Fluid handling – Systems – Multi-way valve unit
Reexamination Certificate
2002-06-05
2004-10-26
Fox, John (Department: 3753)
Fluid handling
Systems
Multi-way valve unit
C137S625390
Reexamination Certificate
active
06807985
ABSTRACT:
FIELD OF THE INVENTION
This invention is directed generally to flow control valves and more specifically to cage-guided control valves.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 4,256,284 describes a high energy loss fluid flow control device that uses a stepped-spiraled-tapered bore and control element to minimize clearance flow. The '284 patent, however, presents a clearance flow minimizing design that is physically and operationally different from the invention. The '284 patent design does not address specific geometry for controlling the pressure recovery of the controlled fluid and it does not allow for high rangeability.
A typical globe valve is a valve with a linear motion closure member, one or more ports and a body typically distinguished by a globular shaped cavity around the port region. The body is the part of the valve which is the main pressure boundary. The body typically provides the pipe connecting ends and the fluid flow passageway. In a globe valve, the closure member is a movable part of the valve that is positioned in the flow path to modify the rate of flow through the valve.
A plug closure member is a part, often cylindrical in nature, which moves in the flow stream with linear motion to modify the flow rate. It may or may not have a contoured portion to provide flow characterization. It may also be a cylindrical or conically tapered part, which may have an internal flow path, that modifies the flow rate with rotary motion. Other closure members include ball, disk and gate, for example.
A flow orifice in the flow passageway (path) interacts with the closure member to close the valve. The orifice may be provided with a seating surface, to be contacted by or closely fitted to the closure member, to provide tight shut-off or limited leakage, i.e., to close the valve.
A cage is typically a part in a globe valve that generally surrounds the closure member to provide alignment and facilitate assembly of other parts of the valve trim. The cage may also provide flow characterization and/or a seating surface. Globe valve trim typically includes the internal parts of a valve which are in flowing contact with the controlled fluid. Examples of valve trim are the plug, seat ring and cage. The body is not considered part of the trim.
FIG. 1
depicts a standard cage-guided globe control valve
10
, comprising a body
12
, that controls flow
14
by modulating the valve plug
16
to expose holes
18
(ports or flow paths) of a port region
19
in the valve cage
20
. Controlling surfaces are surfaces that define an area that throttles the process fluid, i.e., the surface is subject to the application of pressure differential. Other surfaces may be in contact with the fluid, but are not actively involved in the throttling process. The controlling surface is either between the cage port
18
and plug
16
(
FIG. 2
) or the seat ring
22
and plug
16
depending upon plug
16
position within the cage
20
.
To obtain high flow capacities through such a valve, large size seat rings, cages, and plugs are utilized. To allow free movement of the plug
16
within the cage
20
, a radial clearance
24
must be provided between the plug outside diameter
26
and the cage bore
28
(FIG.
3
). This radial clearance
24
typically increases with increasing valve size. As the plug
16
is lifted off of the valve seating surface
30
, and before the initial cage port area
32
is exposed, the radial clearance area
24
is allowed to pass fluid flow
34
. The flow
34
transmitted through this radial clearance area
24
is the minimum flow in the valve
10
. The clearance flow area
24
is important in this type of valve design because this area
24
will limit the minimum controllable flow as defined by the valve characteristic.
The flow characteristic of a cage throttling control valve
10
is defined by the cage port throttling area exposed (see, for example,
FIGS. 2 and 3
, items
38
and
18
, respectively). Throttling below the cage port area causes the entire throttling pressure drop to occur in the clearance flow area
24
(i.e., flow through the guide clearance). Under high-pressure drop conditions, particularly high-pressure liquid letdown (as opposed to gas), clearance flow throttling can be very damaging to metal surfaces, thereby causing erosion
36
. Some cage throttling valves
10
will utilize multiple pressure drop staging
38
throughout the cage flow area, however, the staged flow ports (
40
in
FIG. 2
) located above the throttling area
42
have direct communication to the valve outlet (orifice)
44
through the guide clearance area
24
. This will lead to full pressure drop between the non-exposed staged flow paths and the exposed flow paths (see FIG.
2
). This can ultimately lead to erosion
36
in the guide clearance
24
due to cavitation and high-velocity wear, resulting in eventual valve-clearance vibration problems. Continued erosion will increase the guide clearance and further exacerbate vibration-related problems.
Valve manufacturers define the ratio of maximum controllable flow to minimum controllable flow as the valve rangeability. Most cage-guided globe control valves have a rangeability, limited by the clearance flow, to approximately 100:1.
OBJECTS OF THE INVENTION
Accordingly, it is an object of the invention to provide a valve with rangeability greater than approximately 100:1. A further object is to provide a valve with rangeability greater than approximately 500:1.
Another object is to provide a valve that reduces or eliminates cavitation erosion damage to seating areas.
Another object is to provide a valve with a pressure recovery area, away from the seating area.
Yet another object is to provide a valve with increased rangeability that reduces or eliminates cavitation damage on seating surfaces.
Another object is to provide a valve with a clearance seal.
Yet another object is to provide a valve with a clearance seal and a pressure recovery area.
Other objects and advantages will be apparent from the teachings herein.
SUMMARY OF THE INVENTION
Briefly, in accordance with the foregoing, a control valve comprising a vapor recovery area addresses problems associated with the prior art. A seal is preferably positioned above the vapor recovery area to reduce flow between a closure member and alignment means for the closure member.
In an embodiment of a globe control valve, a plug is aligned in a cage to contact a seat. The vapor recovery area is positioned between the cage and the plug. Preferably, at least when the plug is opened, the vapor recovery area is above the seat. The seal reduces flow through a clearance between the cage and the plug. For some applications, the seal comprises an outer seal contacting the cage and an inner seal between the outer seal and the plug.
More generally, a control valve is provided with means for encouraging collapse of vapor bubbles. In a particular embodiment, a closure member interacts with an orifice to close the valve. A clearance is defined between the closure member and a means for aligning the closure member. Means for reducing flow through the clearance comprises, for example, a seal coupled to move with the closure member.
More specifically, a control valve may be provided with a linearly movable plug positioned in a fluid flow path. The plug moves in a cage comprising a plurality of ports located axially along the cage. Thus, moving the plug will modify the rate of fluid flow. A radial clearance is defined between the cage and the plug. And a seal, comprising an elastomeric inner seal and metallic outer seal, reduces flow through the clearance. The plug defines, at least in part, a vapor recovery gallery between the plug and the cage, wherein the gallery is below the lowest port when the plug is seated. When the plug is lifted to expose, at least in part, the lowest port, the gallery is above a seat that interacts with the plug to close the valve.
It will be understood that use of directional terms such as above and below are for convenience only and not intended to limit the scope of the t
Bittner Christopher
Stares James A.
Dresser, Inc.
Fish & Richardson P.C.
Fox John
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