Valves and valve actuation – Rotary valves – Seat or interface seal
Reexamination Certificate
2002-02-08
2003-12-02
Hirsch, Paul J. (Department: 3754)
Valves and valve actuation
Rotary valves
Seat or interface seal
C251S316000
Reexamination Certificate
active
06655659
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a seat ring for a valve, and more particularly to an offset or eccentric seat ring for a sanitary plug valve.
BACKGROUND OF THE INVENTION
Conventional control valves are comprised of many different components. One component common to plug-type control valves is a seat ring. A seat ring primarily forms part of a flow passageway and is used in conjunction with a closure member to modify a rate of flow through the valve. In the case of a plug valve, the plug seats against the seat ring to halt or otherwise regulate flow through the valve.
In the food processing and bio-technical industries, it is common to employ valves and valve parts that promote sanitary conditions. For example, in the beer brewing industry, there are many applications for large sized sanitary control valves for brewing beer. Control valves often range from smaller sizes of one to two inches, to larger sizes of four or six inches. One conventional type of sanitary control valve is a sanitary butterfly valve. However, conventional butterfly valves have difficulty controlling fluids flowing therethrough, especially at low flow rates in large size valves.
Alternatively, eccentric rotary plug control valves provide better accuracy over a broader range of flow rates. However, these control valves are not as sanitary as the sanitary butterfly valves. A typical eccentric rotary plug control valve is illustrated in
FIG. 1. A
valve body
104
houses an eccentric seat ring
100
. The eccentric seat ring
100
is held in place with a retainer
102
. A valve plug
106
is movable within the valve body
104
and presses against the eccentric seat ring
100
to close the valve. The eccentric seat ring
100
is made eccentric, as evidenced by the eccentric seat ring
100
maintaining a cylindrical portion having a central axis
114
which is offset from a central axis
116
of the entire seat ring
100
. This offset is what defines the eccentric seat ring
100
.
When the valve is assembled, the eccentric seat ring
100
is placed in its approximate position, but is allowed to rotate, changing the position of the seating surface until the eccentric seat ring
100
aligns with the valve plug
106
. The eccentric seat ring
100
is then secured in place with the retainer
102
.
If the eccentric seat ring
100
, as described in this prior art example, were to be sealed, the attempted sealing would create crevices that would not be easily cleanable during standard cleaning processes. More specifically, with reference to
FIG. 1
, a first crevice
108
exists between the retainer
102
and the eccentric seat ring
100
, a second crevice
110
exists between the retainer
102
and the valve body
104
, and a third crevice
112
exists between the eccentric seat ring
100
and the valve body
104
. Fluid flowing in the direction of arrow D flows through the eccentric seat ring
100
and the retainer
102
, passing over the crevices
108
and
110
. Arrow D represents the flow path of a process fluid, or a cleaning fluid, through the valve body
104
. Some fluid will pass into each of the first crevice
108
, the second crevice
110
, and the third crevice
112
, and is difficult to remove.
The additional crevices
108
,
110
, and
112
in the eccentric seat ring
100
example require three seals, and therefore three leak potential locations for failure and bacteria growth. O-rings utilized to seal the eccentric seat ring
100
in a location to block the crevices
108
,
110
, and
112
create possible pooling points between the components including the eccentric seat ring
100
in crevices
108
,
110
, and
112
. Further, the arrangement including the eccentric seat ring
100
is difficult to match to pipes because the components do not combine to conform to a particular pipe dimension. This pipe size matching is important to prevent line gasket over hang and to reduce locations for bacteria growth.
Another variation of the valve is a concentric seat ring (not shown). When the valve is assembled, the seat ring is placed in its approximate position, but is allowed to move up, down, left and right in a sliding fashion until the seat ring aligns with the valve plug. The seat ring is then secured in place with a retainer. The concentric seat valve includes similar crevices to those found between the eccentric seat ring
100
and the valve body
104
. However, the sealing ability of the concentric seat valve is even further challenged during installation and alignment. Instead of rotating an eccentric seat ring, the concentric seat ring slides up, down, left, and right, to align with the valve plug. Such movement will cause a variance in the percentage of squeeze which causes an O-ring type seal to lose sealing ability.
O-rings utilized to seal the concentric seat ring in a location to block the crevices are ineffective because the O-rings will not maintain a seal when the concentric seat ring moves during assembly and/or alignment. As the concentric seat ring moves, the O-ring will not maintain a consistent percentage of squeeze, thus losing its sealing abilities. Therefore, a consistent O-ring seal cannot be maintained or guaranteed at either the concentric seat ring body, or the seat ring retainer interface. Further, the retainer also requires sealing with a seal such as an O-ring.
Standard valve cleaning processes include the use of steam and/or caustic materials, which flow through the valves to clean them out on a periodic basis. Returning to the eccentric seat ring
100
example, the steam and the caustic materials have a difficult time penetrating the first crevice
108
, the second crevice
110
, and the third crevice
112
. The inability to penetrate results in unsanitary conditions because the crevices
108
,
110
, and
112
are not sufficiently cleaned. Furthermore, the presence of the crevices may generate stagnation points in the process flow, which are undesirable and can lead to bacteria growth. Alternatively, if the caustic materials penetrate into the first crevice
108
, the second crevice
110
, and the third crevice
112
, it is very difficult to rinse the caustic materials out of the crevices
108
,
110
, and
112
. There is a significant likelihood that the caustic materials will remain in each of the crevices
108
,
110
, and
112
. This can cause hazardous conditions for food subsequently flowing through the valve, which can pick up the caustic material and carry it through the process to the final destination, and ultimately to a consumer.
SUMMARY OF THE INVENTION
There is a need in the art for a sanitary eccentric seat ring for use with a rotary plug valve in systems requiring sanitary conditions. The sanitary eccentric seat ring supports the ability to properly seal the seat ring in a sanitary manner to facilitate cleaning. The present invention is directed toward further solutions to address this need.
In accordance with one example embodiment of the present invention, a seat ring includes a body having a first section, a second section, and a body central axis passing through the first and second sections. A first bore is disposed within the first section, and has a first bore central axis concentric with the body central axis. A second bore is disposed within the second section, and has a second bore central axis eccentric to the body central axis.
The seat ring, in accordance with several embodiments, includes the first section being generally frusto-conical in shape. The second section is generally cylindrical in shape. The first bore within the first section is generally frusto-conical in shape, while the second bore of the second section is generally cylindrical in shape.
The seat ring can further include a flange disposed at one end of the first section. The flange is suitable for mounting the seat ring in a valve body. The flange can further include a serrated surface disposed thereon for improving the sealing properties of the flange when joined with a gasket. The flanged end of the seat ring can be modified to work with other process pi
Fisher Controls International Inc.
Hirsch Paul J.
Lahive & Cockfield LLP
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