Seal for a joint or juncture – Seal between relatively movable parts – Relatively rotatable radially extending sealing face member
Reexamination Certificate
2003-03-25
2004-11-02
Pickard, Alison K. (Department: 3676)
Seal for a joint or juncture
Seal between relatively movable parts
Relatively rotatable radially extending sealing face member
C277S371000
Reexamination Certificate
active
06811155
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to assembly construction of shaft seal devices. This invention relates especially but not exclusively to the assembly construction of such shaft seal devices for use with a stirrer or the like providing for a seal of a stirred fluid under a high pressure or extremely high pressure.
2. Description of the Related Art
A shaft seal device as a relative art of the present invention is illustrated in FIG.
3
.
FIG. 3
is a half cross-sectional view of a high pressure mechanical seal device.
In
FIG. 3
, a rotary shaft
175
is supported in a rotary movable manner by a bearing portion, not shown in the figure, which is disposed in a housing
151
of the stirrer
150
. The rotary shaft
175
extends throughout the inside and the outside of the housing
151
. The inside of the stirrer
150
is filled with a high pressure sealing fluid A.
The housing
151
through which the rotary shaft
175
extends is divided into three chambers
152
A,
152
B and
152
C. The chamber
152
comprises, counted from the sealing fluid A side, a first chamber
152
A, a second chamber
152
B and a third chamber
152
C.
When the pressure of the sealing fluid A is 20 MPa say, a pressure fluid of 15 MPa which is a little lower than that of the fluid A is supplied to the first chamber
152
A from a first pipe
153
A.
Similarly, a pressure fluid of 10 MPa which is further lower than the pressure of the first chamber
152
A is supplied to the second chamber
152
B from a second pipe
153
B.
Likewise, a pressure fluid of 5 MPa which is yet lower than the pressure of the second chamber
152
B is supplied to the third chamber
152
C from a third pipe
153
C. Therefore, a plurality of chambers
152
A,
152
B,
152
C are disposed in such a manner that the high pressure of the sealing fluid A is decreased step by step.
Without such a means, a high pressure directly acts on a first mechanical seal device
110
and may cause a damage to the device
110
.
The first chamber
152
A, second chamber
152
B and third chamber
152
C contain respective mechanical seal devices
110
,
120
,
130
inside, and these mechanical seal devices
110
,
120
,
130
are referred to, from the sealing fluid A side towards the atmospheric region, a first mechanical seal
110
, a second mechanical seal
120
and a third mechanical seal
130
, respectively.
The first mechanical seal
110
is a high pressure mechanical seal due to a high pressure nature of the sealing fluid A. Likewise, high pressure mechanical seals are used for the second mechanical seal
130
as well as the third mechanical seal
120
in accordance with a level of the pressure to which they are subjected.
Sealing fluid A used in a stirrer
150
, in general, undergoes a high pressure, and mechanical seal devices
110
,
120
,
130
are typically employed because elastic rubber seals cannot sustain such a high pressure.
These mechanical seals
110
,
120
,
130
are specifically prepared for such a high pressure, and they are mounted in such a way that a shaft sleeve
111
is fitted over the rotary shaft
175
via an O-ring. A spring support
112
engages the sleeve
111
at the shoulder part of the sleeve
111
, and a rotary seal ring
113
is fitted to the other end of the sleeve
111
in a movable manner via an O-ring. A biasing spring
114
supported by the spring support
112
is disposed to exert an urging force to the rotary seal ring
113
.
On the other hand, a stationary seal ring
115
is fitted to a retaining portion of the housing
151
via an O-ring which has an opposing seal face making a sealing contact with the slidable seal face of the rotary seal ring
113
.
The second mechanical seal
120
and the third mechanical seal
130
are constructed in a similar manner to the first mechanical seal
110
although some symbols are omitted in the figure.
The first mechanical seal
110
effectively seals the high pressure sealing fluid A within the stirrer in cooperation with the fluid pressure within the first chamber
152
A which is a little lower than the pressure of the fluid A.
Likewise for the second mechanical seal
120
, it seals the pressure fluid within the first chamber
152
A in cooperation with the fluid pressure within the second chamber
152
B which is two-step lower than the pressure of the fluid A.
Similarly, the third mechanical seal
130
, it seals the pressure fluid within the first chamber
152
B in cooperation with the fluid pressure within the second chamber
152
C which is three-step lower than the pressure of the fluid A.
Use of such pressure resistive mechanical seals, which reduce the fluid pressure in a stepwise manner from chamber to chamber, is essential to provide a secure seal for the sealing fluid A under a high pressure. In other words, when sealing a high pressure fluid, without a plurality of mechanical seals gradually reducing the high pressure in multiple steps, a single mechanical seal device cannot sustain such a high fluid pressure and will be worn out or damaged at its early stage.
In such a multiple step mechanical seal device
100
, the inner diameter of step shoulders
151
A,
151
B,
151
C, which receive the stationary seal rings
115
, is formed larger than any of the outer diameters of the stationary seal rings
115
, the rotary seal ring
113
and the spring support
112
. Thus, it will be difficult to dispose the mechanical seals
110
,
120
,
130
in the respective chambers
152
A,
152
B,
152
C as illustrated in FIG.
3
.
Therefore, disposition of the mechanical seals
110
,
120
,
130
requires the housing
151
to be split into two pieces along the axial direction relative to the rotary shaft
175
, and the mechanical seals
110
,
120
,
130
need to be assembled by being inserted along the axial direction relative to the rotary shaft
175
in order for the seals to be disposed in respective chambers
152
A,
152
B,
152
C.
However, splitting the housing
151
along the axial direction relative to the rotary shaft
175
prevents O-rings or the like from being used and sealing of the split faces will be made difficult. In case of sealing a high pressure seal fluid, in particular, the high fluid pressure creates an undesirable gap between the split faces.
Furthermore, splitting the housing
151
axially makes it difficult to align the stationary seal ring
115
with respect to the rotary seal shaft
175
. This will cause a trouble to the seal performance of the stationary seal ring
115
. In particular, the more mechanical seals
110
,
120
,
130
are involved to reduce the pressure, the more serious these troubles become likely.
Use of such multi-step mechanical seals
110
,
120
,
130
will result in a high production cost due to difficulties in their fabrication process as well as the assembly process.
The present invention is introduced to resolve the above mentioned problems. A primary technical goal which this invention tries to achieve is to provide a mechanical seal device at a reasonable cost while avoiding a total cost increase of a shaft seal device which is caused by employing a plurality of expensive mechanical seals.
Another goal for the present invention is to reduce an assembly cost of the shaft seal device.
Sealing a high pressure fluid by means of a plurality of seal devices will lead to a large construction because of requirement of many chambers to retain them. Therefore, yet another goal of the present invention is to reduce the size of the shaft seal device by making the installation space compact.
SUMMARY OF THE INVENTION
A primary object of the present invention is to resolve the above mentioned technical problems, and a solution to such problems is embodied as follows.
A preferred shaft seal device in accordance with the principles of the present first invention is a shaft seal device for providing a seal against a process fluid between a housing and a rotary shaft, the shaft seal device comprising:
a first seal portion which is located within the device and comprises a stationary seal ring retained in
Arent & Fox PLLC
Eagle Industry Co. Ltd.
Pickard Alison K.
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