BACKGROUND OF THE INVENTION Mechanical rotary seals known in the art may be classified into single rotary seals, and dual rotary seals. Single rotary seals have a single sealing unit having respective stationary and rotary sealing elements defining between respective abutting, lapped surfaces thereof a seal. Dual rotary seals, which include tandem seals and double seals, have a pair of sealing units. These seals thus have a degree of redundancy, and are thus less susceptible to total failure.

Various known types of sealing systems are exemplified in the following patents.

A system with a single rotary end face seal is described in US 4, « 8, 82 1, in which a rotary seal element and an end plate stationary seal element form a running seal at faces thereof. A surrogate lip-seal is also provided and, optionally, a channel may exist between the rotary seal and the surrogate seal for passing a buffer liquid, which cools and cleans the sliding faces of the rotary seal.

A system having a double rotary seal is described in US 4,560,173, in which buffer or cooling liquid is pumped into a space formed between rotary seals.

US 4,466,619 describes a double mechanical seal assembly with an integral pumping device. The pumping device includes a shaft sleeve acting as a pumping rotor, and also a surrounding seal stator provided with supply and discharge ports. Due to rotation of the shaft, the described pumping structure pumps and circulates buffer or cooling liquid through a buffer chamber. It should be noted that such a construction is relatively complex and does not provide adequate differential pressure to maintain the required circulation of the buffer liquid through the seal cavity.

US 3,608,910 describes a sealing system having a rotary seal unit in combination with an impeller, formed by a part of a flange rotatable with a main shaft. The impeller

serves tO : : CU fe a coolill. md lubricating liquid in a cavity adjoining the seal and is capable or returning the fluid to an outer source. An auxiliary pump is provided for pumping the flui, 2 into the cavity from the source. Such a construction is actually a single rotary seal, just b-ing provided with means for cooling and lubrication of its elements.

US Re. 34319, entitled"Dynamic Seal Arrangement For Impeller Pump,"teaches a dynamic seal arrangement for a pump which has a main impeller rotating in a main impeller cavity for pumping slurry to an outlet region. The seal arrangement comprises a rotary seal ! unit and a dynamic seal, provided by an expeller impeller. The latter is mounted coaxially with the main impeller and positioned in a separate cavity in flow communication with the main impeller cavity. During operation of the pump the expeller impeller prevents movement of the slurry from the main impeller cavity towards the rotary seal unit. Thus, when the pump operates, the rotary seal unit is disconnected so that the expeller impeller alone, seals the pump.

Although it is simpler than the single seal system of US 3,608,910, the above-described dynamic seal arrangement has several disadvantages. For example, when used with a slurry having abrasive particles, there occurs a'hang-up'of the rotary seal after a time, eventually leading to leakage and, in some cases, to total failure of the outer seal.

Furthermore, the counter-flow action of the expeller impeller requires a high consumption of energy.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an arrangement for sealing a pump shaft, having a novel, hybrid seal system, and which overcomes disadvantages of known art.

There is thus provided, in accordance with a preferred embodiment of the invention, an arrangement for sealing the rotatable pump shaft of a main pump having a housing, and a pump chamber containing a working fluid, wherein the sealing arrangement includes a stationary support arrangement mounted in association with the housing, and a hybrid seal system mounted between the stationary support arrangement and the housing, for sealing therebetween.

The hybrid seal system includes a rotary seal arrange between the stationary support arrangement and the rotatable shaft member for sealing therebetween, and a dual-purpose pump arrange between the stationary support arrangement and the rotatable shaft member for pumping a buffer liquid therebetween, in association with the rotary seal.

The rotary seal and the pump are configured, together with the stationary support arrangement and the rotatable shaft member, to form between the rotary seal and the pump a generally annular liquid chamber surrounding the rotatable shaft member. Furthermore, the dual-purpose pump is operative to pump the buffer liquid through the annular chamber in cooling and cleaning association with the rotary seal, and so as to also constitute a dynamic seal, operative to substantially prevent leakage of the working fluid to the exterior of the main pump housing in the event of failure of the rotary seal.

Additionally in accordance with a preferred embodiment of the present invention, the dual purpose pump is a regenerative pump.

Further in accordance with a preferred embodiment of the present invention, the stationary support arrangement has formed therein an impeller cavity communicating with a liquid intake associable with a supply of liquid, and further has formed therein, in liquid communication with the annular liquid chamber, a liquid outlet ; and the pump is mounted onto the shaft member and is rotatable therewith in the impeller cavity so as to cause an intake of buffer liquid via the liquid intake, and a subsequent circulation of the liquid within the annular liquid chamber in operative association with the rotary seal, there subsequently occurring a discharge of the buffer liquid through the liquid outlet.

Additionally in accordance with a preferred embodiment of the present invention, the regenerative pump is a regenerative side channel pump.

Alternatively, the regenerative pump may be a peripheral pump having blades immersed in the buffer liquid.

Further in accordance with a preferred embodiment of the present invention, wherein the supply of liquid includes a liquid reservoir.

Additionally in accordance with a preferred embodiment of the present invention, the shaft member of the main pump has a generally horizontal orientation, and the level of the buffer liquid in the reservoir is lower than the level of the shaft.

Further in accordance with a preferred embodiment of the present invention, the shaft member of the main pump has a generally vertical orientation, and the upper level of the buffer liquid in the reservoir is not lower than an uppermost wall of the impeller cavitv.

Additionally in accordance with a preferred embodiment of the present invention, the reservoir is provided with apparatus for maintaining therein at least a predetermined liquidlevel.

Preferably, there is provided closed-circuit apparatus for recycling buffer liquid, which includes a liquid reservoir for buffer liquid, a liquid supply conduit for conveying liquid from the reservoir to the liquid intake, a liquid return conduit for conveying liquid from the liquid outlet to the reservoir, and a filter for filtering returned buffer liquid.

Additionally, there may also be provided a sprayer nozzle for spraying the returned buffer liquid onto the filter, subsequent to which the filtered buffer liquid trickles into the reservoir.

Owing to the described arrangement the rotary sealing system has the avantage of the simplicity of a single mechanical seal, while having the reliability normally associated with a double mechanical seal. Replacement of an outer conventional sealing unit with a dynamic seal that simultaneously serves to pump the buffer liquid renders the hybrid system of the invention simple, effective and safe.

Moreover, in the case of failure of the inner seal, the hybrid seal system of the invention will remain workable for a considerable period of time, while providing an indication of the failure of the inner seal, and repair thereof. A process of gradual contamination of the buffer liquid with a pulp pumped by the main centrifugal pump will readily serve for visual indication of the breakdown which has occurred.

BRIEF DESCRIPTION OF THE DRAWINGS : The present invention will be more fully understood and appreciated form the following detailed description, taken in conjunction with the drawings, in which : Fig. 1A is a schematic cross-sectional view of an arrangement for sealing a pump shaft employing a hybrid seal system, constructed and operative in accordance with a preferred embodiment of the invention, and including a side channel regenerative pump, Figs. IB and 1C are partially cut-away isometric views of the hybrid seal system seen in Fig. I A, taken in the directions of arrows B and C therein, respectively; Fig. 2 is a schematic cross-sectional view of an arrangement for sealing a pump shaft having a hybrid seal system constructed and operative in accordance with an alternative embodiment of the invention, having a peripheral regenerative pump and an autonomous buffer liquid reservoir associated therewith, and mounted onto a main shaft having a generally horizontal orientation, Fig. 3 is a plan view of the buffer liquid reservoir seen in Fig. 2. with a cover thereof removed. taken in the direction of arrow 3 therein ; and Fig. 4 is a schematic cross-sectional view of a system similar to that of Fig. 2, but wherein the seal system is mounted onto a main shaft having a generally vertical orientation.

DETAILED DESCRIPTION OF THE INVENTION Referring now to Fig. 1A, there is seen an arrangement for sealing a pump shaft, referenced generally 10. Arrangement 10 employs a hybrid seal system, referenced generally 11, constructed and operative in accordance with a preferred embodiment of the present invention. Arrangement 10 includes a rotatable main pump shaft 12, a stationary support arrangement 16, a cylindrical mounting sleeve 14 mounted onto the shaft 12 for rotation therewith, as well as seal system 11. Arrangement 16 includes a plurality of suitably arranged and sealed metal pieces which form, both thereamong, and together with sleeve 14, various passages and chambers which are described hereinbelow.

: lin sha :'is issociated with a main centrifugal pump, which has a housing 20, a pump. ^ mber. on. inino a working fluid. such as a slurry or pulp, and having a <BR> <BR> <BR> <BR> rotatable main sh. ! 2 extending through a side wall of the housing 20. Hybrid seal system 11 is provided so to prevent leakage of the working fluid to the exterior of the pump.

Referring"w also to Figs. I B and 1 C, hybrid seal system 11 is formed of a rotary, inner seal, referençed generally 22 ; and a dual-purpose pump 30, functioning both as a dynamic seal, and also so as to cool and clean rotary seal 22, as described hereinbelow in more detail.

Rotary seal 22 is of any suitable, known construction, having a first, fixed plate, referenced 24, held in position by a retaining ring 25 disposed between arrangement 16 and sleeve 14. Seal 22 also has a second, rotary plate 26 which is attache, as seen, to a forward flange portion 27 of sleeve 14, so as to rotate therewith. Fixed plate 24 and rotary plate 26 have mutually facing, lapped surfaces which are juxtaposed along a common interface 29.

In operation, rotary plate 26 rotates with respect to fixed plate 24, such that the lapped surfaces thereof slide over each other, thereby providing a rotary seal along interface 29, so as to substantially prevent leakage of the pulp therealong. A plate spring 28 is provided so as to bias fixed plate 24 against rotary plate 26, so as to maintain tight contact between the lapped surfaces thereof In order to prevent early wear of the inner rotary seal 22, cleaning and cooling of the sliding surfaces is required.

In accordance with a preferred embodiment of the invention, pump 30, which preferably is a side channel regenerative pump functioning both as a dynamic seal and as a means of cooling and cleaning rotary seal 22. Pump 30 is fixedly mounted onto seal mounting sleeve 14, and is operative to pump a buffer liquid from an external source (not shown), as shown by arrow 130 (Fig. 1 A), through an intake passage 31 (Figs. 1 A and 1B) and an impeller cavity 32. The buffer liquid is supplied to a generally annular sealing chamber 34 (Fig. 1A) which extends generally along seal mounting sleeve 14, and between the rotary seal 22 and the regenerative pump 30. The buffer liquid enters sealing chamber via a channel 38 which communicates with impeller cavity 32, and a cavity 128 (Fig. 1A) which serves to house plate spring 28. As seen, plate spring 28 has openings 129 (Figs. 1A

and 1C) formed therein, so as to permit liquid communication between cavity 128 and sealing chamber 34. An outlet 39 is provided in liquid flow communication with plate spring housing cavity 128 so as to enable discharge of buffer liquid, thereby enabling refreshin of the supply of buffer liquid to the sealing chamber 34.

The flow of buffer liquid to sealing chamber and in thermally conductive contact with rotary seal 22 serves to clean, cool and lubricate the sliding surfaces thereof Additionally, however, the swirling flow of the buffer liquid created by vanes 36 of pump 30 through the annular sealing chamber 34, also serves as a dynamic seal, which is operative to prevent pulp leakage to the exterior of pump 20, in the event that rotary seal 22 fails. The sealing chamber 34 is also provided with an outlet passage 39 for discharging the used buffer liquid.

Referring now to Fig. 2, there is seen a sealed pump shaft arrangement, referenced generally 40, which incorporates a hybrid seal system, referenced generally 41, constructed an operative in accordance with an alternative embodiment of the invention.

System 41 is generally similar to system 11, shown and described above in conjunction with Figs. IA-IC, and is thus only described herein with respect to differences therebetween. Similarly, like components are denoted in Fig. 2 with like reference numerals.

It is thus seen that system 41 is used in association with a horizontal rotary shaft member 12 which is rotatable with a main pump 20, there being provided a rotary seal 22 for sealing pulp cavity 18, and a dual-purpose pump 46, functioning both as a dynamic seal, and also so as to cool and clean rotary seal 22. In accordance with the present embodiment, pump 46 is a peripheral regenerative pump.

The peripheral regenerative pump 46 is rotatable in a suitable impeller cavity 52, similar to impeller cavity 32 (Figs. lA-1C), and liquid communication between the impeller cavity 52 and sealing chamber 34, for purposes of cooling, lubricating and cleaning, as well as dynamic sealing, is provided generally as shown and described above in conjunction with the embodiment of Figs. 1 A-1 C.

The seal system 41 is provided with an autonomous, closed-circuit, buffer liquid recycling apparatus, referenced generally 60, a plan view of which is seen in Fig. 3. A particular advantage of recycling apparatus 60 is that it obviates much of the maintenance

traditionally associated with centrifugal pumps and rotary seals known to be cooled and cleaned thereby, due to the inherent simplicity and relatively small dimensions of the present system.

Recycling apparatus 60 includes a liquid reservoir 62, to which a suitable buffer liquid, such as, water, is gradually supplied, preferably from an autonomous supply such as a bottle 64, which is provided to as to ensure maintenance of at least a predetermined level of buffer liquid. Bottle 64 is mounted over reservoir 62 as by means of a bridge support 65.

Reservoir 62 has a liquid exit port 61 which communicates with a liquid intake 63 associated with impeller cavity 52 of pump 46, via an intake conduit 66. A return liquid flow is provided between outlet 39 and a liquid return port 67 provided in apparatus 60, via return conduit 69. In view of the fact that the return liquid may have various contaminants therein, the return liquid is preferably filtered prior to being returned to reservoir 62, as by means of a filter shown schematically at 72. Typically, filter 72 is provided by a corrugated sheet of fabric or the like for retaining solid particles from the discharged buffer liquid, although any suitable alternative filter construction may be used.

In accordance with the present embodiment of the invention, it is seen that the level of the buffer liquid, indicated at 75, in reservoir 62, is maintained below the level of horizontal shaft 12. In operation, the regenerative pump 46 continuously sucks buffer liquid from the reservoir 62 via the duct 66 and pumps it from impeller cavity 32 to annular sealing chamber 34, where the liquid cools, cleans and lubricates the sliding faces of rotary seal 22.

It will be appreciated by persons skilled in the art that the liquid is forced through the annular sealing chamber 34 and other channels communicating therewith as a vortex, thereby to provide a dynamic seal. Furthermore, owing to the vortex flow of the buffer liquid, the buffer liquid is discharged solely through the outlet 39 which is connected to the pipe 69. As the pressure in the dynamic seal is greater than atmospheric pressure, the buffer liquid is sprayed from a nozzle 68 which is preferably mounted onto liquid return port 67, onto the filter 72. The liquid trickles through filter 72 back to reservoir 62, being generally cleaned. A certain cooling of the liquid also occurs during this time. It has been found by

the Inventor that any impurities remaining in the filtered liquid form a sediment at the bottom of reservoir 62, and do thus not substantially affect functioning of the system.

Referring now to Fig. 4, there is seen a sealed pump shaft arrangement, referenced generally 70, which incorporates a hybrid seal system, referenced generally 71, which is generally similar to system 41, shown and described above in conjunction with Fig. 2 and is thus only described herein with respect to differences therebetween. Similarly, like components are denoted in Fig. 4 with like reference numerals.

The principal difference between system 71 and system 41 (Fig. 2), is that, whereas system 41 is used in association with a horizontal rotary shaft member 12, system 71 is used in association with a generally vertical shaft member 12'.

Accordingly, it is preferred that the level 75 of the buffer liquid in the reservoir 62 is above the level of the uppermost wall of impeller cavity 52, such that blades 47 of pump 46 are immersed in the buffer liquid at all times. lt will be appreciated by persons skilled in the art that the scope of the present invention is not limited by what has been shown and described hereinabove. Rather, the scope of the present invention is limited solely by the claims, which follow.