Valve seat facing device

Abstract

 The present invention provides a device for lapping valve seats (16) of for example steam valves in a power generating station. The device includes means for providing torque to be applied to a crankshaft (20) which includes an eccentric shaft on (28) at least one of its extreme ends. Mounted on each eccentric shaft (28) by way of a loose fitting bearing (33) is a facing disc (23) which are interchangeable to allow different sizes and abrasive grades to be used. During operation the facing discs (23) are pressured towards their respective valve seats (16) being lapped by helical springs (74) held within counterbores (73) of each eccentric shaft (28) thus urging the discs (23) axially outwardly of the crankshaft (20). During rotation of the crankshaft (20) the discs (23) tend to orbit around the valve seat (16) being faced at a slow rate while moving substantially radially inwardly and outwardly at the rotational frequency of the crankshaft (20). The device therefore provides a relatively fast and accurate refacing operating to the valve seats (16) which may have been worn or scratched during use. Further the apparatus saves the valve having to be removed from its steam line and thus greatly reduces overall time involved in the operation.

Description

[0001] The present invention relates to a valve seat lapping device, which is of particular use in resurfacing valve seats on parallel slide, wedge, globe or non-return valves.

[0002] When valves are used they are subject to wear, and scratches. In the case of steam valves, scratches (which can be induced on valve seats and discs by foreign material, as well as operation of the valve) allow leakage of steam which is usually under high pressure. This is highly undesirable. To compound the situation, many valves are welded into position, thus making maintenance far more difficult, because it will have to be done in situ.

[0003] "Lapping" as used herein will be understood to mean a process whereby a valve disc or seat is ground to the necessary finish for its operation.

[0004] The methods of prior art often required removal of the valve from the line, its disassembly to resurface the valve disc and the hand grinding of the valve seats. Further problems arise when the valves are welded in the line and these operations have to be done in situ. For high pressure steam lines in power stations the wall thickness or the pipe may be 3 or 6 inches thick. Thus to cut the valve from the line and re-weld the line can take many days work thus creating an overhead running into some thousands of dollars even before the valve seat resurfacing is approached. The actual resurfacing itself may take many days of grinding, depending upon the valve seat condition.

[0005] To perform the resurfacing of the valve seat by hand is a time consuming task, involving a combination of both trial and error and skilled technique.

[0006] It is an object of the present invention to provide an apparatus to lap a valve seat. This involves removing the valve "bonnet", stem and discs and hand finishing the valve seat.

[0007] In one broad form the invention provides a valve seat lapping device comprising means for attaching the device to a valve once a valve closure means has been removed, drive means for driving a first shaft, said first shaft, having an eccentric shaft extending from at least one end thereof; a disc, adapted to engage said seat to be lapped, being mounted in an axially rotatable manner on said eccentric shaft, said disc being capable of carrying an abrasive medium on its surface at least in the area coincident with said seat.

[0008] The lapping means, preferably has two discs called facing discs, which are interchangeable with other facing discs of different sizes and abrasive means to suit the different size valves and situations presented to an operator. The lapping means is preferably mounted on "loose fitting" bearing means, to allow the obtainment of a required angle on the facing disc to suit the application e.g. wedge valves. The lapping means and the bearing means are preferably mounted on a crankshaft having eccentric shafts at both ends, the eccentric shafts have their eccentricity in opposite directions to balance the device. The centre portion of the crankshaft is mounted in a frame, with bearing means for the crankshaft to rotate freely, rotation of the crankshaft is provided by drive means from a driveshaft which also has its own bearing means to allow free rotation, the driveshaft contains provision for connection to a motor means e.g. hand cranking or electric motors. The driveshaft is displaced from the crankshaft, the drive means being preferably a pulley arrangement on both the crankshaft and driveshaft, the driveshaft providing rotation to the crankshaft by belt means. Provided in this embodiment is an adjustable tensioning means to take up wear and slack in all bearing-means. The pulleys and the belt means, the mounting frame in which is mounted the crankshaft and its bearing means, the lapping means and its bearing means, the driveshaft and its bearing means also has a mounting means for placement on a valve to be lapped. The valve having a valve seat and removable bonnet is common with valves. The mounting means contains holes to secure the mounting frame in the place of the bonnet, when the bonnet has been removed. The invention may also be used on valves which do not have removable bonnets, by gaining access to the valve seat through inspection plates located at the bases of valves, as is also common to valves.

[0009] One embodiment of the present invention will now be described by way of example only, with reference to the accompanying drawings, wherein:

Fig. 1 is a front elevation of a valve seat lapping apparatus;

Fig. 2 is a side elevation of the apparatus of Fig. 1;

Fig. 3 is a ghost view of a typical wedge valve;

Fig. 4 is a plan view of a portion of a valve seat lapping apparatus in accordance with the invention;

Fig. 5 is a sectional view showing the co-operation of two portions of a valve seat lapping apparatus in accordance with the invention;

Fig. 6 shows a sectional view of the application of the valve seat lapping apparatus when a removable bonnet is not available;

Fig. 7 shows a side elevation of an alternative embodiment of a valve seat lapping apparatus;

Fig. 8 shows a side elevation of a third embodiment of a valve seat lapping apparatus; and

Fig. 9 is a side elevation of a fourth embodiment of the present invention.

[0010] As seen in Figs. 1 and 2 the valve seat lapping device 10 comprises a fabricated mounting frame 11, provided with holes 13 for mounting on valve 14 after removing the bonnet 15 of the valve 14 (Fig. 4). This locates the lapping device 10 in position on the valve 14 such that the facing discs 23 are positioned on the valve seat 16 ready to commence the lapping procedure. The drive shaft 17 is provided with connection means 18 in order for it to be coupled to a motor (not shown). To allow free rotation of driveshaft 17 bearing means 19 are provided, secured to mounting frame 11. The provision of drive means for the crankshaft 20 from the driveshaft 17 is by means of drive pulley 21 on driveshaft 17 and driven pulley 22 on crankshaft 20. The drive means also consists of belt means 26, which interconnects drive pulley 21 and driven pulley 22. Provided in this embodiment is tensioning means 60. The tensioning means 60 is provided with adjustment means 61 which allows the required tension to be chosen due to circumstances such as wear in bearing means 9, crankshaft bearing means 18, drive pulley 21, driven pulley 22 and belt means 26. The crankshaft 20 is mounted in bearings 31 located in the arms 27 of the apparatus 10. The crankshaft 20 has at each end extending outwardly from the arms 27 an offset or eccentric shaft 28. The nature of the eccentricity of the crankshaft 20 is indicated by centre lines 29 and 30. Facing discs 23, are mounted on eccentric shaft 28 by way of "loose fitting" bearing means 33 which allow the facing discs 23 to angle slightly so as to properly contact valve seats 16. The bearing means 33 keep the facing discs 23 at the required angle for as long as contact between valve seat 16 and facing discs 23 is maintained. The "loose fitting" design of the bearing means 33 allows the facing discs 23 to adapt to the required configuration according to the type of valve, e.g. parallel slide, wedge (as shown in Fig. 4), and non-return valves.

[0011] In operation the main driving shaft 17 drives shaft 20 by means of the belt 26. Rotation of shaft 20 about its axis 30 causes eccentric shafts to rotate in a manner such that their axes 29 rotate about axis 30. However as discs 23 are mounted on bearings 33 on the eccentric shaft once in contact with the valve seat they do not rotate due to the friction but instead trace out a reciprocating path, having an amplitude equal to the distance between the axes 29 and 30, substantially at right angles to the central axis 30. The path would very slowly proceed around the circumference of the seat.

[0012] The facing disc surface 23 is coated with an abrasive means, preferably diamond dust or carborundum equivalent to 400 Grit.

[0013] The mounting frame 11 is provided with lifting lugs 24 to ease installment and removal of the lapping device 10, from valve 14.

[0014] The facing discs 21, are interchangeable with other facing discs, having different sizes and abrasive means, to suit the size of the valve seats as well as the required resurfacing effect.

[0015] In another embodiment the valve seat lapping device is also suitable to valves, which do not have removable bonnets, as in Fig. 6. After removal of the inspection plate (not shown) an inspection hole 40 is exposed. Thence the valve stem and other internal components (not shown) are removed. In the stems place is installed a threaded section 41, secured into place by nuts 42 and 43. Assembled on this threaded section 41 are the facing discs 45 and their bearing means 47, and the crank shaft 44 with its bearing means 46.

[0016] The driven pulley 51 is in contact with drive pulley 49 by belt means 48, with the valve seats 52 being lapped by facing discs 45 when rotation is produced through the drive means by connecting a motor means (not shown) to connection means 50.

[0017] As shown in Fig. 7 a further embodiment of the invention includes a modified mounting means 75 in which mounting frame 76 is rigidly attached to a pillar sleeve 78 through which is passed a tubular threaded pillar 79. Threadably engaged upon pillar 79, one either axial side of sleeve 78 are two lock nuts 77. During installation of the valve seating device mounting frame 76 is attached to the valve body as before described. Facing discs 23 are then positioned relative to the valve seats to be faced so that the crankshaft axis 30 is substantially centered on respective valve seats. This alignment is carried out by turning lock nuts 77 so as to screw pillar 79 through sleeve 78 and then when suitably located to rigidly position the device by locking the nuts 77 against sleeve 79.

[0018] A further embodiment of the invention is shown in Fig. 8 where the apparatus is arranged for lapping check or non-return valves in which the plane of the valve seat to be faced is not perpendicular to the plane to which mounting frame 83 is to be attached. This is accommodated simply by attaching frame 86 at the appropriate angle to sleeve 84. The embodiment of Fig. 8 further shows one only facing disc 23. Such embodiment can be used specifically in valves which include one only valve seat such as non-return valves.

[0019] Fig. 4 shows a typical crankshaft 20 including eccentric shaft end portions 28. Crankshaft 20 is held in its axial position relative to bearing means 81 via circlips placed within circlip grooves 70.

[0020] In order to provide the axial force between each facing disc 23 and respective valve seat 16 each eccentric shaft 28 has an axial counterbore 73 (Fig. 5) so as to accept a helical spring 74 which urges the respective facing disc 23 outwardly from crankshaft 20, the facing disc 23 being capable of this movement by virtue of the "loose fitting" bearing means 33.

[0021] Fig. 9 shows a final embodiment of the present invention adapted to face a valve seat which is parallel to the surface to which mounting frame 87 is attached during use. As seen from the figure, this embodiment does not require the pulley drive between separate drive and crankshafts. Instead the drive shaft is elongated with one end including a single eccentric shaft 28 similar to abovedescribed eccentric shafts, and at the opposite end means 18 for accepting drive from an external power source such as a motor (not shown).

Claims

1. A valve seat lapping device for a valve having a body with an opening for receiving a valve closure member, and a seat in the body for closing the valve, said device comprising a base to be fixed to said body, a lapping assembly mounted on said base so as to extend therefrom into said opening, drive means mounted on the base and drivingly coupled to said assembly, and characterised in that said assembly includes a stem extending from said base so as to have one end adjacent said seat, a first driven shaft rotatably supported by the stem so as to be rotatable about a longitudinal first axis, a lapping disc rotatably mounted on said shaft adjacent said end so as to be rotatable about a second axis parallel to said first axis but spaced therefrom.

2. A device as defined in claim 1 wherein said device includes a second shaft mounted parallel to said first shaft and transversely displaced therefrom, said first and second shafts having respective first and second pulleys adapted to run a drive belt therebetween for transmitting torque applied to said second shaft to said first shaft.

3. A device as defined in claim 2 wherein a rigid frame extends between two sets of bearings respectively holding said first and second shafts and forming at least part of said stem.

4. A device as defined in claim 2 wherein said first shaft includes two eccentric shafts at axially opposite ends, said eccentric shafts being mutually 180° out of phase, and each including a respective said disk.

5. A device as defined in claim 1 wherein said device includes a drive portion of said first shaft at an axially opposite end to said disc.

6. A device as defined in claim 4 wherein the axis of each said eccentric shaft is counterbored and has inserted therein a helical spring adapted to urge a respective said disc axially outwardly from said first shaft so as to provide pressure on said seat during lapping.

7. A device as defined in claim 2 wherein said means for attaching the device includes adjusting means allowing preselection of the relative position of said first shaft and said seat.

8. A device as defined in claim 6 wherein each said respective said disc is mounted on a respective eccentric shaft by a loose fitting bearing.

9. A valve seat lapping device as defined in claim 1 wherein said first driven shaft runs transversely of said stem.

10.. A valve seat lapping device as defined in claim 1 wherein said first driven shaft runs parallel to said stem.

Drawing