WO2003040598A1

WO2003040598A1 - Sealing a rotary pump

Info

Publication number: WO2003040598A1
Application number: PCT/IB2002/004518
Authority: WO
Inventors: Robert Denis Todd; Siegfried Geldenhuys
Original assignee: Weir-Envirotech (Proprietary) Limited
Priority date: 2001-11-06
Filing date: 2002-10-30
Publication date: 2003-05-15
Also published as: AP2002002666A0; ZA200207808B

Abstract

A rotary pump (10) includes a casing (12) within which a rotor (14) is rotatable via a shaft (16). The casing includes structure forming a sealing cavity (42) around a static tube (24) including a radially outward, stationary, sealing face (26). A static sealing arrangement includes a rotary closure (30) having a flexible, circumferential sleeve (32) and an annular flange (34) at one end of the sleeve. The closure (30) is a-symmetrically, hingedly mounted on the rotor via said flange. The closure (30) mounts circumferentially arranged masses as shown at (38). A sealing face (36.2) is in register with and surrounds the sealing face (26), remote from the mounting flange (34). During rotation, centrifugal force generated by the masses, dilates the sleeve 36 and causes parting of the sealing faces (26, 36.2) to provide running clearance. When stationary, pressure of a pumping head to which the sealing cavity (42) is exposed, compresses the sleeve (36) and causes sealing between the sealing faces (26, 36.2).

Description

SEALING A ROTARY PUMP

THIS INVENTION relates to sealing a rotor of a rotary pump against a pump head when the pump is stationary. It relates more specifically to a method of operating a sealing arrangement, to a sealing arrangement, and to a rotary pump.

The Applicant expects this invention to be particularly advantageously applicable to pumping of slurry and that application will particularly be borne in mind for purposes of this specification.

In pumps, a working fluid is pumped against a head by means of a rotor or rotary impeller. During rotation of the rotor, pressure is generated which pressure causes flow of the working fluid through the impeller, via an outlet and into a delivery conduit against the head. Sealing is frequently effected by means of an expeller which expels working fluid from areas where leakage can take place. Such an expeller operates as a dynamic seal. In addition, the shaft is sealed by means of a gland. When the rotor is stationary, such pressure is no longer generated and the working fluid is no longer forced to flow against the head. Also, the expeller or dynamic seal is no longer operative. Thus, there is a tendency for reverse flow to take place under the head back along the delivery conduit via the outlet and through the rotor. Unless the reverse flow or reverse leakage is prevented, the impeller is reverse rotated, turbine fashion, and, more importantly, leakage takes place through the gland. Such reverse flow or reverse leakage is generally undesirable, even intolerable. This invention relates to a seal which allows forward flow to take place when the rotor is rotated and which seals to prevent reverse flow through the gland when rotation of the rotor stops.

In accordance with a first aspect of this invention, there is provided a method of operating a static sealing arrangement which static sealing arrangement includes an annular closure member co-axially fast with a rotor of a pump, and a stationary, circumferential sealing face, co-axially arranged relative to said rotor, and fast with a casing of the pump, in which the closure member is flexibly hinged toward a first end thereof, is weighted by means of circumferentially arranged masses fast with the closure member, and includes a circumferential rotary sealing face at a second end thereof axially spaced from the first end, and surrounding and being in register with the stationary sealing face, the method including during rotation of the rotor, causing the closure member to dilate radially progressively from the first end to the second end under the influence of centrifugal force generated by said masses which rotate; and when the rotor is stationary, subjecting the closure member over a periphery thereof between said first and said second ends to a stationary or static liquid head causing the rotary sealing face to bear against and seal against the stationary sealing face.

When the method is applied to pumping of a settable material such as slurry, the method may include breaking any deposit, which has settled or has partially set around the closure member during a time period when the pump was stationary, by means of dynamic deformation of the annular closure member on account of inertia of the masses and the resultant twisting which takes place as a consequence of the masses being located in an axially a-symmetric fashion. At start up, torque to accellerate the masses is transmitted via the a-symmetrically secured closure member, thereby twisting the closure member. Such twisting resembles, much exaggerated, torsional strain. In addition, such breakup may be enhanced by said progressive dilation from the first to the second end of the closure member.

In accordance with a second aspect of this invention, there is provided a static sealing arrangement for a rotary pump having a stationary casing and a rotor supported for rotation in the casing, the static sealing arrangement including a static tube fast with the casing, and defining a circumferential, stationary, sealing face co-axial with the rotor, at an outer periphery thereof; an axially extending closure member hingedly secured at a first end thereof to the rotor, and having a second end, axially spaced from said first end; a circumferential rotary sealing face along an inner periphery of the closure member, toward said second end, co-axial with the rotor, and surrounding and being in register with the stationary sealing face; circumferential masses fast with the closure member for dilating it radially under rotation, progressively from the first end to the second end. In use, under rotation, the centrifugal force generated by rotation of the masses dilates the closure member progressively from the first end to the second end and thus lifts the rotary sealing face off the stationary sealing face of the static tube to provide running clearance.

When the pump is stationary, pressure under the pump head compresses the closure member radially causing the rotary sealing face to embrace the stationary sealing face of the static tube and to seal thereagainst. It is emphasized that the unbalanced portion of the closure member is large compared to the sealing interface. Thus, a small pressure gradient nevertheless causes high sealing force at the sealing interface.

The masses may be symmetrically arranged. The masses may be moulded into pockets or cavities in the closure member.

The closure member may be of a flexible material. It may be of a moulded synthetic polymeric material, preferably of a synthetic rubber material.

In one embodiment, the closure member may taper from the first end to the second end, thus causing the rotary sealing face to be obliquely oriented relative to the static tube. The closure member may furthermore be configured, prior to any wear, such that the rotary sealing face touches the static tube around a narrow circumferential band only. As mentioned above, the smaller the sealing interface, the larger the sealing force for a given pressure gradient, and thus the more effective the sealing.

In accordance with a a third aspect, there is provided a rotary pump including a rotor having an impeller, a casing within which the rotor is rotatable, and a static sealing arrangement as herein described , the static tube being fast with said casing, and the axially extending closure member being hingedly secured to said rotor.

The invention is now described by way of example with reference to the diagrammatic drawing show, fragmentarily, in axial section, a pump arrangement in accordance with the invention. With reference to the drawing, a pump arrangement in accordance with the invention is generally indicated by reference numeral 10. The pump arrangement is shown fragmentarily only as emphasis is placed on a sealing arrangement forming part of the pump arrangement.

The pump arrangement comprises a stationary casing 1 2 around a rotor

14 and rotor shaft 1 6. The shaft and rotary components are supported for rotation in bearings which are not shown.

The rotor 14 comprises a rotary sleeve 18 and rotary flanges 20, 22 secured to the shaft 1 6, to one side of an impeller 1 7.

The casing 12 mainly accommodates the impeller 17, but also includes structure defining an annular sealing cavity 42 generally radially outwardly of the rotary sleeve 18 and flanges 20, 22. A static tube 24 fast with the casing 1 2 and concentrically surrounding the shaft 16 with clearance, projects into the sealing cavity 42 and provides a radially outward stationary sealing face 26.

The sealing arrangement comprises a rotary closure generally indicated by reference numeral 30 and including a moulded sleeve 36 having a radially inwardly turned flange 34 at one end of the sleeve 36, which is a first end indicated by reference numeral 36.1 . At an opposed, second end 36.2, the sleeve defines a radially inwardly directed rotary sealing face. The closure 30 is axially a-symmetrically clamped via the flange 34 between the flanges 20, 22 which define mounting formations snugly receiving the flange 34.

The sleeve 36 is of flexible material, more specifically in the form of synthetic rubber.

The significance of the axially a-symmetric clamping in combination with the flexibility of the sleeve will be explained below.

Integral with the sleeve 36, the closure 30 includes a mass arrangement generally indicated by reference numeral 38 and being in the form of a plurality of pockets or cavities within which masses are moulded into the closure 30. At an outer periphery, the closure 30 defines an outwardly open peripheral groove housing a hoop 40, conveniently of steel or other metal having a high modulus to resist hoop stress.

The second end 36.2 of the sleeve 36 and more specifically the rotary sealing face is in register with the stationary sealing face 26 of the static tube 24.

It is important to appreciate that, at the end 36.1 , the sleeve 36 is flexibly hinged about the flange 34 and that hinging is cantilever fashion.

It is also important to appreciate that the closure 30 is contained within the sealing cavity 42 and that the area within the sealing cavity 42 and also the outer peripheral band of the closure 36 generally intermediate the first end 36.1 and the second end 36.2, are exposed to the same pressure as is experienced at an inlet of the impeller 1 7.

The area, internally of the sleeve 36, and balancing the outer peripheral band between the ends 36.1 , 36.2, is exposed to ambient pressure.

In use, when the rotor 14 rotates, the closure 30 rotates therewith causing centrifugal force to be generated by the mass arrangement 38. It is to be appreciated that the centre of centrifugal force is axially spaced from the anchor point of the flange 34 thus causing the sleeve 36 to hinge outwardly at the first end 36.1 .

This lifts the rotary sealing face off the stationary sealing face 26 and thus prevents touching and thus friction and wear between the stationary sealing face 26 and the rotary sealing face. The hoop 40 limits dilation. Furthermore, it is to be appreciated that the pumping direction via the impeller 1 7 is toward an outlet of the casing 12 and thus away of the sealing cavity 42. There is thus ambient pressure, or event suction, in the sealing cavity 42 and no tendency for leakage to take place from the sealing cavity 42 toward the annular gap between the rotary sleeve 1 8 and the static tube 24. Furthermore, an expeller is provided to displace any working fluid in the sealing cavity 42 radially outwardly and thus away from the sealing interface, thus acting as a dynamic seal.

When the rotor 14 stops, the mass arrangement 38 likewise stops and the centrifugal force ceases. Thus, when working fluid starts flowing or leaking in reverse through the impeller 17 and into the sealing cavity 42, such pressure forces act radially inwardly on the closure 30. The pressure forces on account of the head cannot be balanced by ambient pressure internally of the sleeve 36, and on account of such unbalanced situation, the sleeve 36 is compressed radially inwardly and the rotary sealing face (which has now become stationary) closes on and embraces the stationary sealing face 26, thus causing sealing. It is to be appreciated that the area of the sealing face is small compared to the unbalanced area of the closure. Thus, even a small pressure gradient causes a large sealing force.

It is believed that the structure of the closure 30 and more specifically the offset or asymmetric anchoring thereof to one side of the centre of pressure causes the imbalanced pressure situation causing stationary sealing. It is thus regarded as a particularly elegant, simple and effective way of effecting sealing when the rotor has become stationary. It is regarded as important that, first, the outer peripheral area exposed to pressure, higher than ambient pressure, associated with a stationary pump head, is large, and that, secondly, the sealing interface is a narrow circumferential band and has a small area. Thus, even a small residual pressure will cause a high sealing force over the sealing interface which is conducive to high integrity in sealing.

A further advantage of the invention is that it provides a solution for a problem in that, when a working fluid which can settle or even set partially, such as slurry, is involved, there is a tendency for the slurry to settle or partially set within the sealing cavity 42 and to hold the closure 30 against the sealing face. However, in an arrangement in accordance with the invention, when the rotor starts rotating, the inertia of the masses, in combination with the axially a-symmetrical clamping of the sleeve and the resilient nature of the sleeve, will cause the sleeve and the mass arrangement to twist about a longitudinal axis, progressively from the first end 36.1 to the second end 36.2. Furthermore, centrifugal force on the mass arrangement 38 will cause the sleeve 36 to dilate or flare pivoting around its first end 36.1 thus more easily breaking the settled or partially set slurry to cause it to flow again and to cause the sealing interface to clear. It is believed that especially the first mentioned mechanism is effective in breaking the hold of the settled or partially set slurry.

Claims

CLAIMS:

1 . A method of operating a static sealing arrangement which static sealing arrangement includes an annular closure member co-axially fast with a rotor of a pump, and a stationary, circumferential sealing face, co-axially arranged relative to said rotor, and fast with a casing of the pump, in which the closure member is flexibly hinged toward a first end thereof, is weighted by means of circumferentially arranged masses fast with the closure member, and includes a circumferential rotary sealing face at a second end thereof axially spaced from the first end, and surrounding and being in register with the stationary sealing face, the method including during rotation of the rotor, causing the closure member to dilate radially progressively from the first end to the second end under the influence of centrifugal force generated by said masses which rotate; and when the rotor is stationary, subjecting the closure member over a periphery thereof between said first and said second ends to a stationary or static liquid head causing the rotary sealing face to bear against and seal against the stationary sealing face.

2. A method as claimed in Claim 1 , when applied to pumping of a settable material such as slurry, the method including breaking any deposit, which has settled or has partially set around the closure member during a time period when the pump was stationary, by means of dynamic deformation of the annular closure member on account of inertia of the masses and the resultant twisting which takes place as a consequence of the masses being located in an axially a-symmetric fashion.

3. A static sealing arrangement for a rotary pump having a stationary casing and a rotor supported for rotation in the casing, the static sealing arrangement including a static tube fast with the casing, and defining a circumferential, stationary, sealing face co-axial with the rotor, at an outer periphery thereof; an axially extending closure member hingedly secured at a first end thereof to the rotor, and having a second end, axially spaced from said first end; a circumferential rotary sealing face along an inner periphery of the closure member, toward said second end, co-axial with the rotor, and surrounding and being in register with the stationary sealing face; circumferential masses fast with the closure member for dilating it radially under rotation, progressively from the first end to the second end.

4. A static sealing arrangement as claimed in Claim 3, in which the masses are symmetrically arranged.

5. A static sealing arrangement as claimed in Claim 4, in which the masses are moulded into pockets or cavities in the closure member.

6. A static sealing arrangement as claimed in Claim 3, Claim 4 or Claim 5, in which the closure member is of a flexible material.

7. A static sealing arrangement as claimed in Claim 6, in which the closure member is of a moulded synthetic polymeric material.

8. A static sealing arrangement as claimed in any of Claim 3 to Claim 7 inclusive, in which the closure member tapers from the first end to the second end, thus causing the rotary sealing face to be obliquely oriented relative to the static tube.

9. A static sealing arrangement as claimed in Claim 8, in which the closure member is configured, prior to any wear, such that the rotary sealing face touches the static tube around a narrow circumferential band only.

10. A rotary pump including a rotor having an impeller, a casing within which the rotor is rotatable, and a static sealing arrangement as claimed in any one of Claim 3 to Claim 9 inclusive, the static tube being fast with said casing, and the axially extending closure member being hingedly secured to said rotor.

1 1 . A method of operating a static sealing arrangement, substantially as herein described and illustrated.

1 2. A static sealing arrangement, substantially as herein described and illustrated.