produced by helical groove 26 or lift pad 30
by means of a helical groove 26 or other type of suit-
able port. For the sake of clarity, this feature has not
been shown in the drawings.
With respect to FIGS. I through III, it should be noted
that while it is preferable to dispose helical groove 26
on the inner cylindrical surface of split rings 12, the he-
lical groove may also be disposed on the outer cylindri-
cal surface of shaft 14.
It is therefore to be understood that within the scope
of the appended claims, the invention may be practiced
otherwise than as specifically described herein.
What is claimed as new and desired to be secured by
Letters Patent of the United States is:
1. A high-speed, self-acting shaft seal for use in seal-
ing a rotating shaft between high and low pressure ar-
eas, the combination comprising:
10
15
20
25
30
35
40
45
50
55
60
65
a housing;
at least one ring seal disposed in said housing, said at
least one ring seal having an aperture therein form-
ing an inner cylindrical surface adapted to be dis-
posed around said rotating shaft;
a dam seal at one end of said inner cylindrical surface
of said at least one ring seal, and
means coupled to said cylindrical surface of said at
least one ring seal adjacent to said dam seal for pro-
ducing a net outward radial force only during rota-
tion of said shaft whereby said inner cylindrical sur-
face lifts out of surface contact with said shaft dur-
ing rotation thereof.
2. A high-speed, self-acting shaft seal as recited in
claim 1 wherein said means coupled to said inner cylin-
drical surface comprises:
a helical groove cut in said inner cylindrical surface
of said at least one ring seal;
said helical groove extending from said high pressure
area to said dam seal
said dam seal forming a portion of said inner cylindri-
cal surface;
said helical groove producing an increasing pressure
gradient from said high pressure area to said dam
seal during rotation of said shaft; and
said dam seal being disposed between said low pres-
sure area and said helical groove.
3. A high-speed, self-acting shaft seal as recited in
claim 1 wherein at least two seal rings are disposed in
said housing, said means coupled to said inner cylindri-
cal surface comprising:
a pair of said dam seals, each dam seal being at one
end of said cylindrical surface of a different one of
said seal rings;
each of said dam seals forming a portion of said inner
cylindrical surface;
a slot coupled to said high pressure area and being
disposed between two of said at least two ring seals;
a helical groove cut into said ring seals and extending
from said slot to said pair of dam seals, said helical
groove producing an increasing pressure gradient
from said slot to said dam seals during rotation of
said shaft; and
said dam seals being respectively disposed between
said high pressure area and one end of said helical
groove and said low pressure area in the other end
of said helical groove.
4. A high-speed, self-acting shaft seal as recited in
claim 1 wherein at least two ring seals are disposed in
said housing, said means coupled to said inner cylindri-
cal surface comprising:
a pair of dam seals disposed in surface contact with
each other;
each dam seal being at one end of said cylindrical
surface of a different one of said ring seals;
each of said dam seals forming a portion of said inner
cylindrical surface;
a first helical groove extending from said high pres-
sure area to one of said dam seals, said first helical
groove producing an increasing pressure gradient
from said high pressure area to said one of said dam
seals during rotation of said shaft;
a second helical groove extending from the other of
said dam seals to said low pressure area, and
said low pressure^area being adapted to be immersed
within a liquid such as oil, whereby said second he-
lical groove forces said liquid from said other dam
3,874,677
seal to said low pressure area during rotation of
said shaft.
- ,5.«A high-speed, self-acting shaft seal as recited in
claim 1 wherein at least two seal rings are disposed in
said housing, said means coupled to said inner cylindri- 5
cal surface comprising:
a pair of dam seals;
each dam seal being at one end of said cylindrical
surface of a different one of said seal rings;
each of said dam seals forming a portion of said inner 10
cylindrical surface;
a slot coupled to said high pressure area and being
disposed between two of said at least two seal rings;
a plural i ty of lift pads being respectively disposed be-
tween said slot and one of said dam seals and said 15
slot and the other of said dam seals; and
said dam seals being disposed respectively between
said high pressure area and one of said lift pads and
said low pressure area and the other said lift pads.
6. A high-speed, self-acting shaft seal as recited in 20
claim 5 wherein the plurali ty of lift pads comprises a
ring having a central aperture therein forming an inner
cylindrical surface adapted to be disposed around said
shaft, adjacent lift pads being separated by longitudi-
nally extending channels, said lift pads having a recess 25
disposed therein, the cross-sectional shape of the lift
pad defined from a radial direction with respect to said
aperture, comprising a rectangular cross-section with a
smaller cut-out cross-section having one of its edges in
common with longi tudinal ly extending channels, said 30
smaller cut-out cross-section not bordering on any of
the corners of said rectangular section.
7. A high-speed, self-acting shaft seal as recited in
35
40
45
50
55
60
claim 2 wherein said dam seal has disposed therein a
channel of a cross-sectional shape defined from a radial
direction with respect to said aperture comprising:
a rectangle with a smaller cut-out cross-section hav-
ing one of its edges in common with said axially ex-
tending channel;
said smaller cut-out cross-section not bordering on
any of the corners of said rectangle; and
said channel being coupled to said helical groove by
a port.
8. A high-speed, self-acting shaft seal as recited in
claim 3 wherein said dam seal has disposed therein a
channel of a cross-sectional shape defined from a radial
direction with respect to said aperture comprising:
a rectangle with a smaller cut-out cross-section hav-
ing one of its edges in common with said inner cy-
lindrical surface of said dam seal;
said smaller cut-out cross-section not bordering on
any of the corners of said rectangle; and
said channel being coupled to said helical groove by
a port.
9. A high-speed, self-acting shaft as recited in claim
5 wherein said dam seal has disposed therein a channel
of a cross-sectional shape defined from a radial direc-
tion with respect to said aperture comprising:
a rectangle with a smaller cut-out section having one
of its edges in common with said inner cylindrical
surface of said dam seal;
said smaller cut-out cross-section not bordering on
any of the corners of said rectangle; and
said channel being coupled to said helical groove by
a port.
65



High speed, self-acting shaft seal

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