This invention relates to a sealing arrangement for a bearing which mounts a rotary shaft extending into a housing, the sealing arrangement being intended to prevent contaminant entering into the bearing from the exterior of the housing.

An application for the sealing arrangement exists in a centrifugal pump in which the shaft mounts a rotor having a back plate which runs in close proximity to the housing, the back plate carrying blades which upon rotation of the shaft deliver liquid under pressure to an outlet defined by the housing. The liquid under pressure can seep into the space defined between the housing and the back plate and if unchecked could pass into the bearing. There are other applications for the sealing arrangement for example the shaft could extend from a housing and be connected to a drive motor.

In order to prevent ingress of liquid which may contain suspended solids in the first application above and dirt and possibly liquid in the second application, a shaft seal is employed and this may have a number of forms depending upon the nature of the liquid and the shaft speed. All shaft seals have a limited life which is not always predictable so that for example a new seal may fail after a few hours operation whereas a similar seal may last for many hours. In many instances it is not possible to inspect the seal and the first indication of seal failure may be play or failure of the bearing requiring the replacement of the seal and the bearing and the possible repair of parts damaged as a result of the bearing damage.

The object of the present invention is to provide a sealing arrangement for the purpose specified in a simple and convenient form.

According to the invention a sealing arrangement for the purpose specified comprises first and second seals located between the bearing and the exterior of the housing, and positioned one behind the other between the shaft and housing, the seals forming with the shaft and housing an annular space, reservoir means for supplying lubricant to said space and further means for providing an indication in the event that the volume of lubricant in said reservoir means varies by more than a predetermined amount.

An example of a bearing arrangement in accordance with the invention will now be described with reference to the accompanying drawings in which:-

Figure 1 shows in sectional side elevation, one half of a centrifugal pump,

Figure 2 shows to an enlarged scale a part of the pump seen in Figure 1,

Figure 3 shows to a further enlarged scale a part of the pump seen in Figure 1.

Figure 4 is diagrammatic representation of certain portions of the pump seen in Figure 1.

Referring to Figure 1 of the drawings the pump comprises a shaft 10 which is mounted by a pair of spaced bearings 11, 12 in a bearing housing generally indicated at 13. The bearing housing is of annular form including a

base member 14 which locates the bearing 11 and a hollow truncated part 15 which carries the bearing 12. The shaft extends through the housing and at the upper end the housing carries a conventional lip seal 16 forming a seal with the shaft to prevent ingress of dirt into the bearing 12 and the interior of the housing. A more complex seal assembly 17 is provided to prevent ingress of liquid and dirt into the bearing 11 and housing and this will be described later with reference to Figure 2.

Secured to a support flange 18 formed integrally with the base member 14 of the bearing housing is the inner rim of an outlet volute 19 to which is connected the pump outlet. The outer rim of the outlet volute is secured to an outer annular casing 20 which extends towards the axis of the shaft. Welded -to the lower and inner end of the casing is a hollow cylindrical part 21 to which is secured an annular outwardly extending mounting flange 22. Stiffening plates 23 are located at angularly spaced positions about the axis of the pump to prevent any relative movement of the casing 20, the cylindrical part 21 and the flange 22.

Secured to the underside of the base member 14 of the bearing housing 13 is an annular member 24 of generally triangular section and this forms with part of the outer surface of the base member 14 an outwardly inclined flat surface 25. The surface 25 leads onto a further inclined surface 26 defined by the base member 14 and this leads onto a further inclined surface 27 also on the base member. The surfaces 25 and 27 are substantially parallel and the surfaces 25 and 26 form a recess in which is located a first rotor part 28 of a rotor assembly carried by the shaft. The first rotor part 28 defines an inner surface 29 which is located in

spaced relationship relative to the surfaces 25 and 26. The outer surface of the first rotor part defines with the inner surface of the casing 20 an annular outwardly extending flow passage which leads into the outlet volute 19. Mounted on the rotor part 28 is a plurality of blades 30 which extend within the flow passage towards the outlet volute and the blades are secured to the rotor part 28 in any convenient manner.

The rotor part 28 has a boss portion 31 and is secured to an impellor blade support 32 which carries a plurality of impellor blades 33. The impellor support 32 forms part of the rotor assembly and this also includes a second rotor part 34 having a boss portion 35. The rotor part 34 extends downwardly and outwardly and at its outer and lower end it supports a plurality of inlet blades 35 which are disposed substantially parallel to the axis of rotation of the shaft. The upper ends of the blades 35 are secured in a support ring 36 which is located in an annular recess formed in the undersurface of a fixed blade support 37 which is secured to the underside of the mounting flange 22. The support 37 carries at its inner edge a blade carrier 38 which extends generally at right angles to the support 37 and which locates against the inner surface of the cylindrical part 21. The inner surfaces of the support 37 together with the opposing surfaces of the rotor part 34 form an annular inwardly extending flow passage which leads into the aforesaid outwardly extending flow passage.

The support 37 carries fixed guide blades 39 which are positioned downstream of the inlet blades 35 and the carrier 38 carries fixed guide blades 40 which are positioned between the impellor blades 33 and the blades

30. As the rotor assembly is rotated liquid which may contain solids, is entrained by the blades 35 to induce a flow in the inwardly extending flow passage. The liquid is then directed by the impellor blades 33 into the outwardly extending flow passage and is then directed into the outlet volute 19 by the blades 30. The fixed blades 39 function to direct the liquid onto the impellor blades 33 and the fixed blades 40 ensure lamina flow of the liquid prior to entrainment by the blades 30. Fixed blades 35A may be provided upstream of the blades - 35 to guide the liquid onto the blades 35.

Figure 2 shows in greater detail the method of securing the rotor assembly together and its method of mounting on the shaft. Keys are provided between the boss 31 and the impellor blade support 32 and between the latter and the boss 35. Furthermore, the boss 35 is secured to the support 32 by bolts 41 and the boss 31 is secured to the support 32 by bolts 42. The boss 35 is secured to the shaft by means of proprietory retaining devices 43 which provide axial location of the rotor assembly as well as transmitting drive there between. Secured in the end of the shaft is a bolt 44 the underside of the head of which engages a thrust plate 45 which engage the boss 35. The purpose of the bolt is to facilitate the axial setting of the rotor assembly on the shaft prior to locking the retaining devices.

Turning now to the seal assembly 17. The purpose of the seal assembly is to prevent liquid which is forced into the gap between the surfaces 25 and 29 from reaching the bearing 11. The seal assembly comprises two metal to metal seals 46, 47 and a back up lip seal 48 the latter being positioned adjacent the bearing. The seals are in effect connected in series so that in order to

reach the bearing the liquid must force past the seals in turn.

Each metal to metal seal comprises a pair of metal rings of generally "L" section which are supported by resilient support members on "L" section backing rings respectively. The engaging surfaces of the metal rings are held in sealing engagement by the resilient support members. In the case of the seal 46 the one backing ring is located in a step defined in the boss 31 and the other backing ring is located in a recess formed in an annular support member 49 secured about the annular member 24. Mounted about the shaft 10 is a further annular support member 50 which is shaped to form a clearance 51 with the support member 49. The support member 50 at its lower end engages with the step in the boss and at its upper end forms a sleeve about the shaft for engagement by the sealing lip of the lip seal 48. The latter is pressed into a recess formed by a pair of spaced inwardly extending flanges on the member 24. The one backing ring of the seal 47 is located in a recess defined by the support member 50 and the other backing ring is located about the member 24 in contact with the adjacent flange thereof.

In operation the seal 46 will act to prevent liquid flow towards the bearing ^' 11 from the clearance between the surfaces 25 and 29. If this seal should fail the liquid will flow along the clearance 51 until it reaches the seal 47. If this should fail the lip seal 48 will act to provide temporary protection for the bearing.

It is necessary to lubricate the various seals and as will be described the lubrication system can be used to provide an indication of seal failure. However in

order to make the duty of the seals less arduous it is proposed to reduce so far as possible, the liquid pressure to which they are subjected, the liquid under pressure flowing along the gap between the surfaces 25 and 29.

This is achieved by providing at least one but preferably as shown, a plurality of passages 52 which extend from adjacent the upstream side of the seal 46 through the rotor assembly, the passages opening onto he under surface of the rotor part 34. The lower portions of the passages incline outwardly and may incorporate venturi inserts. As stated the effect of the passages 52 is to reduce the pressure of liquid applied to the seal 46.

Referring now to Figure 4 the seals are shown diagrammatically at 46, 47 and 48 and the aforementioned clearance at 51 and a space 55 defined between the seals

47 and 48. In order to lubricate and cool the seals, the clearance 51 and the space 55 are connected to lubricant reservoirs or tanks 56, 57 respectively. Each tank is connected by way of a first passage or pipe 58 which extends from a low level within the tank to the respective space and lubricant is conveyed away from the space to the respective tank by way of a second passage or pipe 59 which enters the tank at a high level. The first mentioned pipes 58 each incorporate a manually operable on/off valve 58A. With the valves 58A open and with the pump in use, lubricant from the respective tank will circulate through each of the clearance 51 and the space 55 by convection action and once the normal working temperature has been achieved the lubricant level in the tanks 56 and 57 will remain constant. The seals 47 and

48 are exposed to lubricant on both sides whereas the

seal 46 has lubricant on one side but is exposed to the reduced liquid pressure upstream of the seal on the other side. As already mentioned, the liquid pumped by the pump may be heavily contaminated with dirt and it is to be expected that the seal 46 will wear at a greater rate than the seals 47 and 48. When the seal 46 eventually fails contaminated liquid will enter the clearance 51. The seal 47 will therefore take over the main duty of protecting the bearing. However, since liquid can now flow into the clearance 51 the level of lubricant/liquid in the tank 56 will increase and a level sensor 60 can detect this increase to provide a visual or audible warning of failure of the seal 46. The pump however can continue to operate and it is reasonable to expect that the seal 47 will last at least as long as the seal 46. Eventually however the seal 47 will fail so the contaminated liquid now enters the space 55. The level of lubricant in the tank 57 will now start to increase and a further warning given. At this stage it would be prudent to stop the pump and to replace all the seals. However, the lip seal 47 can be relied upon to provide for continued operation of the pump for a limited time.

With the arrangement described it is possible to detect failure of the seals and to stop the pump before damage occurs to the bearing 11. In this manner there will be no damage to any of the rotary parts of the pump such as might occur if failure of the bearing 11 did take place. Two separate tanks are illustrated but these can be formed as a single divided tank providing arrangement such as an overflow, are made to prevent flow of liquid and lubricant from the tank part 56 into the tank part 57.

When the first seal 46 fails and liquid is forced into the space 51, the resulting increase in level in the tank 56, is detected by the sensor 60, and the valve 58A can be closed to prevent further lubricant being supplied to the clearance 51. However, liquid will still flow from the clearance 51 to the tank 56 and although the volume of liquid displaced will be small, an overflow arrangement may be provided on the tank 56 to limit the rise of liquid in the tank or alternatively a valve (not shown) may be opened to partly drain the tank 56. Moreover, both tanks 56 and 57 will incorporate filtering arrangements whereby the lubricant which is returned to the tanks is filtered before it is resupplied. The tanks 57 and 58 may also incorporate low liquid level warning devices 61 to provide an indication to the operator of seepage of lubricant over an extended period of time.

In alternative applications for the sealing arrangement, the seals may not be subject to liquid under pressure tending to force past the seals towards the bearing and the seals are primarily provided to prevent dirt reaching the bearings. In this case for example as the seal 46 wears there will be a tendency for oil to leak past the seal and for the liquid level in the reservoir 56 to fail. This again can be detected by an appropriate sensor to provide an indication of failure of the seal 46. As in the example described above however the seal 47 will take over the duty of preventing ingress of dirt to the bearing and when failure of the seal 47 takes place the lip seal 48 will continue to provide protection for the bearing.

In the example described the lubricant circulates by convection and this is particularly convenient where the tanks 56 and 57 are external and are disposed above the

associated spaces. The circulation of lubricant can be assisted or even effected, by applying air under pressure over the surface of the lubricant in the tanks or by means of separate pumps.