TECHNICAL FIELD

The present disclosure relates to pump systems including a cooling arrangement.

BACKGROUND

In the field of subsea oil and gas production, well fluid is commonly produced and communicated from a well. To increase or boost oil and gas production and recovery, a subsea pump may be used to add energy to the well fluid.

Similar subsea pumps may also be used for subsea seawater injection to inject seawater into a subsea reservoir, thus increasing the pressure in the reservoir so as to enhance oil and gas recovery.

Similar subsea pumps may also be used for subsea SCO2 re-injection to inject CO2 into a subsea reservoir, primarily for storage thereof.

In any of these applications, a subsea pump typically includes parts which generate heat and so benefit from cooling. The cooling may be provided by pumping a suitable fluid to those parts requiring cooling, for example by pumping a fluid through cooling coils surrounding the parts requiring cooling so as to remove heat from those parts via the fluid. It is known in some contexts to provide a cooling pump unit which is separate from the subsea pump, the cooling pump unit being configured to pump a coolant around a coolant loop to cool any parts of the pump in which cooling is required.

The present disclosure provides a simplified pump system, for example suitable for use subsea in any of the applications outlined above. SUMMARY

From a first aspect, the disclosure provides a pump system comprising: a longitudinal axis; and a plurality of pump stages, wherein each pump stage comprises: a rotary component mounted for rotation about the longitudinal axis; a fluid inlet; a fluid outlet; and a main fluid flow path for fluid to flow from the fluid inlet to the fluid outlet, the rotary component extending radially into the main fluid flow path and being drivable to rotate about the longitudinal axis so as to impart a force to fluid in the main flow path, wherein the rotary component of each of the plurality of pump stages is separately drivable so as to be able to rotate at a different speed from the rotary components of the other pump stages, the pump system further comprising a cooling passage, wherein a first pump stage of the plurality of pump stages is configured to pump fluid through the cooling passage, wherein the cooling passage is configured to deliver the fluid to the other pump stages of the plurality of pump stages, wherein the cooling passage is separate from the main fluid flow path of each of the other pump stages of the plurality of pump stages.

In any example of the disclosure, the plurality of pump stages may form or may be located within a housing, wherein the housing may be sealed from an external environment.

In any example of the disclosure, the pressure internal to the housing may be different to that of the external environment. A pump system according to any example of the disclosure may further comprise a variable speed drive for driving the rotary components of the plurality of pump stages, wherein the cooling passage may be configured to deliver the fluid to the variable speed drive.

In any example of the disclosure, the variable speed drive may be located outside the housing.

A pump system according to any example of the disclosure may further comprise a heat exchanger for cooling the fluid in the cooling passage.

In any example of the disclosure, each pump stage may comprise one or more bearings for mounting the rotary component for rotation about the longitudinal axis, wherein the pump system may further comprise a further cooling channel configured for cooling the bearings in one or more of the pump stages, wherein the further cooling channel may be fluidly connected to the cooling passage so as to supply the fluid to the further cooling channel.

In any example of the disclosure, the one or more bearings may include a radial bearing located radially outward of the longitudinal axis, and wherein the further cooling channel may comprise a first further cooling channel extending in an axial direction between the radial bearing of at least one of the pump stages and the longitudinal axis.

In any example of the disclosure, the one or more bearings may further include an axial bearing extending radially outwardly from the radial bearing, and wherein the further cooling channel may further comprise at least one further annular cooling channel extending radially outward from and around the first further cooling channel, the further annular cooling channel being positioned to allow cooling of the axial bearing of at least one of the pump stages. A pump system according to any example of the disclosure may further comprise a connecting channel configured to deliver fluid from the first further cooling channel to the further annular cooling channel before reentering the first further cooling channel.

In any example of the disclosure, the cooling passage may form a closed loop so as to deliver the fluid back to the fluid inlet of the first pump stage, or the cooling passage may be configured to expel fluid to an external environment after it has passed through the cooling passage from the first pump stage.

Each pump stage of a pump system according to any example of the disclosure may further comprise: power features for driving rotation of the rotary component; and a cooling arrangement for cooling the power features, wherein the cooling passage may be configured to supply the fluid to the cooling arrangement in at least one pump stage.

In any example of the disclosure, the fluid outlet of the first pump stage may be fluidly connected to the cooling passage such that the first pump stage is configured to supply the fluid to the cooling passage, wherein the fluid outlet of the first pump stage may be fluidly isolated from the main flow paths of the other pump stages of the plurality of pump stages, and wherein the other pump stages of the plurality of pump stages may be arranged for sequential flow of a process fluid there-through from the fluid inlet of one of the other pump stages to the fluid outlet of one of the other pump stages.

In any example of the disclosure, the plurality of pump stages may be arranged for sequential flow of the fluid there-through from the fluid inlet of the first pump stage to the fluid outlet of one of the other pump stages. In some examples of the disclosure, the fluid outlet of the first pump stage may be fluidly connected to the cooling passage such that the first pump stage is configured to supply the fluid to the cooling passage, and wherein the fluid outlet of the first pump stage may be fluidly connected to the main flow paths of the other pump stages of the plurality of pump stages.

Although certain advantages are discussed below in relation to the features detailed above, other advantages of these features may become apparent to the skilled person following the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more non-limiting examples will now be described, by way of example only, and with reference to the accompanying figures in which:

Figure 1 is a schematic representation of a pump system according to an example of the disclosure;

Figure 2 is a schematic radial cross section through a part of a pump system according to an example of the disclosure;

Figure 3A is a schematic radial cross section through the part of the pump system shown in Figure 2, according to a first example of the disclosure;

Figure 3B is a schematic radial cross section through the part of the pump system shown in Figure 2, according to an alternative example of the disclosure;

Figure 4 is a schematic radial cross section through a part of a pump system according to another example of the disclosure;

Figure 4A is a schematic axial cross section through a part of the pump system of Figure 4;

Figure 5 is a schematic radial cross section through a part of a pump system according to another example of the disclosure; Figure 5A is a detail of part of the schematic radial cross section of Figure 5; and

Figure 6 is a schematic radial cross section through a part of a pump system according to another example of the disclosure.

DETAILED DESCRIPTION

Referring to Figure 1 , a pump system 2 suitable for use in a subsea environment is schematically shown. The pump system 2 has a housing 4 having a longitudinal axis X-X. A plurality of pump stages are positioned within the housing 4. In other examples of the disclosure, the housing may be formed by the bodies of the pump stages themselves as will be described further below. In the example shown in Figure 1 , five pump stages 6, 8, 10, 12 and 14 are shown. It will be understood however that any suitable number of two or more pump stages for a required pumping function could be provided.

As described in further detail below, each pump stage comprises a rotary component mounted for rotation about the longitudinal axis X-X. It will be understood that, if so desired, any suitable number of rotary components may be provided in each pump stage such that each pump stage may include two or more rotary components. Each pump stage also has a fluid inlet, a fluid outlet, and a main fluid flow path for fluid to flow from the fluid inlet to the fluid outlet. The rotary component extends radially into the main fluid flow path and is configured to rotate about the longitudinal axis so as to impart a force to fluid in the main flow path. Further, the rotary components of each of the plurality of pump stages are separately controllable so as to be able to rotate at a different speed from the rotary components of the other pump stages. The pump system also includes a cooling passage 16. A first pump stage 6 of the plurality of pump stages is configured to pump fluid through the cooling passage 16 so as to deliver fluid to the other pump stages 8, 10, 12, 14 of the plurality of pump stages. The cooling passage 16 is separate from the main fluid flow path of each of the other pump stages of the plurality of pump stages as will become apparent from the description below.

In the example of Figure 1 , the cooling passage 16 forms a closed loop, in other words, it is configured such that fluid flows from the first pump stage, through the cooling passage and back into the first pump stage. As shown in Figure 1 , the cooling passage 16 can be configured to provide fluid to each of the other pump stages 8, 10, 12, 14 of the plurality of pump stages and may also provide fluid to a variable frequency drive 20 or to other components (not shown) requiring cooling which may be located either externally or internally of the housing 4. In any example of the disclosure, the cooling fluid used may be any suitable coolant, including water (for example sea water) or glycol. In some examples, the variable frequency drive 20 may be positioned externally of the housing 4 and may be configured to drive each of the two or more pump stages 6, 8, 10, 12, 14 separately. The variable frequency drive can be provided in a separate housing 22. The housing 4 within which the pump stages are located forms a casing enclosing the pump stages. The housing 4 can be sealed against sea water ingress and can be internally pressurised relative to atmospheric pressure if required for use in a subsea environment. In a similar manner, the separate housing 22 forms a casing enclosing the variable frequency drive. It can be sealed against sea water ingress and can be internally pressurised relative to atmospheric pressure if required for use in a subsea environment.

In some examples and as shown in Figure 1 , a heat exchanger 24 is provided to cool cooling fluid passing through the cooling passage 16. The heat exchanger 24 can take any suitable form and can be provided at any desired location along the cooling passage 16. In the example of Figure 1 for example, the heat exchanger 24 is provided externally of both the housing 4 within which the pump stages are located and the separate housing 22 for the variable frequency drive 20.

In the example shown in Figure 1 , the cooling passage 16 forms a closed loop as described above. The first pump stage 6 is fluidly isolated from the other pump stages 8, 10, 12, 14 of the plurality of pump stages and acts as a cooling fluid pump (a coolant impeller) 40. The cooling passage 16 extends from the fluid outlet 42 of the cooling fluid pump 40 and is configured to deliver cooling fluid to the other pump stages 8, 10, 12, 14. In the example of Figure 1 , the cooling passage 16 then extends to the variable frequency drive 20 via the heat exchanger 24. The cooling passage 16 may for example extend through the separate housing 22 for the variable frequency drive 20 so as to cool the variable frequency drive 20. In an alternative example, the cooling passage 16 may extend around the variable frequency drive as a helical coil. The cooling passage 16 is configured to then supply the fluid back to the fluid inlet 44 of the cooling fluid pump 40 such that the cooling fluid pump 40 pumps the fluid to the fluid outlet 42 thereof.

As shown in Figure 1 , an accumulator 50 may be provided in the closed loop formed by the cooling passage 16 for compensating for pressure variations due to thermal expansion of the fluid in the closed cooling fluid loop. In the example of Figure 1 , the accumulator 50 is located externally of the housing 4 between the variable frequency drive 20 and the cooling fluid pump 40. However, it will be understood that the accumulator 50 could be located elsewhere, for example internally of the housing 4.

It will be understood that in other examples, the cooling passage may form an open cooling system instead of a closed loop. In such examples, the cooling passage may be configured to expel fluid to the environment after it has passed through the cooling passage from the first pump. In such examples, a fluid from the surrounding environment (in some examples, seawater from the sea) could be input to the first pump stage 6 and pumped through the cooling passage 16 before being discharged back into the surrounding environment. In such open cooling system examples, no accumulator or heat exchanger (as described below) may be needed.

Referring to Figure 2, the plurality of pump stages of an example pump system 202 such as that shown in Figure 1 are shown in greater detail. In the example shown in Figure 2, a total of four pump stages are provided although, as discussed above, it will be understood that any suitable number of pump stages could be provided.

In the example of Figure 2, the four pump stages 206, 208, 210, 212 comprise respective bodies which are mounted together to form a housing 204. The housing 204 has a longitudinal axis X-X and the four pump stages are mounted sequentially along the axis X-X. It will be understood that in other examples of the disclosure which are not shown here, the plurality of pump stages could be positioned differently for fluid to flow sequentially between the pump stages. Thus, the pump stages could for example be mounted sequentially in a radial direction. As in the example of Figure 1 , the first pump stage 206 of the example shown forms a cooling fluid pump 240.

In some examples, the pump system is configured so as to fluidly isolate the cooling fluid which is pumped through the cooling passage via the cooling fluid pump from the process fluid which is pumped from an inlet to an outlet by the other pump stages of the plurality of pump stages. In the example of Figure 2, this is achieved by the housing 204 including a first body 230 belonging to the first pump stage 206 which forms the cooling fluid pump 240. The rotary component, fluid inlet, fluid outlet, and main fluid flow path of the first pump stage 206 are provided within the first body 230. The first body 230 has a cooling fluid inlet 232 connected to the fluid inlet 244 of the cooling fluid pump 240 such that cooling fluid may be supplied to the cooling fluid pump 240 from outside the housing 204. It will be understood that in some examples, the cooling fluid inlet 232 may be connected to a cooling passage (not shown in Figure 2), for example forming a closed cooling fluid loop as discussed above in relation to Figure 1 .

As seen in Figure 2, the housing 204 also includes a second body 234 which is made up of the bodies belonging to the other pump stages 208, 210, 212 of the plurality of pump stages. Each of the pump stages 208, 210, 212 are mounted in series forming a row along the longitudinal axis X-X such that the fluid outlet 260a of a first pump stage 208 of the other pump stages is fluidly connected to the fluid inlet 262b of a second pump stage 210 of the other pump stages, and the fluid outlet 260b of the second pump stage 210 is fluidly connected to the fluid inlet 262c of a third pump stage 212 of the other pump stages such that a continuous main fluid flow path 264 is formed by the main fluid flow paths 264a-c of each of the other pump stages and extends along the longitudinal axis from the fluid inlet 262a of the first pump stage 208 of the other pump stages to the fluid outlet 260c of the third pump stage 212.

The first body 230 is connected with the second body 234 so as to form a single housing which is sealed against water ingress and may be internally pressurised as required. The second body 234 includes a process fluid inlet 236 through which process fluid may enter the housing 204 and flow into the main fluid flow path 264 via the fluid inlet 262a of the first pump stage 208. The second body 234 further includes a process fluid outlet 238 through which process fluid may exit the housing 204 after flowing out from the fluid outlet 260c of the third pump stage 212.

In any example of the disclosure, such as in the example of Figure 2, each pump stage may comprise a separate modular component. Each pump stage may therefore comprise a distinct body (or housing) in which the pump components of the pump stage are provided as will become more apparent from the description below. When assembled within the pump system 2, the body of the first pump stage 208 may be connected to the body of the second pump stage 210 which may be connected to the body of the third pump stage 212. In one example, the bodies of the respective pump stages may be connected together by bolting. In further examples of the disclosure, one or more seals may be provided between each of the pump stage bodies such that the pump stages are sealed against fluid entering between the respective pump stages via the joints between the pump stage bodies. The seals may also limit or stop leakage of process fluid from the main flow path 264 to the external environment at the joins between respective pump stages.

In any example of the disclosure, including that of the pump system of Figure 2, each pump stage has one or more rotary components mounted for rotation about the longitudinal axis. In the example of Figure 2, the rotary components comprise a number of blades 270 which are circumferentially distributed about the longitudinal axis X-X and which extend radially into the main fluid flow path 264 and are configured to rotate about the longitudinal axis so as to impart a force to fluid in the main flow path. The blades 270 can be mounted for rotation about a static longitudinal shaft 272 by bearings.

In various examples including the pump system of Figure 2, a static diffuser 274 can be provided in each pump stage which is upstream of the static shaft 272 in the intended direction of flow of fluid in the main fluid flow path. The blades 270 can be mounted on the static shaft 272 downstream of the static diffuser 274 by radial bearings 276 extending between an annular base 277 on which the blades 270 are mounted and the static shaft 272. Thrust bearings 278 may also be provided extending radially between the blades 270 and the static diffuser 274 both upstream and downstream of the blades 270.

The rotary components can be caused to rotate about the longitudinal axis by any suitable means. In various examples, power features are provided in each pump stage to cause the rotary components to rotate in use so as to impart a centrifugal force to the fluid in the main flow path. In the example shown in Figure 2, the power features for each pump stage are provided in respective chambers formed within the housing 4 and positioned radially outward of the rotary components. In any one of the pump stages, for example in the first pump stage 208 of the other pump stages, the power features may comprise an electromagnetic motor stator 280 positioned radially outward of a permanent magnet which forms a motor rotor 282 and is positioned radially outward of the rotary components or blades 270 so as to drive the rotation thereof when the electromagnetic motor stator 280 is activated. It will be understood that in any example of the disclosure, each electromagnetic motor stator 280 can be driven separately from the electromagnetic motor stators of the other pump stages.

In any example, the process fluid may comprise any fluid to be pumped through the pump system and in some examples may comprise a multiphase fluid such as a mixture of oil and water and gas. The process fluid may flow into the second body 234 through the process fluid inlet 236 which is provided on a radially outer surface of the second body 234 and is positioned upstream of the blades 270 of the first pump stage 208 of the other pump stages. The second body 234 includes an inflow passage 237 configured such that process fluid will flow radially inward from the process fluid inlet 236 through the inflow passage until it meets the main flow path 264. The main flow path 264 of the example shown is substantially annular in cross section and is formed between a radially inner surface provided by the static shaft and diffusers of each pump stage and a radially outer surface formed in the second body 234. The process fluid will in use flow along the main flow path in an approximately axial direction through each of the other pump stages in turn before exiting the second body 234 via the process fluid outlet 238 which may form an axial extension of the main flow path. In the example shown in Figure 2, the cooling fluid inlet 232 is connected via the coolant pump 240 to a cooling fluid passage. As shown in Figure 3A, in some examples of the disclosure, the cooling passage may include a supply passage formed by a bore 284 extending radially outwardly through the first body 230 to a radially outer surface 286 thereof. The bore 284 may extend from a diffusor ring 288 comprising an annular chamber formed in the first body 230 and fluidly connected to a fluid outlet 290 of the coolant pump 240. Thus, in use, cooling fluid supplied to the coolant pump 240 via the cooling fluid inlet 230 is pumped into the bore 284 such that the velocity and pressure of the cooling fluid in the cooling passage is controlled by the coolant pump 240.

In the example of Figure 3A, the cooling passage further comprises conduits 292 for the cooling fluid which extend externally of the housing 204. Further respective supply bores 294a-d are provided to extend radially from the radially outer surface 286 of the first body 230 or the second body 234 to supply a respective cooling arrangement such as a helical cooling jacket 296a-d located radially outwardly of the electromagnetic motor stator 280a-d in each respective pump stage. As seen in Figure 3A, the bore 284 may be connected to the conduits 292 which in turn are connected to the respective supply bores 294a-d such that cooling fluid may be supplied from the coolant pump 240 to each of the respective helical cooling jackets 296a-d of the respective pump stages.

Respective outflow bores 298a-d are also provided to extend radially from the radially outer surface 286 of the first body 230 or the second body 234 to drain coolant fluid from a respective helical cooling jacket 296a-d in each respective pump stage. As seen for example in Figure 3A, the outflow bores 298a-d are circumferentially spaced from the supply bores 294a-d and may for example, be located opposite the supply bores on the other side of the housing 4 from the longitudinal axis. The outflow bores 298a-d may be connected to further conduits 292 which may be connected via a closed loop such as that described with reference to Figure 1 to the cooling fluid inlet 232.

In alternative examples such as that of Figure 3B, the bore 284’, supply bores 294’a-d and outflow bores 298’a-d do not extend to the radially outer surface of the housing 204. Rather, each of the bore 284’ and supply bores 294’a-d are fluidly connected by a first axial bore 300 in the housing 204. Similarly, the outflow bores 298’a-d are fluidly connected by a second axial bore 302 in the housing 204. The second axial bore 302 is then fluidly connected via a closed loop such as that described with reference to Figure 1 to the cooling fluid inlet 232 via a further radial bore extending to the radially outer surface of the housing 204.

As described above, each of the pump stages may include both radial and thrust bearings for mounting the blades 270 for rotation about the longitudinal axis X-X. Significant heat is generated at these bearings, which may for example be Poly Crystalline Diamond bearings, and so it is desirable to provide additional cooling for them. In some examples of the disclosure therefore and as shown for example in Figure 4, additional cooling passages for providing cooling fluid to the bearings may be formed. In some examples, heat may be transferred away from the bearings by conduction through part of the pump stage body to the additional cooling passages. Heat may then be transferred away from the pump stage body by transfer into the fluid within the additional cooling passages. To improve the cooling of the bearings, parts of a pump stage located between the bearings and the additional cooling passages may be made from materials with high heat conductivity such as aluminium, copper or steel, for example. This may be especially effective for Poly Crystalline Diamond bearings as this material has a high heat conductivity itself. The provision of additional cooling of the bearings can be especially useful in examples in which the bearings are lubricated by the process with multiphase liquid gas mixtures. In these examples, the high gas content in the liquid gas mixtures may limit the heat removal by the multiphase liquid gas mixtures.

Figure 4 shows a part of a pump system of a type similar to that shown in Figure 2, 3A and 3B. Although only two pump stages are shown other than the coolant pump 240, it will be appreciated that any suitable number of pump stages could in fact be used in the pump system of Figure 4.

The structural features of the pump system 202 of Figure 4 are substantially as described above in relation to Figures 2, 3A and 3B and will not be described here again where they are given the same reference number. Figure 4A is a schematic enlarged sectional view through a part of the third pump stage closest to the longitudinal axis X-X. As seen in Figures 4 and 4A, the pump system of this and other examples may include the additional feature of a further cooling channel for supplying cooling fluid to the bearings of each pump stage. In some examples radial bearings 276 may be provided in each pump stage. In some examples therefore, a first further cooling channel 310 may be formed in each pump stage. In some examples, the first further cooling channel may extend around the longitudinal axis XX along the length of each pump stage and through the static longitudinal shaft 272 thereof radially internally of the radial bearings 276. In the example shown in Figures 4 and 4A, the first further cooling channel is made up of two sections 310a, 310b each forming an approximate annular half disk as shown in the axial cross section of Figure 4A. In alternative examples, the first further cooling channel could be annular in axial cross section or could form a bore having a circular cross section. When the pump stages are assembled together to form the pump, the respective first further cooling fluid channels 310 of each pump stage are axially aligned and join to form a single cooling fluid channel. Further, one or more sealing members may be provided at the intersection between each pump stage, adjacent the first further cooling fluid channel 310 so as to avoid process fluid mixing with the cooling fluid. The first further cooling fluid channel 310 may be supplied by cooling fluid from the diffusor ring 288 in the first body 230. To achieve this, a second further channel 312 in the first and second bodies may connect the first further cooling fluid channel 310 to the diffusor ring 288.

After flowing axially along the first further cooling fluid channel 310 and removing heat from the radial bearings 276, cooling fluid from the first further cooling fluid channel 310 may for example flow into further conduits 292 of the type shown in Figure 3A and which may be connected via a closed loop to the cooling fluid inlet 232.

The pump system of Figure 5 includes many of the same features as that of Figure 4 and those are shown with the same reference numerals and not discussed again here. In addition to the features shown in Figures 4 and 4A, the pump system of Figure 5 includes further cooling fluid channels for supplying cooling fluid to the thrust bearings 278 of each pump stage within the second body 234. To facilitate cooling of the thrust bearings 278 therefore, each pump stage may include a further annular cooling channel 314 which is fluidly connected to the first further cooling fluid channel 310. The further annular cooling channel 314 extends radially outward from and around the first further cooling fluid channel 310 at a location just upstream of the thrust bearings 278 of that pump stage. A connecting channel 316 which extends at an angle to the first further cooling fluid channel 310 is configured to join the radially outermost point of the further annular cooling channel 314 to the first further cooling fluid channel 310 at a point upstream of the further annular cooling channel 314. Cooling fluid may thus be taken from the first further cooling fluid channel 310 through the connecting channel 316 to re-enter the first further cooling fluid channel 310 via the further annular cooling channel 314.

If required in any example of the disclosure, an insert may be provided to control the way in which cooling fluid flow is split between different cooling channels. The insert could for example comprise a throttle which could be configured to create a pressure difference between respective channels so as to force fluid to flow into one channel in preference to another. Such an insert 320 could for example be provided at a junction between the diffusor ring 288 and the bore 284 in the first body 230. An insert could also be provided for example to control the way in which cooling fluid flow is split between the further annular cooling channel 314 and the first further cooling fluid channel 310. One possible example of this is shown in Figure 5A. As seen in this example, an insert 322 could be provided in the first further cooling fluid channel 310 upstream of the further annular cooling channel 314 and downstream of the connecting channel 316.

In each of the examples described above and shown in Figures 1 to 5, the coolant pump 40, 240 is fluidly isolated from the other pump stages of the pump system. A first fluid (the cooing fluid) is supplied to the coolant pump and is then supplied by the coolant pump to the cooling passage. A second fluid (the process fluid) is supplied to the remaining pump stages to be pumped there through. In some circumstances such as for example in oil and gas production and recovery it would not usually be appropriate to use the process fluid (typically a mixture of oil and gas) for cooling. However, in other applications such as for example in subsea seawater injection, the process fluid (in this example, seawater) is a suitable fluid to use for cooling such that there is no need to maintain separation between the cooling fluid and the process fluid. Many supercritical fluids would also make suitable cooling fluids such that a supercritical fluid (for example sCO2 in subsea SCO2 re-injection) could also be used without the need to maintain separation between the cooling fluid and the process fluid. In some examples of the disclosure therefore, no fluid separation or isolation is provided between the coolant pump and the remaining pump stages. An example pump system of this type is shown in Figure 6.

In the example of Figure 6, the pump system 602 again comprises a housing

604 which is sealed against water ingress. The housing 604 may be internally pressurised as required and has a longitudinal axis X-X. The pump system 602 may include any suitable number of pump stages, four are shown in the example of Figure 6. The pump stages are mounted in series forming a row along the longitudinal axis X-X. Thus, the fluid outlet 660a of a first pump stage 608 is fluidly connected to the fluid inlet 662b of a second pump stage 610, the fluid outlet 660b of the second pump stage 610 is fluidly connected to the fluid inlet 662c of a third pump stage 612 and the fluid outlet 660c of the third pump stage 612 is fluidly connected to the fluid inlet 662d of a fourth pump stage 614 such that a continuous main fluid flow path 664 is formed by the main fluid flow paths 664a-d of each of the four pump stages and extends along the longitudinal axis from the fluid inlet 662a of the first pump stage 608 to the fluid outlet 660d of the fourth pump stage 614.

The housing 604 includes a process fluid inlet 636 through which process fluid may enter the housing 604 and flow into the main fluid flow path 664 via the fluid inlet 662a of the first pump stage 608. The housing 604 further includes a process fluid outlet 638 through which process fluid may exit the housing 604 after flowing out from the fluid outlet 660d of the fourth pump stage 614.

As described above in relation to Figures 2 to 5, the housing in which the plurality of pumps stages are contained may be configured so as to fluidly isolate the cooling fluid which is pumped through the cooling passage via the cooling fluid pump from the process fluid which is pumped from an inlet to an outlet by the other pump stages of the plurality of pump stages. Thus, in these examples, one of the pump stages of the pump system may be used to pump a cooling fluid into the cooling passages whereas the other pump stages of the pump system may be used to pump a process fluid, which is kept separate from the cooling fluid, through the pump system. In other examples of the disclosure in contrast, all the pump stages of the pump system may be used to pump a process fluid through the pump system. In these examples, such as the example of Figure 6, some process fluid may be diverted from the main flow path of one of the pump stages into the cooling passage such that the process fluid is used as the cooling fluid also. In any of these examples, as the one or more rotary components of each of the plurality of pump stages are separately controllable so as to be able to rotate at a different speed from the one or more rotary components of the other pump stages, the rate at which the process fluid is pumped into the cooling passage may be controlled by controlling the rotary components of the pump stage from which the process fluid is diverted into the cooling passage.

The process fluid may be diverted from the main flow path 664 into the cooling passage at any desired point along the main flow path and from any desired pump stage. In the example of Figure 6, a diversion passage 700 is fluidly connected to the main fluid flow path 664 at a location within the first pump stage 608 and downstream of the rotary components or blades 670a of the first pump stage 608. The diversion passage 700 is connected to the cooling passage which may be configured in a similar manner to that shown in Figure 3 for example, so as to supply diverted process fluid via the diversion passage 700 to respective helical cooling jackets 696a-d located radially outwardly of the electromagnetic motor stator in each respective pump stage.

It will be understood that the additional cooling passages for cooling the bearings as shown in and described with reference to Figures 4 and 5 could equally be provided in a pump system of the type shown in Figure 6 in which the process fluid is used as the cooling fluid also.

It will further be understood that the cooling passage may form a closed loop in which process fluid is returned to the process fluid inlet 636 after passing through the cooling passage. In alternative examples, the cooling passage may be formed to expel process fluid to the environment after passing through the cooling passage. This may be advantageous in examples where process fluids such as clean sea water are used as it may further simplify the cooling circuit and may mean that no heat exchanger or other cooling means for the process fluid are required.

It will be appreciated that the example pump systems shown and described herein have a number of advantages over the prior art systems. Specifically, one of the pump stages of the pump system itself may be used to pump cooling fluid for the pump system. Thus, when used in a subsea or other hostile environment, no additional pump external to the sealed and/or pressurised housing formed by the pump stages or within which the pump stages are housed need be provided. This may improve reliability and efficacy of the pump system according to the disclosure. It may also reduce manufacturing and material costs of the pump system. Further, it may avoid a potential reduction in pressure rating of the pump system which could be caused by the need to connect an additional external cooling fluid pump into the pump system.

While the disclosure has been described in detail in connection with only a limited number of examples, it should be readily understood that the disclosure is not limited to such disclosed examples. Rather, the disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the scope of disclosure. Additionally, while various examples of the disclosure have been described, it is to be understood that aspects of the disclosure may include only some of the described examples. Accordingly, the disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.