GB2188710A - Reduction of wear of the seat gaskets of a ball valve - Google Patents

Abstract

In a top entry ball valve, for gas and oil wells, and chemical plants, made up of a body 10 containing a spherical plug 12 on which rest two seats, an arrangement to reduce wear on 2-directional moving-seat gaskets consists of a ring element or cylindrical collar (78) with smooth walls separating two gaskets (74, 76), the first (76) of which is housed in a recess (75) made in said valve body (10) and the second (74) of which is housed in a recess (72) made in a corresponding position in said seat (39), said recesses (72, 75) being sufficiently narrow to immobilize said gaskets (74, 76) axially in relation to said recesses (72, 75). <IMAGE>

Description

SPECIFICATION Improved arrangement for reduction of wear of the seat gaskets of a 2-directional moving-seat ball valve The present invention relates to fluid control valves of the so-called ball type made up of an external body housing a moving part or plug essentially spherical in shape.

When said valves are employed for controlling fluids highly contaminated by solid particles or corrosive substances it is necessary now and then to remove the plug from the valve body for maintenance or repair, especially for replacement of the worn gaskets.

The removal can be done in two directions, one parallel to the longitudinal axis of the valve body and the other perpendicular to said axis, necessitating two basic types of valves termed by those skilled in the art 'side entry' valves and 'top entry' valves.

In particular the present invention relates to a imoroved 'top entry' ball valve containing a device to reduce wear of the seat gaskets of said valve fitted with seats moving in two directions to permit tightness of the valve even in case of lost of tightness between the spherical plug and one of the seats.

Ball valves are widely used in many fluidcontrol applications, even dangerous ones such as with corrosive or inflammable fluids present in chemical plants, petroleum product extraction facilities such as natural gas wells, crude petroleum wells etc., and especially wells in particular environments such as offshore wells.

It is known that petrpleum products issuing from wells are contaminated by several foreign substances possibly including solid abrasive substances such as sand and scale from the storage rock containing them, corrosive liquid substances such as sea water or brackish water, and even gaseous substances such as hydrogen sulfide (H2S) and carbon dioxide (CO2) which singly or combined with other substances can have quite harmful effects on the piping and valves which convey and control them.

As a consequence of this fact it is sought to eliminate said contaminants at a place as close as possible to the extraction well to limit as far as possible the use of materials having high resistance to abrasion and corrosion and hence being particularly costly. For this reason in the immediate proximity of extraction wells there is installed equipment performing a first decontamination of extracted products and in particular separation of the above mentioned gaseous contaminants from the natural gas or petroleum.

With offshore wells served by platforms said decontamination equipment is usually installed thereon and since said platforms are densely occupied by service and control personnel all decontaminating installations and their components must meet severe safety requirements.

One of the safety requirements which the components of said installations and in particular the ball valves which are the subject of the present invention must meet is the ability to maintain enough tightness to provide the closing function in case of loss of tightness between one of the seats and the corresponding ball plug due to damage to the facing spherical surfaces and/or the gaskets associated with said spherical surfaces.Said safety requirement is met by the use of moving seats pushed by the pressure of the controiled fluid on the ball plug according to the socalled 'double piston effect' which in case of loss of tightness between the upstream seat and the ball plug of the valve, transfers said tightness to between the ball plug and the downstream seat, holding it there until by means of maintenance or repair action said tightness between the upstream seat and the ball plug is restored.

Since tightness between the moving seats and the valve body is provided by a gasket usually of the O-ring type housed in a recess formed by a stepped lowering of the outer surface of the seat and a corresponding internal shoulder of the valve body, it happens that said recess is formed by two adjacent sides belonging to the valve body and two adjacent sides belonging to the moving seat diagonally opposite to the two sides belonging to the valve body so that each movement of the valve seat relative to the body is translated into opposite movements of the outer surface of the seat and the inner surface of the valve body respectively which, being applied to the interior and the exterior of the gasket respectively, compell it to translate axially in one direction or the opposite direction, subjecting it to stresses leading possibly to breakage thereof and certainly wear.

The object of the present invention is therefore to provide reduction of wear of the seat gaskets of ball valves having seats moving in two directions to provide the so-called 'double piston effect'.

Briefly, the original arrangement which serves to reduce wear of said seat gaskets consists of creating in the external surface of the seat and the corresponding internal surface of the cylindrical cavity of the valve body recesses to house gaskets having a width virtually equal to the width of said recesses so that said recesses surround the gaskets on three sides, virtually preventing any axial translation and keeping separate said gaskets by means of a smooth rigid element.

According to a preferred embodiment of the present invention said recesses are virtually opposite to each other when the seats are in their normal position, i.e. resting against the ball plug of the valve so that the gaskets are facing each other and separated by said smooth rigid element.

According to another preferred embodiment of the invention said gaskets are toroidal gaskets of the O-ring type and said smooth rigid separating element consists of a cylindrical collar having an inside diameter such that it fits with mimimal gap on the outer cylindrical surface of the seat and an outside dia meter such as to fit with mimimal gap within the corresponding cylindrical cavity of the valve body.

According to another preferred embodiment of the invention said cylindrical collar in normal position rests against a step on the valve seat while in the position permitting removal of the ball plug with retracted seats or for transfer of tightness to the downstream seat it comes to rest against a shoulder terminating the cylindrical cavity of the valve body which houses it.

The advantages and characteristics of the present invention will be understood better from the following detailed description of an example thereof accompanied by the annexed drawings wherein: FIG. 1 shows a cross section of a top-entry ball valve containing two arrangements for reduction of wear of the seat gaskets in accordance with the present invention, one for, each seat, FIG. 2 shows an enlarged cross section of the detail of the seat gasket and the positioning thereof betwween the valve seat and body in accordance with the prior art, and FIG. 3 shows an enlarged cross-section of the detail of the arrangement which reduces wear of the seat gaskets in accordance with the present invention and how said gaskets are positioned between the valve body and seat.

With reference to FIGS. 1 and 3 a top-entry ball valve is made up of a hollow body 10 in which there turns a ball plug 12 having a through hole 14 and being moved by a shaft 16 passing through a flange 18 fixed to the body 10 by appropriate means such as bolts 20 and being supported at the end opposite that of said shaft 16 by means of a pin 22 in a seat 24 of a closed bottom 26 of said valve body 10. Said valve body 10 is also fitted with means for fixing it to pipes such as the flanges 30 and 32 having through holes 34, 35, 36 and 37 to house members such as nuts and/or bolts to provide said fixing.

Tightness between the valve body 10 and the ball plug 12 is provided by two seats 38 and 39 which rest against the plug 12 by means of spherical surfaces complementary to the spherical surfaces of the ball 12.

Let reference be made now to FIG. 2 which shows an enlarged partial cross section of the detail of the seat gasket according to the prior art. In said figure a seat 39' is formed by an internal tubular seat element 40' having an outward turned flange 42 facing the valve plug 12 with a spherical surface 47 complementary to that of said plug which is surrounded by an outer seat ring 44 which includes an inward turned step 45 terminating in a spherical surface portion 46 also complementary to the spherical surface of the plug 12. Between the internal tubular seat element 40' and the external seat ring 44 there is formed a groove 48 housing a soft gasket 50 the function of which is to provide complete tightness between the plug 12 and the seat 39'.Said external seat ring 44 is fixed by means not specifically illustrated to the flange 42 which is turned outward and integral with the internal tubular seat element 40'. Said outer seat ring 44 is thrust against the ball plug 12 by a set of springs 54 spaced regularly along the circumference and contained in special seats 56 of a spring holding ring 58 having a flange 60 protruding externally which engages with an annular spacer resting on the valve body 10. Said annular spacer 62 is made up preferably of segments connected together by releasable restraints so it can be freed from its engagement between the flange 60 of the spring holding ring 58 and the valve body 10.

The annular spacer 62 rests against a first stepped shoulder 64 of the body 10 in such a manner as to permit the spring holding ring 58 to apply the thrust of the spring 54 to the outer seat ring 44 and then by means of the elastic pins 58 or equivalent elements to the first tubular seat element 40' in such a manner that the walls of the groove 48 can thrust the soft gasket 50 against the ball plug 12 to provide tightness between the seat and the plug. Behind the spring holding ring 58 there is a second stepped shoulder 66 of the valve body 10 having the function of housing said ring when the segments of the annular spacer 62 are removed.

The external cylindrical surface 67 of the tubular seat element 40' has a first stepped lowering 69 facing a corresponding stepped shoulder 80 in the valve body 10 with which it forms a recess designed to house an O-ring 71 the function of which is to provide tightness between the seat 39' and the valve body 10. The lowered external surface 81 of the tubular seat element 40' ends with a subsequent stepped lowering 84 facing a stepped sholder 86 of the valve body 10. From the stepped lowering 84 there emerges a last external cylindrical surface 88 with which the tubular seat element 40' ends. The valve body 10 has a last stepped shoulder 90 which serves to stop rearward movement of the seat 39' if necessary.

From the foregoing description for FIG. 2 it is seen that the gasket 71 housed in said recess formed by the stepped lowering 69, the lowered external surface 81, the stepped shoulder 80 and the cylindrical internal surface,which goes from said shoulder 80 to the shoulder 66, each time the seat 39' moves in relation to the valve body 10 is subjected to stress in opposite directions, rolling until it stops against the lowering 69 and the shoulder 80. This movement of the gasket 71 easily causes serious wear thereof which causes it to lose its tightness characteristics or even to break in one or more places.

To remedy this drawback there has been adopted the seat 39, shown generally in FIG.

1 and in detail in FIG. 3, which greatly reduces wear on the gaskets and provides tightness between the seat 39 and the valve body 10.

For this purpose the seat 39, which is similar to the seat 39' of the previous art, is formed of a tubular seat element 40 similar to the tubular seat element 40' of the previous art except that the cylindrical external surface 67 is reduced in length as indicated by the surface 68 of FIG. 3, having a first stepped lowering 70 followed by a lowered surface 82, 82a broken at a certain point by a recess 72 housing an O-ring 74. A similar recess 75, also housing an O-ring 76,is machined in front of the recess 72 inside the valve body 10 and an element in the shape of a flattened ring or cylindrical collar 78 remains fitted over the lowered surface 82, 82a, being placed between the two O-rings 74 and 76, thus assuring complete overall tightness between the valve body 10 and the seat 40.This time the two gaskets 74 and 76 are imprisoned in the recesses 72 and 75 respectively, not being able to move when the seat 40 moves in relation to the valve body 10 because they are retained by said recesses which embrace them closely. In this case the only moving element is the collar 78 which however exerts on the two O-rings 74 and 76 such slight stresses as to cause virtually no wear. Consequently any movements of the seat 39 in relation to the valve body 10 due to extraction of the ball plug 10 during maintenance or repairs or transfer of tightness from the upstream seat to the downstream seat due to the double piston effect do not apply stress to the 0rings 74 and 76, which maintain their tightness characteristics.

The present description concerns a specific example of an embodiment of the invention and it is expected that full and partial equivalents may occur to those skilled in the art without exceeding the covered scope of the invention. In particular the recesses which house the O-rings can be offset instead of facing and the cylinder sleeve 78 can be either whole or made up of several segments.

Claims (5)

1. Improved arrangement to reduce wear of seat gaskets consisting of machining in the outer seat surface and the corresponding inner cylindrical cavity of the valve body recesses for housing gaskets having a width virtually equal to the width of said recesses in such a manner that said recesses surround the gaskets on three sides to virtually prevent any axial translation thereof and of keeping said gaskets separated by means of a smooth rigid element.

2. Improved arrangement in accordance with claim 1 characterized in that said recesses are virtually opposed when the seats are in their normal position, i.e. resting against the ball plug of the valve in such a manner that the gaskets are facing each other and separated by said smooth rigid element.

3. Improved arrangement in accordance with claim 2 characterized in that said gaskets are toroidal gaskets of the O-ring type and said smooth rigid separating element consists of a cylindrical collar having an inside diameter such as to fit with minimal gap over the cylindrical external surface of the seat and an outside diameter such that it fits with minimal gap in the corresponding cylindrical cavity of the valve body.

4. Improved arrangement in accordance with claim 3 characterized in that said cylindrical collar in its normal arrangement rests against a step in the valve seat while in the position permitting extraction of the spherical plug with the seats retracted or for transfer of tightness to the downstream seat it rests against a shoulder terminating the cylindrical cavity of the valve body which houses it.

5. A wear reducing arrangement substantially as hereinbefore described with reference to the accompanying drawings.