CA1066259A - Double disc gate valve with replaceable spacer ring - Google Patents

Abstract

DOUBLE DISC GATE VALVE WITH
REPLACEABLE SPACER RING
ABSTRACT OF THE DISCLOSURE

A gate valve includes a pair of identically shapped tapered discs defining a tapered self-locking axially translatable gate wherein each disc has an annular hardened seating surface which engages the mating surfaces on the valve body adjacent the flow ports. Tongues on the sides of the discs ride in vertical grooves on the valve body as the gate travels between a raised open and a lowered closed position. The discs are separated by an annular spacer ring of substantially smaller diameter than the seating surfaces surrounding an inter-locking segmented hub formed on the inner juxtaposed surfaces of the discs, the arrangement being such that the spacer ring can be sized to establish an overall gate width which will ensure that the seating surfaces are making proper sealing engagement with the valve seats with the diametral differences increasing the disc flexibility. The spacer ring can be replaced by an appropriately sized spacer ring to compensate for thickness reduction in resurfacing the seating surfaces.

Description

~066;~9 Background of Invention .
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 -:~ B

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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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~ 1066Z59 ' 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 . , ~ 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 , ...
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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~ ;6Z59 -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, _ 4 _ : ' .'' ~ .
.''. . ' , ' ' , ' : ~0~6~Si9 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 :' : . , , ', .
,',' ., ' ', . , ~3662~9 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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Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. 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 respec-tive said valve seat in the closed position when opposed surfaces respectively of the other side of each of said gate pieces are spaced a predetermined distance apart; a single rigid spacer member remote from said stem assembly having end surfaces respectively engaging said opposed surfaces and having a thickness therebetween equal to said predetermined distance; projecting capturing means on each of 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 the capturing means.

2. The gate valve recited in claim 1 wherein said spacer member has a circular peripheral wall which is bounded by said projecting capturing means.

3. The gate valve recited in claim 2 wherein said spacer member is circular and said circular peripheral wall is the outer circumferential wall of the member.

4. 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 respec-tive said valve seat in the closed position when opposed surfaces respectively of the other side of each of said gate pieces are spaced a predetermined distance apart; a single rigid spacer member remote from said stem assembly having end surfaces respectively engaging said opposed surfaces and having a thickness therebetween equal to said predetermined distance; a projecting capturing means on each of 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; said spacer member being circular and having a circular peripheral wall which is the outer circumferential wall of said member and is bounded by said projecting capturing means; said spacer member having a central circular opening formed therein;
and guide means preventing separation of the pieces during gate movement and disengagement of the capturing means.

5. The gate valve recited in claim 3 wherein said pro-jecting capturing means are the circular side walls of a counterbore formed in said other sides of the gate pieces and said opposed surfaces are the circular bases of said counterbores and the side walls of the counterbores have a combined depth of Less than the thickness of the spacer member.

6. A gate valve comprising: a valve body having a pair of flow passages coaxially disposed along a flow axis, said flow passages having inner ends communicating with a central valving control chamber and outer ends connectable at a fluid flow line, said control chamber having an operational axis normal to the flow axis; circular valve seats susceptible to wear and damage surrounding the inner ends of the flow passages adjacent the control chamber, said valve seats being disposed in planes perpendicular to a plane including said flow axis and said operational axis and downwardly converging toward the operational axis and diametrically opposed with respect thereto; a two piece wedge shaped gate, each piece of said gate being iden-tically shaped and having a circular front seating surface inclined parallel to the valve seat so as to be sealingly engageable therewith in a closed position with a planar rear surface thereon transverse to the flow axis, the pieces of the gate having said planar rear surfaces in parallel spaced relation in assembly; a stem supported on the valve body extending along the operational axis into the control chamber and operatively connected to the gate for moving the gate along the operational axis, said stem moving the gate between an upper open position and a lower closed position; a single rigid annular spacer member being loosely retained between the pieces at a location remote from said stem and having opposed parallel planar bearing surfaces spaced a predetermined distance apart, one of said bearing surfaces directly engaging the rear surface of one of the gate pieces, the other of said bearing surface directly engaging the rear surface of the other of said gate pieces thereby spacing the rear surfaces said predetermined distance apart to space the pieces at an overall width which will axially position the gate along the operational axis in the closed position to assure full sealing contact between the seating surfaces and the valve seats, said spacer member being of substan-tially smaller diameter than the seating surfaces to increase the flexibility of the discs thereabout, the material removed from the seats and the seating surfaces during repair thereof for said damage and wear being compensated for by replacement of the original spacer member with a replacement spacer member having a larger predetermined distance sufficient to establish said overall width and related axial position for the gate;
arcuate surfaces adjacent the rear surfaces of the pieces projecting therefrom a combined length which is less than said predetermined width of said spacer member, said arcuate surfaces at least partially bounding the sides of the spacer member to radially restrain the spacer member in assembly with sufficient clearance therebetween to permit limited relative movement between the pieces without interaction with the spacer member; and guide means preventing axial separation of the pieces during gate movement to insure that the arcuate surfaces radially capture the spacer member.

7. The gate valve recited in claim 6 wherein each of said planar rear surfaces includes a base of a counterbore formed in the piece, and said arcuate surfaces includes the cylindrical side walls of the counterbores which circumferentially bound an outer periphery of said sides of the spacer member.

8. The gate valve recited in claim 7 wherein said spacer member is an annular ring with a central circular opening.