Background The invention can has extensive application to reciprocating pumps and has a particular application for use with reciprocating pumps used on oil derricks. In such derricks a stuffing box is provided at the top end of the oil well to accommodate a reciprocating shaft which has a fairly long stroke. The reciprocating shaft of the pump is attached at one end to the well stringer pipe or rod which is attached to the pump piston. The other end of the reciprocating rod is flexibly connected to a mechanical drive comprising two counter balanced arms which convert the rotational action of a drive motor to a partially linear motion. As a result of the motion conversion the other end of the reciprocating shaft moves in an arcuate path and consequently the reciprocating shaft is subjected to radial forces as it passes through the seal which must be accommodated for by the stuffing box to minimise the frictional forces which would otherwise result in excessive wear of the packing seal and reciprocating shaft.

An object of the invention is to provide a stuffing box with a means to ensure that the reciprocating shaft maintains a substantially linear motion in its travel through the seal of the stuffing box and to reduce the radial forces induced on the shaft whilst in engagement with the seal and thus reduce the frictional forces exerted on the reciprocating shaft as it moves through the seal.

Disclosure of the Invention Accordingly the present invention comprises a stuffing box adapted to slidingly and sealingly receive a reciprocating shaft extending from a housing, said stuffing box comprising a base adapted to be supported from the housing and configured to surround the shaft, a seal supported from the base and configured to be sealingly and slidably received over the shaft, a guide supported from the base in axially spaced relation from the seal and having a central axis which is aligned with the central axis of the seal, said guide being adapted to receive the shaft and resist radial displacement of the shaft from the central axis whilst the shaft is in engagement with the guide.

According to a preferred feature of the invention the guide comprises a set of rollers which are angularly displaced around the central axis. According to one particular embodiment a set of four rollers are located an angularly equidistant intervals around the central axis. According to one embodiment the axes of rotation of the rollers are substantially coplanar. According to another embodiment the rollers comprise two pairs of diametrically opposed rollers and the pairs of diametrically opposed rollers of the guide are spaced axially.

According to further preferred feature of the invention the guide is located to each side of the seal.

The invention will be more fully understood in the light of the following description of several specific embodiment.

Brief Description of the Drawings The description is made with reference to the accompanying drawing of which: Figure 1 is a schematic part sectional view of a stuffing box according to the first embodiment: and

Figure 2 is a schematic part sectional view of a stuffing box according to the second embodiment.

Best Modes of Performing the invention The stuffing box according to the first embodiment as shown at Figure 1 comprises a base member 11 comprising a lower tubular portion 12 which is configured to be received over the upper end of a bore hole casing (not shown) A first plate member 13 is mounted to the upper end of the tubular portion 12 and has a central aperture 14 which is coaxial with the central axis of the casing and is dimensioned to receive the reciprocating shaft 10 (shown in broken lines) in a non-contact relationship.

The stuffing box of the first embodiment further comprises an second plate member 15 which is held in spaced relation from the lower plate member 13 by a tubular spacer 16. The second plate member 15 is also provided with a central aperture 18 which is c-axial with the central axis of the casing and is intended to receive and support a seal 17 which in turn is adapted to slidingly and sealingly receive the shaft 10. The seal 17 is of the form described in Australian patent specification AU-A-63788/98 and comprises a sealing element 19 which is supported from one end of a tubular boss 20 which is received in the aperture 17. The sealing element 19 is held in a state of axial and radial compression by means of an elastomeric sleeve 21 which is received over the sealing element between the ends thereof. In addition the sealing element 19 is held in a state of axial compression and the ends are restrained from relative rotational displacement by a coil spring 22. The support bush 20 is provided at its one end with a flange 24 and associated with a locking nut 23 which is threadably received over the bush 20 whereby the flange is located adjacent the face of the second plate member 15 proximate the casing and the locking nut is located adjacent the face of the intermediate plate remote from the casing in order that the locking nut 23 co-operates with the flange 24 to enable the support bush to be clampingly engaged and supported from the second plate member 15.

The stuffing box of the first embodiment further comprises a guide which comprises an third plate member 29 which is supported in spaced relation from the second plate member 15 by a plurality of spacer elements 24 located at four angularly equidistant intervals around the stuffing box. A set of clamping bolts 25 are received through the spacers and extend between the first plate member 13 and the third plate member 29 and serve to hold the upper, intermediate and lower plate members 29,15 and 13 together with the tubular spacer 16 between the first and second plate members and the spacer elements between the second and third plate members. The third plate member 29 is formed with a third central aperture 26 which is c-axial with the central axis of the casing and is dimensioned to receive the shaft 10 in a substantially non-contact relationship. As a result the central axis of the guide is c-axial with the central axis of the seal 19.

The third plate member 29 comprises a pair of plate portions 29a and 29b and the guide further comprises a set of four rollers 27 which are supported from between the plate portions. In this regard the rollers are supported from axles 28 which are received within mating recesses provided in opposed faces of the plate portions 29a and 29b. The rollers 27 are located such that their axes of rotation are co-planar, are perpendicular to each other and are spaced equidistant from the transverse to the central axis of the third opening 26. In addition the axes of rotation spaced radially equidistant from the central axis of the aperture 18 such that the rollers 27 define a space in which the shaft 10 is received. As a result of the positioning of the axles 28 the rollers comprise two pairs of rollers whereby the rollers of each pair are diametrically opposed and the spacing between each of the diametrically opposed pairs of rollers 27 corresponds to the external diameter of the shaft in order that the rollers will engage with the external surface of the shaft. If desired the external periphery of the rollers 27 are provided with tyres formed of a suitable resiliently compressive material which serves to enhance the frictional engagement of the rollers 27 with the shaft.

The function of the guide is to ensure that while the portion of the shaft beyond the guide may be caused to undergo some lateral displacement there is no lateral displacement of the shaft in the region of the guide and the seal. This controlling of the flexing of the shaft serves to reduce the lateral loadings which are applied to the seal by the shaft during its reciprocating movement through the seat and as a result serves to reduce the frictional losses created as a result of the movement of the shaft through the seal. This in turn serves to enhance the life of the seal and the reciprocating shaft.

In the case of the second embodiment as shown at Figure 2 it is generally of the same form as the first embodiment and therefore the reference numerals used in the description of the first embodiment are used for corresponding components in the description of the second embodiment.

In the case of the second embodiment the first plate member of the first embodiment is absent and the seal 17 is supported by a tubular housing 50 mounted at one end to the proximate face of the second plate member 15. The other end of the tubular housing 50 is provided with an inwardly extending flange 52 and the seal 17 is received between the flange 52 and the second plate member 15. In use of the second embodiment the second plate member 15 is sealingly fixed to the upper end of the bore hole casing (not shown).

According to a third embodiment the guide of the first and second embodiment may be located to each side of the seal to resist the tendency of the seal or the mounting of the stuffing box to the housing from becoming a fulcrum.

According to a further embodiment the pairs of diametrically opposed rollers of the guide are spaced axially.

Throughout this specification (including the claims if present), unless the context requires otherwise, the word"comprise", or variations such as"comprises"or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. It should be appreciated that the scope of the present invention need not be limited to the particular scope of the embodiment described above.