WO2025003818A1

WO2025003818A1 - Seal

Info

Publication number: WO2025003818A1
Application number: PCT/IB2024/055824
Authority: WO
Inventors: Pavol Loderer; Robert George MOORHOUSE; Paul CLARENCE; Steven Edward Moore; Rodrigo Ignacio SANTANDER
Original assignee: Weir Minerals Europe Ltd
Current assignee: Weir Minerals Europe Ltd
Priority date: 2023-06-30
Filing date: 2024-06-14
Publication date: 2025-01-02
Anticipated expiration: 2025-12-30
Also published as: GB202310011D0

Abstract

A seal arrangement is described for providing a seal between a rotatable shaft and a housing having a wall through which the shaft extends. The seal arrangement comprises, in series, a double mechanical seal and a gland seal. The double mechanical seal comprises a radially inner seal and a radially outer seal, separated by a barrier chamber. The barrier chamber provides a pressurised barrier fluid cavity independent of the operation of the gland seal.

Description

SEAL

FIELD OF INVENTION

This invention relates to a seal. More particularly, it relates to a seal arrangement for a pump, a pump incorporating such a seal arrangement and to a method of modifying a pump.

BACKGROUND OF THE INVENTION

In equipment, such as a pump, which includes a housing defining a fluid containing chamber (the wet end of the pump) and a rotating shaft which penetrates the housing and extends from a dry end of the pump to the wet end of the pump, use is made of a seal to inhibit the flow of fluid between the shaft and the housing.

One particular type of pump that requires a seal is a centrifugal pump, particularly a centrifugal pump for pumping slurry (a two phase fluid containing insoluble, abrasive, solid particles). Typical slurries used in mineral processing applications have particle sizes of 1 mm or smaller suspended in a fluid, such as water.

There are three types of seals which are commonly used in pumps in mineral processing applications, namely a centrifugal seal, a gland seal and a mechanical seal.

A centrifugal seal is a dynamic seal that only works while the pump is rotating and has no sealing effect when the pump is stationary. A secondary seal maintains the slurry within the pump when it is stationary. The secondary seal can be either a grease- lubricated packing seal or an elastomer lip seal.

A gland seal typically comprises a stuffing box housing which defines an opening through which the rotating shaft extends such that an annular cavity is defined between a radially inner surface of the stuffing box housing and a surface of the shaft or a protective sleeve which is mounted on the shaft for rotation therewith. The seal may be provided by packing rings, elastomer lips, or a combination of these.

An advantage of a gland seal is that it is relatively simple in construction. However, as the packing material wears it is prone to fluid leakage from the pump chamber. When used in mineral processing applications this is undesirable; particularly because water may be expensive where the pump is operated in arid conditions.

One type of mechanical seal is a single mechanical seal. In a single mechanical seal, two flat surfaces (one fixed, the other rotating) are held in close proximity (sometimes of the order of microns) but not touching. One of the flat surfaces is urged against the other by a spring. These flat surfaces are held apart by a thin layer of the pumped fluid, which prevents direct contact of the flat surfaces. Such an arrangement is unsuitable for a slurry pump because the pump fluid is highly abrasive and would damage the flat surfaces. As a result, for pumping slurries, a double mechanical seal is needed.

A double mechanical seal has two sets of flat surfaces (i.e. two seals) with a barrier or buffer fluid area in between those two seals. Essentially, a double mechanical seal comprises two single mechanical seals (or primary seals) arranged in series and axially spaced. However, a barrier chamber pressurised with clean fluid is defined between each of the two single mechanical seals and provides clean fluid to separate the stationary and rotating components of each seal. The faces of the components that are adjacent each other are machined to a high degree of tolerance and surface finish. These faces are urged into contact to provide a seal that virtually eliminates leaks.

A disadvantage of a double mechanical seal is that it is relatively expensive. Furthermore, any failure of a double mechanical seal tends to be catastrophic necessitating the operation of the pump to be halted immediately until the seal can be repaired or replaced. In mineral processing applications this may require the entire process to be halted until the seal is replaced, which is very expensive. Production process loss is a key factor for using scheduled maintenance.

It is an object of this invention to provide means which will ameliorate one or more of these problems or other problems of prior art seals, or will provide a useful alternative.

SUMMARY OF THE INVENTION

According to a first aspect there is provided a seal arrangement for providing a seal between a rotatable shaft and a housing having a wall through which the shaft extends, the seal arrangement including in series a double mechanical seal and a gland seal, wherein the double mechanical seal comprises a radially inner seal and a radially outer seal, separated by a barrier chamber, and wherein the barrier chamber provides a pressurised barrier fluid cavity independent of the operation of the gland seal.

By virtue of this aspect, a double mechanical seal is provided that has the advantage of essentially leak free operation, but in the event of failure thereof, the gland seal operates as a fallback seal, thereby allowing the pump to continue operating, typically until the next scheduled maintenance. It means in practice that catastrophic mechanical seal failure is no longer a concern.

Optionally, the radially inner seal is axially aligned with the radially outer seal.

The seal arrangement may include a seal body comprising an outer annular element which is connected or connectable to the housing and an inner annular element which is connected or connectable to the shaft for rotation therewith, the inner annular element extending radially outwards at a wet end thereof and housing an inner rotating seal component and an outer rotating seal component radially spaced therefrom.

The outer annular element may comprise an annular body; and the inner annular element may comprise an annular sleeve.

Optionally, each of the rotating seal components protrude axially towards a dry end of the pump.

Optionally, the annular body houses an inner fixed seal component and an outer fixed seal component radially spaced therefrom and aligned with the inner and outer rotating seal components.

Optionally, the inner fixed seal component is closely coupled to the inner rotating seal component to provide the radially inner seal; and the outer fixed seal component is closely coupled to the outer rotating seal component to provide the radially outer seal.

Optionally, each seal component has a sealing face that is complementary to its respective opposing seal component.

Optionally, the annular body, the annular sleeve, the radially inner seal and the radially outer seal define a barrier chamber.

Optionally, the barrier chamber has a radial dimension larger than its axial dimension. The radial dimension of the barrier chamber may be 50% more than the axial dimension of the barrier chamber.

Optionally, the annular body defines a delivery channel extending therethrough from a dry end of the pump to the barrier chamber. The delivery channel may be in fluid communication with a pressurised liquid feed source that is operable to inject high pressure barrier liquid to reduce the pressure gradient between the radially inner seal and the radially outer seal (i.e. across the double mechanical seal). One suitable liquid for use as high pressure barrier liquid is water, but other liquids may be used.

The seal arrangement may further comprise a gland seal cavity in which the gland seal is located.

A biasing arrangement (such as a spring) may be mounted in the annular body for urging complementary sealing faces of the inner seal together and for urging complementary sealing faces of the outer seal together.

The double mechanical seal may be positioned on a wet side of the seal arrangement i.e. axially inwardly of the gland seal where fluid is being pumped. Hence, the mechanical seal will form the first stage or primary seal to inhibit leakage between the shaft and the housing and the gland seal will (during normal operation) form a fallback seal.

The advantage with this arrangement is that the double mechanical seal will prevent any leakage of the fluid, however, should the double mechanical seal fail, the gland seal, which forms a fall-back seal, will activate and permit the pump to continue operating permitting the double mechanical seal to be repaired or replaced at a convenient time, e.g. at the next maintenance shutdown of the pump.

The gland seal cavity may open out of the seal body in an axially outward direction and packing may be provided in the gland seal cavity. The packing may include at least two axially spaced annular packing rings. A lantern ring may be provided between adjacent packing rings. Alternatively, or additionally, at least one lip seal may be positioned in the gland seal cavity.

The seal arrangement may include a compression member which includes an annular axially extending protrusion which extends into the axially outer end of the gland seal cavity to compress the packing of the gland seal, the compression member being secured to the fixed outer element of the seal body by fasteners which permit the axial position of the compression member, and hence the compression of the packing, to be adjusted.

A grease feed line may extend from an outer surface of the annular body to the gland seal cavity to permit lubricant (such as grease) to be fed into the gland seal.

The barrier liquid cavity (pressurised cavity) may be maintained at a pressure in the range of 0.1 MPa to 0.2MPa below the pump discharge pressure. The wet end of the pump may operate at a pressure above 0.1 MPa, but typically above 1 MPa.

The dry end of the pump may operate at atmospheric pressure.

This aspect of the present invention is in contrast to the seal arrangement described in WO 2021/005477, in the name of the same assignee as this present application. In WO 2021/005477 a seal arrangement is provided that has a mechanical seal and a gland seal, in series. However, the gland seal is required to operate at all times to maintain a pressurised barrier liquid cavity. It cannot be used merely as a back-up seal that is only activated in the event of failure of the mechanical seal.

According to a second aspect of the invention, there is provided a pump which includes: a housing defining a pumping chamber; an impeller mounted for rotation within the pumping chamber; a drive shaft which is drivingly connected to the impeller and which extends through an aperture in a wall of the housing; and a seal arrangement of the type described above which provides a fluid seal between the housing and the drive shaft.

The pump may be a slurry pump.

Any feature of one of the above aspects may be combined with another of the above aspects to create further aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:

Figure 1 shows a simplified sectional view of part of a pump in accordance with one embodiment of the invention; and

Figure 2 shows a simplified sectional view, similar to Figure 1 , of a pump in accordance with another embodiment of the invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

The following description is provided as an enabling teaching. Those skilled in the relevant art will recognise that many changes can be made to the embodiments described, while still attaining the beneficial results of the present invention. It will also be apparent that some of the desired benefits can be attained by selecting some of the features of the following embodiments without utilising other features. Accordingly, those skilled in the art will recognise that modifications and adaptations to the described embodiments are possible and can even be desirable in certain circumstances, and are a part of the present disclosure. Thus, the following description is provided as illustrative of the principles of the present invention and not a limitation thereof.

In Figure 1 of the drawings, reference numeral 10 refers generally to a pump in accordance with an embodiment of the invention. The pump 10 is designed for pumping highly abrasive slurry, for example, in a mining or mineral processing environment. In this embodiment, the pump 10 is suitable for pumping a liquid having solids suspended therein in the size range from approximately 100 microns to 1 mm (which is one example of a typical mining slurry).

The pump 10 includes a housing or casing 11 , part of which is shown in Figure 1 of the drawings, defining a pumping chamber 12 within which an impeller 14 is mounted for rotation. The area inside the pumping chamber 12 may be referred to as the wet end 15 of the pump 10. A drive shaft 16 extends through an aperture 18 in a wall of the housing 11 and has an inner end 16a which is drivingly connected to the impeller 14 and an outer end 16b which is positioned outside the housing 11 and is connected or connectable to a power source such as an electric motor (not shown). The outer end 16b is located at the dry end 17 of the pump 10.

The pump 10 further includes a seal arrangement in accordance with one embodiment of the invention, generally indicated by reference numeral 20, to provide a fluid seal between the housing 11 and drive shaft 16 as described in more detail below.

The seal arrangement 20 includes a seal body generally indicated by reference numeral 22 which comprises an outer annular element (in the form of an annular body in this embodiment) 24 and an inner annular element (in the form of an annular sleeve in this embodiment) 26. The annular sleeve 26 is fixed to the shaft 16 for rotation therewith.

The annular body 24 is secured to the housing 11 by means of circumferentially spaced bolts extending through circumferentially spaced holes 28 in an annular flange 30 of the annular body 24 and into screw-threaded engagement with complementary holes 32 defined by the housing 11 .

A gland seal cavity 36 is provided between a radially inner surface of the annular body 24 and a radially outer surface of the annular sleeve 26. The gland seal cavity 36 extends longitudinally between (i) an annular shoulder 38 extending radially towards the annular sleeve 26, and (ii) a compression ring end 40 of the annular body 24.

The annular sleeve 26 is positioned around the drive shaft 16 and secured in position by locking screws 42 extending through circumferentially spaced holes in the annular sleeve 26 and into abutment with the drive shaft 16.

The annular sleeve 26 defines a flange portion 44 that extends radially outwards from the shaft 16 and protrudes into the pumping chamber 12. The flange portion 44 defines two annular recesses 46a, b therein, each of which opens axially towards the housing aperture 18. The radially smaller recess 46a is concentric with, and contained entirely within, the radially larger recess 46b.

The annular body 24 defines two annular recesses 48a, b therein, each of which opens axially towards the wet end 15. The radially smaller recess 48a is contained entirely within the radially larger recess 48b.

Annular recess 46a is aligned with annular recess 48a; similarly annular recess 46b is aligned with annular recess 48b.

The seal arrangement 20 comprises a wet end double mechanical seal 50 and a dry end fall-back gland seal 52.

The double mechanical seal 50 comprises a radially inner seal 54 and a radially outer seal 56, which are axially aligned (i.e. on approximately the same vertical centreline) and separated by a barrier chamber 58.

The radially inner and outer seals 54, 56 are essentially identical. Each has a fixed seal component 60a, b mounted in the respective annular body recess 48a, b and protruding axially therefrom; and a rotating seal component 62a, b mounted in the respective annular sleeve recess 46a, b and protruding axially therefrom. A biasing mechanism (in the form of a coil spring in this embodiment) 64 urges each fixed seal component 60a and 60b into close-coupled relation with the corresponding rotating seal component 62a and 62b, respectively. The contact faces of the fixed and rotating seal components, i.e. the protruding face of fixed seal component 60a and the protruding face of rotating seal component 62a; and the protruding face of fixed seal component 60b and the protruding face of rotating seal component 62b, are all machined to allow very close-coupling thereof.

In other embodiments, a different type of spring, such as a leaf spring, or a resilient member other than a spring, may be used as the urging mechanism. The annular body 24 defines a delivery channel 66 extending therethrough from the dry end 17 to the barrier chamber 58. The delivery channel 66 has a generally circular cross-section in this embodiment, but other configurations are possible. The delivery channel 66 opens into the barrier chamber 58 radially outside the annular recess 48a and radially inside the annular recess 48b.

A high pressure fluid source 68 may be coupled to the delivery channel 66 to inject high pressure fluid into the barrier chamber 58 to maintain a high pressure in the barrier chamber 58. When pressurised with high pressure fluid (such as water), the barrier chamber 58 acts as a barrier liquid cavity for the double mechanical seal 50 thereby providing a pressure gradient between the pumping chamber 12 and the dry end 17. The barrier chamber 58 is typically at 0.1 MPa below the pump discharge pressure, in this embodiment.

The high pressure fluid supply serves as a lubricant for the double mechanical seal 50, and also provides coolant therefor, and balances pressure between the fixed parts (the fixed seal components 60a, b) and the rotating parts (the rotating seal components 62a, b)) of the double mechanical seal 50. In one pump, the pressure at the wet end 15 of the pump 10 may be in the region of 10 bar (1.0 MPa), the barrier liquid pressure may be 9 Bar (0.9 MPa), and the dry end 17 of the pump is at atmospheric pressure. This means that the pressure differential across the double mechanical seal 50 is approximately 1 bar (0.1 MPa).

Other than the new orientation, the double mechanical seal 50 operates in a conventional manner.

The fall-back gland seal 52 includes two inner packing rings 72 (nearest the wet end 15), an outer packing ring 74 (nearest the dry end 17) and an intermediate packing ring 76. A lantern ring 78 is positioned between the outer packing ring 74 and the intermediate packing ring 76; another lantern ring 78 is positioned between the intermediate packing ring 76 and the axially outermost (nearest the wet end 15) of the two inner packing rings 72.

The seal arrangement further includes a compression ring, generally indicated by reference numeral 80. The compression ring 80 includes an annular axially extending protrusion 82 which extends into the gland seal cavity 36 through the axially outer end thereof to compress the packing rings 72, 74, 76 to form the gland seal 52. The compression ring 80 is connected to the annular body 24 of the seal body 22 by bolts 86 extending through circumferentially spaced holes 88 in the compression ring 80 into screw-threaded engagement with complementary holes 90 in the annular body 24. By tightening the bolts 86, the compression ring 80 urges the packing rings 72, 74, 76 against the shoulder 38, thereby compressing the packing rings 72, 74, 76.

The gland seal 52 is lubricated by grease from a pair of grease feedlines 92 that extend from an outer surface of the annular body 24 into the gland seal cavity 36 at positions in registration with each lantern ring 78 to permit lubricant to be fed into the gland seal 52 as required. In addition, a cavity between the double mechanical seal 50 and the gland seal 52 is also lubricated by grease from a grease feedline 94 extending through the annular body 24.

When the double mechanical seal 50 is acting normally, then the compression ring 80 is relatively loose so that the gland seal 52 is not providing a sealing function against the shaft 16. However, if the double mechanical seal 50 fails (which may be detected automatically by a leak detector (not shown), then the compression ring 80 may be tightened so that the gland seal 52 engages with the shaft 16 and acts in a conventional manner to provide a sealing function.

Reference is now made to Figure 2 of the drawings, in which reference numeral 100 refers generally to a pump in accordance with another embodiment of the invention, and, unless otherwise indicated, the same reference numerals used above are used to designate similar parts. The main difference between the pump 10 and the pump 100 is in the configuration of the gland seal 52. In particular, in the pump 100, the inner packing rings 72 are replaced with a pair of lip seals 102 which are spaced apart axially by a lip seal spacer 104.

In use, the double mechanical seal 50 of the pump 10, 100, forms the exclusive seal to inhibit the flow of fluid from the pumping chamber 11 through the aperture 18. The gland seal 52 provides a fallback seal that is only engaged in the event that the double mechanical seal 50 fails. This engagement of the gland seal 52 as a back-up seal permits the pump 10, 100 to continue to operate until it is convenient to shut the pump 10, 100 down to repair or replace the double mechanical seal 50.

These embodiments provide the advantages associated with a double mechanical seal, i.e. zero leakage and at the same time obviate the major disadvantage of a double mechanical seal, namely, that should it fail, the failure is catastrophic necessitating an immediate shutdown of the pump 10, 100. Furthermore, seals according to these embodiments can be retro-fitted into the same axial pump space as existing gland seals.

Reference Numerals

Pump 10, 100

Housing or casing (of pump) 11

Pumping chamber 12

Impeller 14

Pump wet end 15

Drive shaft 16

Inner end (of drive shaft) 16a

Outer end (of drive shaft) 16b

Pump dry end 17

Aperture (of housing) 18

Seal arrangement 20

Seal body 22

Outer annular element (annular body) 24

Inner annular element (annular sleeve) 26

Holes (in flange) 28

Annular flange 30

Holes (in housing) 32

Gland seal cavity 36

Annular shoulder 38

Compression ring end (of the annular body) 40

Locking screws 42

Flange portion 44

Annular recesses 46a (smaller diameter), 46b (larger diameter)

Annular recess 48a (smaller diameter) 48b (larger diameter)

Double mechanical seal 50

Fall-back gland seal 52

Radially inner seal (of mechanical seal) 54

Radially outer seal (of mechanical seal) 56

Barrier chamber 58

Fixed seal component 60a, b Rotating seal component 62a, b

Biasing mechanism 64

Delivery channel 66

High pressure fluid source 68 Inner packing rings 72

Outer packing ring 74

Intermediate packing ring 76

Lantern ring 78

Compression ring 80 Protrusion 82

Bolts (for compression ring) 86

Holes (in compression ring) 88

Holes (in annular body) 90

Grease feedlines 92 Grease feedline 94

Lip seals 102

Lip seal spacer 104

Claims

1. A seal arrangement for a pump to provide a seal between a rotatable shaft and a housing having a wall through which the shaft extends, the seal arrangement comprising in series a double mechanical seal and a gland seal, wherein the double mechanical seal comprises a radially inner seal and a radially outer seal, separated by a barrier chamber, and wherein the barrier chamber provides a pressurised barrier fluid cavity independent of the operation of the gland seal.

2. A seal arrangement according to claim 1 , wherein the seal arrangement includes a seal body comprising an annular body which is connected or connectable to the housing and an inner annular sleeve which is connected or connectable to the shaft for rotation therewith, the inner annular sleeve extending radially outwards at a wet end thereof and housing an inner rotating seal component and an outer rotating seal component radially spaced therefrom.

3. A seal arrangement according to claim 2, wherein the annular body houses an inner fixed seal component and an outer fixed seal component radially spaced therefrom and aligned with the inner and outer rotating seal components.

4. A seal arrangement according to claim 2 or 3, wherein the annular body, the annular sleeve, the radially inner seal and the radially outer seal define a barrier chamber.

5. A seal arrangement according to claim 4, wherein the annular body defines a delivery channel extending therethrough from a dry end of the pump and opening into the barrier chamber between the radially inner seal and the radially outer seal.

6. A seal arrangement according to claim 5, wherein the delivery channel is in fluid communication with a pressurised liquid feed source operable to inject high pressure barrier liquid to reduce the pressure gradient between the radially inner seal and the radially outer seal.

7. A seal arrangement according to any of claims 2 to 5, wherein a biasing arrangement is mounted in the annular body for urging complementary sealing faces of the inner seal together and for urging complementary sealing faces of the outer seal together.

8. A seal arrangement according to any preceding claim, wherein the double mechanical seal is located on a wet side of the seal arrangement to form the sole seal to inhibit leakage between the shaft and the housing.

9. A seal arrangement according to any preceding claim, wherein the gland seal includes at least two axially spaced annular packing rings.

10. A seal arrangement according to claim 9, wherein a lantern ring is provided between adjacent packing rings.

11. A seal arrangement according to any preceding claim, wherein at least one lip seal is positioned in a gland seal cavity housing the gland seal.

12. A pump which includes: a housing defining a pumping chamber; an impeller mounted for rotation within the pumping chamber; a drive shaft which is drivingly connected to the impeller and which extends through an aperture in a wall of the housing; and a seal arrangement as claimed in any one of the preceding claims which provides a fluid seal between the housing and the drive shaft.

13. A pump as claimed in claim 12, wherein the pump comprises a slurry pump.