GB2264076A - Valve seat lapping device - Google Patents

Abstract

A valve seat lapping device for lapping the seats of steam valves or the like a pair of lapping discs 37 movable in an orbital path by a pair of arms 47, on a shaft 34, which engage the inner face of a peripheral rim on the inner face of the discs. The shaft is journalled on the lower ends of a pair of vertical legs 29, 30 which depend from a cross-head 21 mounted on the valve body when the valve bonnet is removed, the shaft being driven by a belt-and-pulley arrangement 28, 35, 36 from a driving shaft 25 on the cross-head. <IMAGE>

Description

THIS INVENTION relates to a valve seat lapping device. The invention is particularly suitable for, but not limited to, resurfacing the valve seats in parallel slide or gate valves.

The valve seats in valves (eg. in steam lines) are subject to wear with use and the scratches or other wear on the seats can allow leakage of steam or fluids at high pressures and/or temperatures. This, of course, is highly undesirable and so regular resurfacing of the valve seats is required to ensure proper sealing in the valves.

The maintenance of the valves can often be made more difficult in that many valves are welded into the steam or fluid lines and so the maintenance must be carried out in situ.

Methods of, and apparatus for, the resurfacing of valve seats have been developed which enable in-situ resurfacing of the valve seats and one example is disclosed in AU-B-14442/83 (559693) (Hunter Valley Construction Pty Ltd). One disadvantage of the device disclosed in that Patent is that it requires the use of bearings to support the lapping discs on the eccentric shafts.

It is an object of the present invention to provide a simple, yet efficient device for in-situ lapping of valve seats in large valves.

It is a preferred object to provide a device which can lap both valve seats in parallel slide or gate valves.

It is a further preferred object to provide a device where the pressure applied on the seats by the lapping discs is readily adjustable.

It is a still further preferred object provide a device where the orbital paths of the lapping discs can be easily adjusted.

Other preferred objects will become apparent from the following description.

In a broad aspect the present invention resides in a valve seat lapping device including: means for mounting the frame on a valve once a valve closure means has been removed; a frame; a shaft rotatably journalled on the frame; drive means to drive the shaft; a disc, adapted to engage the valve seat to be lapped, being mounted movably about the shaft, the disc carrying an abrasive medium on its surface at least in the area coincident with the seat; and cam means on the shaft engageable with the disc and operable, as the shaft is rotated, to cause the disc to move in an orbital path about the axis of rotation of the shaft.

Preferably the frame includes a pair of vertical legs depending from a cross-head, with bearings for the shaft at their lower ends. Preferably the cross-head is bolted to the valve body when the valve bonnet (and the spindle and valve member) have been removed from the valve.

Preferably a pulley or sheave is provided on the shaft, preferably between the bearings, and is operably driven by a belt driven by a pulley or a sheave on a driving shaft journalled at the upper ends of arms extending up from the cross-head. The driving shaft is preferably driven by an electric motor.

Preferably a respective disc is provided at each end of the shaft.

Preferably each disc has an outwardly directed lapping face and an inwardly directed peripheral flange or rim. Preferably the disc has a central bore, which may be fitted with a bearing or resilient bush, which has a bore greater than the diameter of the shaft.

Preferably the bore of the disc does not engage the shaft as the disc moves in its orbital path.

Preferably the can means includes an arm, extending preferably radially from the shaft and preferably adjustably extensible, with a roller or bearing means engageable with the inner face of the peripheral flange or rim on the disc.

Preferably an end plate retrains the disc in an outward axial direction relative to the shaft, and spring means (eg. Belville Springs or a compression spring) apply a contact pressure onto the disc in its engagement with the valve seat.

To enable the invention to be fully understood, a preferred embodiment will now be described in which: FIG 1 is an elevational view of the device in a valve; and FIG 2 is a part-sectional end view of the device.

Referring to FIG 1, the valve seat lapping device 10 is fitted to the valve body 11 when the valve bonnet 12 (and its associated hardware) has been removed to enable access to the valve seats (not shown), the valve body being left in-situ in the steam pipeline (not shown).

Referring now to FIG 2, the device 10 has a frame 20 with a cross-head 21 bolted to the peripheral flange 13 on the top of the valve body 11.

A pair of parallel arms 22, 23 extend upwardly from the cross-head 21 and are provided with bearings 24, which journal a driving shaft 25 driven by an electric motor 26 (mounted on a stand 27). A driving pulley 28 is keyed onto the driving shaft 25.

A pair of parallel legs 29, 30 depend from the cross-head 21 and are provided with respective housings 31, 32 with roller bearings 33, which journal a shaft 34.

A driven pulley 35 is keyed to the shaft 34 and is driven by the driving pulley 28 by one on more Vbelts 36.

A lapping disc 37 is provided at each end of the shaft 34 and each disc 37 has a lapping surface 38 (which may be disc-like or annular in elevation) or its outer face. Abrasive paste (not shown) is applied to the lapping surface 38 to polish the adjacent valve seat face.

The disc has a central web 39 which is fitted with a roller bearing 40 (or ball-bearing or resilient bush) which has an inner diameter greater than the diameter of the shaft 34.

An end plate 41, secured by a stand 42, limits the outward axial movement of the disc 37 relative to the end of the shaft 34.

A nut 43, on a screw-threaded portion 34a of the shaft 34, applies an outwardly directed preload on the lapping disc 37 via an inner washer 44, and a pair of Belville springs 43 and an outer washer 46.

An arm 47 is mounted on, and extends substantially radially from, the shaft 36 and rotates therewith. A cam follower 48 (or roller) is rotatably mounted on a pin 49 at the distal end of the arm 47 and leans against the inner face 50 of an inwardly directed peripheral rim 51 on the disc 37. As the arm 47 rotates, it causes the disc 37 to follow an orbital path about the axis of rotation of the shaft 34. As shown, there is a clearance between the ball bearing 40 in the disc 37 and the shaft 34. In addition to its orbital rotation, the disc 37 will progressively rotate about it its own central axis.

In use the device 10 is fitted to the valve 11 and rotation of the shaft 34 will cause the arms 47 to move the lapping discs 37 in their orbital paths hereinbefore described. The abrasive paste on the lapping faces 38 will progressively lap or polish the valve seat faces which they contact.

In a modified embodiment, the arms 47 may be mounted for radial adjustment relative to the shaft 34 to enable the radii of the orbital paths of the lapping discs 37 to be selectively varied.

The arms 47 may be adjusted so that the bearings 40 (or resilient bushes substituted therefor) engage the shaft 34 but the orbital paths of the lapping discs will be maintained.

While the arms 47 are shown parallel on the shaft 34, they may be 180 degrees out of phase and/or balancing counterweights may be provided on the shaft 34 for improved primary (and secondary) balance of the device.

The pulleys 28, 25 and belt 36 may be replaced by a sprocket-and-chain drive, or other mechanical drive, if preferred.

Various changes and modification may be made to the embodiments described and illustrated without departing from the scope of the present invention defined in the appended claims.

Claims (10)

We claim:

1. A valve seat lapping device including: a frame; means for mounting the frame on a valve once a valve closure means has been removed; a shaft rotatably journalled on the frame; drive means to drive the shaft; a disc, adapted to engage the valve seat to be lapped, being mounted movably about the shaft, the disc carrying an abrasive medium on its surface at least in the area coincident with the seat; and cam means on the shaft engageable with the disc and operable, as the shaft is rotated, to cause the disc to move in an orbital path about the axis of rotation of the shaft.

2. A device according to Claim 1 wherein the frame includes: a cross-head bolted to the valve body when the valve bonnet has been removed from the valve; a pair of vertical legs depending from the cross-head; and bearings for the shaft at the lower ends of the vertical legs.

3. A device according to Claim 2 wherein: a pulley or sheave is provided on the shaft, between the bearings, and is operably driven by a belt driven by a pulley or shaft on a driving shaft journalled at the upper ends of the vertical arms, the driving shaft being driven by an electric motor.

4. A device according to any one of Claims 1 to 3 wherein: a respective disc is provided at each end of the shaft.

5. A device according to Claim 4 wherein: each disc has a central bore, fitted with a bearing or resilient bush having a bore greater than the diameter of the shaft, an outwardly directed lapping face having the surface carrying the abrasive medium and an inwardly directed peripheral flange or rim.

6. A device according to Claim 5 wherein: the bore of the bearing or bush does not engage the shaft as the disc moves in its orbital path.

7. A device according to Claim 5 or Claim 6 wherein: the cam means includes an arm, extending radially adjustably extensible from the shaft, with a roller or bearing means engageable with the inner face of the peripheral flange or rim on the disc.

8. A device according to any one of Claims 1 to 7 wherein: an end plate restrains the disc in an outward axial direction relative to the shaft, and spring means apply a constant pressure onto the disc in its engagement with the valve seat.

9. A valve seat lapping device substantially as hereinbefore described with reference to the accompanying drawings.

10. A method of lapping the valve seat(s) of a valve substantially as hereinbefore described with reference to the accompanying drawings.