FLOW RESTRICTING DEVICES IN PUMPS

FIELD OF THE INVENTION

[1] The present invention generally relates to rotary pumps, such as chemical processing pumps or nuclear reactor coolant pumps, and constituent components therefor, such as flow restricting devices.

BACKGROUND OF THE INVENTION

[2] In pressurized water nuclear power plants, a reactor coolant system is used to transport heat from the reactor core to steam generators for the production of steam. The steam is then used to drive a turbine generator. The reactor coolant system includes a plurality of separate cooling loops, each connected to the reactor core and containing a steam generator and a rotary coolant pump. Other venues also present situations where containment of a process fluid is critical, such as in the case of rotary chemical processing pumps .

[3] A rotary pump such as a reactor coolant pump or chemical processing pump typically is a centrifugal pump designed to move large volumes of process fluid (e.g., reactor coolant) at high temperatures and pressures. Such a pump normally includes hydraulic, shaft seal and motor sections. A hydraulic section usually includes an impeller mounted at an end of a pump shaft which is operable within the pump casing to pump process fluid. A motor section includes a motor which is coupled to drive the pump shaft. A middle shaft seal section usually includes tandem sealing assemblies located concentric to.

and near the top end of, the pump shaft. Such sealing assemblies normally are configured for allowing but minimal process fluid leakage along the pump shaft during normal operating condition. Representative examples of known pump shaft sealing assemblies, at least in the context of reactor coolant pumps, may be found in the following U.S. Patents: MacCrum (No. 3,522,948), Singleton (No. 3,529,838), Villasor (No. 3,632,117), Andrews et al (No. 3,720,222) and Boes (No. 4,275,891).

[4] Pump shaft sealing assemblies, as such, must normally be capable of containing a high system pressure without excessive leakage. Tandem arrangements of sealing assemblies, for instance, serve to break down the pressure in stages. Pump sealing assemblies in fact may act as controlled-leakage seals which, in operation, allow a minimal amount of controlled leakage at each stage while preventing excessive leakage of process fluid (e.g., reactor coolant) from the primary fluid system to respective seal leakoff ports. This applies in many scenarios where containment of excess leakage is critical . In the case of nuclear reactor coolant pumps, since pump sealing assemblies can be prone to failure, e.g. in response to unmitigated high temperatures of reactor coolant, any resultant excessive leakage rates could lead to reactor coolant uncovering of a reactor core, and subsequent core damage.

[5] While U.S. Patent No. 5,171,024 (Janocko) discloses a shutdown seal arrangement for preventing and arresting excess fluid leakage along a pump shaft, a need has been recognized in connection with providing an even more effective arrangement, whether in the context of

nuclear reactor coolant pumps or other contexts such as chemical processing pumps.

SUMMARY OF THE INVENTION

[6] There is broadly contemplated herein, in accordance with at least one embodiment of the present invention, a split ring arrangement, disposed about a shaft, that actuates in response to a fluid leak. In a first condition, ends of the split ring arrangement are spaced apart, whereby a flow path for fluid is provided and clearance is provided for ^" a normally moving shaft . In a second condition, these ends of the split ring arrangement converge such that a flow path for fluid is blocked or restricted. Pressure loadings may be employed to hold the split ring arrangement in this second, "closed" position. As an advantageous alternative, a meltable spacer can be initially positioned between ends of the split ring, and melt at a prescribed temperature to actuate a closing of the ring.

[7] In accordance with at least one further embodiment of the present invention, a sliding sleeve is provided about a shaft . Responsive to a pressure drop (e.g., pursuant to high fluid flow rates, a phase change or choked flow) , the sleeve may slide in a direction parallel to the longitudinal axis of the shaft to a position in which fluid flow about the shaft is restricted or blocked.

[8] In accordance with at least one additional embodiment of the present invention, the split ring and sliding sleeve arrangements, as described above, may be provided together in the context of a single pump.

[9] In summary, there is broadly contemplated herein, in accordance with at least one presently- preferred embodiment of the present invention, in a structure comprising a shaft member and a support structure through which the shaft member extends, an arrangement for restricting fluid flow along the shaft member relative to the support structure in at least one annular space defined between the shaft member and the support structure, the fluid flow restricting arrangement comprising: a discontinuous ring member disposed about the shaft member; the discontinuous ring member having two ends; the discontinuous ring member being actuable between: a first condition, wherein the ends are spaced apart over a first distance; and a second condition, wherein the ends are spaced apart over a second distance, the second distance being less than the first distance; wherein, in the first condition, a greater flow path for fluid is afforded, in the at least one annular space defined between the shaft member and the support structure, than in the second condition.

[10] Additionally, there is broadly contemplated herein, in accordance with at least one presently preferred embodiment of the present invention, in a structure comprising a shaft member and a support structure through which the shaft member extends, an arrangement for restricting fluid flow along the shaft member relative to the support structure in at least one annular space defined between the shaft member and the support structure, the fluid flow restricting arrangement comprising: a sleeve member disposed about the shaft member,- the sleeve member being displaceable, in a direction generally parallel to a longitudinal axis of the shaft member, between a first position and a second

position,- wherein, in the first position, a greater flow path for fluid is afforded, in the at least one annular space defined between the shaft member and the support structure, than in the second position.

[11] Further, there is broadly contemplated herein, in accordance with at least one presently preferred embodiment of the present invention, a rotary pump comprising: a motor; a shaft member extending from the motor; an impeller attached to a free end of the shaft member; a housing which encloses a major portion of the shaft member; the housing comprising a seal housing which circumscribes at least a portion of the shaft member, the seal -housing including at least one sealing element for restricting fluid flow along the shaft member; the motor being configured for rotating the shaft in a manner to drive the impeller; and an arrangement for restricting fluid flow along the shaft relative to the seal housing in at least one annular space defined between the shaft member and the seal housing; the fluid flow restricting arrangement comprising a discontinuous ring member disposed about the shaft member; the discontinuous ring member having two ends; the discontinuous ring member being actuable between: a first condition, wherein the ends are spaced apart over a first distance; and a second condition, wherein the ends are spaced apart over a second distance, the second distance being less than the first distance; wherein, in the first condition, a greater flow path for fluid is afforded, in the at least one annular space defined between the shaft member and the seal housing, than in the second condition.

[12] Also, there is broadly contemplated herein, in accordance with at least one presently preferred

embodiment of the present invention, a rotary pump comprising: a motor; a shaft member extending from the motor; an impeller attached to a free end of the shaft member; a housing which encloses a major portion of the shaft member; the housing comprising a seal housing which circumscribes at least a portion of the shaft member, the seal housing including at least one sealing element for restricting fluid flow along the shaft member; the motor being configured for rotating the shaft in a manner to drive the impeller; and an arrangement for restricting fluid flow along the shaft relative to the seal housing in at least one annular space defined between the shaft member and the seal housing; the fluid flow restricting arrangement comprising a sleeve member disposed about the shaft; the sleeve member being displaceable, in a direction generally parallel to a longitudinal axis of the shaft member, between a first position and a second position; wherein, in the first position, a greater flow path for fluid is afforded, in the at least one annular space defined between the shaft member and the seal housing, than in the second position.

[13] The novel features which are considered characteristic of the present invention are set forth herebelow. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of the specific embodiments when read and understood in connection with the accompanying drawings .

BRIEF DESCRIPTION OF THE DRAWINGS

[14] The present invention and its presently preferred embodiments will be better understood by way of reference to the detailed disclosure herebelow and to the accompanying drawings, wherein:

[15] FIG. 1. illustrates, in a partial cross sectional view, a centrifugal pump employing a split ring arrangement .

[16] FIG. 2 provides a close-up of a split ring and surrounding components in the pump of FIG. 1.

[17] FIG. 3A illustrates schematically an elevational view of a first split ring arrangement about a shaft, and deployed in a first position.

[18] FIG. 3B illustrates the split ring from FIG. 3A in plan view.

[19] FIG. 3C is essentially the same view as FIG. 3A but showing the split ring arrangement deployed in a second position.

[20] FIG. 3D illustrates the split ring from FIG. 3C in plan view.

[21] FIG. 4A illustrates schematically an elevational view of a second split ring arrangement about a shaft, and deployed in a first position.

[22] FIG. 4B illustrates the split ring from FIG. 4A in plan view.

[23] FIG. 4C is essentially the same view as FIG. 4A but showing the split ring arrangement deployed in a second position.

[24] FIG. 4D illustrates the split ring from FIG. 4C in plan view.

[25] FIG. 5 illustrates, in a partial cross sectional view, a centrifugal pump employing a sliding sleeve arrangement .

[26] FIG. 6 provides a close-up of a sliding sleeve arrangement and surrounding components in the pump of FIG. 5, with the sliding sleeve arrangement in an actuated position.

[27] FIG. 7A illustrates schematically an elevational view of a first sliding sleeve arrangement about a shaft, and deployed in a first position.

[28] FIG. 7B is essentially the same view as FIG. 7A but showing the sliding sleeve arrangement deployed in a second position.

[29] FIG. 8A illustrates schematically an elevational view of a second sliding sleeve arrangement about a shaft, further including a split ring, and deployed in a first position.

[30] FIG. 8B is essentially the same view as FIG. 8A but showing the sliding sleeve arrangement deployed in a second position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[31] Referring to FIG. 1, a pump 10 generally includes a main pump housing 12. While, in the embodiment shown, housing 12 forms a large portion of an external housing for pump 10, it retracts inwardly to further form an internal seal housing 12a. An impeller housing 14 is also bolted to the main pump housing 12 and houses an impeller 16. Pump 10 can be representative of a wide variety of rotary pumps, including general centrifugal pumps, nuclear reactor coolant pumps and chemical processing pumps (e.g., as commonly used in the chemical processing industry) . Pump 10 may be oriented in any direction appropriate for the application at hand, e.g., a generally horizontal direction or (in the case of a reactor coolant pump) in a generally vertical direction.

[32] The pump 10 includes a pump shaft 18 extending centrally with respect to the pump housing 12 and being sealingly and rotatably mounted within the seal housing 12a. Pump shaft 18, at one end thereof, is connected to impeller 16 (e.g., via a cap 20 as shown), while, at another end, is connected to an electric motor 22. When the motor 22 rotates the shaft 18, the impeller 16 causes pressurized reactor coolant to flow through the general reactor coolant system. At the same time, this pressurized coolant applies an upwardly directed, hydrostatic load upon the shaft 18.

[33] In order that the pump shaft 18 might rotate freely within the seal housing 12a while maintaining a high pressure boundary between the pump high pressure region (i.e., the chambers associated with impeller 16 and extending to the right therefrom with respect to FIG. 1)

and a region (indicated at 24) ambient to the seal housing 12a, sealing assemblies are preferably provided, including a mechanical face seal. The general layout and function of conventional sealing assemblies can be more fully understood from Janocko, supra. In accordance with at least one presently preferred embodiment of the present invention, there is broadly contemplated a split ring 26 which serves to limit fluid flow between shaft 18 and housing 12a under given conditions, as will be better appreciated in the discussion herebelow.

[34] Ring 26 is preferably split (or cut) along a cutting plane at a point along the circumference of ring 26, or presents even a non-planar end treatment as discussed further below. Preferably, ring 26 is configured such that the free ends thereof, absent any intervening structure or any appreciable opposing forces, come into contact when in a "relaxed" or "free" state. As such, ring 26 is further preferably configured such that when these free ends are separated such that a gap between the ends develops and then increases, the ring 26 thereby deforms elastically and the effective diameter of the ring increases. (Thus, conversely, decreasing the gap in the ring 26 to the point that the ends contact allows the effective diameter of the ring to decrease.) It will be appreciated from the discussion herebelow that a split ring 26, in accordance with at least one embodiment of the present invention, may advantageously have its ends spaced apart in a first, initial condition, whereby elastic properties of the ring 26 itself can promote (with or without assistance of another closing force) convergence of the ends towards a second, "closed" condition. To better appreciate the functioning of a split ring 26 in the context of Fig. 1, reference can also be made to Fig.

2 (which is a close-up view of split ring 26 and surrounding components of pump 10) .

[353 While the ends of split ring 26 indeed can be cut along a simple cutting plane that is parallel to a central (longitudinal) axis defining the ring, other types of "end treatment" are of course possible. As known in the art of piston rings (and even other rings) , a split ring 26 may have a "mitred" or diagonal planar cut to define the free ends or even more elaborate end treatments are possible. For instance, a "notched" type of end treatment may be employed where a protrusion at one end may mate with a recess or notch at the other end. In general, various end treatments may be employed to reduce leakage at the junction of the ends while accommodating variations in the circumference of the shaft or split ring due to manufacturing tolerances, thermal expansion or loading. (As such, split ring 26, in a particularly preferred embodiment of the present invention, includes a "mitred" end treatment, where ends of split ring 26 meet at a mitred or diagonal interface, wherein these ends can slide against one another, in response to small displacements from, e.g., thermal expansion, without essentially compromising the capability of the ring to protect against leakage.)

[36] As shown, the split ring 26 is positioned between shaft 18 (or an integral portion thereof) and seal housing 12a, in chamber suitable for accommodating ring 26. This chamber is preferably sized, in particular, to readily accommodate both the initial and closed conditions of ring 26. As such, in the aforementioned first or "initial" condition of ring 26, a gap is maintained between the ends of the split ring 26 such that the split

ring 26 contacts only the housing 12a. This allows for the normal relative motion between the housing 12a and the shaft 18. The sizing of ring 26 is also preferably such that when the gap between the ends of the split ring 26 is allowed to close (as further described below) , the split ring 26 constricts around shaft 18, closing the annular gap between the inner diameter of the split ring 26 and the outer diameter of the shaft 18.

[37] Because the gap between ends of the split ring

26 is more or less artificially created, a suitable arrangement is preferably employed to hold the ends apart in the first, initial condition of ring 26. One such arrangement may preferably be embodied by a spacer composed of a material which, when exposed to certain conditions in the fluid such as temperature or fluid chemistry or other conditions, reacts with the fluid to dissolve, change state, or otherwise be materially compromised (see below regarding Fig. 3B) . Upon such exposure, ends of the split ring 26 would thereby be released, allowing the ring 26 to constrict around the shaft 18. Actuation of the spacer could thus be automatic. Such a spacer could be formed, e.g., from a metal alloy or thermoplastic polymer with a melting temperature in a desired actuation range (though chemical compatibility of the spacer material with the ambient fluid would of course be important) .

[38] Alternatively, a mechanical actuator could be provided, a mechanical actuator could be provided to initially hold the split ring 26 in the first, "initial" condition and then permit split ring 26 to constrict around the shaft 18 into the second, "closed" condition. Such a mechanical actuator could employ a type of

automatic response to a change in the condition of the fluid and mechanically release the ends of the split ring 26 and thus promote constriction about shaft 18 (see below regarding Figs. 4A and 4B) .

[39] To bias ring 26 within its surrounding annular chamber in a direction towards the motor 22 and away from impeller 16 (i.e., in a direction of potential leakage flow or in a direction from high pressure within the pump housing to a lower external pressure outside the pump) , there can be provided a number of springs 28a oriented in parallel to the central axis of pump 10 as shown. Additional springs 28b, oriented in a radial direction with respect to the central axis of pump 10, could assist in promoting closure of the ring 26 by supplementing the normal elastic tendency of the ring 26 towards "closure", or a convergence of the ends of the ring, once an "actuator" (e.g., meltable or mechanical) serves to "release" the spaced-apart ends of ring 26.

[40] Various cross-sectional shapes for a split ring

126 are conceivable, two of which are shown in Figs. 3A- 4D. Figs. 3A-3D illustrate a first such arrangement, namely a shape which approximates a right triangle. As shown, ring 126 may be disposed within a chamber defined by shaft 118 and housing 112a. Biasing springs 128a may also be provided to bias the ring 126 in an upward direction with respect to Figs. 3A and 3C, or in a direction towards a motor and away from an impeller. Figs. 3A and 3B particularly show ring 126 in a first, initial position, where ends of the ring 126 are spaced apart, while Figs. 3C and 3D show ring 126 in a second, closed position, where ends of the ring 126 are together. Dotted lines in Fig. 3B, indicated at 129, illustrate the

prospective location of a meltable or consumable spacer as described heretofore.

[41] In the cross-sectional shape of a right triangle as shown in Figs. 3A and 3C, the legs of the "triangle" forming the right angle could preferably be aligned in parallel to axial and radial directions, respectively, of shaft 118; the inner diameter of the split ring 126 would thereby be approximately parallel to the surface of shaft 118. The angled conical surface formed by the hypotenuse of the right triangle of the section of the split ring could thus interface with a similarly beveled conical surface integral to housing 112a (or with an appurtenance of housing 112a) .

[42] In the embodiment illustrated in Figs. 3A-3D, the split ring 126 and the seating surface of housing 112a are oriented such that a pressure differential resulting from any restriction of flow by the imposition of the split ring 126 would tend to hydrostatically load the split ring 126 against the conical surface in housing 112a. The axial loads applied to the conical interface between the split ring 126 and the housing 112a would result in a radial reaction component acting on the split ring 126, which would also tend to force the split ring 126 radially inward toward the shaft 118, further tending to close the annular gap between the inner diameter of the split ring 126 and the shaft 118, and also thereby tending to close the circumferential gap between the ends of the split ring 126.

[43] With split ring 126 being held open by a mechanical actuator or spacer, the split ring 126 could preferably be held against the conical seating surface of the housing by springs or by another suitable arrangement .

This would restrict any motion of the split ring 126 until such a time that the actuator or spacer released the ends of the split ring 126 and the split ring 126 was allowed to constrict. As the split ring 126 constricts because of the effective change in the diameter of its conical surface, it would tend to move axially toward the conical surface of the seating surface in the housing 112a to maintain contact between the conical interfaces. The springs or alternate arrangement would continue to load the split ring 126 against the conical seating surface of the housing 112a. This continued contact would tend to limit flow between the split ring 126 and housing 112a.

[44] A triangular cross-sectional shape of the split ring 126 is of course only one possible realization. For instance, rather than the beveled conical surfaces resulting from the triangular shape, the split ring 126 may have flat or spherical surfaces of interface with housing 112a which may provide other desirable benefits, such as automatic allowance for misalignment or radial offset of the inner circular shaft member to the outer housing member. Figs. 4A-4D, for their part, illustrate a split ring 126 with an essentially rectangular cross- section. Essentially in parallel with Figs. 3A-3D, Figs. 4A and 4B show a split ring 126 in a first, initial position while Figs. 4C and 4D show a split ring 226 in a second, closed position. Components that are essentially similar to those in Figs. 3A-3D bear reference numerals advanced by 100.

[45] In the embodiment illustrated in Figs. 4A-4D, the annular chamber containing ring 226 is essentially rectilinear in cross-section as well, and thus there is essentially a "flat" interface between ring 226 (at an

upper portion thereof) and housing 212a (or an interface which runs perpendicular with respect to the common central longitudinal axis of shaft 218 and housing 212a.

[46] Figs. 4A and 4B illustrate a mechanical actuator

231 as an alternative to the meltable/consumable spacer 129 shown in Fig. 3B. A mechanical actuator 231 could function analogously to a meltable/consumable spacer, i.e., act to promote closure of ring 226 in response to given conditions. As such, mechanical actuator 231 could be embodied by any of a very wide variety of arrangements. For instance, a spring-loaded retractable plunger could hold the ends of ring 226 apart and, in response to temperature change or other type of change in the ambient fluid, could release the ends of ring 226 which would then converge and close of their own accord. In accordance with such an arrangement, the plunger could be actuated by an electromotive device (e.g., solenoid or motor) that responds to an external electrical signal transmitted when a predetermined condition is met . Alternatively, a plunger arrangement could include differing hydrostatic areas that are in communication with different parts or chambers of the pump such that a plunger would retract when certain pressure conditions in the pump prevail.

[47] A hybrid arrangement is even conceivable, where a spring-loaded plunger itself contains a meltable/consumable member or spacer which, when it melts or is physically compromised in response to temperature, permits the plunger to retract and thus promote convergence of the ends of ring 226. In accordance with such an arrangement, the meltable/consumable material could actually be contained away from the process fluid (e.g., within a chamber associated with the plunger

spring [s]) and be configured for responding to temperature only.

[48] It should be clearly understood that the meltable/consumable spacer 129 of Fig. 3B and the mechanical actuator 231 of Figs. 4A and 4B are essentially interchangeable and can be employed with essentially any split ring arrangement, and thus need not be associated solely with those specific split ring arrangements and geometries shown in the respective drawings.

[49] In the context of all conceivable embodiments, the split ring is preferably sized such that, when released and permitted to contract around the shaft, the inner diameter of the split ring contacts or comes in close proximity to the surface of the shaft, thereby closing or rendering very small the circumferential gap between the inner diameter of split ring and outer diameter of shaft. This will thus have the effect of generally limiting the flow of fluid through the annulus between the shaft and the surrounding housing .

[50] It will further be appreciated that by limiting fluid flow in the second "constricted" condition, the split ring also creates a differential pressure across the contact surfaces between the split ring and the shaft as well as the contact surfaces between the split ring and the housing and that by carefully controlling the locations of these contact surfaces, the locations of pressure drops can be controlled. These contact surfaces and their associated pressure drops would thus define hydrostatic areas to be acted on by the various pressures to generate forces acting on the split ring, which can be utilized to augment the "seating" forces for split ring and the forces acting to further constrict the split ring,

and can preferentially control deformations of the split ring.

[51] A split ring as described heretofore may also incorporate deformable elements to enhance the seating of the contact surfaces between the split ring and inner and outer members and/or between the ends of the split across the circumference of the ring.

[52] The disclosure now turns to a discussion of

"sliding sleeve" arrangements for limiting fluid flow through an annulus between a shaft 318 and a housing 312a, as depicted illustratively yet non-restrictively in Figs. 5-8B. As such, Fig. 5 illustrates, in a partial cross sectional view, a pump 310 employing a sliding sleeve arrangement. (Again, pump 310 can be representative of a wide variety of rotary pumps, including general centrifugal pumps, nuclear reactor coolant pumps and chemical processing pumps.) Fig. 6 is essentially a close-up view taken from Fig. 5, but showing the sliding sleeve in an actuated position (i.e., having slid in a direction towards the motor) . Various pump components illustrated in Figs . 5 and 6 are similar to those shown in Figs. 1 and 2, and corresponding reference numerals are thus advanced by 300. As the discussion presently continues, simultaneous reference may be made to both Figs. 5 and 6 to better understand and appreciate the sliding sleeve arrangement at hand.

[53] Preferably provided is a cylindrical sleeve 330 of specific cross section which is disposed around shaft 318, between shaft 318 and housing 312a, and is free to move in a direction essentially parallel to a longitudinal axis of shaft 318. The inner diameter surface of the cylindrical sleeve 330 preferably does not contact the

surface of the shaft 318, but does maintain a small annular clearance. The outer surface of the cylindrical sleeve 330 is preferably mounted in a close clearance fit with the housing 312a, which permits the cylindrical sleeve 330 to move along the direction of its own central axis .

[54] The close clearance fit between the cylindrical sleeve 330 and the housing 312a may be sealed with an elastomer sealing element (e.g., 0-ring) 332 which seals the joint through compression or contact with the two members while still allowing a sliding fit and relative motion. Alternate suitable arrangements for minimizing leakage across this sliding fit, such as a piston ring, of course may be used.

[55] One end or face of the cylindrical sleeve 330 is preferably designed to interface with a fixed sleeve or appurtenance 334 having a diameter larger than - and mounted to - the shaft 318, such that as the cylindrical sleeve 330 moves axially in one direction, the end or face of the cylindrical sleeve 330 approaches the face of the appurtenance or fixed sleeve 334 on the shaft 318. Normally, since motions between the shaft 318 and housing 312a tend to be large, the cylindrical sleeve 330 is held in a position such that its face maintains a significant clearance with respect to the face of the appurtenance 334 fixed to the shaft 318. Under certain conditions, when normal relative motions are stopped or reduced and when it becomes desirable to limit flow of the fluid between the shaft 318 and the housing 312a, the cylindrical sleeve 330 can be moved toward the appurtenance 334 on the shaft 318 such that their ends come in contact and thereby restrict

any flow of the fluid between the shaft 318 and the housing 312a.

[56] The specific geometry of the contacting surfaces of the cylindrical sleeve 330 and the sleeve or appurtenance 334 fixed to the shaft 318 may be varied to optimize the restriction of flow when in contact. The geometry of the section of the movable cylindrical sleeve 330, the location and dimensions of its sliding fit with the housing 312a and the location and dimensions of the contacting surfaces can all be used to optimize the hydrostatic pressure forces of the fluid such that the balance of forces tend to maintain the contact between face of the movable sleeve 330 and the face of the appurtenance 334 fixed to the shaft 318, once contact is achieved.

[57] Particularly advantageous is the fact that the motive force, which causes the cylindrical sleeve 330 to move axially toward the fixed appurtenance 334 of the shaft 318, closes the gap between the face of the cylindrical sleeve 330 and the face of the appurtenance 334 to the shaft 318, and promotes initial contact of the faces in restricting the flow, is obtained by designing the cylindrical sleeve 330 to utilize certain changes in the conditions of the fluid which alter the pressure forces acting on the cylindrical sleeve 330 and cause the sleeve to move in the direction of the fluid flow.

[58] Flow passing along the annulus defined by the shaft 318 and the inner diameter of the cylindrical sleeve 330 will tend to meet resistance to flow due to the friction at the fluid interfaces and the fluid viscosity as described by standard laws of fluid dynamics. This resistance to flow will create a pressure differential

between the inlet side of the annulus and the outlet side. This differential pressure acting on the hydrostatic areas of the cylindrical sleeve 330, as defined by the region defined between the inner diameter of the circular sleeve 330 and its outer sliding fit diameter, will create a force imbalance which will tend to increase the acting forces toward the direction of flow. When flow through the annulus is at normal low volumetric rates, the differential pressure across the annulus is small and the force developed would normally be insufficient to overcome the body forces and friction forces acting on the cylindrical sleeve 330, and thus move the cylindrical sleeve 330 along its sliding fit. However, when the volumetric flow rate in the annulus increases either due to an increase in the mass flow rate or a phase change of the fluid from liquid to gas, the differential pressure across the annulus will increase and when the hydrostatic pressure forces exceed the body and friction forces, the cylindrical sleeve 330 will tend to move in the direction of flow. To provide additional stability of the sleeve 330 at low volumetric flow rates, the sleeve 330 may be additionally loaded by a spring which counteracts the forces generated by normal flow; or, the sleeve 330 may be locked in place by a suitable alternate device so that the sleeve 330 will not move until a desired flow rate or condition is reached.

[59] Figs. 7A-8B illustrate sliding sleeve arrangements schematically but in somewhat more detail. Accordingly, Fig. 7A illustrates schematically an elevational view of a first sliding sleeve arrangement about a shaft, and deployed in a first, initial position, while Fig. 7B is essentially the same view as Fig. 7A but showing the sliding sleeve arrangement deployed in a

second, "advanced" position (i.e., in a position closer to the pump motor) . On the other hand, Fig. 8A illustrates schematically an elevational view of a second sliding sleeve arrangement about a shaft, and deployed in the first, initial position, while Fig. 8B is essentially the same view as Fig. 8A but showing the sliding sleeve arrangement deployed in the second, "advanced" position.

[60] As shown, the geometry or surface of the inner diameter of the cylindrical sleeve 430 may incorporate features which tend to increase the resistance to flow or increase the differential pressure along the annulus . These may, e.g., involve a series of circumferential grooves (indicated at 436) disposed along all or a portion of the length of the surfaces, forming a labyrinth seal or pressure breakdown device. These may offer a resistance to flow that, depending on, e.g., the mass flow rate, absolute pressures, temperatures and nature of the fluid, a phase change or flashing from liquid to vapor, may occur at some position along the length of the annulus. As choking of the flow occurs, the result could be a more significant pressure differential between the inlet and outlet of the seal, generating larger forces to move the cylindrical sleeve 430.

[61] Figs. 7A-8B each illustrate an O-ring 432/532 similar to that indicated at 432 in Figs. 5 and 6.

[62] In accordance with an additional embodiment of the present invention, a given "split ring" arrangement and a given "sliding sleeve" arrangement, substantially as described and contemplated hereinabove, could be combined in the context of a single pump. As such, one of these flow restricting arrangements could be disposed about a shaft and within a seal housing in one location and the

other could be disposed about the shaft and within the seal housing at another location; the relative locations could be chosen with a view to maximizing the attendant advantages of each flow restricting arrangement at particular locations along the shaft.

[63] Figs. 8A and 8B illustrate a very interesting and advantageous alternative in which a split ring 526, which is configured (and functions) substantially as described heretofore, is mounted in a groove in the inner diameter of the cylindrical sleeve 530 and which is disposed along with the cylindrical sleeve around the outer diameter of the shaft 518. The concentric ring would split or cut radially across its circumference in one location as discussed heretofore. With the sleeve 530 in the first, initial position as shown in Fig. 8A, ring 526 itself is in a first, initial position as described heretofore (i.e., where ends of the split ring are spaced apart) . On the other hand, with the sleeve 530 in the second, "advanced" position as shown in Fig. 8B, the ends of the split ring 526 have converged so that ring 526 is more constricted about shaft 518. The release of the ends of the split ring 526, to actuate it from the first position to the second position between what is shown in Figs. 8A and 8B, respectively, may be accomplished by essentially any suitable device or mechanism which senses or responds to a change in the conditions of the fluid or by a positive operator action. As such, a "meltable" spacer/actuator as discussed heretofore would likely produce favorable results.

[64] It should be appreciated that, in accordance with the embodiment illustrated in Figs. 8A and 8B, the split ring 526 actually enhances actuation of the sliding

sleeve 530. Particularly, as the split ring 526 closes, flow is restricted through the sleeve annulus, thereby- causing a differential pressure along the sleeve 530 which (as described earlier) causes the sliding sleeve 530 to move toward the annular face of shaft appurtenance 534.

[65] It should be appreciated that a very wide variety of alternate applications and environments for the salient features of the embodiments of the present invention are possible. Essentially, the "split ring" and "sliding sleeve" arrangements discussed heretofore are incorporable into any workable environment in which it is desired to make a provision for limiting fluid flow through an annulus between two circular members, the inner member being a circular shaft which is normally rotating or reciprocating relative to the second member, and the second member being a housing which surrounds the inner circular shaft member. (In actuality, depending on the application, normal motion need only be relative between the two members and either one may move in the absolute sense.) While the inner circular member and the outer housing combine to form a pressure boundary to a fluid and the interface between the circular inner member, and the outer housing is normally sealed by an arrangement which can accommodate the normal relative motion between the members, the embodiments of the present invention provide yet additional conceivable arrangements for limiting fluid flow through the annulus between the inner circular member and the outer housing member when the normal motion has ceased, and any subsequent displacements between the members is much more limited.

[66] As such, the additional arrangements for limiting fluid flow could be embodied by a split ring

arrangement or sliding sleeve arrangement, or combination of both, substantially as described hereinabove but employed in essentially any context involving a shaft and surrounding housing in which there is relative movement of at least one with respect to the other as described immediately hereabove.

[67] Without further analysis, the foregoing will so fully reveal the gist of the present invention and its embodiments that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute characteristics of the generic or specific aspects of the present invention and its embodiments .

[68] If not otherwise stated herein, it may be assumed that all components and/or processes described heretofore may, if appropriate, be considered to be interchangeable with similar components and/or processes disclosed elsewhere in the specification, unless an express indication is made to the contrary.

[69] If not otherwise stated herein, any and all patents, patent publications, articles and other printed publications discussed or mentioned herein are hereby incorporated by reference as if set forth in their entirety herein.

[70] It should be appreciated that the apparatus and method of the present invention may be configured and conducted as appropriate for any context at hand. The embodiments described above are to be considered in all respects only as illustrative and not restrictive. All changes which come within the meaning and range of

equivalency of the claims are to be embraced within their scope .