GB2286032A

GB2286032A - Telescopic seat seal arrangements for plug valve,ball valve or gate valve

Info

Publication number: GB2286032A
Application number: GB9501759A
Authority: GB
Inventors: Tep Ungchusri; Roy C Bates; Robert L Witt
Original assignee: FMC Corp
Current assignee: FMC Corp
Priority date: 1994-02-01
Filing date: 1995-01-30
Publication date: 1995-08-02
Anticipated expiration: 2015-01-30
Also published as: GB9501759D0; GB2286032B; DE19502570A1; CA2140491A1; NL9500138A; FR2715706A1; FR2715706B1

Description

4 2286032 1 TELESCOPIC SEAT SEAL-ARRANGEMENTS FOR PLUG VALVE. BALL VALVE

OR GATE VALVE

BACKGROUND OF THE INVENTION

The present invention relates to valves f or controlling fluid flow and, more particularly, to a valve that includes a movable closure member such as rotatable plug or movable gate which cooperates with at least one seat f or controlling and sealing fluid flow.

Known valve designs include a ball, plug or gate that is rotatably or movably mounted in a valve body and that has a through hole through which f luid f lows when the hole is aligned with inlet and outlet ports. Such valves are closed when the plug or gate is rotated or moved so that a solid side of the plug or gate entirely blocks the flow path of the inlet port. The plug or gate presses against seats, one positioned on each of the upstream and downstream sides, which press against the valve body. Typically, the plug or gate has some float so that in a sealing situation the upstream fluid pressure causes the plug or gate to be strongly biased against the downstream seat which, in turn, is biased against the valve body forming a seal therewith.

Under the stop flow condition described above, there is ordinarily a large amount of pressure within the valve cavity which houses the plug or gate and seats because fluid under pressure enters between the plug or gate and seats. The downstream seat is strongly biased against the valve body by the f luid in the f low path which is transmitted by the plug or gate. In the event that f luid pressure is suddenly bled of f upstream, the upstream seal f ormed between the upstream seat and the valve body will have a tendency to trap pressure in the cavity such that resultant pressure f orce on the upstream side of the upstream seat will cause the upstream seat to be biased against the plug or gate. This trapped pressure condition requires a significantly higher operating 2 torque to rotate the plug or to move the gate and may result in overstress of components if a temperature change occurs while the valve is in this condition. Also, in some prior valve designs, upstream fluid pressure may bias the upstream valve seat against the plug or gate once again making it difficult to move.

It is an object of the invention to design a valve that solves at least some of the aforementioned problems and, in preferred embodiments, provides a reliable seal during any mode of operation, has easily removable parts and is easily serviceable, and comprises components that are easily manufactured.

SUMMARY OF THE INVENTION

The present invention provides a valve f or controlling flow comprising:valve body provided with a port; movable valve closure member received in the body and including a through bore that can be selectively aligned with the port to define a flow path; a seat positioned between the closure member and the valve body forming a seat-to-closure member seal surrounding the flow path; and sealing means arranged between the seat and valve body to surround the flow path, wherein the perimeters of the seat-to-closure member seal and of the sealing means are relatively conf igured so as to ensure that friction between the closure member and seat arising from pressure within the valve body is minimised.

More specifically, the invention may provide a valve for controlling flow comprising:- valve body having a cavity and at least two ports; valve closure member movably received within said cavity and including a through bore that can be selectively aligned with said valve ports to define a flow path; a seat having an opening therethrough aligned with one 3 of said ports, said seat being positioned between said closure member and said valve body forming a closed, continuous seat-to-closure member seal surrounding said flow path; said seat having f irst sealing means forming a closed, continuous seal between said seat and said valve body surrounding said flow path and having a first diameter which is less than the diameter of said seat-to- closure member seal; said seat having second sealing means forming a closed continuous seal between said seat and said valve body surrounding said flow path and having a second diameter which is greater than the diameter of said seat- to-closure member seal.

Yet further, the invention may provide a valve for controlling flow comprising:- valve body having a cavity and at least two ports; valve closure member movably received within said cavity and including a through bore that can be selectively aligned with said valve ports to define a flow path; a seat having an opening therethrough aligned with one of said ports, said seat being positioned between said closure member and said valve body forming a closed, continuous seat-to-closure member seal surrounding said flow path; said seat having sealing means forming a closed, continuous seal between said seat and said valve body surrounding said flow path and having a diameter which is greater than the diameter of said seat-to-closure member seal.

Still further, the invention may provide a valve for controlling flow comprising:- valve body having a cavity and at least two ports; valve closure member movably received within said cavity and including a through bore that can be selectively aligned with said valve ports to define a flow path; a seat having an opening therethrough aligned with one 4 of said ports, said seat being positioned between said closure member and said valve body forming a closed, continuous seat-to-closure member seal surrounding said flow path; said seat having f irst sealing means f orming a closed, continuous seal between said seat and said valve body surrounding said flow path and having a first diameter which is less than the diameter of said respective seat-to-closure member seal; said seat having at least one satellite sealing means forming a closed, continuous seal between said seat and said valve body and being positioned outside the perimeter of said first sealing means.

Further optional features of the invention are in the dependent claims.

Illustrative embodiments of the invention are described below with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG.1 is a partial, sectional view of a plug valve and seat assembly in a valve body cavity.

FIG.2 is a sectional view of a continuous seal.

seat having one FIGS.3 and 3A are respectively elevation and sectional views of a seat having one continuous seal and at least one satellite seal.

FIG. 4 is a partial, sectional view of a gate valve and seat assembly in a valve body cavity.

FIG.5 is a partial, cross-sectional view of a seal.

FIG.6 is a partial, cross-sectional view of another embodiment of a seal.

i 1 p FIG.7 is a partial, cross-sectional view of yet another embodiment of a seal.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Shown in FIG.1 is a partial, cross-sectional view of a valve body (10) having a generally cylindrical body cavity (12) housing therein a rotatable plug (14) having a through bore (16). The valve body (10) has an inlet port (18) and an outlet port (20). The plug (14) is attached to a stem (22) by conventional means for applying torque to rotate the plug (14) such that the through bore (16) is aligned with the inlet and outlet ports (18, 20) to allow flow through the valve body (10) forming a flow path. On the upstream side of the plug (14) an upstream seat (24) having a central opening (26) therethrough is positioned between the plug (14) and valve body (10). On the downstream side of the plug (14) a downstream seat (28) having a central opening (30) therethrough is positioned between the plug (14) and the valve body (10). Each seat (24, 28) is shaped generally like a cylindrical segment and has inner (32) and outer (34) sealing members. The sealing members are flexible, continuous seals that surround the flow path and form continuous seals between the seats (24, 28) and the valve body (10). The sealing members (32, 34) can be received in channels (36) on the seats (24, 28). Each seat has a notch (38) or similar means on top and bottom ends for orienting the seats during assembly.

The sealing members (32, 34) are positioned generally concentrically around the flow path such that each inner sealing member (32) has a first diameter and each outer sealing member (34) has a second diameter greater than the first diameter. The sealing contact point (40) between each seat (32, 34) and the plug (14) forms a continuous metal-tometal seal that has a diameter which is greater than the first diameter and less than the second diameter for a reason 6 which will now be discussed.

The plug (14) is arranged to float somewhat in the valve cavity such that during stop f low conditions, the upstream fluid pressure in the valve cavity causes the plug (14) to be biased against the downstream seat (28) which, in turn, is biased against the valve body (10) downstream. By sizing the diameter of the inner seals (32) to be less than the plugseat seal diameter, a downstream seal and upstream seal are more effectively maintained. For example this arrangement helps ensure that the required valve plug closure torque is not excessive as it ensures that the upstream seat is not forced against the plug by upstream fluid pressure. Such sizing prevents f low path pressure from producing resultant f orces acting between the seats (24, 28) and the plug (14). By sizing the outer seal (34) diameter to be greater than the plug-seat diameter, a large resultant f orce due to cavity pressure which exists in the valve cavity (12) outside the flow path is prevented from acting between the valve seats (24, 28) and the plug (14). The sealing members (32, 34) in the upstream seat (24) bias the upstream seat (24) against the plug (14). Normally, the plug (14) and downstream seat (28) are biased against the valve body (10) downstream.

When the valve plug (14) is in a closed position and fluid pressure is suddenly bled off upstream, the upstream seal formed between the upstream seat (24) and the valve body (10) will have a tendency to trap pressure in the cavity (12) such that pressure force on the upstream side of the upstream seat (24) will cause the upstream seat (24) to be biased against the plug (14). To prevent this trapped pressure condition which requires a significantly higher operating torque to rotate the plug (14) and which may result in overstress of components if a temperature change occurs while the valve is in this condition, it is critical that the outer seal member (34) has a greater diameter than the plug-seat seal as discussed above, to reduce the resultant force of trapped cavity pressure on the seat (24).

Another embodiment of the seats (100) as shown in FIG.2 r 7 requires only one seal member (102) for applications involving relatively small diameter flow paths where contact between an upstream seat and a plug would result in friction forces of relatively low magnitude such that required operating torque with the upstream f low path pressurised would not be excessive. In this embodiment, it is essential that the diameter of the seal (102) be greater than the plugseat seal diameter to prevent large forces from cavity pressure between the seat and valve body (10).

In another embodiment of the seats (200) as shown in FIG. 3, one seal member (202) having a diameter smaller than the diameter of the plug-seat seal acts as described above with reference to FIG.1. one or more satellite seals (203) in the form of continuous, closed, flexible seals outside the circumference of the inner seal (202) act to prevent cavity pressure from acting over the entire area of the seat surface in which they are housed, so as to reduce the resultant force. The number and size of such seals (203) can be selected to prevent the force arising from cavity pressure acting in the space between the seat and valve body from overcoming the remaining cavity pressure acting in the space between the seat and plug, so preventing the seat from being biased against the plug.

The embodiment of FIG.4 is an example of the present invention utilizing the seat seal arrangement of FIG.1 with a gate (300) of a gate valve. A cylindrical cavity (302) and seats (304) having cylindrical outer contours are utilized. The operation is essentially the same as that of the embodiment described with reference to FIG 1.

FIG.5 shows one form of the inner and outer seal members (32, 34) having a cross-sectional shape with a convex portion (400) adapted to contact the valve body (10) and antiextrusion elements (402). FIGS. 6 and 7 illustrate the seal member (32,34) with one anti-extrusion element (404) and no anti-extrusion element, respectively. other suitable crosssections may be used.

In the seat embodiments using inner and outer seal 8 members (32,34), it is advantageous to provide a small drilled hole adjacent to the outer seal groove and communicating between this groove and the area enclosed between the inner and outer seals, to prevent pressure buildup therein caused by grease or the like used during installation.

While a preferred embodiment has been described and shown, it is understood that variations and modifications can be made without departing from what is regarded as the scope of the invention as defined in the claims.

9

Claims

CLAIMS:

1. A valve for controlling flow comprising:- valve body provided with a port; movable valve closure member received in the body and including a through bore that can be selectively aligned with the port to define a flow path; a seat positioned between the closure member and the valve body forming a seat-to-closure member seal surrounding the flow path; and sealing means arranged between the seat and valve body to surround the flow path, wherein the perimeters of the seat-to-closure member seal and of the sealing means are relatively configured so as to ensure that friction between the closure member and seat arising from pressure within the valve body is minimised.

2. A valve as claimed in claim 1, wherein the sealing means def ines an outer boundary on an end f ace of the seat remote f rom the closure member and the seat-to-closure member seal defines an outer boundary on an end face of the seat adjacent to the closure member, and the area of the remote end face outside the sealing means outer boundary is less than the area of the end face adjacent the closure member outside the seat-toclosure member seal outer boundary.

3. A valve as claimed in claim 1 or claim 2 wherein the sealing means defines an inner boundary on an end face of the seat remote from the closure member and the seat-to-closure member seal def ines an inner boundary on an end f ace of the seat adjacent to the closure member, and the area of the remote end face inside the sealing means inner boundary is less than the area of the end f ace adjacent the closure member inside the seat-to-closure member seal inner boundary.

4. A valve as claimed in any preceding claim wherein the sealing means comprises an inner sealing member surrounded by an outer sealing member.

5. A valve as claimed in any of claims 1-3 wherein the sealing means comprises an inner sealing member and one or more satellite sealing members positioned outside the perimeter of the inner sealing member.

A valve for controlling flow comprising:a valve body having a cavity and at least two ports; a valve closure member novably received within said cavity and including a through bore that can be selectively aligned with said valve ports to define a flow path; a seat having an opening therethrough aligned with one of said ports, said seat being positioned between said closure member and said valve body forming a closed, continuous seat-to-closure member seal surrounding said flow path; said seat having first sealing means forming a closed, continuous seal between said seat and said valve body surrounding said flow path and having a first diameter which is less than the diameter of said seat-to-closure member seal; said seat having second sealing means forming a closed continuous seal between said seat and said valve body surrounding said flow path and having a second diameter which is greater than the diameter of said seat-to-closure member seal.

7. A valve for controlling flow comprising:a valve body having a cavity and at least two ports; a valve closure member movably received within said cavity and including a through bore that can be selectively aligned with said valve ports to define a flow path; a seat having an opening therethrough aligned with one of said ports, said seat being positioned between said closure member plug and said valve body forming a closed, continuous seat-to-closure member seal surrounding said flow v 11 path; said seat having sealing means forming a closed, continuous seal between said seat and said valve body surrounding said f low path and having a diameter which is greater than the diameter of said seat-to- closure member seal.

8. A valve for controlling flow comprising:a valve body having a cavity and at least two ports; a valve closure member movably received within said cavity and including a through bore that can be selectively aligned with said valve ports to define a flow path; a seat having an opening therethrough aligned with one of said ports, said seat being positioned between said closure member and said valve body forming a closed, continuous seat-to-closure member seal surrounding said flow path; said seat having first sealing means forming a closed, continuous seal between said seat and said valve body surrounding said flow path and having a first diameter which is less than the diameter of said respective seat-toclosure member seal; said seat having at least one satellite sealing means forming a closed, continuous seal between said seat and said valve body and being positioned outside the perimeter of said first sealing means.

9. A valve for controlling f low substantially as described with reference to the drawings.