GB2180626A - Ball valve - Google Patents

Abstract

A ball valve for controlling the flow of fluid in a pipeline comprises valve stem sealing means 28 including a seal surrounding the valve stem which is arranged to fail before stem locating means can be removed. The valve stem 14 is operatively coupled to the ball 8 by means of a drive key 22 cooperating with a correspondingly shaped aperture, the key and aperture being of polygonal form having at least five sides. The ball 8 is mounted on a pair of trunnions 10,12 at least one of which is arranged for adjustment so that the positioning of the centre of the ball may be adjusted. Sealing means 9 arranged to seal between the pipeline bore and the surface of the ball are provided with a passage (92, Figure 6) for dispensing grease to the surface of the ball, the passage having an opening to the pipeline bore, the said opening being provided with closure means (96) arranged so that fluid can pass through the opening from the pipeline bore to the passage, but passage of any material through the opening from the passage to the pipeline bore is prevented. <IMAGE>

Description

SPECIFICATION Ball valve This invention relates to a trunnion type ball valve and particularly to the trunnion and stem assemblies of such a valve. Such valves are particularly, but not exclusivelysuitableforoil and natural gastransmission pipelines from drilling platform to shore, and for distribution. Generally speaking they have an internal diameter offrom fifteen to thirty centimetres.

A common problem experienced in trunnion type ball valves is the dangerofthevalve stem being "blown out", bythe high pressure within the pipeline in the stem cap is removed ortampered with while the pipeline is pressurised, for example for maintenance purposes. It is sometimes necessary to remove this cap to gain access to the stem sealing arrangement, so that elements of the stem seal can be renewed,which seal may be formed by pressurised grease or plastics material. Hence safely to conduct such a maintenance operation, it is necessary to depressurise, i.e. shut-down, the pipeline.

Another problem is the provision of both trunnion support and drive means to the ball. The support provided by the trunnions has to besufficienttowith- stand the forces which the pressure of the fluid in the pipeline exerts on the ball when the valve is in the closed position. Therefore the area ofthetrunnion in contact with the ball has to be sufficient to withstand the bending forces exerted thereon by the pressure forces on the ball. The drive means has to enable a sufficientturning moment to be applied to the ball in order to turn it. Both these support and driving features have commonly been incorporated on the trunnions, utilising a purely supportive lower trunnion and a partially supportive partially driving uppertrunnion.To provide a sufficient lever arm to transmitthe requisite turning momenta rectangular driving key mating with a slot has been used. Due to wear and the practicalities of manufacturing tolerances,the rectangular drive keys are unableto bear any of the supportive load of the trunnion. Therefore the supportive portion of the trunnion has to be capable of withstanding the whole of the forces exerted thereon bythe ball, and hence the trunnion incor porates a non-load bearing drive section and a sup port section which bears the whole load require ment,thus resulting in a largetrunnion arrangement.

Afurtherproblem occurs in supporting the usually large and heavy ball within the casing since it is necessaryto carrytheweightofthe ball completely on thetrunnions in order to prevent the seals between the ball and the pipeline becoming unduly deformed and worn due to them bearing some load from the ball. When these valves are mounted for rotation about a horizontal axis perpendicularto the pipe, the ball may be out of balance and this has to be overcome to turn the valve. In horizontal pipelines, therefore, large ball valves are usually mounted for rotation about a vertical axis, so that this may be avoided.

This arrangement results in theweightofthe ball fal ling, as an end load, wholly on the lowertrunnion, hence the dimensions and assembly of the lower trunnion are critical to ensure that the ball isfully supported and in precise alignment with the pipeline seals. In prior lower trunnion arrangementsthecom- plete lowertrunnion has been machined from a single piece. This method of manufacture requires the complete removal ofthe lowertrunnion for adjust stment and precise alignment ofthe ball during assembly, and is wasteful of material during manufacture.

Another problem experienced in trunnion type ball valves is that of sealing between the ball and the pipe flanges. A common arrangement for achieving such a seal isto have annular sealing members provided with nylon orPTFE sealing rings which aretelescopically mounted within the pipe flanges, the sealing rings being maintained in contact with the ball by the action ofthe pipeline pressure and the force of a spring on the sealing member. The pipeline pressure holding the seal member on the ball can be used to advantage in a number of different ways. For example, high pressure can build up inthecavitiessur- rounding the trunnion mounts, which pressure needs to be released when line pressure drops.In these circumstances high cavity pressure on one side ofthe sealing member will overcome low line pressure on the otherto lift the seal from the ball and thereby release the cavity pressure to line. As a further precaution against leakage past the sealing ring grease is applied to the vicinity ofthe contact betweenthe ring andtheball.Arrangementforsuch grease supply usually involves the grease itself being interposed between line pressure and the sealing member. However, due to size constraints on the ealing member and in orderto limitthe amount of grease which is delivered, it is necessary for the grease to pass through a small bore hole.Such a small bore hole lends itselfto problems of blockage due to foreign particles or coagulated oxidised lumps ofgrease. If the grease delivery passage becomes blocked then the pipeline pressure can no longer bear upon the grease and thereby on the sealing member. It is therefore necessary to exposethe grease to pipeline pressure via an alternative route, yet the grease must not be able to issue into the pipeline by this route. Prior art arrangements for sealing this alternative route have been complex and/orex- pensive. For example one arrangement uses the clearance around an 0 ring seal such that gas or liquid within the pipeline can flow past it yet the more viscous greast cannot. However such an arrangement is highly dependent upon fine manufacturing tolerances and has often been found to be ineffective.

According to the present invention there is provided a ball valveforcontrolling theflowoffluid in a pipeline comprising a ball having a boretherethrough, a valve stem arranged to rotate the ball to adjust the orientation of the bore with respect to the pipeline, valve stem locating means which locatethe valve stem, and valve stem sealing means including a seal surrounding the valve stem which is arranged to fail before the locating means can be removed.

Preferablythesealing means include an end memberwhich acts on the seal, which allows the seal to breakwhen it is removed and which must be removed before the locating means can be removed.

The end member may be bolted overthe location means. Alternatively the end member could be screwed to the location means.

In a preferred form the sealing means include a pressurised fluid on which the end member acts to maintain the pressure of the fluid, the fluid maybe retained between chevron section annular rings.

Preferably the valve includes a secondary partial seal which is operable when the seal provided by the sealing meansfails.

According to a further aspect of the present invention there is provided a ball valve for controlling the flowoffluid in a pipeline comprising a ball having a bore thereth rough, a valve stem arranged to rotate the ball to adjustthe orientation of the bore with respecs to the pipeline, valve stem locating means which locate the valve stem, and valve stem sealing means including a seal surrounding the valve stem, the stem being operatively coupled to the ball by means of a drive key cooperating with a correspondingly shaped aperture, the key and aperture being of polygonal form having at least five sides. Preferably the key is integral with the stem and the aperture is formed in the ball. The drive key is preferably hexagonal.

According to another aspect ofthe presentinven- tion there is provided a ball valve for controlling the flow of fluid in a pipeline comprising a ball having a bore therethroug h, a valve stem arranged to rotate the ball to adjustthe orientation of the bore with respectto the pipeline, valve stem locating means which locate the valve stem, and valve stem sealing means including aseal surrounding the valve stem in which the ball is mounted on a pairoftrunnionsat least one of which is arranged for adjustment so that the positioning of the centre ofthe ball may be adjusted.

Preferably, the adjustment of the trunnions is effected by changing the size orthe number ofshims between the trunnion and a member on which the trunnion is supported.

According to another aspect of the present invention there is provided a ball valve for controlling the flowoffluid through the bore of a pipelinecompris- ing a ball having a bore thereth rough and sealing means arranged to provide a seal between the pipeline bore and the surface ofthe ball, the sealing means being provided with a passagefordispensing grease to the surface ofthe ball, the passage having an opening to the pipeline bore, the said opening being provided with closure means arranged so that fluid can pass through the opening from the pipeline bore to the passage, but passage of any material through the opening from the passage to the pipeline bore is prevented.

The closure means may be an annular sealing ring, preferably in the form of an 'o' ring.

Preferably, the passage and the closure means are constructed and arranged such that the closure means cannot entirely prevent flow of material through the passage.

In a preferred form the passage adjacent the closure means has no linear cross sectional dimension smallerthan the maximum cross sectional dimension ofthe closure means.

It will be appreciated that when the grease pres sure is greaterthan the line pressure the closure means will be maintained in a closed position so that no material may flow from the passage to the pipe bore. Alternatively when the line pressure is greater than the grease pressure the line pressure will tend to move the closure means from the closed position so that material may flow from the pipeline bore to the passage.

It will also be appreciated that each of the features ofthevarious aspects ofthe invention described above may be used either alone or in combination with any nu m ber of other featu res of the variuos aspects ofthe invention.

The invention may be carried into practice in various ways and two specific embodiments will now be described by way of example with reference to the accompanying drawings of which: Figure lisa longitudinal cross sectional elevation ofatrunnion mounted ball valve; Figure2 is a more detailed scrap sectional view to a larger scale of the valve stem mounting arrangement shown in Figure 1; Figure 3 is an end elevation of the uppertrunnion shown in Figure 1,to a larger scale, showing the valve drive key configuration; Figure 4 is a more detailed scrap sectional view to a larger scale of the lowertrunnion shown in Figure 1; Figure5is a similarview to that shown in Figure 2 showing a second embodiment of the stem cap; and Figure 6 is a cross sectional view, to an enlarged scale, of an annular seal member and flange arrange mentwhich may be used in the ball valve shown in Figure 1.

The valve 2 comprises a generally cylindrical housing 4which is located between two pipe flanges 6 each having a bore which is the same size as the bore of a pipeline within which pipelinetheflanges 6 are arranged for connection. A ball 8 having a hole 7 of diametersimilartothatofthe bore ofthe pipe flanges 6through its centre is mounted within the housing 4 on trunnions 10 and 1 2 so that the hole7 is axiaily aligned with the bore of the pipe flanges 6.The trunnions 10 and 12 are diposed on either side ofthe axis ofthe hole7 along a diameterofthe ball 8which extends perpendicularly to the axis of the hole 7, so that the ball 8 can rotate aboutthetrunnion axis to a position in which the axis of the hole 7 is perpendicularto that ofthe pipeflanges 6. Between the pipeflanges 6 and the ball 8 are annular seal members9,thepur- pose of which is to seal the bore of the flanges 6 and the hole 7 from the exterior of the ball 8, however in practice some leakage past these seals 9 occurs.

As is shown in Figure 6, the annularseal members 9 comprise a main body ring 60, a sealing ring 62, a spring biassing ring 64 and several springs 66, and several seals each of which will be described in more detail below. The sealing members 9 are arranged to fit within a first second and third bores 72,74,76 which are enlarged from the pipeline bore of the flange 6 by respective steps 71,73 and 75. Each flange 6 has a grease nipple, not shown, which is connected to supply grease to the second bore 74 of the flange 6 via a grease supply hole 70.The outer diameter of the main body ring 60 is also stepped, from a first diameter 82 which is a close fit within a part of the third bore 76 ofthe pipe flange 6, through first second, third and fourth steps 83,85,87 and 89 to second third fourth and fifth diameters 84,86,88 and 90 respectively. The end ofthe main body ring 60 which is not stepped has a chamfered face 61 which is arranged to fit closely overthe surface ofthe ball 8.

The sealing ring 62 isoftrapezoidal cross section, and is located within a groove in the chamfered face 61 in such a waythatan exposed side ofthesealing ring 62 lies substantially parallel to, but slightly proud ofthe chamfered face 61. In this way the sealing ring 62 comes into contact with the surface ofthe ball 8 leaving a small gap between the chamfered face 61 ofthe main body ring 60 and the surface ofthe ball 8. The spring biassing ring 64 is of'h'shaped cross section having legs 63,65 a bridge section 67 and an upper portion 69. It is radially located between the second and third diameters 84,86 of the main body ring 60 and the bore 76 ofthe pipe flange 6 and axially between the first and second steps 83,85 ofthe main body ring 60 and the third step 75 ofthe pipe flange 6.The springs 66 are located at regular intervals between the legs 63,65 and the 'h' section spring biassing ring 64. These springs 66 react againstthethird step 75 in the bore of the flange 6 and bias the biassing ring 64towards the ball 8. The biassing ring 64 in turn reacts through a PTFE spacing washer 68 (which is disposed between the top side ofthe bridge 67 and the second step 85 ofthe main body ring 60, against the second step 85 ofthe main body ring 60, thus biassing the main body ring 60 and hence the scraper ring 62 toward the ball 8.

The upper portion 69 ofthe 'h' section biassing ring 64 overlaps the second step 85 and diameter 84 ofthe main body ring 60 and extends towards the first step 83 ofthe main body ring 60. Between the end ofthe upper portion 69 ofthe 'h' section spring biassing ring 64andthefirststep 83 ofthe main body ring 60 is a rectangular section compressible graphite ring 80 which is located between the third bore 76 of the pipe flange 6 and the second diameter 84 ofthe main body ring 70, and acts as a primary seal in the event offire or other excess heating levels. Iffire or sufficient heating levels to destroy the other elastomer seals should occurthen the spacerwasher 68 would melt and the upper portion 69 of the spring biassing ring 66 would bear upon the graphite ring 80, com pressing itundertheforce ofthe springs 66 and thereby causing ittoform afire seal between the third bo e 76 of the pipeline and the second diameter 84 ofthe main body ring 60.

The melted PTFE washer 68 would also form a seal between the top side of the bridge 67 and the second step 85 ofthe main body ring. A series of stepped holes 92 extend axially through the main body ring 60, from the chamfered face 61, at which end the holes are a small diameter, to the fourth step 89at which end the holes area larger diameter.

A cup seal 94 is located adjacent the third step 87 of the main body ring 60 and seals between thefourth diameter 88 ofthe main body ring 60 and the second bore 74 ofthe pipe flange 6, and an 'o' ring 96 is located on the fifth diameter 90 ofthe main body ring 60 between the fourth step ofthe main body ring 60 and the second step 73 ofthe pipe flange 6. A portion of the fifth diameter ofthe main body ring 60 is a close fit with part of the third diameter 86 ofthe main body ring 60 with a part of the second bore 74 of the pipe flange 6.

When operative grease is introduced to a void 79 formed between the second step 73 and second bore 74 of the pipe flange 6 and the fourth step 89 and fourth diameter 88 ofthe main body ring 60. The grease passes along the hole 92 and issues onto the chamfered face 61 ofthe main body ring 60 art a point in the vicinity ofthe sealing ring 62. From this point the grease may be moved by the influence of any fluid which is leaking pastthesealing ring 62 to the position of leakage and block it, because the viscosity ofthegreaseisgreaterthanthatofthefluid,andthe grease will therefore not pass through the small gaps through which the fluid leaked.The grease is prevented from leaking from the void in any way otherthan via the hole 92 by the cup seal 94 and the 'o' ring 96 the latter of which seals the corner between the fifth diameter 90 ofthe main body ring 60 and the second step 73 ofthe pipeflange 6 thereby preventing grease leakage into the pipe bore.

For the seal member 9 to function properly it is nec essary that the fluctuating pipeline pressure be active upon the annular area provided by the third and fourth steps 87 and 89 ofthe main body ring 60 in orderto supplement the small force provided by the springs 66to bias the sealing ring 62 towards the ball 8.By utilising the pipeline pressure over an area of the main body ring 60 to provide the main biassing force component a safety feature is built in, in that high pressure on the ball 8 side ofthe seal acts on the annular end area ofthe main body ring 60 which is of greaterareathan annulararea provided bythethird and fourth steps 87 and 89 ofthe main body ring 60, therefore the high pressure on the ball side ofthe seal 9 can force the seal 9 away from the ball 8surface andthusallowthe pressu res to equalise, thereby preventing higherthan desired pressures building up in the valve housing 4.The pipeline pressure can act on the annular area provided by the third and fourth steps 87 and 89 of the main body ring 60 either through the grease hole 92 and or by unseating and passing the 'o' ring 96. Therefore if the grease hole 92 becomes blocked the seal 9 will still function and eventually with pressure build up in the void 79 the grease hole 92 should clear itself. Thus it can be seen that the 'o' ring 96 functions as a one way valve, preventing grease leaking out into the bore oftheflange 6yetallowing pipeline pressureto unseat it and pressurise the void 79. The cross sectional size of the 'o' ring 96 is markedly lessthan the largerdiameterof the hole 92 so that in conditions where the 'o' ring 96 is squeezed, and hence sealing, between the fourth step 89 of the main body ring 60 and the second step 73 ofthe pipeflange6 if it is lifted offthefifth diameter90 ofthe main body ring 60 by pipeline pressure, it soon reaches a position, at the mouth of the hole 92, where it is no longer squashed, and therefore sealing, between the steps 73 and 89 in which position the pipeline pressure can by passthe'o' ring 96 and pressurise the void 79.

The uppertrunnion 10is integral with a stem 14 which extends through and is rotatablysupported by the housing 8 as shown in Figure 2, and a stem cap 16 locates the stem 14 in relation to the housing 4. The stem 14 is in the form of a stepped shaft, having shank 18, the upper end ofwhich shank 18 is flat- tened to provide a driving surface for a valvewheel, notshown, a largerdiameterjournal bearing section 20, a hexagonal drive key section 22 and the integral trunnion 10. The stem cap 16 is in the form of an annular plate having a stepped bore 24 and a stepped lower face 25.When assembled the stem cap 16 is sealably secured to the housing 4 by bolts 26 so that the stepped lower face 25 extends partially into a holewhich passesthrough the side of the housing 4 and within which hole the stem 14 is located. The shank 18 ofthe stem 14 passes through the bore 24 of the stem cap 16 which bore 24 is adjacent the shank 18 at its lower end, but increases in diameter so that sealing means 28 between the stem cap 16 and the shank 18 may be accommodated.

Acover plate 40 which has a bore that is a closefit around the diameter ofthe shank 18 is secured to upperface ofthe stem cap 16 by bolts 42, thereby closing the upper end of the bore 24 and concealing the heads ofthe stem cap bolts 26.

The sealing means 28 comprise an upper end ring 30 which abuts the cover plate 40 and is a close fit between the bore 24 and the shank 18, three chevron section sealing rings 34, a pressure ring 32, an an nular pressure chamber 36, another pressure ring 32 and three more chevron section sealing rings 34. The seal is operative when either grease or a deformable plastics material is injected into the pressure chamber 36 through a nipple, now shown, which extends through the side ofthe stem cap 16. The grease/plastic is pressurised to a greater pressure than that in the pipeline, and exerts a force on the pressure rings 32 which in turn force the chevron rings 34to compress against the step in the bore 24 and the upper end ring 30 respectively.This com pression ofthe chevron rings 34 causes them to flatten and hence press firmly against the bore 24 and the shank 18, thus sealing the shank 18 in the bore 24 so that any pressurised fluid from the pipeline which may have leaked aroundthe annular seals 9 is pre vented from leaking to the atmosphere.

The stem 14 is prevented from being axially with drawn from the housing 4 by a shoulder 21 produced bythe difference in diameters ofthe shank 18andthe bearing section 20, therefore when the stem 14 tends to be withdrawn from the housing 4the shoulder 21 abuts a spacer arrangement 44 which extends around the lower end ofthe shank 18 and is located between the lower face 25 of the stem cap 16 andthe shoulder 21. The spacer arrangement 44 comprises a spacer ring 46 and a thrust washer 48. It is therefore evident that the stem 14 cannot be removed without firstly removing the stem cap 16, and to remove the stem cap 16 it is necessary to unscrew the bolts 26.

Howeverto gain access to the bolts 26 it is necessary to removethe cover plate40 whereupon the sealing means 28 becomes de-pressurised, because the upper end ring can move outwardly thereby allowing the pressurised grease or plastics material to ex pand. This expansion is minimal, a few percent by volume,sincethe material in the pressure chamber 36 is such that a high pressure is produced by a small volumetric compression. When the sealing means 28 is de-pressurised, the seal between the shank 18 and the bore 24 is broken. Any pressure from the pipeline which may have leaked past the seals 9 will betending toforcethe stem 14 upwardly outofthe housing 4, howeverthe stem 14will still be held in place by the shoulder 21 and the stem cap 16.Such pressure will however leak past a partial seal 47 produced by the spacer ring 46 between the shoulder 21 and the cover face 25, and leak to atmosphere producing a hiss which serves as a warning, to a person attempting to remove the stem cap 16, that the pipeline is pressurised and that if the bolts 26 are removed the stem will probably be 'blown out' ofthe housing. In this condition of strip down of the valve i.e. with the cover plate 40 removed, it is possible to gain access to and replace if necessary elements of the sealing arrangements 28, since one could easily perform this function despite the slight hissing pressure leakage.

If on the otherhand the partial seal 47 was not very effective and the pipeline pressure which had leaked pastthe annular seals 9 was very high, on unscrewing the bolts 42, to release the cover plate 40, and de-pressurising the sealing means 28, the cover plate 40 may be 'blown out'. Although such an occurrence would be fairly hazardous, the presence of the cover plate 40 would at least serve to deflect the jet of es capping pressure outwardly, and away from the person who was removing the cover plate.

An alternative form of cover plate and stem cap is shown in Figure 5, but since this arrangement is essentially similarto that described above only therelevant differences will be described and the same reference numerals prefixed by the number 1 will be used, for example cover plate 40 will be referred to as cover plate 140. In this alternative arrangement the step cap 116 is arranged sothatthe bolts 126 are countersunkin its upperface, and the bore 124 is extended by a larger diameter threaded portion at its upper end. The cover plate 140 is in the form of a screw threaded cap with a flange that overlaps the heads of the bolts 126.The remaining feature of both cover plate 140 and stem cap 116 are the same as those described above, hence it is apparent that it is still necessary to remove the cover plate 140 and thus break the sealing arrangement 128 before the stem cap can be removed, therefore the warning and ac cessibil ity feature are still present.

The drive key 22 is shown in greater detail in Figure 3, the hexagonal shape of which has sides which are tangential to the circumference ofthetrunnion 10. It engages a hexagonal hole in the ball 8 the sides of which are tangential to the circumference of a hole in the ball 8 into which the trunnion 10 fits. The hexa gonal drive key shape provides more area contact with the hexagonal hole in the ball 8than a re ctangular shaped key would provide, hence the contact area of the hexagonal drive key can be utilized to bear some of the forces produced by the fluid in the pipeline on the ball 8thus enabling the trunnion 1 Oto be sized to bear only the remainder of those forces ratherthanallofthemaswould be necessaryifa non-supportive rectangular key shape were used.

The hexagonal shaped drive key in a hexagonal shaped hole also provides six driving points through which theforceto turn the ball 8 may be transmitted ratherthan thetwo driving points of a rectangular key in a slot. Thus wear on the driving points ofthe hexagonal key will be markedly less than those of a rectangular key.

The lowertrunnion 12 isjournalled within a bush 50 in a hole in the ball 8 and extends into a hole in the housing 4. The end ofthetrunnion 12oppositethe end which is in the ball 8 abuts a stackof shims 52 and is pegged to an end cap 54 by pegs 56. The end cap 54 is releasablysecuredtothe housing 4, sothat the ball 8 is completely supported for rotation relat ivetothetrunnion 12 by the trunnion 12, shims 52 and end cap 54 arrangement.In assembling the valve 2the ball 8 is supported within the housing 4in such a way that no load from the ball 8 is imposed on the seals 9, the lowertrunnion 12 is inserted andthe number or size ofthe shims 52 is adjusted until the lowertrunnion 12 supports the whole of the load of the ball 8when the end cap 54 istightened up. Such adjustment is compensated for by adjustment of the uppertrunnion 10 by way of the spacer 46 between the stem 14 and the stem cap, hence it is possibleto finely adjust the lowertrunnion 12to achieve the des ired support ofthe ball 8. By utilising a split lower trunnion arrangement comprising lowertrunnion 12,shims 52 and end cap 54wastage of material during manufacture is saved. By making the lower trunnion 12from one diameter of barstockandthe end cap 54 from a larger diameter bar stock, rather than manufacturing an integral componentfromthe larger size of bar stockthe material which would have been machined away around the smaller dia meter lowertrunnion portion is saved.

Claims (22)

1. A ball valve for controlling theflow of fluid ion a pipeline which comprises a ball having a boretherethrough, a valve stem arranged to rotate the ball to adjust the orientation of the bore with respect to the pipeline, valve stem locating meanswhich locatethe valve stem, and valve stem sealing means including a seal surrounding the valve stem which is arranged to fail before the locating means can be removed.

2. Avalve as claimed in Claim 1 in which the seal ing means includes an end member which acts on the seal, which allows the seal to breakwhen it is re moved and which must be removed before the locating means can be removed.

3. Avalve as claimed in Claim 1 or Claim 2 in which the end member is bolted overthe location means.

4. Avalve as claimed in Claim 1 or Claim 2 in which the end member is screwed to the location means.

5. Avalve as claimed in any of Claims 2-4, in which the sealing means includes a pressurised fluid on which end end memberactstomaintainthepres- sure ofthefluid.

6. A valve as claimed in Clai m 5 in wh ich the pres- surisedfluid is retained between chevron section an nular rings.

7. Avalve as claimed in any of the preceding claims in which a secondary partial seal is operable when the seal provided bythesealing meansfails.

8. A ball valve for controlling the flow of fluid in a pipeline which comprises a ball having a bore there- through, a valve stem arranged to rotate the ball to adjust the orientation of the bore with respect to the pipeline, valve stem locating means which locate the valve stem, and valve stem sealing means including a seal surrounding the valve stem,the stem being operatively coupled to the ball by means of a drive keycooperatingwith a correspondinglyshaped aperture, the key and aperture being of polygonal form having at least five sides.

9. Avalve as claimed in Claim 8 in which the key is integral with the stem and the aperture is formed in the ball.

10. Avalve as claimed in Claim 8 or Claim 9 in which the drive key is hexagonal.

11. A ball valveforcontrolling theflowoffluid in a pipeline which comprises a ball having a bore therethrough, a valve stem arranged to rotate the ball to adjustthe orientation of the bore with respect to the pipeline, valve stem locating means which locate the valve stem, and valve stem sealing meansinclud- ing a seal surrounding the the valve stem inwhich the ball is mounted on a pair of trunnions at least one of which is a rranged for adjustment so that the posi- tioning of the centre ofthe ball may be adjusted.

12. Avalve as claimed in Claim 11 in which the adjustmentofthetrunnion is effected by changing the size or the number of shims between thetrunnion and a member on which the trunnion is supported.

13. A ball valveforcontrolling the flow offluid through the bore of a pipeline comprising the ball having a bore therethrough and sealing means arranged to provide a seal between the pipeline bore and the surface ofthe ball,thesealing means being provided with a passage for dispensing grease to the surface of the ball, the passage having an opening to the pipeline borethesaid opening being provided with closure means arranged so that fluid can pass through the opening from the pipeline bore to the passage, but passage of any material through the opening from the passagetothe pipeline bore is prevented.

14. Avalve as claimed in Claim 13 in which the closure means is an annular sealing ring.

15. Avalve as claimed in Claim 13 or Claim 14 in which the closure means is an 'o' ring seal.

16. Avalve as claimed in any of Claims 13 to 15 in which the passage and the closure means are constructed and arranged such that the closure means cannot entirely prevent flow of material through the passage.

17. Avalve as claimed in Claim 16whereinthe passage adjacent the closure means has no linear cross sectional dimension smaller than the maximum cross sectional dimension of the closure means.

18. Avalve substantially as described herein with reference to the accompanying drawings.

19. Avalve comprising valve stem locating means as substantially described herein with reference to Figures 1,2 and 5 of the accompanying drawings.

20. Avalvecomprising ball drive key means as substantially described herein with reference to Figures 1,2,3 and 5 ofthe accompanying drawings.

21. Avalve comprising trunnion mounting means as substantially described with reference to Figures 1 and 4 ofthe accompanying drawings.

22. Avalvecomprising sealing means as sub stantially described with reference to Figures 1,25 and 6 ofthe accompanying drawings.