WO1987003050A1

WO1987003050A1 - Seal assembly

Info

Publication number: WO1987003050A1
Application number: PCT/AU1985/000278
Authority: WO
Inventors: Rowland Thomas Dixon
Original assignee: Sealing Devices Pty. Ltd.
Priority date: 1985-11-13
Filing date: 1985-11-13
Publication date: 1987-05-21
Also published as: JPS63501374A; EP0245241A1

Abstract

A mechanical seal assembly (11) for the rotating shaft (13) of a pump (10) having an axially adjustable bearing assembly (20, 21) and extending into the pump through an opening in the wall thereof. The seal assembly comprises stationary and rotatable seal members (31, 32) having abutting sealing faces (33, 34) and retained within a seal housing (25) which is axially moveable with the shaft, with portion of the seal housing abutting portion of the bearing assembly to prevent axial movement of the housing outwardly of the pump. Fluid pressure within the pump acts on one end of the housing for the seal assembly to force the housing and the seal assembly axially outwardly until the other end of the housing contacts the bearing assembly. The seal housing further supports a diaphragm (4) defining a cavity (45) therein containing a relatively incompressible fluid. Portion of the external surface of said diaphragm is exposed to fluid pressure within the pump, and another portion of the external surface supports the stationary seal member (32) on the side thereof opposite to its sealing face (34), whereby any increase in fluid pressure within the pump and acting on the diaphragm causes a corresponding increase in the pressure of the fluid within the diaphragm, and thus the pressure on the stationary seal member, to increase the seal force between the seal members.

Description

SEAL ASSEMBLY Technical Field

This invention relates to a seal assembly, and more particularly a mechanical seal assembly for a rotating shaft passing through the housing of a pressurized vessel such as a pump.

Background Art

One common method of sealing rotating shafts relative to the housings of pumps, is one involving use of mechanical seals which incorporate a pair of seal members having opposed and abutting sealing faces which substantially prevent leakage of fluid between the faces and therefore pass the seal. One of the seal members is conventionally fixed with respect to the pump housing and is therefore the fixed or stationary seal member whilst the other seal member rotates with the shaft so as to be a rotating seal. With conventional seal assemblies various forms of biasing means have been utilized to hold the abutting faces of the seal member in relatively tight contact to prevent the escape of fluid passed the seal assembly. However, conventional biasing means apply a constant force to keep the faces of the seal members in relatively tight contact and the integrity of the seal is reliant on the sufficiency of that force and on the requirement that the biasing means will not deteriorate to a point that the force applied is insufficient to form a proper seal particularly where for some reason or another the fluid pressure within the pressurized vessel increases substantially.

In addition, with conventional seal assemblies the necessity to ensure that the abutting faces of the seal members form a proper seal is important, and thus the position of the'rotating seal member is important in ensuring that the seal assembly operates satisfactorily. However, there are situations where the axial position of the rotating shaft for the pump needs to be adjusted relative to the pump housing, particularly where the pump is a centrifugal pump for pumping slurries where the rotor of the pump and/or the adjacent internal surface of the pump housing becomes worn due to the abrasive action of the solid particles within the slurry. Axial adjustment of the rotor position is difficult as adjustment of the position of the rotor relative to the pump housing is necessary.

One solution to the above problem is to provide a pump in which adjustment of the rotor is achieved by a rotor shaft which is supported in a cartridge type bearing assembly which in turn is adjustably supported on a base structure which is moveable relative to the base for the pump housing. However, such solutions do not allow for an adjustment of the shaft which will ensure that the abutting relationship between the faces of the seal members of the mechanical seal is not disturbed. One solution to this further problem is embodied in the seal assemblies disclosed in the specifications of U.S. Patents Nos. 3,977,737 and 4,509,773, in which a housing supporting the fixed seal member is attached to the adjustable bearing assembly such that the bearing assembly is actually axially adjusted through an opening in the housing of the pump and is sealed with respect thereto. With such an arrangement the housing for the fixed seal member moves with the shaft as it is axially adjusted and the two seal members move together thus maintaining the abutting relationship between their sealing faces and no separate adjustment therebetween is necessary.

However, the assemblies of both U.S. Patent Specifications 3,977,737 and 4,509,773 also incorporate biasing means which also apply a constant force, namely the use of springs acting on one of the seal members in the case of the assembly of U.S. Specification 3,977,737 and the use of an elastomeric ring in the case of U.S. Specification 4,509,773.

In addition, the seal assemblies of both U.S. Patent Specification Nos. 3,977,737 and 4,509,773 require the housing for the fixed seal member to be rigidly attached with bolts to the bearing assembly which does not allow for lack of correct tolerances and alignment of the components of the assembly, whilst the rigid attachment also allows undesirable vibrations to be transmitted through the components to the seal faces causing damage, such as chipping and cracking, which reduces seal face life. In addition, the requirement to screw and unscrew bolted attachments complicates assembly and disassembly of the unit during installation, maintenance and service, particularly in environments where slurries, which in some cases may be corrosive, are being pumped and which make bolts difficult to remove after a period of time. Disclosure of the Invention

It is an object of a first aspect of the invention to provide a seal assembly incorporating means which applies a biasing force to keep the faces of the sealing members in tight sealing engagement and which allows for the biasing force to progressively increase in proportion to increases of fluid pressure within the pressurized vessel.

Therefore, in accordance with the first aspect of the invention, there is provided a mechanical seal assembly for a rotating shaft extending into a pressurized vessel through an opening in the wall thereof, said seal assembly comprising stationary and rotatable seal members having abutting sealing faces and retained within a seal housing and wherein said housing supports a diaphragm defining a cavity therein containing a relatively incompressible fluid, with portion of the external surface of said diaphragm being exposed to fluid pressure within said pressurized vessel, and another portion of said external surface supporting said stationary seal member on the side thereof opposite to its sealing face.

With such an arrangement, any increases in fluid pressure within said pressurized vessel, and acting on said diaphragm, progressively increases the pressure of the fluid within the diaphragm and thus pressure exerted on said stationary seal member to therefore increase the sealing force between the faces of the sealing members.

It is an object of a second aspect of the invention to avoid rigid attachments between the housing for the fixed sealing member and the bearing assembly. In accordance with the second aspect of the invention there is provided a mechanical seal assembly for a rotating shaft having an axially adjustable bearing assembly and extending into a pressurized vessel through an opening in the wall thereof, said seal assembly comprising stationary and rotatable seal members having abutting sealing faces and retained within a seal housing which is axially moveable with said shaft, and wherein portion of the seal housing abuts portion of said bearing assembly to prevent axial movement of the housing outwardly of said pressurized vessel.

With such an assembly, fluid pressure within the pressurized vessel and acting on one end of the housing for the seal assembly forces the housing and the assembly therein axially outwardly until its other end contacts the bearing assembly and no rigid attachment between the housing and the bearing assembly is necessary thus avoiding the problems with such rigid attachments referred to previously.

Brief Description of the Drawings

One preferred embodiment incorporating both aspects of the invention will now be described with reference to the accompanying drawings, in which; Figure 1 is a side elevational view, partly sectioned, of a pump assembly' incorporating bearing assemblies and a mechanical seal assembly in accordance with the present invention; and

Figure 2 is an enlarged view of the mechanical seal assembly of Figure 1.

Best Mode for Carrying Out the Invention

Referring to Figure 1 of the drawings, there is shown a pump assembly 10, incorporating a mechanical seal assembly 11 in accordance with the present invention. The pump assembly 10 includes a centrifugal impeller 12 rotated by a shaft 13 driven by a motor, such as an electric motor (not shown) . The impeller is located in a housing 14 attached to a support 15. The housing 14 has an inlet 16 through which fluid enters the housing and an outlet 17 through which fluid is discharged. The shaft 13 is supported and fixed to be carried by a cradle 18 which in turn is supported by, and axially adjustable with respect to, a fixed base structure 19. The housing 14, the support 15 and the base structure 19 are all fixed together. The cradle 18 supports a pair of spaced roller bearings 20 and 21, each abutting bearing brackets 22 and 23 respectively which in turn are bolted by bolts 22a and 23a to the bearing assembly. The bearings 20 and 21 are journalled to the shaft 13^" and the bearing bracket 22 has a dust/dirt seal 24 associated therewith and surrounding the shaft 13. The mechanical seal assembly 11 is constructed and arranged to substantially prevent the leakage of fluid from the pump housing along the shaft 13, and the seal assembly surrounds the shaft 13 and is located between the bearing bracket 23 and the pump housing and is furthermore supported within a seal housing 25.

Axial adjustment of the impeller 12 with respect to the housing 14 allows for the clearance C therebetween to be adjusted, and such axial adjustment is achieved by axially moving the cradle 18 and therefore the bearing assembly,^" shaft and impeller. As shown in Figure 1, the cradle is provided with an external lug 26 passing through an elongate slot 27 in the base structure 19. The lug 26 is internally threaded and receives a screw 28 which in turn is axially fixed by locating collars 29 to the base structure 19. The cradle 18 is attached to the base structure 19 by bolts 30 which pass through slots (not shown) in the cradle 18 and into threaded openings (also not shown) in the base structure. When the bolts 30 are loosened the screw 28 is rotated and the axial position of the cradle 18, together with the shaft 13 and the impeller 12, can be moved to adjust clearance C, whereafter retightening of the bolts 30 fixes the assembly at the adjusted position.

The mechanical seal assembly comprises a pair of seal members 31 and 32, in the form of sealing rings surrounding the shaft 13, and formed from a suitable material such as sintered Alpha Silicon Carbide. The seal means have abutting lapped seal faces 33 and 34. As shown in Figures 1 and 2, the seal member 31 is connected via a connecting ring 35 to a cylindrical sleeve 36 surrounding the shaft 13 to rotate therewith and extends into the pump housing to abut the adjacent side of the impeller 12. The fixed or stationary seal member 32 is connected via a diaphragm assembly 37 to the seal housing 25 which in turn passes through the opening into the pump housing and a sealing ring 38 is provided in a groove 39 around the opening to seal against the external surface of the seal housing but at the same time allow for relative axial movement of the seal housing within the opening of the pump housing.

As shown, the opposite end of the seal housing 25 abuts the bearing bracket 23 and is held thereagainst by fluid pressure acting on the end of the seal housing 25 within the pump housing, thus avoiding the necessity for a rigid attachment between the seal housing and the bearing assembly, such as by means of bolted connections as is the case with the assemblies of the aforementioned U.S. patent specifications. The absence of such fixed attachments allows for any lack of correct tolerances or alignment of the components, and avoids both the difficulties with attaching and detaching bolted connections and the transference of vibration which might damage the seal faces.

In order to prevent the seal assembly from rotating with the shaft, the seal housing 25 has a plurality of circumferentially spaced slots 25a therein in the ends of which the heads of the bolts 23a are engaged to act as abutments to prevent rotation of the seal housing and therefor the seal assembly. As stated previously, the fixed or stationary seal member 32 is supported by a diaphragm assembly comprising a diaphragm 40 formed from neoprene or like material held in position relative to the seal housing 25 via a clamping member 41. The diaphragm 40 is of U-shaped cross-section with the free edge of one side of the U being clamped between the end of the seal housing and the clamping member 41 which in turn is screwed at 42 into the end of the housing as shown, whilst the other free edge of the U-shaped of the diaphragm is clamped between the clamping member 41 and an internal locking nut 43 screwed at 44 into the end of the clamping member 41. As shown the diaphragm defines an internal cavity 45 which is filled with a relatively incompressible fluid. Portion of the o diaphragm bearing against the fixed or stationary seal member 32 at the side opposite to its sealing face is held thereagainst by a holder 46 cooperating with the compression spring 47 retained within a blind hole 48 in the clamping member 41 and acting against the holder 46. The exterior of portion of the wall of the diaphragm above the stationary seal member 32 is exposed to the pressure of fluid within the pump housing and the pressure of that fluid is transmitted to the fluid within the diaphragm which in turn acts on the portion of the diaphragm adjacent the stationary seal member 32 via the holder 46. It will therefore be apparent that as fluid pressure increases or decreases within the pump housing the fluid pressure within the diaphragm increases or decreases proportionally and as does the biasing force acting on the stationary seal 32 to force its sealing face into tight sealing engagement with the abutting sealing face of the rotating seal member 31. By increasing or decreasing the width of the annular surface adjacent the stationary seal member 32, to increase or decrease the surface area at that point, the force transmitted to the stationary seal member increases or decreases accordingly and therefore the diaphragm can be formed to have a width at that surface which meets the biasing force requirements for any particular situation.

A secondary mechanical seal assembly 49 is provided within the seal housing 25 and comprises a rotating seal member 50 fixed to and rotatable with the sleeve 36 surrounding the shaft, and an 0-ring 51 is interposed between the seal member 50 and the shaft, whilst the stationary of fixed seal member 52 is fixed to the seal housing and biased into engagement with the rotating seal member 50 by compression springs 53, supported within blind holes 54 in a radially inwardly directed flange 55 forming part of the seal housing, and acting on the stationary seal member 52 such as to force it into sealing engagement with the rotatable seal member. A further 0-ring is interposed between the flange 55 and the stationary seal member 52. A chamber 56 is defined by the seal housing, the sleeve and the two mechanical seal assemblies, and a cooling fluid, such as water, is circulated through the chamber 56 from an inlet 57 to an outlet (not shown). Such water circulating against the seal members 31 and 32 within the chamber 56 serves to clean away any dirty fluid, such as slurry fluid, which might pass between the sealing faces of the seal members, and in addition the circulating fluid serves to keep the seal assembly wet in situations where, through accident, particularly with unsupervised pumps, the pump runs dry which would remove the lubricating effect of the fluid being pumped and cause the faces of the seal members to become dry resulting in overheating and/or accelerated wear. A circulating rate of in the order of 2 to 3 gallons per hour is normally sufficient.

Claims

CLAIMS :

1. A mechanical seal assembly for rotating shaft extending into a pressurized vessel through an opening in the wall thereof, said seal assembly comprising stationary and rotatable seal members having abutting sealing faces and retained within a sealed housing and wherein said housing supports a diaphragm defining a cavity therein containing relatively incompressible fluid, with portion of the external surfaces of said diaphragm being exposed to fluid pressure within said pressurized vessel, and another portion of said external surface supporting said stationary seal member on the side thereof opposite to its sealing face.

2. A mechanical seal assembly as claimed in Claim 1, wherein said seal housing also defines a chamber through which fluid is circulated in contact with the seal members on the sides thereof opposite to the interior of said pressurized vessel and serving to wash an escaping fluid away from said seal members and to lubricate said sealing faces if necessary.

3. A mechanical seal assembly for a rotating shaft having an axially adjustable bearing assembly and extending into a pressurized vessel through an opening in the wall thereof, said seal assembly comprising stationary and rotatable seal members having abutting sealing faces and retain within a seal housing which is axially movable with said shaft, and wherein portion of the seal housing abuts portion of said bearing assembly to prevent axial movement of the housing outwardly of said pressurized vessel.

4. A mechanical seal assembly as claimed in Claim 3, wherein said seal housing also defines a chamber through which fluid is circulated in contact with the seal members on the sides thereof opposite to the interior of said pressurized vessel and serving to wash an escaping fluid away from said seal members and to lubricate said sealing faces if necessary.

5. A mechanical seal assembly for a rotating shaft having an axially adjustable bearing assembly and extending into a pressurized vessel through an opening in the wall thereof, said seal assembly comprising stationary and rotatable seal members having abutting sealing faces and retain within a seal housing axially movable with said shaft, and wherein said housing supports a diaphragm defining a cavity therein containing a relatively incompressible fluid, with portion of the external surface of said diaphragm being exposed to fluid pressure within said pressurized vessel, and another portion of said external surface supporting said stationary seal member on the side thereof opposite to its sealing face, and wherein portion of the seal housing abuts portion of the bearing assembly to prevent axial movement of the housing outwardly of said pressurized vessel.

6. A mechanical seal assembly as claimed in Claim 5, wherein said seal housing also defines a chamber through which fluid is circulated in contact with the seal members on the sides thereof opposite to the interior of said pressurized vessel and thereby to wash any escaping fluid away from said seal members and to lubricate said sealing faces if necessary.

7. A mechanical seal assembly substantially as hereinbefore described with reference to the accompanying drawings.

8. A mechanical seal assembly as claimed in any one of Claims 1 to 7 in combination with a rotating shaft, bearing assembly and pressurized vessel.