Valve with pressure adaptable seat

A seat assembly extending about an inlet passage of a valve and engaging a valve member is disclosed. The seat assembly includes an annular seat carrier having an annular groove formed therein, and a seat positioned in and extending from the annular groove of the seat carrier. The seat has an inner side, an outer side, and a plurality of spaced apart, concentric seal rings extending from the inner side of the seat to the outer side thereof. The seal ring nearest the inner side of the seat is engageable with the valve member to provide an innermost seal when the seat assembly is acted upon by a pressure within a pressure range and the seal ring nearest the inner side of the seat is deflectable in a radially outward direction and out of sealing engagement with the valve member when the pressure exceeds the pressure range to cause the adjacent seal ring to provide the innermost seal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to seats for ball valves, and more particularly, but not by way of limitation, to an improved seat assembly for a trunnion mounted ball valve wherein the seat assembly is capable of adapting to varying working pressures.

2. Brief Description of Related Art

In the typical construction of a trunnion mounted ball valve, the ball is machined to provide “trunnions” that are mounted in bearings. The bearing-trunnion combination is intended to support the ball in a stationary position relative to the flow path, but allow rotation of the ball. The ball engages a pair of seat assemblies to form a seal around the ball.

The seat assemblies typically include an annular seat carrier and a ring-shaped seat positioned in a groove formed in the seat carrier. In a trunnion ball valve, the seat assemblies are free to move and respond to the internal line pressure because of differential surface area. That is, the surface area of the seat assembly being acted on by line pressure is greater on the end of the seat assembly positioned away from the ball valve than it is on the end engaging the ball. Consequently, the line pressure forces the seat assembly toward and against the ball valve. Both the upstream and downstream seat assemblies respond to line pressure in the same way, thus leading to the feature of a trunnion valve known as “double block and bleed.”

Another feature of a trunnion ball valve is reduced operating torque at higher working pressures. Operating torque is primarily a function of the friction created by the seat contacting the ball at the sealing interface. The design considerations that affect the amount of friction generally are: (1) the axial force of the seat against the ball; (2) the contact area of the seat on the ball, combined with the hardness or compressive strength of the seat; and (3) the surface finish on the ball.

Traditional design efforts have been directed at minimizing the operating torque for opening and closing the valve at maximum working pressure. To achieve this desired result, it has generally been necessary to sacrifice low pressure sealability. As a result, trunnion mounted valves have notoriously poor performance when sealing at working pressures much less than maximum rated pressure. To produce the lowest torque at the most critical point (maximum rated working pressure), one would choose a seat with a thin seal surface to reduce contact area, a hard sealing material to reduce friction, and a small differential area to reduce the axial force. The low pressure sealability of such a design would be poor. To improve sealing at reduced pressures, one would need to change to a softer sealing material and then add springs to create a preload of axial force. In each case, the seal is not optimized except within a narrow range of pressures.

To this end, a need exists for an improved seat assembly that is capable of adapting to varying working pressures. It is to such an improved seat assembly that the present invention is directed.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly toFIG. 1, shown therein is a valve10constructed in accordance with the present invention. The valve10includes a body assembly12, a valve member14disposed in the body assembly12for rotation between an open position (FIG. 1) and a closed position (not shown), and a stem16for rotating the valve14between the open position and closed position. The valve10further includes a pair of seat assemblies18and20for forming a seal between the body assembly12and the valve member14.

The body assembly12, as shown inFIG. 1, includes a body22, a first end adaptor24connected to one end of the body22, and a second end adapter26connected to the opposing end of the body22. It will be appreciated by those of ordinary skill in the art that the body assembly12may be fabricated in two portions where one of the end adaptors24or26and the body22are integrally fabricated as one piece.

The body assembly12has a centrally disposed valve chamber28, and an inlet passage30and an outlet passage32in communication with the valve chamber28to form a flow passageway through the body assembly12about a longitudinal flow axis34. A first seat pocket36is formed about the inlet passage30, and a second seat pocket38is formed about the outlet passage32. The first seat pocket36is adapted to receive the seat assembly18, and the second seat pocket38is adapted to receive the seat assembly20.

The stem16extends through a stem bore40formed through the wall of the body22. The stem16has a lower portion44with an enlarged diameter. The lower portion44is adapted to be received in a corresponding enlarged diameter portion46of the stem bore40. The stem16is mounted within the stem bore40in a manner well known in the art for rotation about a trunnion axis48. A key50is formed on the lower end of the stem16. The key50extends diametrically across the end of the stem16and is adapted to matingly engage with the valve member14.

The valve member14is mounted within the valve chamber28for rotation about the trunnion axis48between the opened position and the closed position wherein the valve member14is rotated substantially 90 degrees from the opened position to the closed position. The valve member14has a central bore52which aligns with the inlet passage30and the outlet passage32in the open position of the valve member14to permit the passage of fluid through the valve10when the valve member14is in the open position thereof. In the closed position of the valve member14, the seat assemblies18and20engage the exterior surface of the valve member14and internal surfaces of the body assembly12to form fluid tight seals which disrupt fluid communication between the inlet passage30and the outlet passage32.

The valve member14has the general form of a spherical ball with the central bore52formed therethrough extending circumaxially about a diameter thereof. Portions of the valve member14are cut away to form a circular first trunnion54and a circular second trunnion56which is diametrically opposed to the first trunnion54and coaxial therewith. A central slot58is formed in the distal end of the first trunnion54and is oriented along a line normal to the plane defined by the axis of the central bore52and the common axis of the first trunnion54and the second trunnion56. The slot58is sized to receive the key50of the stem16so that the valve member14can be rotated about the trunnion axis48via rotation of the stem16.

A first trunnion bushing or bearing60is mounted on the first trunnion54, and a second trunnion bushing or bearing62is similarly mounted on the second trunnion56. A first bearing retainer64is positioned about the first bearing60and extends longitudinally across the valve chamber28to engage opposing surfaces of the body assembly12so as to longitudinally support the first trunnion54of the valve member14within the valve chamber28. Similarly, a second bearing retainer66is positioned about the second trunnion bearing62and extends across the valve chamber28to engage opposing surfaces of the body assembly12so as to longitudinally support the second trunnion56within the valve chamber28.

In the preferred embodiments of the present invention, the seat assembly20is identical to the seat assembly18and is positioned in the second seat pocket38in the same manner that the seat assembly18is positioned in the first seat pocket36. Accordingly, it is not believed necessary to describe the construction and positioning of both seat assemblies18and20. Rather, it will suffice to describe the construction and positioning of the seat assembly18for the purposes of the present disclosure.

Referring now toFIG. 2A, an enlarged view of the seat assembly18is shown. The seat assembly18includes a seat carrier70and a seat72. The seat carrier70is annularly shaped and formed of a metal, such as steel or stainless steel. The seat carrier70has an inner side74, an outer side76, an inward facing end78, and an outward facing end80. The outer side76is provided with an outer groove82dimensioned to receive a seal member84. A portion of the outer side76of the seat carrier70also defines a shoulder86which permits a spring88to be positioned between the shoulder86and an opposing surface90of the body assembly12to bias the seat assembly18toward the valve member14. The inner facing end78of the seat carrier70is provided with a frusto-conical surface92which has an annular grove94formed therein. It should be appreciated that references to “inner” and “outer” are made with respect to the longitudianal flow axis34(FIG. 1), and references to “inward facing” and “outward facing” are made with respect to the valve member14.

The seat72is positioned in the annular groove94of the seat carrier70and extends therefrom so as to allow for sealing engagement with the valve member14in a manner to be discussed below. The seat72has an inner side96, an outer side98, and a plurality of spaced apart, concentric seal rings100a–100cextending from the inner side96of the seat72to the outer side98thereof.

The seat assembly18moves along the longitudinal flow axis34(FIG. 1) in a piston like fashion in response to internal line pressure within the valve10. The movement of the seat assembly18toward the valve member14is a result of the difference in surface areas between the outward facing end80of the seat carrier70and a combination of the inward facing end78of the seat carrier70and the seat72which are exposed to the line pressure. That is, as shown inFIG. 2A, the surface area of the outer facing end80of the seat carrier70(represented by line102) that is exposed to the internal line pressure is greater than the combination of the surface area of the inward facing end78of the seat carrier70and the seat72(represented by line104) that is exposed to the internal line pressure. The difference in the surface area, commonly referred to as “differential area” and represented by line106, times the internal line pressure creates the axial force that pushes the seat assembly18against the valve member14to form the seal between the seat assembly18and the valve member14.

As mentioned above, previous design efforts have been directed at minimizing the operating torque for opening and closing a trunnion valve being operated at maximum working pressure. To achieve this desired result, it has generally been necessary to sacrifice low pressure sealability. To produce the lowest torque at the most critical point (maximum rated working pressure), one would generally choose a seat formed with a thin seal surface to reduce contact area, a hard sealing material to reduce friction, and position the seat to provide a small differential area to reduce axial force. The low pressure sealability of such a design is poor. To improve sealing at reduced pressures, one would need to change to a softer sealing material and then add springs to create a preload of axial force to compensate for the reduction in axial force due to the lower line pressure while the differential area remains substantially unchanged. In contrast, the seal rings100a–100cof the seat72of the present invention are adapted to provide low pressure sealability by providing a softer low pressure seal coupled with a differential area that results in increased axial force being applied to the low pressure seal, as well as high pressure sealability by providing a firmer high pressure seal coupled with a reduced differential area that mitigates the effects of an increase in axial force created by the higher line pressure.

Referring toFIGS. 2A–2C, the seal ring100aprovides a low pressure seal, the seal ring100ban intermediate pressure seal, and the seal ring100ca high pressure seal. To achieve the varying degrees of sealability, the seal rings100a–100care spaced from one another to permit radial deflection relative to one another. More particularly, the seal ring100a, which is nearest the inner side96of the seat72, is configured to provide an innermost seal when the seat assembly18is acted upon by a pressure within a first pressure range and to be deflected in a radially outward direction and out of sealing engagement with the valve member14when the pressure exceeds the first pressure range and cause the adjacent seal ring100bto provide the innermost seal. Similarly, the seal ring100bis configured to provide the innermost seal when the seat assembly18is acted upon by a pressure within a second pressure range, which is greater than the first pressure range, and to be deflected in a radially outward direction and out of sealing engagement with the valve member when the pressure exceeds the second pressure range and cause the adjacent seal ring100cto provide the innermost seal.

By way of example, for a valve having a pressure rating of 1,500 psi, the first pressure range may extend from 0 psi to about 500 psi, the second pressure range from about 500 psi to about 1,000 psi, and the third pressure range being greater than about 1,000 psi. It will be appreciated, however, that the pressure ranges may be altered by changing the flexibility of the seal rings100a–100crelative to one another.

The seat72is fabricated of an elastomeric material, such as polyethylene, polypropylene, nylon or acetal. To achieve the desired differences in deflection strength between the seal rings100a–100c, the seal ring100cis supported by the seat carrier70so that outward deflection of the seal ring100cis prevented. Also, the seal ring100bhas a generally thicker configuration than the seal ring100a. As such, the seal ring100cis stiffer or more resistant to being deflected than the seal ring100b, and the seal ring100bis stiffer or more resistant to being deflected than the seal ring100a. Each seal ring100a–100cis also provided with a generally tapered configuration with a seal surface108a–108c, respectively, at the distal ends thereof. The seat72is configured so that the seal surfaces108a–108cof the seal rings100a–100care arranged to substantially conform to the contour of the valve member14. The tapered configuration of the seal rings100aand100b, in particular, provide the seal rings100aand100bwith a stable base to permit the seal rings100aand100bto provide a compression seal against the valve member14, but then because of the spacing between the seal rings100a–100c, the seal rings100aand100bare able to be deflected in a radially outward direction so that the seal surfaces1008aand108bmove out of sealing engagement from the valve member14when the line pressure exceeds that which the seal rings100aand100bare capable of supporting. The seal rings100a–100care separated from one another by generally V-shaped notches110aand110b. Again, such a configuration provides each of the seal rings100a–100cwith a stable base portion, yet permits the seal surface108a–108cto be deflected out of seating engagement with the valve member14. However, the seal ring100cis supported by the seat carrier70so that outward deflection of the seal ring100cis prevented.

FIGS. 2A–2Cillustrate the seat assembly18being acted upon by a low line pressure, an intermediate line pressure, and a high line pressure, respectively. With the low line pressure shown inFIG. 2A, the seal ring100ais sealingly engaged with the valve member14. With the seal ring100ain sealing engagement with the valve member14, the differential area106created by the difference in surface area102and surface area104has the affect of creating an axial force in the direction of the valve member14to provide an effective low pressure seal. As shown inFIGS. 2A–2C, employment of the spring88will supplement the axial force created due to the differential area106, thereby ensuring an effective low pressure seal. However, if the differential area106is great enough when the seal ring100ais in engagement with the valve member14, it may be determined that the spring88is not required to create the desired seal, and thus may be omitted.

FIG. 2Billustrates the seal ring100ahaving been deflected in a radially outwardly direction against the seal ring100band out of sealing engagement with the valve member14due to the lateral force acting on the seal ring100aby a line pressure that exceeds that which the seal member100ais able to withstand. As such, the seal ring100bnow forms the innermost seal and the surface area104is increased while the surface area102remains constant, thereby causing the differential area106to also decrease. Therefore, while the internal line pressure has increased and thus the axial force on the seat assembly18has in turn increased, the increase in axial force will be mitigated due to the decrease in differential area106. This results in the creation of an effective seal when the seat assembly18is being acted upon by an intermediate pressure while still permitting the valve member14to be easily rotated between the open and closed positions.

FIG. 2Cillustrates the seal rings100aand100bhaving been deflected in a radially outward direction against the seal ring100cand out of sealing engagement with the valve member14due to the lateral force acting on the seal rings100aand100bby a line pressure that exceeds that which the seal members100aand100bare able to withstand. As such, the seal ring100cnow provides the innermost seal. Consequently, the surface area106which is exposed to the internal line pressure increases while the surface area102has remains constant. The result is the differential area106further decreases thus mitigating the increase in axial force created by the higher line pressure.

FIG. 3illustrates another embodiment of a seat assembly18athat includes a seat112positioned in the seat carrier70. The seat112has two seal rings114aand114b, as opposed to the three seal rings100a–100cof the seat70shown inFIGS. 2A–2C. The seal rings114aand114bare substantially similar in construction and function to the seal rings100band100c, respectively, of the seat assembly18.

FIG. 4shows yet another embodiment of a seat assembly18bthat includes a seat116positioned in a seat carrier118. The seat116is provided with a single seal ring120. The seal ring120is formed to be inwardly biased so that the distal portion of the seal ring120is spaced from the seat carrier118. At lower pressures, the seal ring120provides an effective seal because the differential area is increased, and thus the axial force is increased, due to the inward bias of the seal ring120. However, as the line pressure increases, the seal ring120will be deflected outwardly into engagement with the seat carrier118which prevents additional deflection of the seal ring120and permits the seal ring120to provide an effective high pressure seal while also causing the differential area to be reduced to mitigate the effects of the increased axial force applied to the seat assembly18b.

The seat carrier118is similar in construction to the seat carrier70described above with the exception that the seat carrier118is provided with a lip122which serves to secure the seat116in the seat carrier118.

FIG. 5illustrates another embodiment of a seat assembly18cthat includes a seat124positioned in the seat carrier70. The seat124includes three seal rings126a–126c. The seal ring126ais intended to provide a low pressure seal, the seal ring126ban intermediate pressure seal, and the seal ring126ca high pressure seal. The distal portions of the seal rings126a–126care spaced from one another to permit radial deflection relative to one another. However, to achieve the desired differences in deflection strength between the seal rings126a–126c, the seal ring126cis fabricated of a harder material than the seal ring126b, which in turn is fabricated of a harder material than the seal ring126a. As such, the seal ring126cis stiffer or more resistant to being deflected than the seal ring126b, and the seal ring126bis stiffer or more resistant to being deflected than the seal ring126a. Like the seal rings100a–100cdescribed above, each seal ring126a–126cis also provided with a generally tapered configuration with a seal surface at the distal ends thereof. The seat124is configured so that the seal surfaces are arranged to substantially conform to the contour of the valve member14.

By way of example, the seal ring126amay be fabricated of a material commonly used for low pressure seal rings, such as fluorocarbon. The seal ring126bmay be fabricated of a harder material, such as nylon. Finally, the seal ring126cmay be fabricated of an even harder material commonly used for high pressure seal rings, such as acetal.

FIG. 6shows another embodiment of a seat assembly18dthat includes a seat130positioned in a seat carrier132. The seat130has two seal rings134aand134b, each formed of a different type of material. The seal ring134ais intended to provide a low pressure seal and the seal ring134ba high pressure seal. A distal portion135of the seal ring134ais tapered to create a space between the seal ring134aand the seal ring134bto permit radial deflection of the seal ring134arelative to the seal ring134b. A proximal portion of the seal ring134ais provided with an annular groove136.

The seal ring134bis provided with a ridge138sized and shaped to mate with the groove136of the seal ring134aand interlock the seal ring134awith the seal ring134b. The seal ring134bhas an inner surface139positioned to support the distal portion135of the seal ring134awhen the seal ring134ais in a outwardly deflected condition. The seal ring134bis further provided with a notch140that creates a space between the inner surface138and a seal surface142. The space allows for a change in differential area upon the seal ring134abeing deflected out of sealing engagement with the valve member14. It will be appreciated that the shape of the seal rings134aand134bmay be changed to effect the extent to which the differential area will change between when the seal ring134ais in sealing engagement with the valve member14and when the seal ring134ais deflected out of sealing engagement with the valve member.

Like the seat assembly18c, the seal rings134aand134bof the seat assembly18dmay be fabricated of a variety of different materials. By way of example, the seal ring134amay be fabricated of a material commonly used for low pressure seal rings, such as nylon, while the seal ring134bmay be fabricated of a harder material, such as acetal.

FIG. 7illustrates another embodiment of a seat assembly18ethat includes a seat carrier150and a seat152. The seat assembly18eis similar to the seat assembly18ofFIGS. 2A–2Cwith the exception that the seat carrier150is provided with an inner lip154and an outer lip156to which the seat152conforms to help secure the seat152in the seat carrier150. It should be appreciated that only one of the inner and outer lips154and156may be necessary to hold the seat152in the seat carrier150.

FIG. 8illustrates the seat carrier70described in detail above providing a secondary metal seat along the frusto-conical surface92if the seat72should be destroyed by fire or be damaged otherwise.

FIG. 9illustrates a modified seat carrier70apositioned in a modified body assembly12a. The body assembly12ahas a sealant injection port159, and the seat carrier70ahas been provided with a sealant injection port160aligned with the sealant injection port159of the body assembly12afor injecting a sealant between the seat carrier70aand the valve member14. The sealant injection port160intersects the annular groove94of seat carrier70aso that sealant is injected on the inner side of the seat72.

Changes may be made in the combinations, operations and arrangements of the various parts and elements described herein without departing from the spirit and scope of the invention as defined in the following claims.