Seal for a joint or juncture – Seal between relatively movable parts – Circumferential contact seal for other than piston
Reexamination Certificate
1999-05-19
2002-01-01
Knight, Anthony (Department: 3626)
Seal for a joint or juncture
Seal between relatively movable parts
Circumferential contact seal for other than piston
C277S551000
Reexamination Certificate
active
06334619
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to hydrodynamic rotary seal assemblies that are suitable for environmental exclusion and lubricant retention, and for maintaining a film of lubricant at the dynamic sealing interface when the environment pressure is higher than the lubricant pressure. More particularly, the present invention provides a non-circular support surface which efficiently supports the non-circular flank of a hydrodynamic rotary sealing element against environmental pressure, thereby maintaining the functional integrity of the non-circular lubricant edge and the abrupt circular environment edge of the sealing element.
2. Background of the Invention
This invention relates to the commonly assigned prior art hydrodynamic rotary seals and sealing assemblies of U.S. Pat. Nos. 4,610,319, 5,195,754, 5,230,520, 5,678,829, 5,738,358, 5,823,541, 5,873,576, 6,120,036, 6,109,618, and 6,036,192 and PCT WO 95/03504. FIGS. 1-1C of this specification are cross-sectional views which represent prior art which is discussed herein to enhance the readers' understanding of a problem associated with the prior art.
A typical example of such prior art hydrodynamic rotary seals is shown in the uninstalled condition in
FIG. 1
generally at
2
, and is shown in the intended installed condition in
FIG. 1A
in a rotary sealing assembly.
The hydrodynamic rotary seal consists of a resilient generally circular body
4
, which incorporates a dynamic sealing surface
8
, a hydrodynamic inlet curvature
7
and a non-circular flank
10
. The dynamic sealing surface
8
has a has an abrupt circular environment exclusion edge
12
, and also has a non-circular lubricant edge
14
established by the non-circular flank
10
and hydrodynamic inlet curvature
7
.
Such hydrodynamic rotary seals are employed within a seal gland
16
of a housing
18
, and are used to retain a lubricant
20
and to exclude an environment
22
which may contain contaminate matter. The dynamic sealing surface
8
establishes a sealing interface when compressed against a mating relatively rotatable surface
24
, the footprint of said sealing interface having a footprint lubricant edge
28
and a footprint environment edge
30
. The non-circular character of non-circular flank
10
causes the footprint of said sealing interface to be of varying width.
As relative rotation of relatively rotatable surface
24
takes place, the non-circular lubricant edge
14
, which has a gradually converging relationship with the relatively rotatable surface
24
as a result of hydrodynamic inlet curvature
7
and non-circular flank
10
, generates a hydrodynamic wedging action that forces a lubricant film between dynamic sealing surface
8
and relatively rotatable surface
24
per the teachings of U.S. Pat. No. 4,610,319. The lubricant is wedged into the dynamic sealing interface by the normal component Vn of the rotational velocity V acting on non-circular lubricant edge
14
of dynamic sealing surface
8
. This lubricant film physically separates dynamic sealing surface
8
and relatively rotatable surface
24
, and thereby prevents the typical frictional wear and heat damage associated with conventional non-hydrodynamic seals, and thereby prolongs seal life. Abrupt circular environment exclusion edge
12
does not generate a hydrodynamic wedging action with the environment in response to relative rotary motion because it is not skewed relative to rotational velocity V, and thereby functions to exclude environment
22
per the teachings of U.S. Pat. No. 4,610,319.
The prior art seals are best suited for applications in which the pressure of lubricant
20
is either higher than, or substantially balanced with, the pressure of environment
22
.
FIG. 1A
shows the seal being held against environment-side gland wall
32
by pressure differential-induced hydrostatic force resulting from the lubricant
20
being at a higher pressure than environment
22
. Owing to the complimentary shapes of the seal environmental end
34
and the environment-side gland wall
32
, the seal is well supported by environment-side gland wall
32
in a manner that resists distortion and extrusion of body
4
when the pressure of lubricant
20
is higher than the pressure of environment
22
.
As depicted in
FIG. 1B
, if the pressure of environment
22
is substantially higher than the pressure of lubricant
20
, the resulting differential pressure-induced hydrostatic force can severely distort body
4
, footprint lubricant edge
28
and a footprint environment edge
30
. The hydrostatic force presses body
4
against lubricant-side gland wall
36
, and can cause body
4
to twist and deform such that non-circular flank
10
and hydrodynamic inlet curvature
7
are substantially flattened against relatively rotatable surface
24
. Such distortion and flatting can inhibit or eliminate the intended hydrodynamic lubrication, resulting in premature seal wear because footprint lubricant edge
28
can become substantially circular under such conditions, and the gently converging relationship between body
4
and relatively rotatable surface
24
(which is necessary for hydrodynamic lubrication) can be eliminated. Such distortion can also cause abrupt circular environment exclusion edge
12
to distort to a non-circular configuration and may also cause portions of dynamic sealing surface
8
to lift away from relatively rotatable surface
24
, producing a low convergence angle
38
between dynamic sealing surface
8
and relatively rotatable surface
24
, and causing the footprint environment edge
30
to become non-circular and skewed relative to rotational velocity V. Such distorted geometry is eminently suitable for the generation of a hydrodynamic wedging action in response to relative rotation of the relatively rotatable surface
24
; such wedging action can force environmental contaminants into the sealing interface and cause rapid wear.
To effectively exclude a highly pressurized environment, one must use a pair of oppositely-facing prior art hydrodynamic seals; one to serve as a partition between the lubricant and the environment, and the other to retain the lubricant, which must be maintained at a pressure equal to or higher than the environment. This scheme ensures that neither seal is exposed to a high differential pressure acting from the wrong side, but requires a mechanism to maintain the lubricant pressure at or above the environment pressure. For example, see the first pressure stage of the drilling swivel of U.S. patent application Ser. No. 09/018,261.
Many applications, such as the oilfield drilling swivel, the progressing cavity artificial lift pump, centrifugal pumps, and rotary mining equipment would benefit significantly from a hydrodynamic rotary seal having the ability to operate under conditions where the environment pressure is higher than the lubricant pressure, because the resulting assembly would avoid the complexity and expense associated with lubricant pressurization.
SUMMARY OF THE INVENTION
The objective of the present invention is to provide a simple and compact rotary sealing assembly for lubricant retention and high pressure environmental exclusion which employs the advantage of maintaining a film of lubricant at the dynamic sealing interface during operation to thus promote efficiency and longevity of service.
A principle feature of the present invention is a seal gland wherein at least a portion of the lubricant-side gland wall is a non-circular support surface which supports the non-circular flank and hydrodynamic inlet curvature of a hydrodynamic rotary seal or packing against pressure-induced distortion when the environment pressure is higher than the lubricant pressure, so as to retain the hydrodynamic wedging function of the non-circular lubricant edge of the seal, and so as to retain the exclusionary function of the abrupt circular environment edge of the seal.
Another feature of the present invention is a seal gland wherein at least a portion of the non-circular support surface
Dietle Lannie
Kalsi Manmohan S.
Jackson James L.
Kalsi Engineering, Inc.
Knight Anthony
Mayor Day Caldwell & Keeton, LLP
Patel Vishal
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