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(11) | EP 0 636 791 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Regenerative pump control |
| (57) A regenerative pump comprises a housing (1) an impeller (5) having a plurality of
vanes (13) spaced angularly around the axis of rotation of the impeller (5) within
a flow channel (4) extending between an inlet (19) and outlet (20), a flow stripper
(17) located between the inlet (19) and outlet (20) and through which the vanes pass,
a second fluid inlet (33) that opens into the flow channel (4) between the inlet (19)
and outlet (20), and control means (34) to control the supply of fluid selectively
to one or the other, or one or both of said fluid inlets (19,33), thereby to vary
the output of the pump. The stripper (17) incorporates a fluid flow loop (22) which
intersects the path of rotation of the vanes (13). The first fluid inlet (19) is preferably
spaced downstream of the stripper (17), for example, within an angular range of 15°
to 90° from the fluid exit port (29) of the stripper (17), and preferably 45° to 75°
from the exit port (29). |
Technical Field
[0002] Regenerative pumps comprise a housing with a fluid inlet and a fluid outlet, and an impeller rotatably mounted within the housing and having a plurality of vanes spaced angularly around the axis of rotation of the impeller and accommodated within a flow channel within the housing extending between the inlet and outlet, the vanes serving to induce a spiral or helical flow of fluid along the length of the flow channel as the impeller is rotated. The spiral flow is induced by the centrifugal and frictional effects of the vanes on the fluid and causes the fluid to be re-circulated repeatedly across a plurality of the vanes between the inlet and outlet, thereby progressively increasing the fluid pressure. A stripper block is located between the inlet and outlet and has sufficient clearance with the impeller and vanes to allow them to pass but to restrict direct fluid flow from the higher pressure fluid outlet to the lower pressure fluid inlet.
[0003] In a known type of regenerative pump, an annular core is provided in the flow channel and the fluid flows in said spiral path about the core. The vanes project from the impeller into the flow channel and either terminate just short of a fixed core or are connected to the core so that the core rotates with the rotor. The vanes may have an aerofoil cross-section to enhance the fluid flow effects, and means may be provided to assist the initial spiral flow of fluid at the inlet. An example of such a regenerative pump is shown in British Patent No. 2068461.
[0004] British Patent No. 2074242 discloses a regenerative pump in which fluid flows in a spiral path about a core between an inlet and outlet, and which incorporates a stripper block between the inlet and outlet that serves to preserve the annular motion of the fluid as it passes with the vanes of the impeller through the stripper block. This is achieved by providing a fluid flow loop in the stripper block which intersects the path of the rotation of the vanes. The fluid flow loop may comprise one or more closed loops each of which is formed by a separate duct which re-circulates the fluid through the vanes, or may comprise a single quasi-helical loop formed by a succession of ducts between the outlet and inlet side of the stripper block. In the latter arrangement, the quasi-helical flow loop serves to preserve the annular motion of the fluid to a maximum extent so as to maintain increased pump efficiency and pressure rise.
[0005] Regenerative pumps of the aforesaid kind are mechanically simple and reliable and are capable of operating at high speed and have low specific weight. Regenerative pumps are also capable of generating high pressures and high flows, the pressure generally being proportional to the square of the impeller speed, and the flow generally being proportional to the impeller speed. However, in some applications, for example, as engine driven fuel pumps for aviation gas turbine engines, this pressure/ flow speed characteristic can be a problem at some operating conditions. Thus a regenerative fuel pump may be designed to produce a desired fuel pressure and flow at low speed, engine light-up conditions, but the fuel pressure, and/or flow at some maximum engine speed may then be excessive, resulting in fuel heating and high Delta T because of the high energy input of the pump.
Disclosure of the Invention
[0006] An object of the present invention is to provide a regenerative pump in which the aforesaid problem of excess pressure and/or excess flow at higher speeds can be reduced or avoided.
[0007] According to one aspect, the present invention consists in a regenerative pump comprising a housing with a fluid inlet and a fluid outlet, an impeller rotatably mounted within the housing and having a plurality of vanes spaced angularly around the axis of rotation of the impeller and accommodated within a flow channel within the housing extending between the inlet and outlet, and a flow stripper located between the inlet and outlet and through which the vanes pass, characterised in that a second fluid inlet is provided in the housing to open into the flow channel between said fluid inlet and fluid outlet, and in that control means is provided to control the supply of fluid selectively to one or the other, or one or both of said fluid inlets, thereby to vary the output of the pump.
[0008] It will be appreciated that if the second inlet is used instead of the first inlet, the effective length of the flow channel is shortened and thus the pressure rise generated in the flow channel is reduced for any particular output flow. That portion of the flow channel between the stripper and the second inlet becomes redundant, but a reduced pressure is produced therein which can cause vaporisation if the fluid pumped is a liquid, and thereby reduces the drag on the impeller.
[0009] If the second inlet is used as well as the first inlet, then the pressure rise and output flow are each reduced, but to a lesser extent compared with that when only the second inlet is used.
[0010] In alternative embodiments of the invention, three or more circumferentially spaced fluid inlets may be provided along the length of the flow channel, and the inlet supply of fluid connected to these selectively either as alternatives or in combination.
[0011] The invention therefore gives the ability to vary the output of a regenerative pump by controlling the supply of fluid to alternative inlets, and thereby provides a wide possible choice of pump outputs. The particular outputs produced will be dependent upon the relative positions of the inlets and outlets along the length of the channel.
[0012] Preferably, the stripper is adapted to preserve the annular motion of the fluid as it passes through the stripper, and may incorporate a fluid flow loop in the stripper which intersects the path of rotation of the vanes. Further, the first fluid inlet is preferably spaced downstream of the stripper block rather than being located immediately after the stripper block, thereby allowing the annular flow of fluid from the stripper block to establish itself before it meets the flow through the inlet. An optimum location is preferably determined to ensure that the helical flow has not dissipated by the time it reaches the inlet and to allow the maximum possible flow channel length after the inlet. Generally, the centre of the inlet is located within an angular range of 15° to 90° from the fluid exit port of the stripper block, and preferably within the angular range of 45° to 75° from the exit port.
[0013] According to another aspect, the present invention consists in a regenerative pump comprising a housing with a fluid inlet and a fluid outlet, an impeller rotatably mounted within the housing and having a plurality of vanes spaced angularly around the axis of rotation of the impeller and accommodated within a flow channel within the housing extending between the inlet and outlet, and a flow stripper located between the inlet and outlet and through which the vanes pass, characterised in that said fluid inlet is spaced downstream of the stripper block, thereby allowing the annular flow of fluid from the stripper block to establish itself before it meets the flow through the inlet. Preferably, the inlet is located in an optimum position within the range 15° to 90° downstream of the exit port of the stripper block, or within the preferred range of 45° to 75° downstream of the exit port.
Description of the Drawings
[0014] The invention will now be described by way of example with reference to the accompanying drawings in which:
Figure 1 is a schematic section on the line I-I in Figure 2 through a regenerative pump according to the invention;
Figure 2 is a schematic view of the inner face of the left hand section of the pump housing in Figure 1;
Figure 3 is a schematic drawing showing the operation of the flow stripper of the pump in Figure 1;
Figure 4 is a schematic side view of the pump of Figures 1 to 3 showing the external fluid connections of the two pump inlets, the outlet, and the diverter value;
Figures 5 to 7 are similar to Figure 4 but each shows a different setting of the control means of the pump inlets;
Figure 8 is a graph showing the pump characteristic of pressure rise δP and flow Q for the different control settings of Figures 5 to 7;
Figure 9 is a schematic side view of a pump similar to that of Figure 4 but with alternative control means for the pump inlets;
Figure 10 is a schematic side view of a pump similar to that Figure 4 but with three pump inlets controlled by common control means.
Mode of carrying out the invention
[0015] The regenerative pump illustrated in Figures 1 to 3 comprises a housing 1 formed in two sections 2, 3 which are connected face-to-face and define an internal cavity 4 therebetween to receive an impeller 5 which is mounted on a drive shaft 6 supported in the housing by combined journal and thrust bearings 7. One end of the shaft 6 is received in a blind bore 8 in an end plate 9, and the other end of the shaft 6 is sealed in the housing by a mechanical shaft seal 10 and is formed with internal splines 11 for driving connection to a power source.
[0016] The impeller 5 comprises an inner annular body 12 and an outer toroidal ring 14 with a plurality of radially projecting curved section vanes 13 connected therebetween. The body 12 of the impeller 5 is a close fit with the inner walls 15 of the cavity 4 in the housing 1, but the vanes 13 and toroidal ring 14 project radially into an enlarged peripheral portion of the cavity 4 in the form of a toroidal chamber 16 concentric with the shaft 6 and symmetrical with the impeller 5 about the radially extending dividing plane along which the housing sections 2,3 meet.
[0017] A flow stripper block 17 is located within the toroidal chamber 16 and comprises a pair of blocks 18 which are secured in opposed recesses in the housing sections 2,3 and have inner faces which cooperate to closely surround the vanes 13 and the toroidal ring 14, as shown in Figure 1. A first inlet port 19 is provided in the housing section 2 so as to open into the toroidal chamber 16 adjacent to the downstream side of the stripper block 17, given that the impeller 5 rotates in the direction of arrow R, as shown in Figure 2. An outlet port 20 is provided in the housing section 2 so as to open into the toroidal chamber 16 adjacent to the upstream side of the stripper block. The chamber 16 between these inlet and outlet ports 19,20 forms a flow channel in which the impeller induces a helical flow of fluid about the toroidal ring 14 as it is rotated, passing repeatedly through the vanes 13 and being progressively raised in pressure.
[0018] The flow stripper block 17 serves to separate the high pressure outlet end of the flow channel 16 from the lower pressure inlet end of the flow channel 16 and limits the direct flow of fluid between the two. However, the stripper block is formed with an internal helical flow channel or loop 22 which advances in the same sense as the helical fluid flow about the toroidal ring 14 in flow channel 16, as shown in Figure 3. The upstream end of the helical flow loop 22 opens into the outlet end of the flow channel 16 at a shaped port 23, and the downstream end of the helical loop 22 opens into the inlet end of the flow channel 16 at a shaped exit port 29. The exit port 29 directs the flow of fluid from the loop 22 circumferentially of the toroidal ring 14 through the vanes 13 into the inlet end of the flow channel 16. The fluid supplied to the loop 22 therefore flows in a helical path through the loop and tends to continue in the same helical path within the flow channel 16 after leaving the exit port 29. This circumferentially directed jet of fluid from the exit port 29 tends to induce a helical flow of fluid in the region of the inlet port 19, and thereby serves to enhance the pressure rise in the flow channel 16 caused by the repeated passage of the fluid through the vanes 13.
[0019] As described so far, the pump has a fluid inlet port 19 and a fluid outlet port 20. However, the pump also has a second fluid inlet port 33 which opens into the flow channel 16 approximately half way along its length between the inlet port 19 and the outlet port 20. Both of these inlet ports 19,33 are connected to a diverter valve 34, as shown in Figure 4, which is adapted to switch a supply of fluid from inlet 35 to either inlet port 19,33, or to divide the inlet supply of fluid in any selected ratio between the two inlet ports 19,33. The diverter valve 34 also serves to connect the two inlet ports 19,33 together so as to allow recirculation of fluid through the valve 34 between the two inlet ports under certain flow conditions.
[0020] If the supply of fluid to the diverter valve 34 is switched fully to the second inlet port 33, as shown in Figure 6, then the output of the pump takes the form shown by curve C in Figure 8 with a reduced pressure rise δP for similar output flows Q compared with the output of the pump, shown as curve A, when the inlet supply 35 is connected to the first inlet port 19. This reduction in pressure is explained by the fact that the flow channel 16 is effectively shortened in length, and thus the fluid is re-circulated through the vanes 13 to a lesser extent. The length of the flow channel between the inlet ports 19 and 33 becomes redundant, but the drag exerted on the impeller by the fluid when this is a liquid, is reduced by vaporisation of the liquid in the channel caused by the reduced pressure due to the continued pumping action of the impeller.
[0021] If the diverter valve 34 is set to split the inlet supply of fluid between the two inlet ports 19 and 33, as shown in Figure 5, then the output of the pumps is as shown by curve E in Figure 8, with the output flow Q increased at all pressure rise values δP as compared with the output shown by curve C when only the second inlet port 33 is used, but the pressure rise δP reduced at most flow values Q compared with the output shown by curve A when only the first inlet port 19 is used as shown in Figure 7. Above a certain upper value of output flow Q, the pressure rise δP of the pump with twin inlet supplies, shown in Figure 5, is higher than that of the pump using just the first inlet port 19, shown in Figure 7.
[0022] Figure 9 illustrates an alternative embodiment of the invention in which the diverter valve 34 controlling fluid flow to the two inlet ports 19,33, is replaced by a variable restrictor valve 35 in the inlet connection 36 to the port 19 and a non-return valve 37 in the inlet connection 38 to the port 33. A fluid supply connection 41, supplies fluid to a connection 40 between the restrictor valve 35 and non-return valve 37 so as to supply fluid in parallel to both of them. The non-return valve 37 prevents re-circulation of fluid through connection 40 between the higher pressure second inlet port 33 and the lower pressure first inlet port 19, but is responsive to a pressure demand signal produced at the inlet port 33 by the setting of the variable restrictor valve 36. For example, if the restrictor valve 36 is opened fully, the pressure generated at the second inlet port 33 by the impeller will be a maximum and will close or limit opening of the non-return valve 38 so that there is zero or a minimum flow of fluid through the second inlet port 33. However, if the restrictor valve 36 is only partially opened, a lower pressure will be generated at the second inlet port 33, and therefore the non-return valve 37 will open more to increase the flow of fluid through the second inlet port 33. At the other extreme, if the restrictor valve 35 is closed, the non-return valve 38 will open to a maximum extent to supply fluid to the second inlet port 33.
[0023] It will be appreciated that whilst the pump has been described so far with only two inlet ports 19,33 in the flow channel 16, it is possible to provide three or more inlet ports spaced apart along the length of the flow channel 16 with appropriate means to control the supply of fluid to each of them. An example of a pump with three inlet ports is shown in Figure 10 with a diverter valve 41 controlling the supply of fluid to each of three inlet ports 19,42,33.
[0024] In all of the embodiments described above, the particular outputs produced by the pump will depend upon the relative position of the inlets 19,33 or 19,33,42 and outlet 20 along the length of the flow channel 16. However, an improved output is obtained if the first inlet 19 is spaced downstream of the stripper block 17, as shown in Figure 2, rather than being located immediately after the stripper block. This downstream spacing of the inlet 19 may serve to allow the helical flow of fluid from the exit port 29 to establish itself before it meets the flow through the inlet 19. However, if the downstream spacing is too large, the helical flow may dissipate and, for a fixed position of the outlet port 20, the effective length of the flow channel 16 will be reduced. An optimum position of the inlet 19 lies within the range 15° to 90° downstream of the exit port 29, or the preferred range 45° to 75° downstream of the exit port 29.
1. A regenerative pump comprising a housing (1) with a fluid inlet (19) and a fluid outlet
(20), an impeller (5) rotatably mounted within the housing (1) and having a plurality
of vanes (13) spaced angularly around the axis of rotation of the impeller (5) and
accommodated within a flow channel (4) within the housing (1) extending between the
inlet (19) and outlet (20), and a flow stripper located between the inlet (19) and
outlet (20) and through which the vanes (13) pass, characterised in that a second
fluid inlet (33) is provided in the housing (1) to open into the flow channel (4)
between said fluid inlet (19) and fluid outlet (20), and in that control means (34)
is provided to control the supply of fluid selectively to one or the other, or one
or both of said fluid inlets (19,33), thereby to vary the output of the pump.
2. A pump as claimed in claim 1 in which three or more circumferentially spaced fluid
inlets (19,42,33) are provided along the length of the flow channel, and the control
means (34) controls the supply of fluid to these inlets (19,42,33) selectively either
as alternatives or in combination.
3. A pump as claimed in claim 1 or 2 in which the stripper (17) is adapted to preserve
the annular motion of the fluid as it passes through the stripper (17), and incorporates
a fluid flow loop (22) which intersects the path of rotation of the vanes (14).
4. A pump as claimed in any one of claims 1 to 3 in which the first fluid inlet (19)
is spaced downstream of the stripper (17).
5. A pump as claimed in claim 4 in which the centre of the first fluid inlet (19) is
located within an angular range of 15° to 90° from a fluid exit port (29) of the stripper
(17).
6. A pump as claimed in claim 5 in which the first fluid inlet (19) is located within
the angular range of 45° to 75° from the fluid exit port (29) of the striper (17).
7. A regenerative pump comprising a housing (1) with a fluid inlet (19) and a fluid outlet
(20), an impeller (5) rotatably mounted within the housing (1) and having a plurality
of vanes (13) spaced angularly around the axis of rotation of the impeller (5) and
accommodated within a flow channel (4) within the housing (1) extending between the
inlet (19) and outlet (20), and a flow stripper (17) located between the inlet (19)
and outlet (20) and through which the vanes (13) pass, characterised in that said
fluid inlet (19) is spaced downstream of the stripper (17), thereby allowing the annular
flow of fluid from the stripper (17) to establish itself before it meets the flow
through the inlet (19).
8. A pump as claimed in claim 7 in which the inlet (19) is located within the range 15°
to 90° downstream of an exit port (29) of the stripper (17),
9. A pump as claimed in claim 8 in which the inlet (19) is located within the range 45°
to 75° downstream of the exit port (29).