Flow inducing ring for a mechanical seal

A flow inducing ring for a mechanical seal includes a body portion having a first edge face and a second edge face, and at least one first groove extending both axially and circumferentially in one direction across the body portion from the first edge face to the second edge face. At least one second groove extends both axially and circumferentially in an opposite direction across the body portion from the first edge face to the second edge face. Each of the first groove and the second groove includes an entry portion, configured to draw a barrier fluid into the groove from the first edge face, and an exit portion, that is configured to expel barrier fluid from the groove to the second edge face and to impede the drawing of barrier fluid into the groove from the second edge face. The first and second grooves preferably have substantially constant cross-sections throughout the entirety of their lengths for enhanced uniform fluid flow.

BACKGROUND OF THE INVENTION

Technical Field of the Invention

The present invention relates, generally, to a flow inducing ring for directing barrier fluid along a desired flow path within a mechanical seal.

More particularly, the present invention relates to a mechanical seal comprising a flow inducing ring with grooves that are preferably of constant, or equal, cross-section throughout their lengths for providing a more uniform fluid flow.

Description of the Prior Art

Mechanical seals are typically used to separate a first fluid from a second fluid. In the context of a pump, for example, a mechanical seal is mounted so as to extend between the pump shaft and the pump housing.

A mechanical seal for separating a first fluid from a second fluid includes a rotary assembly for mounting on a rotatable shaft for rotation therewith and a stationary assembly for securing to a fixed structure within which the rotary assembly is located. Such a seal includes a “floating component” which forms part of either the rotary or the stationary assembly and which is axially moveable relative to the rotatable shaft. In addition, the seal includes a “static” component which forms part of the other of the rotary and stationary assemblies, this component being axially fixed relative to the rotatable shaft. The floating component has a flat angular end face or seal face which is directed toward the static component, usually by means of one or more springs, to close the seal faces together to form a sliding face seal.

A seal with a floating component forming part of the rotary assembly is described as a rotary seal and a seal whose floating component forms part of the stationary assembly is referred to as a stationary seal.

If the sliding seal between the rotary and stationary components is assembled and pre-set prior to despatch from the manufacturer, the seal is referred to as a “cartridge seal”. If the rotary and stationary components are despatched in unassembled form from the manufacturer, the seal is a “component seal”.

A mechanical seal may be single mechanical seal or a multiple mechanical seal, typically a double or triple mechanical seal. Furthermore a mechanical seal may include a barrier fluid system by means of which a third fluid, normally a liquid, is fed to the seal and this third or barrier fluid acts to separate the first and second fluids and is intended to facilitate the removal of heat generated between the sliding seal faces, thereby helping to prolong the life of the seal.

In order for the barrier fluid system to be effective, the barrier fluid has to be fed to the seal and, within the seal, to one or more areas where cooling is to be effected and thence is fed away from the seal. This involves axial movement of the barrier fluid and to some extent this is adversely affected by the forces induced as a result of the rotation of the rotary assembly relative to the stationary assembly.

Previously, a flow inducing ring has been used to direct barrier fluid within a mechanical seal. Furthermore, the deleterious effects of rotation on the axial movement of the barrier fluid have been overcome by using a flow inducing ring113as described in United Kingdom Patent Application No. 2,347,180 and depicted inFIGS. 3 and 4thereof. The flow inducing ring113is located within the mechanical seal and is mounted to rotate with the shaft.FIG. 3indicates the flow inducing ring comprises at least one groove115extending both axially and circumferentially in one direction across the ring and at least one other groove116extending both axially and circumferentially in the opposite direction across the ring. Grooves extending in the same direction are configured to form “single grooves”1137, whereas grooves extending in opposite directions and converging on the inboard or outboard edge of the body portion1131form “double grooves”1138. An example of a resulting pattern of grooves is shown inFIG. 4and comprises alternating double and single grooves. The grooves are arranged such that barrier fluid is caused to flow in the same direction regardless of the direction of the rotation of the shaft. In the flow inducing ring depicted inFIGS. 3 and 4, the grooves are arranged to always propel barrier fluid from the inboard side towards the outboard side of the flow inducing ring, i.e. in the outboard direction. When the shaft and thereby flow inducing ring is rotated in a first direction, grooves115are effective to cause the barrier fluid to flow from the inboard side of the ring to the outboard side of the ring in the outboard direction. Then, when the shaft (and flow inducing ring) rotates in the second and opposite direction, grooves116are effective to cause barrier fluid flow in the same outboard direction (from the inboard side to the outboard side of the ring). Accordingly, the barrier fluid is directed to flow in a particular direction irrespective of the direction of rotation of the flow inducing ring and shaft.

Unfortunately, there is a significant problem with this particular design. It has been found that barrier fluid is not only directed in the desired barrier fluid flow direction when the flow inducing ring is rotated. More specifically, it has been found that barrier fluid is also drawn into and directed along the grooves in the opposite direction to the desired flow path whilst the flow inducing ring is rotating. For example, whilst the fluid inducing ring rotates in the first direction and grooves115act to propel barrier fluid in the outboard direction, barrier fluid is also drawn into grooves116and directed along these grooves in an inboard direction from the outboard side towards the inboard side of the ring. Likewise, when the fluid inducing ring rotates in the second and opposite direction and grooves116act to propel barrier fluid in the outboard direction, barrier fluid is also drawn into grooves115from the outboard side of the ring and directed along these grooves in the inboard direction to the inboard side of the ring.

SUMMARY OF THE INVENTION

The present invention seeks to counteract the barrier fluid flow problems incurred by the above-mentioned prior art device. Embodiments of the present invention seek to control the flow of barrier fluid in one direction only. Embodiments of the invention seek to direct barrier fluid along a desired flow path and prevent or minimize any back-pumping effects of barrier fluid.

In a first aspect of the invention there is provided a flow inducing ring for a mechanical seal comprising a body portion having a first edge face and a second edge face; at least one first groove extending both axially and circumferentially in one direction across the body portion from the first edge face to the second edge face; and at least one second groove extending both axially and circumferentially in the opposite direction across the body portion from the first edge face to the second edge face; and characterized in that: each groove comprises an entry portion for drawing barrier fluid into the groove from the first edge face and an exit portion for expelling barrier fluid from the groove to the second edge face.

Preferably, each groove has a substantially constant, or fixed, cross-section along its entire length. Providing the grooves with a constant cross-section has the surprising advantage over “non-constant” grooves, or grooves with unequal cross-sections, in that grooves with varying cross-sections are more likely to give rise to suction and fluid discharge problems, as well as fluid and heat/turbulence, whereas a constant cross-section for the grooves throughout their lengths provides a more uniform fluid flow.

Alternatively, each groove comprises an entry portion shaped and configured to draw barrier fluid into the groove from the first edge face and an exit portion shaped and configured to expel barrier fluid from the groove to the second edge face and to impede the drawing of barrier fluid into the groove from the second edge face.

Preferably, the at least one first groove extends circumferentially in a clockwise direction across body portion from the first edge face to the second edge face and the at least one second groove extends circumferentially in an anticlockwise direction across the body portion from the first edge face to the second edge face.

The first edge face may be an inboard side of the body portion and the second edge face is an outboard side of the body portion. Alternatively, the first edge face may be an outboard side of the body portion and the second edge face is an in board side of the body portion.

Preferably, the entry portion has a plan view angle of between 1° and 89° and the exit portion has a plan view angle of approximately 90°.

Preferably, each groove has a curved profile with one or more radii.

The base of each groove may be inclined relative to the longitudinal axis of the ring.

The body portion between at least two grooves may be is inclined relative to the longitudinal axis of the ring.

The at least one first groove is preferably axially adjacent or separated from the at least one second groove.

A second aspect of the invention relates to a mechanical seal comprising:

(a) a rotary assembly for mounting on rotatable shaft rotation therewith;

(b) a stationary assembly for securing to a fixed structure within which the rotary assembly;

(c) said rotary assembly and said stationary assembly each carrying a respective mating sealing face;

(d) one of said seal faces being located on a floating component mounted for axial movement with respect to said shaft;

(e) means for urging the floating component in a direction toward the other of said seal faces;

(f) means for feeding a third fluid to a location within the seal which, when the seal is in use, lies between the first and second fluids; and characterized in further comprising:

(g) means for promoting axial flow of said third fluid within the seal, said axial flow promoting means comprising:a body portion having a first edge face and a second edge face;at least one first groove extending both axially and circumferentially in one direction across the body portion from the first edge face to the second edge face;at least one second groove extending both axially and circumferentially in the opposite direction across the body portion from the first edge face to the second edge face; and,

each groove comprising an entry portion for drawing barrier fluid into the groove from the first edge face and an exit portion for expelling barrier fluid from the groove to the second edge face with each groove having a substantially constant cross-section for the entirety of its length.

In an alternative second aspect of the invention there may be provided a mechanical seal comprising:

(a) a rotary assembly for mounting on rotatable shaft rotation therewith;

(b) a stationary assembly for securing to a fixed structure within which the rotary assembly;

(c) said rotary assembly and said stationary assembly each carrying a respective mating sealing face;

(d) one of said seal faces being located on a floating component mounted for axial movement with respect to said shaft;

(e) means for urging the floating component in a direction toward the other of said seal faces;

(f) means for feeding a third fluid to a location within the seal which, when the seal is in use, lies between the first and second fluids; and,

characterized in further comprising:

(g) means for promoting axial flow of said third fluid within the seal, said axial flow promoting means comprising:a body portion having a first edge face and a second edge face;at least one first groove extending both axially and circumferentially in one direction across the body portion from the first edge face to the second edge face;at least one second groove extending both axially and circumferentially in the opposite direction across the body portion from the first edge face to the second edge face; and whereby each groove comprises an entry portion shaped and configured to draw barrier fluid into the groove from the first edge face and an exit portion shaped and configured to expel barrier fluid from the groove to the second edge face and to impede the drawing of barrier fluid into the groove from the second edge face with each groove having a substantially constant cross-section for the entirety of its length.

Preferably, the means for promoting axial flow of said third liquid within the seal comprises any of the features relating to the first aspect of the invention.

Preferably, the body portion forms part of the rotary assembly. The fixed structure may comprise a housing having a component located radially outside the body portion, the component having an inner face which is inclined relative to the longitudinal axis of the seal. Alternatively, the fixed structure may comprise a housing having a component located radially outside the body portion, whereby an eccentric annular space is defined between the component and body portion.

The body portion may instead form part of the stationary assembly.

The present invention may be applied to rotary and stationary seals whether they are of cartridge or component type.

The present invention may be applied to a single or multiple mechanical seal. Other objects and features of the present invention will become apparent when considered in combination with the accompanying drawing figures which illustrate certain preferred embodiments of the present invention. It should, however, be noted that the accompanying drawing figures are intended to illustrate only certain embodiments of the claimed invention and are not intended as a means for defining the limits and scope of the invention.

DETAILED DESCRIPTION OF THE DRAWING FIGURES AND PREFERRED EMBODIMENTS

The present invention will now be described, by way of examples only, with reference to the accompanying drawings:

Referring toFIG. 1of the accompanying drawings, there is illustrated a double stationary mechanical seal located about a rotatable shaft6. The seal is a cartridge seal and includes on the inboard side of the seal a stationary component1and, a rotary component2which together define sealing faces3. Rotary component2is located radially outwardly of a sleeve5, which is fixed for rotation with shaft6.

As well as the inboard sealing components mentioned above, the seal includes an outboard sealing arrangement providing sealing faces11. Barrier fluid is fed to the seal via inlet9located in gland10. The barrier fluid follows a path located radially outwardly of a deflector ring7in a direction towards seal face3, this path being indicated by the arrows in the upper part ofFIG. 1. The barrier fluid then follows a path located radially inwardly of deflector7, as indicated by the arrows in the lower part ofFIG. 1. The barrier fluid exits from the seal via outlet12located in gland10. The barrier fluid may then be recycled back to inlet9.

A flow inducing ring13is located between the inboard sealing faces3and the outboard sealing faces11. As best seen inFIGS. 2, 5, 6 and 7, ring13includes a main body portion131from the inner edge of which extends an integral channel132housing an O-ring133. O-ring133bears against sleeve5.

Extending in an outboard direction from main body portion131of ring13is a flange134, which steps outwardly to provide a space between this flange and the rotary component135of the outboard seal. Located in this space is a further O-ring136. Accordingly, the flow inducing ring13forms part of the rotary assembly with which it is in sealing engagement through O-rings133and136.

Extending into main body portion131of ring13is a plurality of deep grooves, slots or vanes15,16each of which extend from the inboard face of main body portion131to the outboard face thereof. Each groove15,16is rectangular in cross-section and extends not only axially, but also circumferentially across the main body portion131of ring13. Some of the grooves15extend circumferentially in one direction and others (grooves16) in the opposite direction. From the patterns of grooves depicted inFIGS. 8aand 9ait can be seen that some grooves137are single grooves and others138are double grooves due to the meeting of two single grooves where they converge on the inboard or outboard edge of body portion131. The resulting patterns comprise alternating double and single grooves, the double grooves being of chevron shape in plan.

In the example depicted inFIGS. 5, 6 and 7, grooves15extend circumferentially in an anticlockwise (counterclockwise) direction across the main body portion131from the inboard side of the ring13to the outboard side of the ring, i.e., the grooves15extend left to right across the body portion from the inboard side to the outboard side of the ring. Meanwhile, grooves16extend circumferentially in a clockwise direction across the main body from the inboard side to the outboard side of the ring13, i.e., the grooves16extend right to left across the body portion from the inboard side to the outboard side of the ring13. It can be seen from the figures that groove16is essentially a mirror image of groove15. The grooves15and16are located on ring13such that, when the ring13rotates with the seal barrier, fluid is propelled axially in an outboard direction from the inboard side of the ring13to the outboard side of the ring13. When the shaft6rotates in the direction indicated by arrow W′, then grooves15are effective to cause the barrier fluid to flow in the outboard direction and when the shaft rotates in the opposite direction (in the direction indicated by arrow W), grooves16are effective to cause barrier fluid flow in the same outboard direction. By arranging the grooves15,16circumferentially in opposite directions across the ring13, barrier fluid is able to flow in the same direction irrespective of the direction of the rotation of flow inducing ring with the shaft.

FIGS. 8ato 9billustrate different groove patterns that are effective to produce barrier fluid flow in the desired direction irrespective of the direction of rotation of the shaft. It can be seen that in each of these groove patterns there are some grooves15which extend circumferentially in one direction from the inboard side to the outboard side of the ring13and others (grooves16) extend circumferentially in the opposite direction from the inboard side to the outboard side of the ring13. The grooves extend circumferentially in either a clockwise or anticlockwise across the ring13. The pattern of grooves, as well as the shape of each groove, may be varied to suit the performance required from the flow inducing ring.

As best illustrated inFIGS. 8aand 8b, each groove preferably has a substantially constant, or fixed, cross-section along its entire length. Providing the grooves with a constant cross-section has the surprising advantage over “non-constant” grooves, or grooves with unequal cross-sections, in that grooves with varying cross-sections are more likely to give rise to suction and fluid discharge problems, as well as fluid and heat/turbulence, whereas a constant cross-section for the grooves throughout their lengths provides a more uniform fluid flow.

FIGS. 8ato 9balso illustrate different groove patterns that are effective to produce barrier fluid flow in only one direction (the desired direction), irrespective of the direction of rotation of the shaft. It will be seen that each groove15,16comprises an entry portion100and exit portion200. The entry portion100is shaped for drawing the barrier fluid into the groove. The exit portion200is shaped for directing fluid from the groove into the mechanical seal. The exit portion200is also shaped to impede, minimize or prevent the drawing of barrier fluid into the groove. Hence, barrier fluid may only flow in one direction along the grooves from the entry portion to the exit portion. Any back-pumping of barrier fluid into groove from the exit portion is prevented or minimized.

The entry portion100of each groove15,16is shaped such that it is angled with respect to the longitudinal axis (axis of rotation) of the flow inducing ring13. The entry portion100of each groove has a leading edge100A and a trailing edge100B in accordance with the direction of rotation. The angle of the leading edge, λ, with respect to the longitudinal axis may vary from 1° to 89°, typically from 5° to 85°. Likewise, the angle of the trailing edge, α, with respect to the longitudinal axis may vary from 1° to 89°, typically from 5o to 85°. The angle of the leading edge, λ, may be smaller or identical to the angle of the trailing edge, α. The angles of the leading edge and trailing edges are chosen such that the entry portion100is shaped to “cut” into the barrier fluid as the flow inducing ring rotates and draw barrier fluid into the groove.

The exit portion200of each groove15,16is also shaped such that it is angled with respect to the longitudinal axis (axis of rotation) of the flow inducing ring13. The exit portion has a leading edge200A and trailing edge200B, in accordance with the direction of rotation. The angle of the leading edge,, and the angle of the trailing edge, β, are preferably identical and preferably substantially 90°. The exit portion200is shaped to expel barrier fluid from the groove. More specifically, the exit portion200is shaped such that barrier fluid is directed from the groove in a direction that is substantially parallel to the axis of rotation. The exit portion200is not shaped to “cut” into the barrier fluid like the entry portion100. Thus, barrier fluid is not drawn into the exit portion200. Accordingly, barrier fluid may only flow in one direction along the groove; from the entry portion100to the exit portion200. Hence, the back-pumping effect associated with the prior art device is avoided.

Since the entry portion100and exit portion of each groove are arranged at different angles with respect to the axis of rotation, the entry portion100and exit portion200are shaped and configured such that the groove has a curved profile. The curved profile may have one or more radii.

FIGS. 8aand 8billustrate a groove pattern where barrier fluid is drawn from the inboard side towards the outboard side of the flow inducing ring13. Grooves15extend axially and circumferentially in an anticlockwise direction (left to right) from the inboard side to the outboard side of the ring13. Grooves16extend axially and circumferentially in a clockwise direction (right to left) from the inboard side to the outboard side of the ring. The entry portion100of each groove15,16is shaped and configured such that the angle of the leading edge, λ, and angle of the trailing edge, α, are identical and approximately 30°. The exit portion200of each groove15,16is shaped and configured such that the angle of its leading edge,, and the angle of its trailing edge, B, is substantially 90°.FIG. 8bshows that when the flow inducing ring13rotates in direction indicated by arrow, ω, the entry portion100of grooves16cuts through the barrier fluid and draws fluid into the grooves16. Barrier fluid is then directed to flow along length L1of the entry portion, along a curved portion with radius r and along length L2of the exit portion200of groove16. The barrier fluid is then directed by the exit portion200into the mechanical seal in a direction that is substantially parallel to the axis of rotation. The exit portions of both grooves15and16are configured such that they are unable to “cut through” barrier fluid so the flow of any barrier fluid into the exit portions in either groove15or16from the outboard side of the ring13is prevented or restricted. Hence, when the flow inducing ring rotates in direction of ω, the barrier fluid may only flow along grooves16. In this case, barrier fluid is drawn into grooves16from the inboard side of the flow inducing ring13via the entry portion and it is expelled from the outboard side of the ring13via the exit portion. It follows that when the flow inducing ring rotates in the direction indicated by arrow {acute over (ω)}, barrier fluid may only flow along grooves15from the inboard side to the outboard side of the ring13. As the ring13rotates in the direction of {acute over (ω)}, barrier fluid is drawn into grooves15from the inboard side of the ring13via the entry portions100of grooves15, it is impeded or prevented from entering the exit portions200of both grooves15and16and it is expelled from the outboard side of the ring13via the exit portions200of grooves15in a direction that is substantially parallel to the axis of rotation.

FIGS. 8aand 8billustrates a groove pattern of a flow inducing ring according with the grooves15and16having a constant cross-section along the entirety of their lengths, which provides a more uniform fluid flow and avoids problems often associated with grooves having irregular cross-sections. Such problems frequently encountered with pertain to suction and discharge irregularities and fluid and heat turbulence.

FIGS. 9aand 9bdepict an alternative groove pattern where the angle of the leading edge X is smaller than the angle of the trailing edge, α, of the entry portions100of the grooves15,16. Furthermore, the grooves are provided with a curved path having radii r1, r2and r3. This curved path is configured so as to restrict the generation of eddy currents within the barrier fluid as it is drawn into and flows along the grooves15,16. In order to restrict the flow of barrier fluid in only the outboard direction, the exit portions200of the grooves15,16are shaped such that the angle of its leading edge,, and the angle of its trailing edge, B, is substantially 90°. As with the groove pattern depicted inFIGS. 8aand 8b, the grooves15and16in the groove pattern ofFIGS. 9aand 9bare arranged such that barrier fluid is drawn into the entry portions100of grooves16and expelled from the exit portions200of grooves16when the flow inducing ring rotates in the direction of ω, and then barrier fluid is drawn into the entry portions100of groove15and expelled from the exit portions200of grooves15when the flow inducing ring rotates in the {acute over (ω)} direction. The exit portions200are shaped to prevent or minimize any barrier fluid from being drawn into either grooves15or16from the outboard side of the ring13. Hence, barrier fluid may only flow from the inboard side towards the outboard side of ring13when the ring rotates.

FIG. 10depicts a second embodiment of the present invention where the outer radial surface18of the flow inducing ring83is provided with grooves84, each of which has an inclined base87, the inclination being in an outward direction from the inboard to the outboard side of the seal.

FIG. 11depicts a third embodiment of the present invention where the flow inducing ring93has an inclined outside diameter98, the inclination again being outwardly from the inboard to the outboard side of the seal.

Referring toFIGS. 12 to 12cof the accompanying drawings, there are illustrated different groove cross-sections which may be used in the flow inducing ring13of the present invention. InFIG. 12a, the groove15has a cross-section similar to that shown inFIGS. 5, 6 and 7. The groove in cross-section has a base which is curved to follow the circumferential surface of the ring at that diameter. The sides of the groove extend radially outwardly from the base.

The groove15shown inFIG. 12bis gently curved from the centre of its base where it follows the circumference at that diameter, the curve changing direction to provide the curved sides of the groove extending to the outer surface of the ring. InFIG. 12cthe grooves15are also curved but much more sharply at the sides of the groove so that each side is channel-shaped.

FIG. 13depicts a fourth embodiment of the present invention where the inner radial surface96of housing97is inclined in a direction outwardly from the inboard to the outboard side of the seal. Furthermore, the outer radial surface18of flow inducing ring93is also inclined in the same direction to provide a gap between housing97and ring93which is constant from the inboard to the outboard side.

Where the inner radial surface of the housing and/or the outer radial surface of the flow inducing ring is inclined, the angle of inclination may vary from 1° to 89°.

FIG. 14depicts a fifth embodiment of the present invention where the inner radial surface126of housing127is inclined in a direction outwardly from the inboard to the outboard side of the seal. The outer radial surface128of flow inducing ring123is parallel to the longitudinal axis of the seal so that the gap between the two adjacent radial surfaces increases from the inboard to the outboard side of the seal.

FIG. 15depicts a sixth embodiment of the present invention where the housing137is eccentrically mounted or the inner radial surface136of the housing is eccentrically shaped such that the annular space defined between the stationary and rotary components varies between a region of minimum radial dimension and a region of maximum radial dimension offset circumferentially to each other. Hence, an eccentric annular space or clearance is provided between the housing137and flow inducing ring133. Accordingly, the pumping effect of barrier fluid within the mechanical seal and across the flow inducing ring133is improved.

It should be appreciated that the present invention may be applied to a seal to be provided between a stationary shaft and a rotatable housing.

It should also be appreciated that the flow inducing means may be located anywhere in the flowpath of the barrier fluid. For instance, in another embodiment in accordance with the present invention, the flow inducing means may be integral with the sleeve (item5of theFIG. 1embodiment) and may be positioned below a deflector (item7A ofFIG. 1) which in turn extends below the inboard sealing faces.

While only several embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that many modifications may be made to the present invention without departing from the spirit and scope thereof.