Regenerative pump and processes

Abstract

A regenerative pump includes a housing defining a cavity with a fluid inlet arrangement and a fluid outlet arrangement, and a channel with an open volume extending between the fluid inlet and outlet arrangements. A rotating shaft extends within the housing. A turbine is mounted on the shaft within the cavity and has a plurality of blades spaced circumferentially around the axis and opening into the channel. An arm arrangement defines at least part of the channel walls. The arm arrangement is radially movable to vary the channel volume. Enlarging the channel volume inhibits regenerative circulatory flow during pumping and limits the generated pressure. Figure for the abstract: Fig. 1

Description

Title of the invention: Regenerative pump and methods [0001 ] RELATED APPLICATIONS

[0002] The present application claims the benefit of U.S. Provisional Patent Application No. 63 / 219,243, filed July 7, 2021, which is hereby incorporated by reference in its entirety. Technical field

[0003] The present disclosure relates to pumps and more particularly to regenerative pumps, including methods of use.

[0004] BACKGROUND

[0005] Pumps, including regenerative pumps, are useful in many different types of systems. While one example includes aircraft engine fuel systems, the present disclosure relates to a regenerative pump that can be used in a variety of systems.

[0006] In some system examples, a regenerative pump may be used to allow the pressure to build up quickly, which is useful. However, if the pressure is allowed to build up too much, the system could experience degradation due to overpressure. Improvements are desired.

[0007] SUMMARY

[0008] A regenerative pump is provided which improves upon the prior art.

[0009] In one concept, a regenerative pump is provided comprising: a housing defining a cavity having a fluid inlet arrangement and a fluid outlet arrangement, and a channel having an open volume extending between the fluid inlet arrangement and the fluid outlet arrangement; a rotatable shaft extending into the housing having a longitudinal axis; an impeller mounted on the shaft within the cavity; the impeller having a plurality of vanes circumferentially spaced about the axis and opening into the channel; and an arm arrangement at least partially defining walls of the channel; the arm arrangement being radially movable relative to the axis to vary the volume of the channel.

[0010] In an exemplary embodiment, the pump further includes a biasing arrangement controlling radial movement of the arm arrangement.

[0011] In exemplary implementations, the arm arrangement includes a first arm and a second arm; and the biasing arrangement includes a first spring member between the housing and the first arm; and a second spring member between the housing and the second arm.

[0012] The fluid inlet arrangement may include at least one pair of fluid inlets circumferentially spaced from each other and in communication with the channel; and the fluid outlet arrangement may include at least one pair of fluid outlets circumferentially spaced from each other and in communication with the channel.

[0013] In many examples, the first arm is an arcuate segment having a first end and a second end; the first arm being radially adjustable relative to the turbine such that the second end moves radially further from the turbine than the first end; and the second arm is an arcuate segment having a first end and a second end; the second arm being radially adjustable relative to the turbine such that the second arm second end moves radially further from the turbine than the second arm first end.

[0014] In another aspect, a regenerative pump is provided comprising an impeller rotatable about an impeller axis, the impeller including a first axial side and a second axial side, the impeller including a first plurality of regenerative pump vanes spaced about a circumference of the impeller at the first axial side of the impeller, the impeller also including a second plurality of regenerative pump vanes spaced about the circumference of the impeller at the second axial side of the impeller;and a pump housing in which the impeller is rotatably mounted, the pump housing defining an inlet and an outlet, the pump housing also defining a channel that extends circumferentially around the impeller between the inlet and the outlet, the channel including first and second regenerative flow sections corresponding to the first and second pluralities of regenerative pump blades, respectively, the pump housing including an arm that defines at least a portion of the channel, the arm movable away from the impeller axis to enlarge a volume of the channel and movable toward the impeller axis to reduce the volume of the channel. ;

[0015] In many implementations, the arm is movable relative to the turbine axis between a first position and a second position, wherein the arm is closer to the turbine axis in the first position compared to the second position.

[0016] In some examples, when the arm is in the first position, the first and second regenerative flow sections are positioned to cooperate with the first and second pluralities of regenerative pump vanes to generate a regenerative circulatory flow in the channel from the inlet to the outlet during pumping, and wherein when the arm is in the second position at least portions of the first and second regenerative flow sections are spaced apart far enough from the turbine that this regenerative circulatory flow is inhibited along these portions during pumping.

[0017] In one or more embodiments, the housing includes a main housing assembly, wherein the arm is pivotally connected to the main housing assembly adjacent the inlet at a pivot axis so as to be pivotally movable between the first and second positions, wherein the arm extends generally from the inlet to the outlet of the pump housing, and wherein the pivot axis is parallel to the impeller axis.

[0018] In examples, when the arm is in the first position the channel has a cross-sectional flow area that is constant as the channel extends from the inlet to the outlet, and wherein when the arm is in the second position the cross-sectional flow area of ​​the channel increases as the channel extends from the inlet to the outlet.

[0019] In another aspect, a method of reducing pressure rise in a regenerative pump is provided. The method comprises: radially moving an arm arrangement away from an impeller to expand a volume of a channel holding a fluid.

[0020] In an exemplary method, the step of radially moving the arm arrangement includes radially moving a first arm and a second arm away from the turbine, the turbine being within a cavity in a housing and attached to a rotating shaft.

[0021] Many exemplary methods further include a step of controlling radial movement of the first arm and the second arm using a first spring between the housing and the first arm, and a second spring between the housing and the second arm.

[0022] In another aspect, a regenerative pump is provided comprising: an impeller rotatable about a turbine axis, the impeller including a plurality of regenerative pump vanes spaced about a circumference of the impeller; a pump housing in which the impeller is rotatably mounted, the pump housing defining an inlet and an outlet, the pump housing also defining a channel that extends circumferentially around the impeller between the inlet and the outlet; and wherein the channel includes a regeneration section and a pressure relief section; each of the regeneration section and the pressure relief section having a length that varies in response to an amount of pressure in the channel.

[0023] In one exemplary aspect, the pump further includes an arm arrangement constructed and arranged to influence a size of the channel.

[0024] A variety of examples of desirable methods or product features will be set forth in part in the following description, and in part will be apparent from the description, or may be learned by practicing various aspects of the disclosure. Aspects of the disclosure may relate to individual features as well as combinations of features. It is to be understood that both the foregoing general description and the following detailed description are for purposes of explanation only and are not limiting of the claimed invention. Brief description of the drawings

[0025] [Fig.l] is a schematic view of the system including a centrifugal pump and a regenerative pump, constructed in accordance with the principles of the present disclosure, with only the impeller of the regenerative pump being shown.

[0026] [Fig.2] is a graph showing how pump drive speed influences the outlet pressure of both a centrifugal pump and the regenerative pump of the exemplary system given in [Fig.l].

[0027] [Fig.3] is a front schematic view of the regenerative pump of [Fig.l], shown in a normal regeneration position.

[0028] [Fig.4] is a schematic end view of the regenerative pump of [Fig.l], similar to [Fig.3], but shown in a pressure limiting position.

[0029] [Fig.5] is an exploded perspective view of a portion of the regenerative pump of [Fig.3] and 4.

[0030] [Fig.6] is a side view of the regenerative pump of [Fig.3] and 4.

[0031] [Fig.7] is a sectional view of the pump of [Fig.3], the cross-section being taken along line AA of [Fig.6]; the pump being in the normal regeneration position.

[0032] [Fig.8] is a sectional view of the pump similar to [Fig.7], but showing the pump in the pressure limiting position of [Fig.4].

[0033] [Fig.9] is a sectional view of the pump similar to [Fig.7] and [Fig.8], but showing the pump in a partial pressure limiting position, between the position of [Fig.7] and [Fig.8].

[0034] [Fig. 10] is a schematic sectional view of a portion of the pump of [Fig. 7], in a normal regeneration position adjacent the outlet of the pump housing.

[0035] [Fig. 11] is a schematic sectional view of a portion of the pump of [Fig. 8], in a pressure limiting position adjacent the outlet of the pump housing. DETAILED DESCRIPTION

[0036] Reference is now made in detail to the exemplary embodiments of the present description which are illustrated in the accompanying drawings. Where possible, the same reference numerals will be used throughout the drawings to refer to the same or similar parts.

[0037] [Fig. 1] shows a system 100 including a main stage pump 102 and a regenerative pump 104 that are each connected to a rotating drive shaft 106 operatively coupled to an engine. In a non-limiting example, the system 100 may be part of an aircraft engine fuel system. In this example, the engine rotates the drive shaft 106, which rotates both the pumps 102, 104 simultaneously. For example, the pumps 102, 104 may be sealingly mounted to a shaft 170 and isolated from each other via seals 172. The main stage pump 102 may be a centrifugal pump and include an inducer, a turbine, or both. In the example shown, a turbine 103 is illustrated. The regenerative pump 104 includes a regenerative pump impeller 105. Located between the regenerative pump impeller 105 and the shaft 179 are plain and thrust bearings 173. [Fig.l] has omitted, for the sake of clarity, the housing of the regenerative pump 104. .

[0038] Although regenerative pumps can be used in many types of systems, in this particular example for an aircraft engine, during startup, fuel is made available to both the main stage pump 102 and the regenerative pump 104. The fuel pressure supplied to the engine is produced by the regenerative pump 104. When a predetermined engine speed is reached, the regenerative pump 104 is cut off from the fuel supply. The predetermined engine speed is chosen so that the fuel pressure obtained from the main stage pump 102 is sufficient to operate the engine.

[0039] [Fig. 2] illustrates a graph 180 of the output pressure of both the main stage pump 102 (labeled "HSC Stage Discharge Pressure (psia)") and the regenerative pump 104 (labeled "Regen Disch Pressure (psia)") as a function of a percentage of the maximum rated pump drive speed at which the pumps 102, 104 are driven. As shown, the regenerative pump 104 produces a significantly higher output pressure than the centrifugal pump 102 at low drive speeds (e.g., less than 10% of the maximum rated drive speed). As will be described herein, the system 100 is configured to limit the pressure produced at the outlet of the regenerative pump 104 as the pump drive speed increases.

[0040] Still referring to [Fig. 2], the regenerative pump 104 provides high fuel pressure even at low engine speeds. As the engine speed increases, the regenerative pump 104 provides increasingly higher fuel pressure. Allowing the regenerative pump 104 to continue to pump an unrestricted amount of fuel at engine speeds beyond the predetermined engine speed would cause excessive pressure and torque, which could lead to failure of the fuel pump system 100. When the output pressure of the regenerative pump 104 reaches a predetermined level, it is desirable to limit the pressure generated by the regenerative pump 104. [Figs. 3] through 11 show an implementation for this purpose.

[0041] Referring now to [Fig. 3] and 4, an exemplary embodiment of regenerative pump 104 is shown schematically. [Fig. 3] illustrates regenerative pump 104 in a normal regenerative operating position, while [Fig. 4] illustrates regenerative pump 104 in a pressure limiting position. By the term "normal regeneration" it is meant that regenerative flow generally occurs from the inlet to the outlet to maximize the amount of energy transferred to the fluid transported through the pump. By the term "pressure limiting" position, regenerative flow is prevented along at least a portion of the pumping channel that extends circumferentially between the inlet and the outlet.

[0042] Referring now to [Fig. 3] and 5, the regenerative pump 104 includes a housing 120. The housing 120 is shown in [Fig. 5] in exploded cross-section with first and second housing sections 120a, 120b. The housing 120 defines a cavity 121 having a fluid inlet arrangement 122 and a fluid outlet arrangement 124. A channel 126 defines an open volume extending between the fluid inlet arrangement 122 and a fluid outlet arrangement 124. The channel 126 extends circumferentially between the inlet arrangement 122 and the outlet arrangement 124.

[0043] In one example, when the pump 104 is operated in the pressure limiting state, regenerative flow occurs along a first portion of the pumping channel 126 and does not occur along a second portion of the pumping channel 126. The relative circumferential lengths of the first and second portions may vary to limit the output pressure of the pump 104. For example, as the rotational speed of the pump 104 increases above a rotational speed corresponding to a pressure limit of the pump 104, the circumferential length of the first portion may decrease, and the circumferential length of the second portion may increase. In one example, the first portion may extend circumferentially from the inlet arrangement 122 at an intermediate location between the inlet arrangement 122 and the outlet arrangement 124, and the second portion may extend circumferentially from the intermediate location to the outlet arrangement 124.

[0044] The inlet arrangement 122 and the fluid outlet arrangement 124 can take many forms. In the embodiment shown in [Fig. 3], the inlet arrangement 122 includes a pair of fluid inlets 140, 142 spaced circumferentially from each other and in communication with the channel 126. The outlet arrangement 124 includes a pair of fluid outlets 144, 146 spaced circumferentially from each other and in communication with the channel 126.

[0045] Referring again to [Fig.l], the regenerative pump 104 includes the rotary shaft 170, which extends into the housing 120. The rotary shaft 170 has a longitudinal axis 171 ([Fig.l]). The impeller 105 is mounted on the shaft 170 and within the cavity 121 ([Fig.5]) of the housing 120 and is rotated about the axis 171.

[0046] In [Fig. 5], it can be seen how the impeller 105 includes a first axial side 130 and a second axial side 132. Spaced around a circumference of the impeller 105 of the first axial side 130 is a first plurality of regenerative pump vanes 134. Similarly, along the second axial side 132 is circumferentially positioned a second plurality of regenerative pump vanes 136. The first vanes 134 and the second vanes 136 are generally positioned at an angle relative to the central axis 171 and open into the channel 126.

[0047] The channel 126 includes first and second regenerative flow sections 126a, 126b ([Fig. 10] and 11) corresponding to the first and second pluralities of regenerative pump blades 134, 136, respectively. As can be seen in [Fig. 10], each of the first and second regenerative flow sections 126a, 126b has a rounded cross-sectional profile. The first and second pluralities of regenerative pump blades 134, 136 regenerate a regenerative circulatory flow in the channel 126 from the inlet 140, 142 to the outlet 144, 146 during pumping in the normal regeneration state. In general, a fluid delivered to the regenerative pump 104, such as fuel, enters the housing 120 through the inlets 140, 142. From there, the fluid flows along the blades 134, 136 of the turbine 105, while the channel 126 is shaped (e.g., rounded, see [Fig.10]) to divert the fluid in the channel 126 back to the inner diameter of the turbine blades 134, 136. The fluid is recirculated (regenerated) to a lower point in the diameter. As fuel flows along the blades and into the channel 126, pressure builds and forces the fluid out of the outlets 144, 146.

[0048] To limit the pressure increase in the pump 104, an arm arrangement 150 is provided. The arm arrangement 150 at least partially defines walls of the channel 126. The arm arrangement 150 is movable radially relative to the axis 171 to vary the volume of the channel 126. In [Fig. 3], the arm arrangement 150 is shown in the normal regenerative position, while in [Fig. 4], the arm arrangement 150 is shown in the pressure limiting position. Comparing [Fig. 3] / [Fig. 10] with [Fig. 4] / [Fig. 11], the arm arrangement 150 is moved radially away from the impeller 105 to expand the volume of the channel 126 holding the fluid. By expanding the volume, this limits the amount of pressure generated by the pump 104. In [Fig. 11], it can be seen how the fluid within the first and second regenerative flow sections 126a, 126b is slowed down, compared to [Fig. 10], due to the larger volume of [Fig. 11].

[0049] The arm arrangement 150 may be implemented in many different forms. In the embodiment shown, the arm arrangement 150 includes a first arm 162 and a second arm 164. A biasing arrangement 152 for controlling radial movement of the arm arrangement 150 may be provided as a first spring element 166 between the housing 120 and the first arm 162 and a second spring element 168 between the housing 120 and the second arm 164.

[0050] [Figs. 5] and 7-9 show one of the arms, which is representative of both the first arm 162 and the second arm 164. It can be seen that each arm 162, 164 is an arcuate segment 182 having a first end 184 and a second end 186. The arm 162, 164 is radially adjustable relative to the turbine 105 such that the second end 186 moves radially further from the turbine 105 than the first end 184. When the second end 186 moves away from the turbine 105, this enlarges the volume of the channel 126. When the second end 186 moves toward the turbine 105, this reduces the volume of the channel 126. When the volume of the channel 126 is enlarged, the pressure is limited, and when the volume contracts, the pressure that can be generated by the pump 104 increases.

[0051] In the non-limiting example shown ([Fig.3] and 7), each of the arms 162, 164 is pivotally connected to the housing 120 adjacent the inlets 140, 142 ([Fig. 3] and 4) at a pivot axis 192, 194. In this exemplary embodiment, the pivot axis 192, 194 is generally parallel to the longitudinal axis 171. Thus, the first arm 162 and the second arm 164 are pivotally movable between first (or normal regeneration) and second (or pressure limiting) positions. When the arms 162, 164 are in the first position ([Fig. 3] and 7), the first and second regenerative flow sections along the channel 126 are positioned to cooperate with the first and second pluralities of regenerative pump vanes 134, 136 to generate a regenerative circulatory flow in the channel 126 from the inlet 140, 142 to the outlet 144, 146 during pumping. When the arms 162, 164 are in the second position ([Fig. 4] and 8), at least portions of the first and second regenerative flow sections in channel 126 are spaced sufficiently far from turbine 105 that regenerative circulatory flow is inhibited along these portions during pumping. [Fig. 9] shows an intermediate position, between the first and second positions. In the intermediate position, arms 162, 164 are partially spaced from turbine 105, enlarging the volume of channel 126 to cause limited pump pressure.

[0052] The foregoing may be used in a method of reducing pressure increase in the regenerative pump 104. The method includes radially moving the arm arrangement 150 away from the impeller 105 to expand the volume of the channel 121 holding a fluid.

[0053] The step of radially moving the arm arrangement 150 may include radially moving the first arm 162 and the second arm 164 away from the turbine 105.

[0054] The method may further include a step of independently controlling radial movement of the first arm 162 and the second arm 164 using a first spring 166 between the housing 120 and the first arm 162, and a second spring 168 between the housing 120 and the second arm 164.

[0055] The method may further include a step of controlling radial movement of the first arm 162 and the second arm 164 using a link arrangement 190 ([Fig.3]) between the arms 162, 164 to synchronize their movement so as to balance the pressure limiting effects on both sides.

[0056] Inventive aspects

[0057] Aspect 1. A regenerative pump comprising: (a) a housing defining a cavity having a fluid inlet arrangement and a fluid outlet arrangement, and a channel having an open volume extending between the fluid inlet arrangement and the fluid outlet arrangement; (b) a rotatable shaft extending into the housing having a longitudinal axis; (c) an impeller mounted on the shaft within the cavity; the impeller having a plurality of blades circumferentially spaced about the axis and opening into the channel; (d) and an arm arrangement at least partially defining walls of the channel; the arm arrangement being radially movable relative to the axis to vary the volume of the channel.

[0058] Aspect 2. A pump according to aspect 1 further including a biasing arrangement controlling radial movement of the arm arrangement.

[0059] Aspect 3. A pump according to aspect 2 wherein: (a) the arm arrangement includes a first arm and a second arm; and (b) the biasing arrangement includes a first spring element between the housing and the first arm; and a second spring element between the housing and the second arm.

[0060] Aspect 4. A pump according to aspect 1 wherein: (a) the arm arrangement includes a first arm and a second arm; and (b) a linkage arrangement between the first arm and the second arm for synchronizing the movement of the first and second arms to balance pressure limiting effects.

[0061] Aspect 5. A pump according to aspect 1 wherein: (a) the fluid inlet arrangement includes at least one pair of fluid inlets circumferentially spaced from each other and in communication with the channel; and (b) the fluid outlet arrangement includes at least one pair of fluid outlets circumferentially spaced from each other and in communication with the channel.

[0062] Aspect 6. A pump according to aspect 3 wherein: (a) the first arm is an arcuate segment having a first end and a second end; the first arm being radially adjustable relative to the impeller such that the second end moves radially further from the impeller than the first end; and (b) the second arm is an arcuate segment having a first end and a second end; the second arm being radially adjustable relative to the impeller such that the second end of the second arm moves radially further from the impeller than the first end of the second arm.

[0063] Aspect 7. A regenerative pump comprising: an impeller rotatable about an impeller axis, the impeller including a first axial side and a second axial side, the impeller including a first plurality of regenerative pump vanes spaced about a circumference of the impeller at the first axial side of the impeller, the impeller also including a second plurality of regenerative pump vanes spaced about the circumference of the impeller at the second axial side of the impeller;and a pump housing in which the impeller is rotatably mounted, the pump housing defining an inlet and an outlet, the pump housing also defining a channel that extends circumferentially around the impeller between the inlet and the outlet, the channel including first and second regenerative flow sections corresponding respectively to the first and second pluralities of regenerative pump blades, each of the first and second regenerative flow sections having a rounded cross-sectional profile, the pump housing including an arm that defines at least a portion of the channel, the arm movable away from the impeller axis to enlarge a volume of the channel and movable toward the impeller axis to reduce the volume of the channel. ;

[0064] Aspect 8. A regenerative pump according to aspect 7, wherein the arm is movable relative to the turbine axis between a first position and a second position, wherein the arm is closer to the turbine axis in the first position compared to the second position.

[0065] Aspect 9. A regenerative pump according to aspect 8, wherein when the arm is in the first position the first and second regenerative flow sections are positioned to cooperate with the first and second pluralities of regenerative pump vanes to generate a regenerative circulatory flow in the channel from the inlet to the outlet during pumping, and wherein when the arm is in the second position at least portions of the first and second regenerative flow sections are spaced sufficiently far from the impeller such that this regenerative circulatory flow is inhibited along these portions during pumping.

[0066] Aspect 10. A regenerative pump according to aspect 8, wherein the housing includes a main housing assembly, wherein the arm is pivotally connected to the main housing assembly adjacent the inlet at a pivot axis so as to be pivotally movable between the first and second positions, wherein the arm extends generally from the inlet to the outlet of the pump housing, and wherein the pivot axis is parallel to the impeller axis.

[0067] Aspect 11. A regenerative pump according to aspect 8, wherein when the arm is in the first position the channel has a cross-sectional flow area that is constant as the channel extends from the inlet to the outlet, and wherein when the arm is in the second position the cross-sectional flow area of ​​the channel increases as the channel extends from the inlet to the outlet.

[0068] Aspect 12. A method of reducing pressure increase in a regenerative pump; the method comprising: radially moving an arm arrangement away from an impeller to expand a volume of a channel holding a fluid.

[0069] Aspect 13. The method of aspect 12 wherein the step of radially moving the arm arrangement includes radially moving a first arm and a second arm away from the turbine, the turbine being within a cavity in a housing and secured to a rotating shaft.

[0070] Aspect 14. The method of aspect 13 further including a step of controlling radial movement of the first arm and the second arm using a first spring between the housing and the first arm, and a second spring between the housing and the second arm.

[0071] Aspect 15. The method of aspect 13 further including a step of synchronizing movement between the first arm and the second arm to balance a pressure limiting effect on two sides of the turbine.

[0072] Aspect 16. The method of aspect 15 wherein the step of synchronizing movement includes using a linkage arrangement between the first arm and the second arm.

[0073] Aspect 17. A regenerative pump comprising: an impeller rotatable about a impeller axis, the impeller including a plurality of pump blades regenerative spaced around a circumference of the impeller; a pump housing in which the impeller is rotatably mounted, the pump housing defining an inlet and an outlet, the pump housing also defining a channel that extends circumferentially around the impeller between the inlet and the outlet; and wherein the channel includes a regenerative section and a pressure-limiting section; each of the regenerative section and the pressure-limiting section having a length that varies in response to an amount of pressure in the channel.

[0074] Aspect 18. A regenerative pump according to aspect 17 further including an arm arrangement constructed and arranged to influence a size of the channel.

[0075] The above represents principles given by way of example. Many embodiments can be made using these principles.

Claims

Claims

1. 1 A regenerative pump (104) comprising: an impeller (105) rotatable about an impeller axis (171), the impeller (105) including a plurality of regenerative pump vanes (134, 136) spaced about a circumference of the impeller; a pump housing (120) in which the impeller (105) is rotatably mounted, the pump housing (120) defining an inlet (122) and an outlet (124), the pump housing (120) also defining a channel (126) that extends circumferentially about the impeller (105) between the inlet (122) and the outlet (124); and wherein the channel (126) includes a regeneration section (126a, 126b) and a pressure limiting section;each of the regeneration section (126a, 126b) and the pressure limiting section having a circumferential length that varies in response to an amount of pressure in the channel (126), the regenerative pump (104) including an arm arrangement (150) at least partially defining walls of the channel (126), the arm arrangement (150) being radially movable relative to the axis (171) to vary the volume of the channel (126).;

2. 2 A regenerative pump (104) according to claim 1 further including a biasing arrangement (152) controlling radial movement of the arm arrangement (150).

3. 3 A regenerative pump (104) according to claim 2 wherein the arm arrangement (150) includes a first arm (162) and a second arm (164).

4. 4 A regenerative pump (104) according to claim 3 wherein the biasing arrangement (152) includes a first spring element (166) between the housing (120) and the first arm (162); and a second spring element (168) between the housing (120) and the second arm (164).

5. 5 A regenerative pump (104) according to claim 1 wherein: (a) the arm arrangement (150) includes a first arm (162) and a second arm (164); and (b) further comprising a link arrangement (190) between the first arm (162) and the second arm (164) for synchronizing the moving the first and second arms (162, 164) to balance the pressure limiting effects.

6. 6 A regenerative pump (104) according to claim 1 wherein the inlet includes at least one pair of fluid inlets (140, 142) circumferentially spaced from each other and in communication with the channel (126).

7. 7 A regenerative pump (104) according to claim 1 wherein the outlet includes at least one pair of fluid outlets (144, 146) circumferentially spaced from each other and in communication with the channel (126).

8. 8 A regenerative pump (104) according to claim 3 wherein the first arm (162) is an arcuate segment having a first end and second ends; the first arm (162) being radially adjustable relative to the impeller (105) such that the second end moves radially further from the impeller (105) than the first end.

9. 9 A regenerative pump (104) according to claim 8 wherein the second arm (164) is an arcuate segment having a first end and second ends; the second arm (164) being radially adjustable relative to the impeller (105) such that the second end of the second arm (164) moves radially further from the impeller (105) than the first end of the second arm (164).

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