WO2003056217A1

WO2003056217A1 - External mechanical seals for rotating equipment

Info

Publication number: WO2003056217A1
Application number: PCT/CA2002/001966
Authority: WO
Inventors: Rammy A. Shellef
Original assignee: Enviroettem Innovations Ltd.
Priority date: 2001-12-31
Filing date: 2002-12-18
Publication date: 2003-07-10
Also published as: CA2366885A1; AU2002351595A1

Abstract

An annular spiral throat bushing (96) for use with rotating fluid equipment can be located at least partially withing the entrance to a seal cavity (16) of such equipment. The bushing has an annular body adapted for securement to the equipment housing (14) adjacent a seat member thereof. The bushing has an inner circumferential surface which in use is adjacent and spaced from a rotatable shaft (12) of the equipment, which surface has a spiral groove (100) formed therein, the hand thereof being the same as the direction of rotation of the shaft. During rotation of the shaft particulate material entrained in operating fluid within the cavity will be redirected towards the cavity by the spiral groove in the bushing and thus prevented from lingering at the interface between the seal face (38) of a rotating seal (36) member and a complementary face (92) of the seat member (90).

Description

EXTERNAL MECHANICAL SEALS FOR ROTATING EQUIPMENT

FIELD OF THE INVENTION

The present invention relates in general to rotating fluid processing equipment and in particular to arrangements for improving the wear characteristics of external mechanical seals utilized with such equipment.

BACKGROUND OF THE INVENTION

External mechanical seals are often the preferred type of seals for sealing rotating processing equipment for corrosive fluids, because no metal parts of the seal come in contact with the fluid. On the other hand, the sensitivity of such seals to abrasive particles held in a slurry is very high because the seals contain the fluid at their internal diameter and the particles within the fluid tend to centrifuge outwardly and erode the seal faces. Since most industrial process fluids contain particles to some degree, this sensitivity is a significant factor in determining the service life of the seal.

U.S. Patents Nos. 5,553,868 and 6,167,418 as well as others describe stationary devices for the removal of solids (particulate material) from seal cavities or chambers of rotating equipment for extending the life of either internal mechanical seals or internal packing. These devices are placed at the bottom of the seal chamber and basically separate the seal chamber and the inside of the pump (the "process side") into two regions, one containing particulate material and one free of such material.

With such devices, the removal of particulate material is accomplished by means of specific flow regimes developed within the seal cavity or chamber due to the geometry of the devices in cooperation with shaft rotation. Such devices utilize at least one spiral groove in a face surface facing inwardly of the seal cavity to control the removal of particulate material from within the seal cavity through a small annular gap between the device and the rotating shaft. These devices are not intended for use with external seals because the flow created by the spiral groove(s) cannot remove particles from the narrow gap within the internal diameter of the external seal.

SUMMARY OF THE INVENTION

The present invention is intended to improve the wear characteristics of external mechanical seals used with rotating fluid processing equipment, especially with such equipment that develops potentially damaging particulate material during the operation thereof, which material could damage the rotating seal at the interface thereof with a stationary seal or seat member. The invention utilizes the principles exhibited by the internal spiral bushings disclosed in U. S. Patent No. 5,553,868 and applies those principles to a bushing that can be positioned at the entrance to the seal cavity, so that such a bushing will redirect particulate-containing operating fluid back towards the seal cavity and away from the seal interface established by the external mechanical seal of such equipment. By removing particulate material from the seal interface area the life of the mechanical seal components will be substantially extended, thereby reducing the operating cost of the equipment. Not only will the life of the seal components be extended by so will the operating life of the equipment, meaning that less will be expended on expensive repairs and downtime.

With the present invention the stationary seat member, against which the rotating seal member would normally abut in sealing engagement, is modified so as to accept a spiral throat bushing inboard thereof, but at the entrance to the seal cavity. The spiral throat bushing acts to remove the particulate material contained in the operating fluid from the interface area between the rotating and stationary seal components. The modified seat member and the spiral throat bushing occupy essentially the same volume as did the seat member prior to the introduction of the spiral throat bushing and hence no other major modifications to the equipment are required to convert such equipment and thereby reap the benefits of the invention. Depending on the operating fluid and the operating parameters of the equipment it may be possible to replace an existing stationary seat member with a new or modified seat member which incorporates therein the spiral groove or grooves that would be otherwise provided on a separate spiral throat bushing.

In summary of the foregoing the present invention may be generally considered to provide in one embodiment an arrangement for protecting rotating fluid equipment. Such equipment typically includes: a rotatable shaft; a housing surrounding at least a lengthwise portion of the shaft and defining with an outer surface of the shaft an annular seal cavity of outer diameter greater than that of the shaft; an annular stationary seat member at an outboard ambient end of the cavity, the seat member being mounted to the housing; and an annular rotating seal assembly secured to the shaft and including an annular seal member having a seal face biased into face-to-face sealing contact with a complementary face of the seat member. The arrangement of the invention comprises an annular spiral throat bushing member secured to the housing adjacent the seat member so as to be located at least partially within the cavity at the outboard end thereof. The bushing member has an inner circumferenetial surface adjacent and spaced from the shaft outer surface. The bushing member inner circumferential surface has a spiral groove therein , the hand of the groove being the same as the direction of rotation of the shaft. During rotation of the shaft particulate material entrained in operating fluid within the cavity will be redirected towards the cavity by the groove in the spiral bushing and thus prevented from lingering at the interface between the seal face of the rotating seal member and the complementary face of the seat member.

The invention may also be considered as providing an annular spiral throat bushing member for protecting rotating fluid equipment. Such equipment typically includes: a rotatable shaft; a housing surrounding at least a lengthwise portion of the shaft and defining with an outer cylindrical surface of the shaft an annular seal cavity of outer diameter greater than that of the shaft; an annular stationary seat member at an outboard ambient end of the cavity, the seat member being mounted to the housing; and an annular rotating seal assembly secured to the shaft outboard of the seat member and including an annular seal member having a seal face biased into face-to-face sealing contact with a complementary face of the seat member. The bushing member comprises a generally annular body adapted for securement to the housing adjacent the seat member so as to be located at least partially within the cavity at the outboard end thereof. The bushing member body has an inner circumferential surface which in use is adjacent and spaced from the shaft outer surface, and the bushing member inner circumferential surface has a spiral groove therein, the hand of said groove being the same as the direction of rotation of the shaft. During rotation of the shaft particulate material entrained in operating fluid within the cavity will be redirected towards the cavity by the groove in the spiral bushing member and thus prevented from lingering at the interface between the seal face of the rotating seal member and the complementary face of the seat member.

Additional aspects and features of the present invention will be described hereinbelow with reference to the drawings provided herewith.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates in partial cross section a first prior art external mechanical seal arrangement.

Figure 2 illustrates in partial cross section a second prior art external mechanical seal arrangement.

Figure 3 illustrates in partial cross section a first embodiment of the present invention, relating to an arrangement as found in Figure 1.

Figure 4 illustrates in partial cross section a second embodiment of the present invention, relating to an arrangement as found in Figure 1.

Figure 5 illustrates in partial cross section a third embodiment of the present invention, relating to an arrangement as found in Figure 1.

Figure 6 illustrates in partial cross section a fourth embodiment of the present invention, relating to an arrangement as found in Figure 1.

Figure 7 illustrates in partial cross section a fifth embodiment of the present invention, relating to an arrangement as found in Figure 2.

Figure 8 illustrates in partial cross section a sixth embodiment of the present invention.

Figure 9 illustrates in partial cross section a seventh embodiment of the present invention, relating to the embodiment of Figure 4.

Figure 10 illustrates in partial cross-section an eighth embodiment of the present invention, relating to the embodiment of Figure 3.

Figure 11 is a vertical cross section through a typical spiral bushing as used with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 illustrates a typical prior art seal arrangement as found in many types of rotating equipment and with respect to which the present invention represents an improvement. The arrangement 10 includes a rotating shaft 12 and a housing 14 surrounding a lengthwise portion of the shaft at the process or inboard side of the equipment. The housing helps to define an annular seal chamber 16 by way of a blind bore 18 having a diameter greater than that of the shaft 12. The bore 18 terminates at an annular bottom face 20 found on an inboard annular flange 22. A gland plate 24 abuts or is in close proximity to the outboard face of the housing and is secured thereto by gland nuts 26 arranged symmetrically around the gland plate. There is an annular gap between the gland plate 24 and the outboard face of the housing 14, which gap is filled by an annular seat member 28 and a pair of positioning washers 30, 30'. The washers may be formed of a resilient material and they serve to hold the seat member 28 in place relative to the housing and the gland plate 24 when the gland nuts 26 are tightened. Washer 30' in contact with housing 14 also acts as a sealing gasket. As can be seen from Figure 1 there is a narrow annular gap G between the inner circumferential surface of the seat member 28 and the outer cylindrical surface of the shaft 12. The seat member 28 is stationary relative to the shaft and it includes a radial, annular outboard seal face 32.

It should be noted that there are some situations in which the flange 22 is eliminated, resulting in so-called "open bore" seal chambers. The present invention can be used with such equipment as well.

A rotating seal assembly 34 is provided on the ambient or outboard side of the rotating equipment. This assembly includes a rotating seal member 36 which has a protruding annular portion 38, the inboard face of which is in sealing contact with a complementary outboard face 32 of the stationary seat member 28. There is an annular pocket 40 between the protruding annular portion 38 and the shaft 12 in which particulate material coming from the seal cavity 16 is trapped. The rotating seal member 36 is biased to its sealing position relative to the stationary seat member 28 by an intermediate annular member 42 and an outer wedge assembly 44. The intermediate member 42 includes a plurality of compression springs 46 spaced circumferentially thereabout, which springs bear against the seal member 36 and bias it towards the seat member 28. A plurality of circumferentially spaced drive pins 48 positioned radially outwardly of the springs 46 positively rotate the seal member 36. The outermost surface 50 of the intermediate member 42 abuts an annular wedge member 52 of the wedge assembly 44, which member has a sliding friction fit with the shaft 12. An annular clamp member 54 has an angled wedge surface 56 at its inner diameter, which surface mates with the angled radially outer surface 58 of the wedge member 52. A plurality of circumferentially spaced bolts 60 extend through the clamp member 54 and are threadedly received in the intermediate member 42. When the bolts are tightened the wedge effect between the annular surfaces 56, 58 will effectively clamp the rotating seal assembly 34 to the shaft 12 for rotation therewith.

The other style of seal arrangement that is part of the prior art and with respect to which the present invention represents an improvement is shown in Figure 2. The structure defining the seal cavity 16 is the same as is shown in Figure 1. The main difference lies in the rotating seal assembly, identified in this view by reference number 62. This is the so-called "bellows" arrangement.

The bellows type of rotating seal as shown in Figure 2 includes an annular seal member 64 which has an annular protruding seal face 66 and which is driven by circumferentially spaced threaded pins 70. The bellows member 68 has an inner end section 72 to which the seal member 64 is secured, an intermediate section 74 formed as a bellows to permit axial compression or movement, and an annular outer end section 76 which has a sliding friction fit with the outer surface of the shaft. As can be seen in Figure 2 particulate material from the seal cavity 16 can migrate to within the confines of the bellows member 68. A bifurcated annular clamp member 78 serves to clamp the outer annular end section 76 of the bellows member to the shaft for rotation therewith. An annular outer sleeve member 80 includes relatively slidable inner and outer sections 82, 84 which are biased apart in the axial direction by a plurality of circumferentially spaced apart compression springs 86. The inner section 82 of the sleeve member 80 abuts the inner end sections 72 of the bellows member 68 to apply an axially inwardly directed biasing force against the seal member 64 to in turn force the protruding seal face 66 against the stationary seal 28. An annular guide member 88 is positioned between the inner end of the inner section 82 and the seal member 64 to ensure that the seal member does not expand radially outwardly during rotation of the seal assembly 62. The present invention provides structure, based on the principles enunciated in the earlier-identified patents, which will deal with particulate material in the vicinity of the external seals of rotating equipment so as to reduce the wear and damage occasioned by such particulate material. In the following, several arrangements applicable to both types of external seal constructions will be described. Figures 3 to 6, 9 and 10 illustrate arrangements applicable to the rotating seal structure of Figure 1. Figure 7 illustrates an arrangement applicable to the bellows-type rotating seal structure of Figure 2. Figure 8 illustrates an arrangement which relates to that of Figure 1 but includes additional structure.

With regard to Figure 3 like reference numbers as found in Figure 1 are found in this figure, since the rotational seal assembly 34 is unchanged. Similarly, the shaft 12, housing 14 and gland plate 24 are unchanged. However, in order to better protect the rotational seal and the annular seat member, the latter is modified in accordance with this invention. The modified annular seat member carries reference number 90 and it will be seen that a portion thereof facing into the cavity 16 has been cut away. The seat member still presents a smooth face 92 to the protruding seal face 38 of the rotational seal member 36 and a flange portion 94 of the seat member still is adjacent one of the gland washers 30. The portion of the seat member that was cut away is replaced by an annular spiral throat bushing member 96 such that the overall external configuration of the original seat member 28 is essentially unchanged. The bushing member 96 is provided with an annular radial flange 98 that abuts the portion 94 of the seat member and also abuts the other gland washer 30. The bushing 96 has a spiral groove 100 in the inner circumferential surface thereof, which groove opens towards or faces the outer surface shaft 12 and serves to redirect fluid containing particulate material back towards the seal cavity, thereby reducing the amount of particulate material that would otherwise linger in the vicinity of the protruding seal face of the seal member 36. The operation of the grooved surface of a spiral throat bushing such as bushing 96 has been well documented in earlier patents, including US Patent No. 5,553,868 and need not be repeated here. Figure 11 has been provided however to illustrate a typical spiral throat bushing member as would be used with the present invention so that the reader will better appreciate the structure and principles of operation thereof. Such principles of operation will be utilized for the other arrangements as discussed hereinafter.

With the embodiment of Figure 3 it is possible to improve the operation of the rotating equipment at a minimum cost as there are no changes to the mechanical seal portion of the arrangement. It is only necessary to replace the standard annular seat member with the modified seat member and the grooved spiral bushing 98. This is thus the simplest arrangement of the present invention. This embodiment can remove particulate material along most of the axial length of the gap between the seat member and the shaft, and eliminates build-up of particulate material inside the seal's interface as long as the shaft rotates. The only drawback to this simple modification to the seat member is that particulate material that is trapped just inside the protruding rotating seal face 38 will stay there and continue to be centrifuged into the seal's interface during shaft rotation. With this modification the volume of particulate material is reduced at the interface; it is not eliminated completely.

Figure 4 illustrates another embodiment which utilizes a spiral throat bushing and which also addresses the drawback associated with the embodiment of Figure 3. In this embodiment the mechanical seal assembly is modified, as is the annular seat member. A spiral throat bushing 96 as described earlier with respect to Figure 3 can be used with this embodiment, the bushing having a spiral groove 100 cut in its inner surface facing the shaft 12.

With this embodiment the annular seal member 36 is modified from the Figure 1 configuration by removal therefrom of the protruding seal face portion 38, such that the modified seal member 102 presents an annular seal face 104 facing towards the seal cavity 16. The annular seat member 90 of Figure 3 is also modified such that it includes an annular protruding section 106 that extends away from the cavity 16. The seal face 104 extends radially inwardly to where it just clears the shaft, while the protruding section is radially spaced away from the shaft, defining a gap G_x between itself and the shaft. The inner surface 108 of the protruding section 106 converges slightly towards the shaft in the direction of the seal member 102. With this embodiment fluid carrying particulate material will circulate in the gaps G and G_t under the influence of the spiral groove 100 in the bushing 96 and will not become trapped at the interface between the seal face 104 and the end face of the protruding seat member section 106. Any particulate material that lingers within the gap when the equipment is shut down will be circulated out of the interface zone when the shaft 12 starts rotating again once the equipment restarts.

In the embodiment of Figure 5 the annular seat member 110 is axially truncated so that its outboard radial end face is essentially coplanar with the outer surface of the gland plate 24. The annular bushing member 112 is similar to that of Figure 4 in that it is clamped, along with the seat member 110, in position by the gland plate 24 and the gland washers 30, 30'. In this embodiment the bushing member includes an annular outer extension 114 that mates with the inner circumferential surface 116 of the seat member 110 and extends beyond the seat member such that its outer radial surface 118 is in sealing engagement with the annular seal surface 104 of the seal member 102.

The bushing 112 has a spiral groove 120 cut in the inner surface thereof facing the shaft, the inner surface, and hence the groove, tapering slightly towards the shaft in the direction away from the cavity 16. Particulate material suspended in operating fluid within the cavity 16 will flow through the gap between the bushing member and the shaft and will be redirected back to the cavity by the spiral groove 120 such that there will be little or no particulate material lingering at the interface between the stationary and rotating components of the mechanical seal.

Figure 6 shows a modification of the embodiment according to Figure 4. This embodiment would be highly effective for removal of particulate material in highly concentrated slurries where lubrication of the seal interface becomes marginal and yet the presence of liquid lubricant must be always ensured. In this case the gland plate has been modified so that it is fitted with an inlet 122, connectable to a source of lubricant under pressure. The inlet 122 connects via a passageway 124 with an annular space 126 that is radially outward of the outer cylindrical surface defined by the outer cylindrical surfaces of the seat member 90, the bushing 96, and the gland washers 30. A plurality of circumferentially spaced apart through holes connect the space 126 with the gaps G and Gi between the bushing 96 and the seat member 90 respectively and the shaft 12. The holes can be directed radially through the components; they can be directed tangentially; or they can be directed at any other angle that ensures good lubricant flow to the gaps. The pressurized lubricant will find its way to the seal interface for effective lubrication thereof.

The embodiment of Figure 7 takes the features of the bushing of Figure 5 and applies them to the bellows type of arrangement as shown in Figure 2. Thus, the bellows type of rotating seal assembly 62 will cooperate with a seat memberllO and a spiral throat bushing 112 having a spiral groove 120 therein to effect removal of particulate matter within the operating fluid from the interface area between the rotating seal face 128 and the radial end face 118 of the bushing 112.

The embodiment of Figure 8 is similar to that of Figure 4, utilizing as it does a spiral throat bushing 96 which cooperates with a seat member having a protruding section 106 against which the seal face 104 of a rotating seal member 102 abuts in a sealing fashion. In this embodiment the mechanical seal assembly 130 comprises a dual "back-to-back" arrangement.

Rotating with the shaft 12 is a pair of identical intermediate clamping members 132 which are arranged on the shaft back to back. Each intermediate member has a plurality of axially directed blind bores 134, each of which will receive a compression spring 136. The compression springs 136 bear against the back face of opposing seal members 102, 138, pushing them away from the intermediate members. A plurality of circumferentially spaced apart drive pins 140 extend through the intermediate members and the seal members to ensure that the seal members are positively driven with the shaft. The rotating seal memberl02 is in sealing engagement with the stationary seat member 90 as previously described, while the rotating seal memberl38 is in sealing engagement with a stationary seat member 141 at the atmospheric side of the equipment. The stationary seat member 141 is held in position by surrounding gland plates 142, 144 which are secured to the stationary housing 14 by a plurality of circumferentially spaced apart clamping bolts 146. An annular o-ring 148 is located between the mating end faces of the gland plates 142, 144 to prevent any egress of buffer fluid from the confines of the seal assembly.

With the embodiment of Figure 8 the spiral throat bushing 96 will effectively remove particulate material via the spiral groove 100 from within the seal interface defined by the seal face 104 and the end face of the protruding section 106 of the stationary seat member 90, while the seal 138 on the atmospheric side operates as a conventional internal seal, containing the particulates-free fluid in the buffer zone between the seals.

Depending on the nature of the fluid material and the particulate material contained within the cavity 16 it would be possible to form the seat member and the bushing as a single component, i.e. from a single piece of material. If the material within the cavity would be deleterious to the normal seat member material then a bushing milled from a different, resistant, material would have to be used. Reinforced TEFLON™ would normally be a satisfactory material for bushings used in all embodiments of the present invention. This embodiment is illustrated in Figure 9 wherein the integrated seat member and bushing is shown by reference number 150. Otherwise the embodiment is as shown in Figure 4. . Figure 10 illustrates an embodiment which is a particular derivative of the embodiment shown in Figure 3. As seen in Figure 3 the sealing end face 38 of the seal member 36 has an inner diameter that is greater than the inner diameter of the section of the seat member 90 against which the sealing end face abuts. There are certain situations which do not allow such an arrangement to be incorporated in the rotating equipment, whether for "political" or other reasons, as for example concern that too much particulate material may still linger at the interface between the seal face 38 and the stationary seat member. In such instances the problem can be reduced by having the inner diameter of the section of the seat member 152 against which the end face 154 abuts be the same as the inner diameter of the end face 154. This match of diameters will theoretically eliminate particulate material from being trapped at the interface. While matching of the diameters will represent an improvement over the embodiment of Figure 3 there is a possibility that due to naturally occurring eccentricity between the rotating and stationary elements, there will always be some slight mismatch of diameters and hence it becomes impossible to completely eliminate particulate material from the interface. A second drawback is that this is a non-standard sealing assembly and thus extra machining and cost will be encountered as an attempt is made to match the diameters of the rotating and stationary elements.

Figure 11 illustrates in vertical cross section a typical spiral throat bushing as used with the present invention. It should be understood that all of the spiral throat bushings used in the various embodiments are based on the same principles of operation and will share generally the same structural features, modified as required to permit the bushing to fit into the specific environments of such embodiments. The general principles of operation of the spiral throat bushing are as described in US Patent No. 5,553,868 and are incorporated by reference herein.

The spiral throat bushing 156 is annular in overall configuration, having a first outer circumferential surface 158 that is received within the stationary housing 14 and against which the inner circumferential surface of the inboard gland washer 30' will abut. An intermediate radially outwardly extending flange 160 will abut the outboard side of the inboard gland washer 30' as well as the inboard end face of the annular stationary seat member 110(as for example in the embodiment of Figure 5). The bushing 156 has a second outer circumferential surface 162 that is received within and mates with the inner circumferential surface of the seat member 110.

The inner circumferential surface 164 of the bushing 156 is milled or cut so that it is provided with a spiral groove 1166 that extends axially of the bushing. The hand of the groove 166 is the same as the direction of rotation of the shaft 12 so that operating fluid and the particulate material contained therein will be directed "rearwardly" of the shaft by the groove 166. As the operating fluid is flung outwardly of the shaft by centrifugal forces operating thereon the fluid will enter the groove and be forced to follow the groove back towards the seal cavity, thereby keeping the particulate-containing material away from the rotating seal interface and allowing only particulate-free fluid to lubricate the seal faces.

The foregoing has described several arrangements for improving the life and operating effectiveness of external mechanical seals in rotating fluid equipment, based on the principle of removing particulate material from the seal interface using a spiral throat bushing that redirects particulate-containing operating fluid away from the interface. It is expected that other arrangements and variations based on the present invention may be equally viable and may occur to a skilled person in the art. Accordingly the protection to be afforded this invention is to be determined from the scope of the claims appended hereto.

Claims

1. An arrangement for protecting rotating fluid equipment, which equipment includes: a rotatable shaft; a housing surrounding at least a lengthwise portion of said shaft and defining with an outer surface of said shaft an annular seal cavity of outer diameter greater than that of the shaft; an annular stationary seat member at an outboard ambient end of said cavity, said seat member being mounted to said housing and defining an annular gap between an inner annular surface thereof and said outer surface of said shaft; and an annular rotating seal assembly secured to said shaft and including an annular seal member having a seal face biased into face-to-face sealing contact with a complementary face of said seat member; said arrangement comprising: an annular spiral throat bushing member secured to said housing adjacent said seat member and inboard thereof so as to be located at least partially within said cavity at said outboard end thereof; said bushing member having an inner circumferential surface adjacent and spaced from said shaft outer surface; and said bushing member inner circumferential surface having a spiral groove therein, the hand of said groove being the same as the direction of rotation of said shaft, whereby during rotation of said shaft particulate material entrained in operating fluid within said cavity will be redirected towards said cavity by said groove in said spiral bushing and thus prevented from lingering at the interface between said seal face of said rotating seal member and said complementary face of said seat member.

2. The arrangement of claim 1 wherein said seal member seal face is at an inboard end of an annular section protruding from said seal member, and said complementary face of said seat member is on an outboard flange portion of said seat member and extends radially outwardly from said inner annular surface thereof, said bushing member interfitting with said seat member such that an outboard end of said bushing member abuts an inboard annular radial surface of said seat member, said groove extending from said outboard end of the bushing member towards the inboard end thereof.

3. The arrangement of claim 1 wherein said complementary face of said seat member is on an outboard end of an annular section protruding outwardly from a flange portion of said seat member, said bushing member interfitting with said seat member such that an outboard end of said bushing member abuts an inboard annular radial surface of said seat member, said groove extending from said outboard end of the bushing member towards the inboard end thereof.

4. The arrangement of claim 2 wherein the inner circumferential diameter of said seal member seal face is substantially the same as the inner circumferential diameter of said complementary face of said seat member.

5. An arrangement for protecting rotating fluid equipment, which equipment includes: a rotatable shaft; a housing surrounding at least a lengthwise portion of said shaft and defining with an outer surface of said shaft an annular seal cavity of outer diameter greater than that of the shaft; an annular stationary seat member at an outboard ambient end of said cavity, said seat member being mounted to said housing; and an annular rotating seal assembly secured to said shaft outboard of said seat member and including an annular seal member having a seal face; said arrangement comprising: an annular spiral throat bushing member secured to said housing within said seat member so as to be located at least partially within said cavity at said outboard end thereof; said bushing member having an inner circumferential surface adjacent and spaced from said shaft outer surface; said bushing member including an annular sealing face at an outboard end thereof against which said seal member seal face is biased; and said bushing member inner circumferential surface having a spiral groove therein, the hand of said groove being the same as the direction of rotation of said shaft, whereby during rotation of said shaft particulate material entrained in operating fluid within said cavity will be redirected towards said cavity by said groove in said spiral bushing and thus prevented from lingering at the interface between said seal face of said rotating seal member and said sealing face of said bushing member.

6. The arrangement of claim 5 wherein said spiral groove in said bushing member extends from adjacent said annular sealing face towards the inboard end of said bushing member.

7. An arrangement for protecting rotating fluid equipment, which equipment includes: a rotatable shaft; a housing surrounding at least a lengthwise portion of said shaft and defining with an outer surface of said shaft an annular seal cavity of outer diameter greater than that of the shaft; an annular stationary seat member at an outboard ambient end of said cavity, said seat member being mounted to said housing and defining an annular gap between an inner circumferential surface thereof and said outer surface of said shaft; and an annular rotating seal assembly secured to said shaft outboard of said seat member and including an annular seal member having a seal face biased into face-to-face sealing contact with a complementary face of said seat member; said seat member inner circumferential surface having a spiral groove formed therein, the hand of said groove being the same as the direction of rotation of said shaft, whereby during rotation of said shaft particulate material entrained in operating fluid within said cavity will be redirected towards said cavity by said groove in said seat member and thus prevented from lingering at the interface between said seal face of said rotating seal member and said complementary face of said seat member.

8. An annular spiral throat bushing member for protecting rotating fluid equipment, which equipment includes: a rotatable shaft; a housing surrounding at least a lengthwise portion of said shaft and defining with an outer cylindrical surface of said shaft an annular seal cavity of outer diameter greater than that of the shaft; an annular stationary seat member at an outboard ambient end of said cavity, said seat member being mounted to said housing; and an annular rotating seal assembly secured to said shaft outboard of said seat member and including an annular seal member having a seal face; said bushing member comprising: a generally annular body adapted for securement to said housing adjacent said seat member so as to be located at least partially within said cavity at said outboard end thereof; said bushing member body having an inner circumferential surface adjacent and spaced from said shaft outer surface; and said bushing member body inner circumferential surface having a spiral groove therein, the hand of said groove being the same as the direction of rotation of said shaft, whereby during rotation of said shaft particulate material entrained in operating fluid within said cavity will be redirected towards said cavity by said groove in said spiral bushing member and thus prevented from lingering at the interface between said seal face of said rotating seal member and said complementary face of said seat member.

9. The throat bushing member of claim 8 wherein said bushing body includes an annular flange member extending radially outwardly thereof for axial abutment with a radial flange portion of said seat member, said flange member and said flange portion enabling securement of said seat member and said throat bushing member to said housing.

10. The throat bushing member of claim 8 wherein said bushing body includes a first outer circumferential surface inboard of said flange member which mates with an inner circumferential surface of said housing and a second outer circumferential surface outboard of said flange member which mates with an inner circumferential surface of said seat member.

11. The throat bushing member of claim 10 wherein said bushing body has an outboard end face which abuts an inboard surface of an outboard radial flange portion of said seat member, which flange portion defines said complementary face of said seat member.

12. The throat bushing member of claim 11 wherein the diameter of said body inner circumferential surface at said outboard end is substantially the same as the inner diameter of said seat member outboard flange portion and is also substantially the same as the inner diameter of said seal face of said seal member.

13. An annular spiral throat bushing member for protecting rotating fluid equipment, which equipment includes: a rotatable shaft; a housing surrounding at least a lengthwise portion of said shaft and defining with an outer cylindrical surface of said shaft an annular seal cavity of outer diameter greater than that of the shaft; an annular stationary seat member at an outboard ambient end of said cavity, said seat member being mounted to said housing; and an annular rotating seal assembly secured to said shaft outboard of said seat member and including an annular seal member having a seal face; said bushing member comprising : a generally annular body adapted for securement to said housing within said seat member so as to be located at least partially within said cavity at said outboard end thereof; said bushing member body having an inner circumferential surface adjacent and spaced from said shaft outer surface; said bushing member body including an annular sealing face at an outboard end thereof against which said seal member seal face is biased; and said bushing member body inner circumferential surface having a spiral groove therein, the hand of said groove being the same as the direction of rotation of said shaft, whereby during rotation of said shaft particulate material entrained in operating fluid within said cavity will be redirected towards said cavity by said groove in said spiral bushing member and thus prevented from lingering at the interface between said seal face of said rotating seal member and said sealing face of said bushing member body.