Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Background of Invention
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This invention relates to gate valves and in par-
ticular to a gate valve construction using a split gate
construction.
Double disc gates have been proposed for gate valves
because of certain inherent functional and manufacturing
advantages. Such constructions, in view of the larger
freedom of movement of the independent discs, can conform
to larger manufacturing variations in the discs and the
valve seats while, at the same time, provide complete
sealing despite distortion of the seats due to differ-
ential heating and cooling rates and system stresses.
-~ The present invention improves upon prior double disc
constructions by providing a unit which has additional
manufacturing, performance and reliability features.
Summary of the Inve tion
According to the invention, there is provided a gate
; valve comprising: a valve body having flow passages
communicating with a central valving control chamber;
valve seats in the valve body at the ends of the flow
passages adjacent the control chamber; a two piece gate ;
movable between an open position and a closed position by
an external stem assembly operably connected to said gate;
a seating surface formed on one side of each of said gate
~: pieces sealingly engageable with its respective said valve
seat in the closed position when opposed surfaces respec-
tively of the other side of each of said gate pieees ~re
spaced a predetermined distanee apart; a single rigid
spacer member remote from said stem assembly having end
surfaees respectively engaging said opposed surEaces and
having a thickness therebetween equal to said predeter-
mined distance; projecting capturing means on each of
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said gate pieces bounding a peripheral wall of said spacer
member and projecting from said opposed surfaces an
effective combined distance less than the thickness of
the spacer member; and guide means preventing separation
of the pieces during gate movement and disengagement of
t~ eapturing means.
Preferably, therefore, the gate of the present valve
comprises two juxtaposed identically formed discs. In
assembly, the discs are spaced a predetermined distance
apar~ by an annular spacer ring, retained in place by
means of projecting capturing surfaces. The individual
discs allow independent axial flexing such that, despite
dimensional and angular variations between the respective
seating surfaces and the valve seats, the downstream seat
can independently conform to its seating surface. The
spacer ring is peripherally bounded, and thereby captured, ~;
internally in one form and externally in another form, by
projecting circumferential suraces. The spacer ring,
more importantly, establishes the desired overall width
of the gate. In this manner, the spacer ring can be
appropriately independently sized and selected to accommo-
date various tolerances in the individual disc while still
providing a predetermined overall width necessary to ensure
sealing mating of the seating surfaces in the valve closed
position.
- Additionally, when the valve seats and seating
- surfaces become scored or otherwise damaged such that
regrinding is necessary, the amount of
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removed material can be compensated for by increasing the width of the spacer
ring to once again re-establish the desired relationship between the seating
surfaces in the fully closed position. The spacer ring has a substantially smaller
diameter than the seating surfaces to increase the disc deflection capability.
The discs additionally include slots transverse to the flow passage
which capture a T-head end of a non-rotating valve stem. Because the disc or
! wedge is larger at the top than the bottom, sufficient material exits for forming
cavities transverse to the valve seating surfaces while being located radially
there-between. In contrast to conventional gate valves wherein the slot for the
` 10 T-head is parallel to the fluid flow, the entire stem head retaining section is
exterior of the valve seating surfaces, this adds considercbly to the height oF the.~
valve and, as a consequence, the present design is considerably more compact.
Further fracture of the stem presents the possibility that the stem end will enter
` the flow line. This possibility is precluded by the present captured design. The
" individual gate discs ride up and down the valving control chamber by
cooperation between guide tongues formed at the sides of the discs and recessed
` guide rails formed on the sides of the valve bodyO This provides for guided
controlled axiai movement of the gate assembly between the open position and
the closed position. With the aforementioned stem connection oriented
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~ 20 perpendicular to the flow line, rather than parallel to it, there are no reactive
;~ ~ forces on the discs causing relative rotation of the two valve discs. Accordingly,
no pin connection or the like is necessary.
The above and other features of the present invention wi l l be
apparent to those skilled in the art upon reading the following detailed
description, reference being made to the drawings in which:
Figure I is a cross-sectional view of a gate valve made in accordance
with the present invention, showing the two piece gate in the closed position;
Figure 2 is a view taken along line 2-2 of Figure I, showing the inter-
locking hub and spacer ring between the valve discs;
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Figure 3 is a fragmentary view showing the assembly oF the seat ring
to the valve body and its engagement with the seating surface on the gate disc;
Figure 4 is a view taken along line 4-4 of Figure 1, showing the
tongue and groove guides between the gate and the valve body;
Figure 5 is an enlarged fragmentary view taken along line 5-5 of
Figure 1, showing the stem head connection at the valve discs;
Figure 6 is an enlarged fragmentary perspective view of the stem
head in assembly with the valve discs;
Figure 7 is an enlarged perspective view of the stem head configura-
10 tion;
: Figure 8 is an enlarged perspective view of a valve disc illustrating
. the stem head slot and the segmented locating hub;
Figure 9 is a fragmentary cross sectional view of the discs spaced bythe spacer ring retained by the peripheral surface of counterbores in the discs;
and
, Figure 10 is a view taken along line 10-10 of Figure 9.
Descri~ion of the Preferred Embodiments
Referring to Figure I, there is shown a gate valve 10 made in
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accordance with the present invention of the type used for high pressure fluid
20 applications such as electric power generation systems of either the fossil or
nuclear type. Such a gate valve is usable in a product line ranging between
nominal sizes of 1-1/2 inches and 42 inches and in ANSI pressure classes of 600,
` 900, 1500, 250û and 450û.
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The gate valve 10 generally comprises a vqlve body 12, a bonnet
assembly 14, a yoke assembly 20 and a handwheel assembly 22. As hereinafter
described, rotation of the handwheel assembly 22 raises and lowers an internal
stem assembly 24 and a double disc gate 26 to open and close a fluid passage :
extending through the valve body 12 along axis 28 between a left hand outlet 30
and a right hand outlet 32. The direction of flow is dependent on the system and :
3û the present ea,ually facilitates flow in either direction.
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The vqlve body 12 is a generally T-shaped cast carbon steel construc-
tion and includes outlet sections 33 and 34 and a control section 35 mutually
intersecting at ~ valving chamber occupied by the gate 26. The section 33
includes the aforementioned outlet 3û and a flow passage 36. The section 34
includes the aforementioned outiet 32 and a flow p~ssage38. The passages 36 and
38 are co-axially disposed along the flow axis 28. The end of control section 35defines an upwardly opening cylindrical section 4û having an operational axis 42which perpendicularly intersects the flow axis 28~
. The inner ends of the sections 33 and 34 are formed with counter-
10 bores 50 and 52 which contain cylindrical seat rings 54. The seat rings 54 are
. provided with hardened annulqr seats 56 (Figure 4). The seats are formed in
planes inclined five degrees with respect to the operqtional axix 42. The planes. of the seats 56 ~re symmetrically disposed with respect to the axes 42 and 28.
The seat rings 54 are fixed to the inner surfqce of the valve body 12 at
continuous circumferential welds 58.
- The bonnet assembly 14 is retained at the upper end of the section 40
;. on the outer end of the section 35 by means of a split retainer ring 60. E~olts 62
clamp and ring 60 to draw the outer flange 63 of the bonnet 64 upwardly agqinst
the retainer ring retained in a peripheral circumferential channel section 65.
20 The bonnet 64 is centrally apertured and receives the stem 70 of the assembly24. The handwheel assembly 22 is attached at its outer end to the stem assembly
24 and at its lower end to the gate 26. A packing gland assembly 76 seals the
.: ~ periphery of the stem 70.
.- The yoke assembly 20 is retained at the top of section 35 by means of
a split yoke lock ring 78. A pair of roller bearings 80 and 82 have their outer
. races received in counterbores at the upper end of the yoke 2û and have their
- inner races fixedly carried at opposite ends of rotatable bushing 84 which has an
internal thread engaging the threaded end 86 of the vqlve stem 70. The bushing
84 is keyed to the handwheel 22 such that rotation of the hqndwheel 22 rotates
,: 30 the bushing 84 to rise and lower the stem 70 through the packing assembly 76,
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thereby raising and lowering the gate 26 between the illustrated lowered closed
position and a raised opened position as guided by the cooperation between guidetongues formed at the sides of the discs and the grooves between guide rods
formed at the sides of the body (Figure 4). In the open position the gate 26 is
housed within a generally hemispherical depression 90 in a lower surface of the
bonnet 64 so as to reduce the vertical height of the valve.
The gate 26 comprises two identically formed gate discs lOû and 102.
In assembly the discs 100 and 102 have opposed seating surfaces hereinafter
described which sealingly engage the seats 56 of the seat rings 54 to prevent
10 migration of fluid past the sealing interfaces. Each disc has a projecting
; hardened seating surface 104 which is ground flat in a plane inclined with respect
to its plqnar back surface at an angle equal to the inclination of the seat 56 or, in
other words, five degrees with respect thereto. The outer diameter of the
surface 104 is slightly larger than the surface 56. In initial assembly, the fully
seated closed position, the overall thickness of the wedge is sized such that the
axis 106 of the wedge assembly is located above flow axis 28. As the seating
surfaces wear, the axis 106 will shift downwardly and will maintain complete
sealing contact until the outer diameter of surface 104 is unacceptably below the
outer diameter of seat 56 at the upper center thereof.
Referring to Figure 8, the rear surface I lû of the gate disc lû2 is
`~- substandially planar being interrupted only by three projecting segmented lugs
112 whlch form means for capturing and retaining the spacer ring and are equally; circumferentially disposed with respect to the axis lû6. This arrangement
provides an uninterrupted datum surface for convenient accurate machining of
the seating surface 104 and other critical machine operations on the individual
discs. In assembly, the lugs 11 2 interf it with corresponding lugs on the
juxtaposed gate disc to form a segmented annular hub as shown in Figure 2
having a projecting exterior peripheral cylindrical surface. The sides of the
individual lugs are formed so as to provide a circumferential spacing with the
30 adjoining lugs such that limited relative movement is accommodated without a
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corresponding interaction. The segmented hub captures an annular spacer ring
120. The spacer ring 12û has a predetermined thickness which, in combination
with the thickness of the individual discs, establishes an overall width for gate 26
sufficient to ensure proper seating of the gate discs against the seats. The ring
120 is substantially smaller in diameter than the seating surfaces to increase the
deflection of the latter under pressure and stem loading.
Should excessive wear occur at the seating interfaces or should any of
the seating surfaces become scored or otherwise damaged during operation, the
gate must be removed and the seating surfaces refinished. Inasmuch as this wiil
result in the removal of metal, there would be excessive downward travel of the
gate past the point where sealing contact is established. This would normally
necessitate the replacement of the entire gate. In the present instance,
however, only the spacer ring 12û must be replaced. The only replacement
` requirement is that the thickness of the spacer ring compensate for material
reduction occasioned by the machining operation so as to re-establish the desired
operationai relationships between the seating surfaces.
In a modification of the means for capturing and retaining the spacer
ring shown in Figures 9 and 10, the planar rear surfaces comprise the circular
bases 110' of the counterbores 111' formed coaxial with the axis 106 in the
mutually facing opposed sides of the discs lûû,102. The spacer ring 12û has a
~- predetermined thickness which, in combination with the thickness of the
individual discs as measured from the circular bases 110', establishes an overall
width for the gate sufficient to ensure proper seating of the gate discs againstthe seats. The cylindrical side wall 112' of the counterbore forms an inwardly
facing peripheral surface which circumferentially bounds and thereby captures
the outer peripheral surface of the spacer ring 120. The diameter of the side
wall is slightly larger than the outer diameter of the spacer ring such that the~` latter is received with a slight radial clearance therewithin. The combined
depths of the counterbores is less than the thickness of the spacer ring such that
limited relative movement is accommodated without a corresponding interaction.
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The ring 120 is substantially smaller in diarneter than the seating surfaces to
- increase the deflection of the latter underpressure stem loading.
The lower end of the stem 70 is provided with a T-head construction
comprising an actuating collar 130, a cylindrical neck 132 and a T-wedge 134. As
;; shown in Figures 5, 6 and 7, the collar 130 has a substantially frustoconical
surface provided with a lower annular bearing surface 136. The T-wedge 134 has
outer faces 137 substantially identical in diameter to the outer diameter of the
collar 130 and inclined side surfaces 138 symmetricqlly disposed with respect to
the axis 42 to thereby form a downwardly tapering wedge shaped section.
As shown in Figures 6 and 8, the individual discs 10~ include an upper
bearing surface 140 engageable by the surface 136, a semi-circular axial groove
144 adapted to loosely surround the neck 132 and a wedge shaped transverse slot
146 extendingtransverse to the axes lû6 and 42. The slot is within the confines
- of the seating areas of the gate, resulting in a lowered profile. Pairs of raised
inclined pads 148 are formed at the sides of the slots 146 and operationally have
a slight clearance with respect to the inclined surfaces 138 of wedge 134. In
assembled relationship as shown partially in Figure 6, the stem head end is
received within the slot 146 and the other half of the gate qssembly is received
; thereover such that the wedge 134 is captured within the confines of the slots
20 146. The transverse slot design affirmatively retains the stem end and wil I
- permit entry thereof to the fluid line in the event of stem fracture.
Due to the wedge shape of the gate 26, the force transmitted by the
; stem assembly 24 to the seating surfaces is greatly magnified, resulting in a
Iarge sealing force between the mating seating surfaces. The independent
flexure of the seating surfaces accommodated by the split wedge design allows
the individual seating surfaces to flex and conform to the mating surfaces under
fluid pressure without a corresponding reaction by the opposite disc. It also
substantially equalizes the seating forces on the individual seating surfaces.
` ~ Accordingly, when it is desired to move the gate assembly to the opposed
30 position, the upper surface of the T-head 134 engages the undersurfaces of the
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slot !46 and, inasmuch as the discs are independent, the flexure thereby provided
relives the seating force sufficiently to disengage the seating surfaces.
The gate assembly has been translated upwardly through rotation of
the handwheel 22 and upward movement of the stem 24 until such time as the
conical back seat 13û of the stem 7û engages the back seat 150 on the bonnet 64
the tongue and grooves and the projecting peripheral surfaces preventing axial
separation of the discs and providing axial capturing of the spacer ring. Thereat
flow through the passages 36, 34 is substantially unrestricted.
It should be noted that only during the final closing and initial opening
10 movement of the gate is there any mechanical or pressure loaded sliding
movement of the seating surfaces across the seats, thereby, resulting in reduced
cycle wear to these surfaces.
Although only the above forms of this invention have been shown and
described, other forms will be readily apparent to those skilled in the art. I
Therefore, it is not intended to limit the scope of this invention by the
- embodiments selected for the purpose of this disclosure but only by the claims
which foliow.
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