Pressure regulating buffer seal

Details Pressure regulating buffer seal Pressure regulating buffer seal

2000-09-25

2003-07-22

Knight, Anthony (Department: 3676)

Seal for a joint or juncture

Seal between relatively movable parts

Piston ring or piston ring expander or seat therefor

C277S437000, C277S510000, C277S552000, C277S558000, C277S928000

Reexamination Certificate

active

06595524

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to sealing elements for hydraulic and pneumatic machine elements. Specifically, the present invention relates to a buffer seal for providing a fluid seal between relatively moving parts, such as a piston or rod moving within a bore and, in particular, the present invention relates to a buffer seal providing a controlled pressure at a primary seal.
2. State of the Art
Seals adapted to provide a fluid seal between two relatively moving machine elements are well known in the art. For example, one or more sealing elements are commonly used to provide a fluid seal between a piston or rod moving within, and relative to, a bore extending through a housing or other machine element. Although a single seal may be disposed between an outer cylindrical surface of the piston or rod and an inner cylindrical surface of the bore, it is a common practice to employ a combination of two or more sealing elements (i.e., a seal assembly) to provide a robust fluid seal between the two relatively moving machine elements.
A conventional seal assembly is shown in FIG.
1
. The conventional seal assembly
5
is configured to provide a fluid seal between, for example, a rod
11
of a first machine element
10
moving within a bore
21
of a second machine element
20
and relative thereto. Although the first machine element
10
is shown including a rod
11
and the second machine element
20
is shown including a bore
21
, it will be appreciated by those of ordinary skill in the art that each of the first and second machine elements
10
,
20
, respectively, may be comprised of multiple machine parts or elements. For example, the rod
11
of first machine element
10
may comprise two or more separately formed parts that are subsequently attached to one another to form the assembled rod
11
.
The rod
11
and bore
21
of the first and second machine elements
10
,
20
, respectively, are generally mutually concentric to a central longitudinal axis
15
. Further, the rod
11
of first machine element
10
and the bore
21
of second machine element
20
are cooperatively dimensioned to enable the rod
11
and bore
21
to slide and/or rotate relative to one another. A clearance gap
90
between an outer cylindrical surface
12
of the rod
11
and an inner cylindrical surface
22
of the bore
21
enables relative motion between the rod
11
and bore
21
. It should be noted that in
FIG. 1
the size of the clearance gap
90
has been exaggerated for clarity; however, those of ordinary skill in the art will understand that such a clearance gap
90
may, in practice, be extremely small in comparison to the dimensions of the rod
11
and bore
21
. For example, the clearance between the outer cylindrical surface
12
of the rod
11
and the inner cylindrical surface
22
of bore
21
may be on the order of a few thousandths of an inch or less.
Relative motion between the first machine element
10
and the second machine element
20
may be the result of the rod
11
traveling longitudinally along axis
15
through the bore
21
of a relatively stationary second machine element
20
or the result of the second machine element
20
traveling longitudinally along axis
15
over a rod
11
of a relatively stationary first machine element
10
. Alternatively, relative motion between the first and second machine elements
10
,
20
may be the result of longitudinal travel of both the first and second machine elements
10
,
20
, respectively, along axis
15
. Also, relative motion between the first machine element
10
and second machine element
20
may be the result of relative rotary motion between the first and second machine elements
10
,
20
, or the result of a combination of relative longitudinal motion and relative rotary motion therebetween.
The seal assembly
5
comprises a wiper
30
, a primary seal
50
, and a buffer seal
70
. The wiper
30
is disposed in an annular groove or gland
40
, formed about the circumference of the inner cylindrical surface
22
of the bore
21
extending through second machine element
20
. Similarly, the primary seal
50
is disposed in a gland
60
formed about the circumference of the inner cylindrical surface
22
of bore
21
and the buffer seal
70
is disposed in a gland
80
formed about the circumference of the inner cylindrical surface
22
of bore
21
. Although the glands
40
,
60
,
80
are shown disposed about the inner cylindrical surface
22
of bore
21
, and the wiper
30
, primary seal
50
, and buffer seal
70
disposed therein, respectively, it should be understood by those of ordinary skill in the art that one or more of the glands
40
,
60
,
80
could be disposed about the circumference of the outer cylindrical surface
12
of the rod
11
of first machine element
10
.
The wiper
30
is a generally ring-shaped member disposed in the gland
40
. The wiper
30
is adapted to prevent the ingress of solid particulates and other contaminants into the clearance gap
90
from the ambient side
92
of the seal assembly
5
(i.e., the end of the seal assembly
5
exposed to ambient environmental conditions) to a region
94
between the wiper
30
and the primary seal
50
where such contaminants could potentially damage or inhibit proper functioning of the primary seal
50
. Wipers for use in hydraulic and pneumatic fluid sealing applications are well known in the art.
The purpose of the primary seal
50
disposed in gland
60
is to prevent the flow of fluid from the system side
98
of the seal assembly
5
(i.e., the end of the seal assembly
5
exposed to pressurized fluid) and through the clearance gap
90
to the ambient side
92
of the seal assembly
5
. Any leakage of fluid past the primary seal
50
to the ambient side
92
of the seal assembly
5
may compromise system fluid pressure and operation. For example, the proper functioning of a hydraulically-actuated piston used to apply a load over a specified distance (e.g., hydraulic cylinders on construction equipment) depends upon the maintenance of system fluid pressure. Seals adapted for use as a primary seal
50
in hydraulic and pneumatic fluid sealing applications are well known in the art. These seals may be statically loaded or, alternatively, dynamically loaded during operation.
A statically loaded seal typically comprises a generally ring-shaped, resiliently elastic body exhibiting a geometry adapted to provide a necessary sealing force. For example, with reference to
FIG. 1
, a statically loaded primary seal
50
may comprise a resilient body disposed in the gland
60
and having a geometry such that, upon insertion of the rod
11
into the bore
21
of the first and second machine elements
10
,
20
, respectively, the resilient body deforms or compresses and exerts radially inward-directed forces about the circumference of the outer cylindrical surface
12
of the rod
11
. The resilient body further exerts corresponding radially outward-directed forces about the circumference of the outer wall
61
of the gland
60
and/or exerts longitudinally directed forces about the periphery of one or both of the side walls
62
,
63
of the gland
60
. The forces exerted by the resilient body against the outer cylindrical surface
12
of the rod
11
and one or more of the walls
61
,
62
,
63
of the gland
60
prevent, or at least substantially inhibit, the flow of fluid around the resilient body. Therefore, fluid pressure on such a statically loaded seal is unnecessary for the statically loaded seal to maintain a fluid seal and, further, excessive system pressure on a statically loaded seal can cause high friction, heat generation, increased wear, and reduced seal life.
A dynamically loaded seal typically comprises a generally ring-shaped, resiliently elastic body. However, the resilient body is configured to provide a necessary sealing force, or at least a significant portion of the sealing force, when subjected to system fluid pressure. The resilient body may include a structure, such as

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