Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FIELD OF THE INVENTION
The present invention relates to axial mechanical
seals, and more particularly to seals used in apparatus
subjected to heavy vibrations.
BACKGROUND OF THE INVENTION
Basically, an axial mechanical seal includes a pair
of flat sealing faces forming part of a rotating seat ring and
a stationary sealing ring; these flat faces are urged into
fluid sealing engagement with one another by the application
of force (usuall~ springs) to one or both of -them. In
addition, these aces are subjected to the pressurized fluid
contained within a portion of the seal housing into which a
rotatable shaft extends.
Vibrations which are transmitted from the machine to
the seal cause difficulties, especially in large units such as
turbines, sterntubes, etc. Depending on the frequency and the
amplitude of these vibrations, there occurs periodical lift-
off of the sealing faces resulting in significant leakage
therebetween. In extreme cases, this effect can cause very
short suction and discharge periods in the sealing gap with
high speed leakage ~low and extreme high pressure differences
leading to erosion of the sealing surfaces and rapid damage of
the seal. These vibrations may be divided into radial and axial
movements. Radial movements lead to the sliding of the sealing
ring and the seat ring in the radial direction of the faces of
each other; however, these movements are, in most cases, accepted
by standard axial mechanical seals. On the other hand, axial
movements generate forces in the area of the seals which may
be divided into mass forces and hydraulic forces. In order to
30 ~ reduce mass forces, parts subject to such forces are
usually made as light as possible. Also, by adjusting the
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load of the springs urging the faces in contact with one
another, the area of resonance can be avoided.
The hydraulic forces are significantly larger than
the mass forces as considerable amounts of fluid must be
displaced and suctioned within very short time intervals.
Because of the above-mentioned periodi~cal lift-off, these
hydraulic forces may lead to a constant opening of the seal
faces as the forces in the springs are not capable of
restoring ~he contact of the sealing faces in the short time
intervals. This condition leads to a constant and very high
leakage, eliminating the advantage of low leakage and high
life expectancy of axial mechanical seals as compared to
other types of seals.
OBJECT AND STATEMENT OF THE INVENTION
It is therefore an object of this invention to
provide a seal which is capable of tolerating vibrations
without the aforementioned negative effects.
Basically, the present invention provides
compensators in the housing of an axial mechanical seal, which
compensators are capable of accepting the displaced fluid
without high flow velocity and forces and of disposing of
this fluid according to frequency.
The present invention therefore provides a series ~-
of pockets annularly disposed in the housing of an axial
mechanical seal and of compensator means in each of these
pockets. The compensator means consist of resilient means
having a portion in contact with the fluid under pressure and
yielding in the pockets to accept the fluid displacement
caused by the axial movement of the seal ring and the seal
ring carrier means when they are subject to high vibrations.
~ The scope of applicability of the present invention
will become apparent from the detailed description given herein-
after; it should be understood, however, that the detailed
description 9 while indicating preFerred embodiments of the
invention, is given by way of illustration only since various
changes and modifications within the spirit and scope of the
invention will become apparent to those skilled in the art.
IN THE DRAWINGS:
Figure 1 is a cross-sectional view of an axial
- mechanical seal made in accordance with the present invention;
Figure 2 is an enlarged cross-sectional view taken
along lines 2-2 of Fig. l; and
Figures 3-9 show enlarged sectional views of various
compensator means made in accordance with the present
invention.
Referring to Figs. 1 and 2 of the drawings, there is
shown part of an axial mechanical seal which, for example,
could be inserted inside the housing of a sterntube of a ship
or to a water turbine, which applications involve heavy
vibrations in operation. A rotatable shaf~ 10 extends through
the seal housing, generally denoted as 11, and consisting of
a bas~ ring 12, a main housing portion 14 and a cover 16.
An annular clamp member 18 coaxially mounted to shaft 10
secures an inflatable seal 20 (partly shown in Fig. 1) which
is used for maintenance and replacement purposes. The base
ring 12, the main housing portion 14 and the cover 16 define
therein an enclosed annular chamber 22 which is opened to
pressurized fluid through inlet 23. In chamber 22, a
rotatable seat ring 24 is keyed at 26 and coaxially mounted
to the rotatable shaft 10. Also received in annular chamber
22, a stationary carrier ring 28 is coaxially mounted to
shaft 10 and is provided with an annular recess 30 in which
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is received a seal ring 32 having a flat face 34 in
frictional sealing contact with a flat face 36 provided on
one side of the seat ring 24. These sealing faces are
substantially normal to the shaft axis 10. The seal ring 32
may consist of a carbon element.
Face 38 of carrier ring 28 o~pposite to the face
in which the seal ring is mounted, includes a series of
annularly disposed pockets 40 which are axial1y aligned with
a first set of similar shaped pockets 42, also annularly
provided on the inner face 44 of cover 16. The aligned
pockets 40 and 4~ each contains a relatively weak compression
spring 46 which serves to exert a compress;ve force on the
carrier ring 28 to thereby maintain contact between the
sealing faces 34 and 36.
Carrier ring 28 is stationary and is held against
rotation by a series of a stopping element 48 which are
circumferentially mounted on the carrier ring 28 and which
are shaped to fit into longitudinal slots 50 extending in
the interior wall 51 of housing portion 14.
An outlet passageway, in fluid connection with
annular space 22 has a threaded portion 53 for proper
connection with a conduit (not shown) adapted to be connected
to a compensating chamber for taking up small pressure
variation in the fluid. However, it has been mentioned above
that vibrations in large units, such as turbines, sterntubes
and the like, cause sealing difficulties. The hydraulic
forces resulting from these vibrations are significantly
~large as considerable amounts of fluid must be d-isplaced
and suctioned within very short time intervals and this
result in life-off in the sealing region of faces 34 and 35
causing leakage. The present invention is concerned with the
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provision of compensators which are capable of accepting the
displaced fluid without high flow velocity and forces and of
disposing of this fluid according to the frequency.
In the embodiment illust:rated in Figs. 1 and 2,
these compensator means consist of a second series of
annularly disposed pockets 54 in interior 44 of the cover.
A piston 56 of a shape corresponding substantially to that
of pockets 54 is adapted to slide in each pocket. This
piston is pressure loaded by means of a spring 58 acting
10 between the bottom wall 60 of the pockets and the inner wall
of pistons 56. In the embodiment illustrated, a gasket 62
is mounted in a groove provided in wall 54 to limit the
stroke of the piston inside the pocket. Hence, this piston
will accept the displaced fluid of chamber 22 and will return
15 thereafter to its original position under the action of
spring 58.
Referring to Fig. 3, the stroke of the piston is,
ln this case, limited by a shoulder portion 64 in the
interior wall 54.
Referring to Fig. 4, the compression of the spring 58
may be adjusted by means of a screw member 66 which is
threadedly mounted to an adapter 67 tightly fitted in the bore
of pocket 54.
Referring to Fig. 5 9 the construction shown is
25 somewhat similar to Fig. 3; however, in this case, the spring
is no longer present and the force applied on the piston is
exerted by a pressurized gas supplied to pocket 54 through
a conduit (not shown) adapted to threadedly engage the orifice
68 of a cover adapter 70. --
Fig. 6 shows the use of a bellow construction 72
mounted inside pocket 54 and pressure-loaded by means of a
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spring 74 acting between a bottom element 76 of the bellow
and the cover adapter 78. This bellow member 72 may be made
of an elastomeric material or of a flexible metal.
Fig. 7 illustrates a compensator similar to that
shown in Fig. 6; however, in this case, spring 74 may be
adjusted by a screw member 80 which is threadedly mounted to
a cover adapter 81.
The compensating element illustrated in Fig. 8
consists of an elastomeric cup-shaped member 82 which is
pressure-loaded by means of a pressurized gas inserted throuyh
the orifice 84 of a cover adapter 86.
Fig. 9 shows a different type of pocket construction;
enclosed pocket 88 contains a gas pressurized elastomeric
hollow member 90 which will deform and accept the displaced
fluid as explained hereinabove.
Although the invention has been described above with
respect to specific forms of the invention, it will be evident
to the man skilled in the art that it may be further refined
and modified in various ways. It is therefore wished to have
it understood that the present invention is not to be limited
in interpretation except by the terms of the following claims.
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