Metal working – Method of mechanical manufacture – Valve or choke making
Reexamination Certificate
2002-07-16
2003-11-11
Jordan, Charles T. (Department: 3644)
Metal working
Method of mechanical manufacture
Valve or choke making
C029S890129, C029S890131, C029S469000
Reexamination Certificate
active
06643929
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of producing a ball valve to be connected to a fluid piping system, and more particularly to a method of assembling a housing, adapted to contain a ball therein, by welding.
BACKGROUND ART
(1) U.S. Pat. No. 4,265,427 (corresponding to JP-A-55-14394) discloses one example ball valve which comprises, as main component members, a ball, and a housing containing the ball.
In the ball valve, a spherical shut-off member (i.e. a ball), contained in a hood (or a housing), has a pair of projections (or stems), and the projections are rotatably supported by a pair of support rings attached to an inner surface of the hood, respectively. The hood is assembled by welding a pair of hood halves together, and butt welding end faces of the pair of hood halves lie in a plane including an axis of rotation of the spherical shut-off member. Namely, the pair of hood halves are mirror-symmetrical with respect to the plane including the axis of rotation of the spherical shut-off member.
The hood has an operation hole (or window) provided for rotating the spherical shut-off member around the axis, and hemi-circular recesses, corresponding to the operation hole, are formed respectively in the pair of hood halves before the two hood halves are jointed together by welding.
The pair of support rings serve to receive a thrust force from a fluid, are provided respectively at opposed positions on the inner surface of the hood, and are disposed near to the axis of rotation of the spherical shut-off member in surrounding relation thereto, wherein one of the support rings surrounds the operation hole. Each of the two support rings comprises a combination of support ring halves corresponding respectively to the pair of hood halves, and the support ring halves are secured respectively on the inner surfaces of the pair of hood halves by welding prior to welding of the hood halves. Therefore, when the pair of hood halve are jointed together by welding, each pair of support ring halves are abutted against each other at their butting end faces to form the circular ring.
In order to prevent the inside of the hood from being affected by the welding operation (by which the pair of hood halves are jointed together), a partially cut off grooved ring is attached by welding on the inner surface adjacent to the welding face (i.e. the butt welding end face) of one of the hood halves. The grooved ring extends toward the mating hood half in the direction of the width thereof so as to extend circumferentially along the inner side of the butted end faces of the pair of hood halves for welding.
In the ball valve having such a structure, since the pair of support rings, which receive a thrust force from fluid, and the operation hole of the hood, are located close to the butt welded faces of the pair of hood halves, there is a possibility that thermal strain is induced in the hood due to welding heat resulting in a displacement of each support ring half from its proper position. In this case, the precision of the axis of rotation of the spherical shut-off member is affected, so that incomplete contact between valve seats, which are provided on the inner surface of the hood, and the spherical shut-off member occurs.
(2) U.S. Pat. No. 4,235,003 discloses a method of producing a ball valve. In the disclosed ball valve, a ball is contained in a hollow member (i.e. a housing), and the ball is rotatably supported by a pair of rings (i.e. valves seats). In the ball valve having such structure, unlike the ball valve disclosed in U.S. Pat. No. 4,265,427, the rings receive a thrust force from fluid.
The hollow member of the ball valve, disclosed in U.S. Pat. No. 4,235,003, is formed by jointing a pair of symmetrical pipe members together by welding. Each pipe member has a hemi-spherical enlarged portion (of a bowl-shape) formed at one end thereof, and open end faces of the two enlarged portions are butted and welded together at the end faces, thereby forming the hollow member. When the ball valve is opened or closed, the ball within the hollow member is operated by an operation stem passing through a hole formed in the hollow member, the hole being formed by a combination of hemi-circular recesses which are formed respectively in the open ends of the two enlarged portions prior to the welding for obtaining the hollow member. Here, the remaining portion of each pipe other than the enlarged portion will be referred to as a straight pipe portion, and a sleeve of a wedge-shaped cross-section for holding a ring (i.e. a valve seat) is fitted into each of the straight pipe portion, and is fixedly secured thereto by welding.
In the ball valve, although the straight pipe portions have an inner diameter corresponding to that in a fluid piping, there is a disadvantage that the sleeves and the rings (i.e. valve seats) narrow a fluid passage. Further, since the hemi-circular recesses are formed respectively in the enlarged portions of the two pipe members prior to welding for obtaining the hollow member, there is a possibility that the operating stem-passing hole, formed by the combination of the hemi-circular recesses, is affected by thermal strain which is induced in the hollow member by welding, so that the center of the hole is displaced out of a proper position.
(3) A third example of known ball valves is shown in FIG.
5
. The ball valve comprises, as main components, a housing
01
, having openings
02
A and
03
A formed respectively at opposite sides thereof, a ball
05
, which is contained in the housing, and has a central through bore
05
A, and a pair of stems
07
and
08
supporting the ball. The ball
05
is rotated by the operation stem
08
about the axis of the both stems. There are provided valve seat rings
06
and
06
between the housing
01
and the ball
05
which is kept always in contact with the valve seat rings
06
and
06
.
The housing
01
consists of three members, that is, a first member
02
, a second member
03
and a third member
04
, the first and second members being mirror-symmetrical. The three members each having a generally tubular shape are butted and welded (W) at their open end faces.
The stems
07
and
08
extend through the third member
04
. The stem
07
extends through the third member
04
and is fixed thereto. It is also rotatably fitted in a bore for stem of the ball
05
. The other stem
08
is of an operation stem for rotating the ball valve, which rotatably extends through the third member
04
, is supported by a separate support member
09
, and is fitted in a bore for stem of the ball
05
so as not to rotate relatively to the ball.
This ball valve is of such a structure that the pair of stems
07
and
08
receive a thrust force from fluid. The housing
01
is assembled by jointing the three sectional members together by welding, which is disadvantageous from an economical point of view since the number of the components is large. Besides, since the two weld lines W, W are close to the valve seat rings
06
and
06
, respectively, there will occur an unconformity with respect to the contact relationship between each of the valve seat rings
06
,
06
and the ball
05
under the influence of thermal strain induced in the housing. Further, since the weld lines W, W are close to the stems
07
and
08
, the shape of the respective holes of the third member
04
for the stems is affected by the thermal strain, whereby the precision of the stems
07
and
08
, that is, the axis of rotation of the ball
05
, is deteriorated, also resulting in an unconformity with respect to the contact relationship between each of the valve seat rings
06
,
06
and the ball
05
.
The present invention has been proposed under the above technical background.
Problems to be solved by the invention are to reduce the number of components, in producing a so-called trunnion type ball valve, in order to save the production cost for the trunnion type ball valve, such as the first conventional example of U.S. Pat. No. 4,265,427 and the third conventional example shown in
Jordan Charles T.
Nguyen T.
Rader & Fishman & Grauer, PLLC
Tix Corporation
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