Valves and valve actuation – Rotary valves – Ball valve
Reexamination Certificate
2001-05-10
2001-11-27
Lee, Kevin (Department: 3753)
Valves and valve actuation
Rotary valves
Ball valve
C251S315160, C251S368000, C029S890126, C029S890132
Reexamination Certificate
active
06322050
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to valves for controlling fluid flow and, more particularly, to an element having high strength and both corrosion and erosion resistance for use in a valve. Specifically, the present invention relates to a metallic element having a non-metallic, cylindrical insert secured therein to provide resistance to corrosion and erosion, wherein a coupling mechanism on a metallic portion of the element provides a high-strength element-to-shaft connection. The present invention also encompasses a method of manufacturing a high-strength, erosion and corrosion resistant element for a valve.
2. State of the Art
Many industrial processes consume, or make use of, fluids that may be either highly corrosive, highly abrasive, or both. Corrosive fluids include a broad array of chemicals that may be corrosive to both ferrous and nonferrous metals, as well as other materials. Abrasive fluids include slurries comprising a primary fluid or fluid mixture in which solid particulate matter is suspended. Particles of contaminates carried by an otherwise non-abrasive fluid may also cause erosion. Also, industrial applications often necessitate the delivery of corrosive and/or erosive fluids at high flow rates, high temperature, or both. Industrial processes, as well as scientific or laboratory applications, consuming or making use of corrosive or abrasive fluids—whether at high flow rate or high temperature—require fluid delivery systems adapted to function in severe operating environments.
Industrial fluid delivery systems routinely include one or more fluid valves configured to control the rate of, or completely terminate, fluid flow through the system. These fluid control valves must be constructed of components adapted to withstand the severe operating environments created by corrosive and/or erosive fluids flowing at high temperature or high flow rate. High temperatures may increase the rate at which a fluid chemically attacks (i.e., corrodes) internal components of a valve, and high temperatures may also subject a valve to thermal stresses, especially if thermal cycling is present. Process conditions in the fluid may dictate high pressure drops or high flow rates, subjecting the valve to higher stresses.
A type of valve commonly employed in industrial fluid transportation systems is the ball valve. A conventional ball valve is shown in cross-section in FIG.
1
. The conventional ball valve
1
includes a ball or ball element
10
configured to control the rate of fluid flow through the conventional ball valve
1
. The ball element
10
comprises a generally spherical body
12
having a cylindrical-shaped fluid passageway
14
extending therethrough and defined by an interior surface
16
. Fluid passageway
14
defines a flow path through the ball element
10
. The direction of fluid flow through the conventional ball valve
1
and fluid passageway
14
is indicated generally by an arrow
5
. The ball element
10
further includes a coupling mechanism
18
configured for attachment of one end of an actuation shaft
20
to the ball element
10
.
The conventional ball valve
1
also includes a housing
30
having an inlet
32
and an outlet
34
. The inlet
32
and outlet
34
each define a generally cylindrical hole having a diameter of substantially the same size as a diameter of the fluid passageway
14
extending through ball element
10
. Supporting the ball element
10
within the housing
30
are seats or seals
40
. Each seat
40
comprises a generally cylindrical-shaped structure including a cylindrical aperture
42
extending therethrough and further including a circumferential seating surface
44
. The diameter of the aperture
42
of each seat
40
is substantially the same as the diameter of the fluid passageway
14
extending through the ball element
10
. The circumferential seating surface
44
of each seat
40
contacts the spherical body
12
along a continuous, circumferential contact region
90
. Biasing elements
50
may elastically bias the seating surface
44
of each seat
40
into contact with the ball element
10
. The interface between the circumferential seating surface
44
of a seat
40
and the outer surface of ball element
10
at the circumferential contact region
90
functions as a seal, preventing fluid present within inlet
32
, fluid passageway
14
, outlet
34
, and apertures
42
from leaking past, or flowing around, ball element
10
and seats
40
. The conventional ball valve
1
may also include a shaft seal
22
guiding the actuation shaft
20
into the housing
30
and preventing fluid leakage therebetween.
Rotation or stroking of the actuation shaft
20
and attached ball element
10
effects a change in flow rate through the conventional ball valve
1
. In
FIG. 1
, the conventional ball valve
1
is depicted in the fully-open position wherein the inlet
32
, fluid passageway
14
, and outlet
34
are substantially concentrically aligned. Rotation of the ball element
10
away from the fully-open position results in decreased fluid flow through the conventional ball valve
1
as the cross-sectional area of fluid passageway
14
that is open to receive fluid flow from inlet
32
decreases, thereby increasing the resistance to fluid flow through the conventional ball valve
1
. In the fully-closed position, the ball element
10
is rotated such that no portion of fluid passageway
14
is open to receive fluid flow from the inlet
32
and the flow of fluid through the conventional ball valve
1
is shut off.
Components of the conventional ball valve
1
—in particular, the ball element
10
—are constructed of metal and typically perform poorly in the severe environments characteristic of erosive, corrosive or abrasive fluid flow. High temperatures and large flow rates further accelerate degradation of metal surfaces within the conventional ball valve
1
. To adapt the conventional ball valve
1
for use with erosive, corrosive and/or abrasive fluids, various non-metallic materials exhibiting high resistance to corrosion and erosion have been incorporated into the conventional ball valve
1
. One specific approach commonly used by valve designers is to construct the ball element
10
from a ceramic material. Ceramic materials typically have corrosion and erosion resistance properties superior to those of most metals. The seats
40
may also be fabricated of a ceramic or other non-metallic material.
Constructing a ball valve having a solid ceramic ball element may greatly improve the ability of the ball valve to operate in the severe operating environments characteristic of corrosive or abrasive fluid flow; however, use of a solid ceramic ball element typically results in degradation of the structural integrity of the ball valve. Specifically, ceramic materials are less ductile than are metals and, therefore, are much more susceptible to fracture under tensile loads. The reduced fracture toughness of a solid ceramic ball element—as compared to a solid steel ball element—gives rise to a weak linkage between the ball element and an actuation shaft secured thereto. Also, outer surfaces of a solid ceramic ball element oriented generally perpendicular to the flow stream are more susceptible to fracture and cracking due to impact by solid particulate matter present in the fluid flow.
For ball valves incorporating a solid ceramic ball, a conventional ball-to-shaft coupling comprises one end of a metal actuation shaft secured in a mating hole on the ceramic ball element. When torsional loads are applied to the actuation shaft, such a ball-to-shaft connection exhibits high tensile stresses in the ceramic ball element proximate the outer circumference of the mating hole in the ball element where the actuation shaft is inserted. A large pressure drop across the ball valve places a large load on the ball element, thereby increasing the torque load on the actuation shaft and, accordingly, the tensile loads in the ceramic ball element proximate the ball-to-shaft coupling. Build-up o
Flowserve Corporation
Lee Kevin
TraskBritt
LandOfFree
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