GB2620694A

GB2620694A - An apparatus for mixing hot and cold fluid flows

Info

Publication number: GB2620694A
Application number: GB2315264.8A
Authority: GB
Inventors: McKay Steven; O'donnell James
Original assignee: Motion Control Products Ltd
Current assignee: Motion Control Products Ltd
Priority date: 2019-12-19
Filing date: 2020-12-18
Publication date: 2024-01-17
Also published as: GB2604554B; WO2021123155A2; GB2604554A; WO2021123155A3; GB202208749D0

Abstract

An apparatus for mixing hot and cold fluid flows comprises a fluid mixing chamber, a first pump 10A and a second pump 10B. The first pump has an impeller 14 provided in a pump chamber 12, and a first electric motor for driving the impeller to cause a heated fluid to flow out of the pump chamber of the first pump to the mixing chamber. The second pump has an impeller provided in a pump chamber, and a second electric motor for driving the impeller to cause an unheated fluid to flow out of the pump chamber of the second pump to the mixing chamber. The first pump and the second pump are controlled separately of each other by one or more motor controllers to thereby control at least one of a first set pressure and/or a first set temperature of a mixed fluid flowing from the mixing chamber resulting from mixing of the heated fluid flow from the first pump with the unheated fluid flow from the second pump.

Description

An Apparatus For Mixing Hot and Cold Fluid Flows

Field of the Invention.

The invention relates generally to an apparatus for mixing hot and cold fluid flows.

Background of the Invention.

In many countries, domestic mains water supplies are often installed as gravity fed systems whereby the water pressure of the installation is dependent on a height of a cold-water tank typically installed in the loft of the domestic premises. This can lead to generally low water pressure which may result in poorly performing showers for bathing and in slow running water from faucets, taps or the like.

With the very much increased installations of domestic showers for bathing over recent decades, there has been an increasing demand for booster pumps to boost the domestic mains water pressure or at least to boost the pressure of water in kitchens, bathrooms, and showers.

Conventional booster pumps are typically arranged to simultaneously pump both heated and unheated water -normally referred to as 'hot' and cold' water. The reason for pumping both hot and cold water via the same pump is to achieve a balanced supply into the shower mixer valve thus preventing one of the hot water flow or the cold water flow overwhelming the other and thereby compromising the temperature adjustment parameters of the mixer valve.

0B24625392 and 0B2506280 each disclose a twin ended water pressure booster pump for a shower or the like. The pump comprises an electric motor delivering rotational energy through a shaft. The shaft is driven to rotate by the rotor of the motor. The shaft extends to a first end of the motor through a first backplate assembly of a first pump chamber to drive an impeller in said first pump chamber to deliver fluid under pressure to a first outlet. The shaft also extends to an opposing end of the motor through a second backplate assembly of a second pump chamber to drive an impeller in said second pump chamber to deliver fluid under pressure to a second outlet. Suitable rotational seals are provided around the motor shaft where it extends through each respective backplate assembly.

The foregoing prior art twin ended pump is typical of known twin ended pumps in that it utilizes a single electric motor having a shaft extending through each respective backplate assembly at the ends of the motor to drive hot water and cold water impellers simultaneously. As such, the impellers are driven at the same speed to create a fluid pressure at their respective outlets which is balanced, i.e., each at an equal pressure.

One of many problems which arise with such pumps, whether twin ended or single ended pumps, is leakage through the rotational seals. Rotational seals typically comprise a first fixed stationary part and a second part which rotates with the shaft. Consequently, the seal surface of the fixed stationary part and the seal surface of the second rotating part, which slide over each other to form the fluid seal, tend to wear against one another. Water in the pump chamber acts as a lubricant to reduce such wear, but, if the pump chamber runs dry, is starved of water, or the water in the chamber cavitates, the degree of wear can increase considerably leading to early failure of the rotational seal.

Known twin ended pumps of the type illustrated by GB24625392 and 0B2506280 exhibit additional problems. For example, sometimes the pump chamber outlets of the pump are connected directly to respective hot and cold water faucets (taps). In the event that only one faucet is opened, water is required from only one pump chamber of the pump. The impeller of the other pump chamber not required to supply water is still driven by the motor shaft. This creates pressure and friction between the impeller and the water in the pump chamber and can cause the water to become heated and even in some cases to boil. As such the water temperature (be it the hot or cold side of the pump) may exceed the temperature rating of the pump seals which can, as a result, become hardened, damaged, and then leak. Also, as the temperature increases in the pump chamber, the cavitation of the water increases which starves the rotational seals of the thin film of lubricating water between the seal surfaces leading to damage of the seal surfaces as hereinbefore described. In the event that the water in the pump chamber does boil to the point that the chamber becomes dry, the seal surfaces may become irreparably damaged in a very short timescale.

To overcome the foregoing issue, 0B2517719 illustrates a solution comprising a fluid bypass connection between the two pump chambers. The fluid bypass connection fluidly connects one pump chamber to the other thus allowing water to flow from the non-flowing side of the pump to the flowing side of the pump. The fluid bypass connection should allow sufficient water to flow from one pump chamber to the other to prevent a full closed head running situation causing water to overheat or even boil in the non-flowing pump chamber.

However, to fit the fluid bypass connection, a fluid bypass tube is connected to respective water fittings at each end of the pump and the water fittings are connected to respective pump chamber outlets thereby introducing several more potential leak paths in the pump installation. It would be useful to provide an apparatus for mixing hot and cold fluid flows which obviate or mitigate problems associated with booster pumps.

Objects of the Invention.

An object of the invention is to mitigate or obviate to some degree one or more problems associated with known booster pumps.

The above object is met by the combination of features of the main claims; the sub-claims disclose further advantageous embodiments of the invention.

Another object of the invention is to provide an improved apparatus for mixing hot and cold fluid flows.

One skilled in the art will derive from the following description other objects of the I 5 invention. Therefore, the foregoing statements of object are not exhaustive and serve merely to illustrate some of the many objects of the present invention.

Summary of the Invention.

In a first main aspect, the invention provides an apparatus for mixing hot and cold fluid flows. The apparatus comprises a fluid mixing chamber, a first pump comprising an impeller provided in a pump chamber of said first pump, and a first electric motor for driving said impeller to cause a heated fluid to flow out of the pump chamber of the first pump to the mixing chamber, and a second pump comprising an impeller provided in a pump chamber of said second pump, and a second electric motor for driving said impeller to cause an unheated fluid to flow out of the pump chamber of the second pump to said mixing chamber. The first pump and the second pump are controlled separately of each other by one or more motor controllers to thereby control at least one of a first set pressure and/or a first set temperature of a mixed fluid flowing from the mixing chamber resulting from mixing of the heated fluid flow from the first pump with the unheated fluid flow from the second pump.

In a second main aspect of the invention, there is provided a method of operating an apparatus according to first main aspect, the method comprising the steps of: mixing a pumped heated fluid flow from the first pump with a pumped cold fluid flow from the second pump; and separately or independently controlling operation of the first pump and the second pump to control at least one of a set pressure and/or a set temperature of a resulting mixed fluid flow. Preferably, the method involves separately controlling the first and second pumps to reduce or negate the need for a mixing valve or the like for mixing the pumped fluid flows from said first and second pumps. A simple mixing chamber may be used in replacement of a conventional mixing valve.

The summary of the invention does not necessarily disclose all the features essential for defining the invention; the invention may reside in a sub-combination of the disclosed features.

The forgoing has outlined fairly broadly the features of the present invention in order that the detailed description of the invention which follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It will be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the invention.

Brief Description of the Drawings.

The foregoing and further features of the present invention will be apparent from the 20 following description of preferred embodiments which are provided by way of example only in connection with the accompanying figures, of which: Figure 1 is a perspective view of a twin ended pump for an apparatus in accordance with the invention; Figure 2 is a partially exploded perspective view of the twin ended pump apparatus of Fig. 1 Figure 3 is a fully exploded side view of the twin ended pump apparatus of Fig. 1; Figure 4 is a partially exploded side view of one end of the twin ended pump apparatus of Fig. 1; Figure 5 is a perspective view of one embodiment of a pump chamber inner end plate 30 for the twin ended pump apparatus of Fig. 1; Figure 6 is a block schematic diagram of a motor controller for the apparatus of Fig. I: and Figure? is a table showing savings in the materials of the present invention.

Description of Preferred Embodiments.

The following description is of preferred embodiments by way of example only and without limitation to the combination of features necessary for carrying the invention into effect.

Reference in this specification to 1one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may he exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments, but not other embodiments.

It should be understood that some elements shown in the FIGS, may be implemented in various forms of hardware, software, or combinations thereof These elements may be implemented in a combination of hardware and software on one or more appropriately programmed general-purpose devices, which may include a processor, memory, and input/output interfaces.

The present description illustrates the principles of the present invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope.

Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.

Thus, for example, it will he appreciated by those skilled in the art that the block diagrams presented herein represent conceptual views of systems and devices embodying the principles of the invention.

The functions of the various elements shown in the figures may be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared. Moreover, explicit use of the term "processor" or,'controller" should not be construed to refer exclusively to hardware capable of executing software, and may implicitly include, without limitation, digital signal processor ("DSP") hardware, read-only memory ("ROM") for storing software, random access memory ("RAM"), and non-volatile storage.

References in the following description to a twin ended pump or a twin ended fluid pump are to he taken as references to a twin ended pump apparatus.

I 5 Referring to the drawings, shown is an embodiment of a twin ended fluid pump 10 for an apparatus in accordance with the invention. The pump 10 has a first end I OA and a second end 10B. At said first end 10A is a pump chamber 12 housing an impeller 14 for causing a fluid entering a fluid inlet 16 to flow out under pressure from a fluid outlet 18 of the pump chamber 12. The pump chamber 12 is defined between and bounded by a pump chamber inner end plate 20 and a pump chamber outer end plate 22. The outer end plate 22 comprises a volute for the pump chamber 12, although in other embodiments, a front face of the inner end plate 20 may fully or partially define said volute or the pump volute is defined by both the inner end plate 20 and the outer end plate 22.

Either or both of the inner end plate 20 and the outer end plate 22 may be formed as extruded or molded components. Either or both of the inner end plate 20 and the outer end plate 22 may be formed from high grade plastics material.

The inner end plate 20 is attached to a first end of a motor housing 24 such that a peripheral edge of a rear face of the inner end plate 20 forms a fluid-tight seal with a peripheral edge of the first end of the motor housing 24. A first "0" ring seal 26 or the like may be provided to ensure the integrity of the seal between the rear face of the inner end plate and the first end of the motor housing 24. The outer end plate 22 is attached to the inner end plate 20 to thereby enclose the impeller 14 in the pump chamber 12. The arrangement is such that a peripheral edge of the rear face of the outer end plate 22 forms a fluid-tight seal with a peripheral edge of the front face of the inner end plate 20. A second "0" ring seal 28 or the like may be provided to ensure the integrity of the seal between the rear face of the outer end plate 22 and the front face of the inner end plate 20.

As can best be seen in Fig. 2, the outer end plate 22 can be secured by a set of bolts or screws 25 through the inner end plate 20 to the first end of the motor housing 24.

The pump 10 includes at least one motor unit 29 (Fig. 3) for driving the impeller 14. The motor unit 29 comprises the stator 30 which is positioned on a dry' side of the inner end plate 20 and the rotor 32 which is positioned on a 'wet' side of said inner end plate 20 and the motor housing 24 if present. As such, the inner end plate 20 defines a fluid-sealed boundary separating said pump chamber 12 from the stator 30/motor housing 24.

In this embodiment, the stator 30 has a plurality of stator windings 30A. The rotor 32 preferably comprises a permanent magnet rotor which, in operation, is driven by the electromagnetic fields of the stator windings 30A when such stator windings 30A are driven in a predefined sequence by a motor controller 100 (Fig. 6). Preferably, the motor unit 29 comprises a brushless direct current (BLDC) motor unit. The BLDC motor unit can be a six wire BLDC motor unit or a three wire BLDC motor unit. Use of a BLDC electric motor provides many advantages as will be more fully explained in the following description. The motor unit 29 can be considered, in effect, as comprising an electric motor in that it can be an "off the shelf" electric motor. It will be understood, that, in other embodiments, other types of electric motors may be utilized in the pump 10 for driving the impeller 14 and thus the pump 10 in accordance with the invention is not limited to using BLDC motor units 29.

In the embodiment shown in the drawings, the stator 30 is accommodated in the first end of the motor housing 24.

The inner end plate 20 is preferably substantially cup shaped about a rotational axis of the rotor 32. A cup part 20A of the inner end plate 20 preferably extends into the first end of the motor housing 24 by an amount sufficient to support, accommodate or mount the stator 30 around an exterior cylindrical face of said cup part 20A. Alternatively, the stator 30 can be supported by or mounted in the motor housing 24. The rotor 32 is preferably accommodated within an interior volume of the cup part 20A of the inner end plate 20 such that the rotor 32 is positioned concentrically with the stator 30 when the pump 10 is assembled. The rotor 32 is therefore positioned for rotation within the cup part 20A when driven by the stator 30. Consequently, the rotor 32 is located on a 'wet' side of the fluid-sealed boundary defined by the inner end plate 20 which separates the pump chamber 12 from the stator 30/motor housing 24 and the stator 30 is positioned on a dry side of said boundary.

It can be seen therefore that there is no need for the motor unit 29 to have a motor shaft which extends through the fluid-sealed boundary, i.e., through the inner end plate 20 separating the pump chamber 12 from the stator 30/motor housing 24.

To better facilitate rotation of the rotor 32, there may be provided a shaft or spigot 34 extending from an internal end face of the cylindrical cup part 20A of the inner end plate 20 as best seen in Fig. 5. In this embodiment, the rotor 32 is mounted to said shaft or spigot 34 for rotation about a longitudinal axis of the shaft or spigot 24. The shaft or spigot 34 may he fixed and thus non-rotating. In another arrangement, the shaft or spigot 34 may be mounted such as to be able to rotate about its longitudinal axis, i.e., the shaft or spigot 34 is rotatably mounted to the internal end face of the cup part 20A. In such arrangement, the rotor 32 is preferably keyed on or otherwise affixed to said shaft or spigot 34 to rotate therewith. In this latter arrangement, the impeller 14 may also be keyed on or otherwise affixed to said shaft or spigot 34 to rotate therewith. Thus, rotation of the rotor 32 causes rotation of the shaft or spigot 34 which in turn causes rotation of the impeller 14. In a yet alternative arrangement, one or more bearings may be provided in said cup part 20A of the inner end plate 20 for mounting the rotor 32 for rotation within said cup part 20A.

In some embodiments, the impeller 14 is assembled with the rotor 32 such that the impeller 14 is fixed to the rotor 32 for rotation therewith.

In some embodiments, the rotor 32 is formed integrally with the impeller 14. This may 25 be as an extruded or molded component.

In light of the fact that the rotor 32 is on the wet side of the fluid sealed boundary separating the pump chamber 12 from the stator 30/motor housing 24, it is preferred that at least the rotor 32 is enveloped in a material which is not reactive, non-contaminating and/or non-polluting of the fluid to be pumped. More specifically, where the fluid to be pumped is potable water then it is preferred that at least the rotor 32 is enveloped in a material which meets a regulatory standard and/or quality standard for contact with potable water. For example, for the United Kingdom the material is preferably a Water Supply (Water Fittings) Regulations (WRAS) compliant material. Certain high wearing rubber compounds which are WRAS compliant may be used. Preferably, the rotor 32 and impeller 14, whether formed integrally as a single component or affixed to each other, are enveloped in the material which is not reactive, non-contaminating and/or non-polluting of the fluid to be pumped, e.g., enveloped in a material which meets a regulatory standard and/or quality standard for contact for potable water.

In the foregoing description of the twinned ended pump 10 depicted by the drawings, a pump unit 35 comprising the inner and outer end plates 20, 22, the impeller 14, the pump chamber 12 and its associated motor unit 29 comprising the stator 30, the rotor 32 and the motor housing, if present, has been described. It will be understood, however, that, in preferred embodiments, a pump unit 35 (including a motor unit 29) to be provided at the second end of the motor housing 24 is preferably identical to the pump unit 35 provided at the first end of the motor housing 24. Consequently, the pump 10 can be formed from two identical pump units 35 together with the motor housing 24 or by two pump units 35 without any common motor housing. In this latter embodiment, the two pump units 35 can he connected together at the ends of respective motor housings (not shown).

One means of connecting the two pump units 35 together is to provide said two pump units 35 with physical connecting means, preferably complimentary connecting means. The two pump units 35 could be connected such that they are connected with their axes of rotation in parallel or in alignment. Preferably, a connecting means of a first one of the pump units 35, denoted by dashed line 33 in Fig. 3, is provided at one end of the one of the pump units 35 and a connecting means 33 of the other one of the pump units 35 is provided at an opposing end of the other one of the pump units 35 such that, when said two pump units 35 are connected, they are connected with their axes of rotation in alignment. The connecting means 33 may be extruded or molded integrally on the exterior end faces of the inner end plates 20 of the two pump units 35 or on exterior end faces of motor housings of said two pump units 35. The connecting means 33 may comprise complimentary quarter turn lugs which enable said two pump units 35 to be quickly assembled together even within a common motor housing 24 in the arrangement where said connecting means 33 are provided on the exterior end faces of the inner end plates 20 of the two pump units 35.

Two such pump units 35 can be connected together, or provided in a common housing 24, to provide a twin ended pump 10 for pumping two separate fluid flows, especially hot and cold water for mixing in a bathing shower installation or the like. This negates the need to provide any rotational shaft seals in the motor units 29 or any bypass fluid connections between the pump chambers of the pump units 35.

Where the pump 10 is formed from two identical pump units 35 including identical motor units 29, it will be understood that only one design and configuration of pump unit 35/motor unit 29 is required which provides savings and more versatility. The rotors 32 of the identical motor units 29 will rotate counter to each other when arranged in the embodiments of the pump 10 shown in the drawings.

It will also be understood that it is possible to form a single ended pump from the pump 10 by providing said pump with only one pump unit 35/motor unit 29. In such a case, the motor housing 24, if included, can he shortened to accommodate a single motor stator 30 within the shortened motor housing 24 and with an opposing open end of the motor housing 24 being closed by a motor end plate (not shown). Thus, only one design and configuration of pump unit 35/motor unit 29 is required to assemble single ended pumps in accordance with the invention and twin ended pumps 10 in accordance with the invention. The top part of Fig. 3 can be considered as illustrating one embodiment of a single ended pump in accordance with the invention.

For any of the embodiments of the twin ended pump 10 as described herein, each pump unit 35 may be controlled independently of the other pump unit 35.

As shown in Fig. 6, a single motor controller 100 may be provided for independently controlling the two pump units 35. Additionally, or alternatively, separate motor controllers 100A, 100B may be provided to control the two pump units 35.

The motor controllers 100, 100A, 100B may each comprise a processor 102, 102A, 102B and a memory 104, 104A, 104B. The memories 104, 104A, 104B store machine readable instructions which, when executed by the processors 102, 102A, 102B, cause the processors 102, 102A, 102B to control, either singly or in combination, the pump units 35 in accordance with the methods described herein.

In known twin ended pumps using a single motor to drive the twin impellers in their respective pump chambers this results in a same pressure of fluid exiting the respective pump chamber outlets. Where such a pump is employed in a system such as a domestic shower installation for pumping hot and cold water, it is necessary to a mixing valve or the like to mix portions of the balanced pressure pumped hot and cold water flows to achieve a desired temperature of a mixer output flow from the mixed hot and cold water flows. However, mixing valves are very variable in efficiency and often the temperature set at the mixing valve vary considerably resulting in a poor showering experience for a user.

By enabling the twin impellers 14 of the twin ended pump 10 in accordance with the invention to be operated independently, variably and in unison enables much better control of mixed hot and cold water flows. In fact, it is possible to provide flows of mixed water at desired set temperatures and/or at desired set pressures using just the control of the independently operating impellers 14 and a simple mixing chamber (not shown) and thus it is possible to reduce the complexity or even eliminate the need for a mixing valve or like device or system.

For example, the operation of each pump unit 35 can be separately controlled by separately controlling the respective speeds of the impellers 14 to achieve a first set pressure fluid output when the pumped fluid output of the first pump unit 35 is mixed with the pumped fluid output of the second pump unit 35.

Where the first pump unit 35 is arranged to pump heated fluid, e.g. hot water, and the second pump unit 35 is arranged to pump unheated fluid, e.g. old water, the operation of each pump unit 35 can be separately controlled by separately controlling the respective speeds of the impellers 14 to achieve a first set pressure fluid output at a first set temperature when the pumped heated fluid output of the first pump unit 35 is mixed with the pumped unheated fluid output of the second pump unit 35.

The operating speed of each pump unit 35 can be changed in tandem to reach a second set pressure fluid output, i.e., the speeds of the impellers can be increased or decreased proportionally in tandem to reach said second set pressure fluid output. The operating speed of each pump unit 35 can be changed in tandem to reach a second set pressure fluid output at said first set temperature in a similar manner.

Furthermore, the operating speed of each pump unit 35 can be changed differentially to 30 reach a second set temperature when the pumped heated fluid output of the first pump unit 35 is mixed with the pumped unheated fluid output of the second pump unit 35. The operating speed of each pump unit 35 can be changed differentially to reach a second set temperature at a set pressure fluid output when the pumped heated fluid output of the first pump unit 35 is mixed with the pumped unheated fluid output of the second pump unit 35. In either case, changing the speeds of the impellers 14 differentially can allow the temperature of the mixed flow to be raised or lowered whilst keeping the pressure of the mixed flow at the same level as previously.

For example, with hot water being pumped through the first pump unit at say 65 degrees C and cold water being pumped through the second pump unit 35 at say 5 degrees C, it is possible, by changing the speeds of the independent impellers 14 differentially, to mix water to a temperature anywhere within a range of 5 to 65 degrees C. For example, where the speed of the impeller 14 of the cold water pump unit 35 is say X revolutions per minute (rpm) and the speed of the impeller 14 of the hot water pump unit 35 is say Y rpm to result in a mixed water temperature of say 45 degrees C then the relative speeds of the two impellers 14 can be differentially changed to respectively increase or decrease the hot and cold water flows to achieve a new desired set temperature. If the speeds of the two impellers are then increased or decreased in tandem this will result in an increased or decreased set pressure of the mixed water flow.

To assist the foregoing control of two pump units 35, it is preferred that pump chamber inlet and/or outlet flow sensors 106 and/or inlet and/or outlet temperature sensors 108 are included or associated with the pump units 35. The inlet and/or outlet flow sensors 106 and/or the inlet and/or outlet temperature sensors 108 may be arranged to feedback flow and temperatures data to one or more of the motor controllers 100, 100A, 100B to thereby vary the individual and/or combined speeds of the impellers as required and directed by said sensor data and in response to use inputs which may be inputted by a user to one of the motor controllers 100, 100A, 100B and which may he varied by a user over time.

The invention also provides a method of assembling a pump 10. The method comprises: arranging an impeller 14 of the pump 10 to be driven by a rotor 32 of an electric motor unit 29, the impeller 14 causing a fluid to flow out of a pump chamber 12 when driven by the rotor 32. The stator 30 may be accommodated a motor housing 24. The rotor 32 is arranged on a pump chamber side of a fluid-sealed boundary 20 separating said pump chamber 12 from the stator 30/motor housing 24.

The invention provides another method of assembling a pump 10. This method comprises: connecting a first pump unit 35 to a second pump unit 35.

Each pump unit 25 is therefore able to be controlled independently of the other pump unit 35. The speed of the impeller 14 of one pump unit 35 can be changed differentially with respect to the speed of the impeller 14 of the other pump unit 35.

The invention provides a method of operating a twin ended pump 10, the method comprising the steps of: mixing a pumped heated fluid flow from the first pump unit 35 with a pumped cold fluid flow from the second pump unit 35; and independently controlling operation of the first pump unit 35 and the second pump unit 35 to control at least one of a set pressure and/or a set temperature of a resulting mixed fluid flow. Independently controlling operation of the first pump unit 35 and the second pump unit 35 may comprise independently controlling the speeds of the impellers 14 of the first pump unit 35 and the second pumps unit 35, although their speeds may he changed proportionally in unison to change to a different desired pressure of mixed fluid flow. The method preferably involves controlling the first and second pumps units 35 differentially to reduce or negate the need for a mixing valve or the like for mixing the pumped fluid flows from said first and second pumps units 35. A simple mixing chamber may be used in replacement of a conventional mixing valve.

The following is an example of the benefits of using two motor units 29 in the pump 10 motor compared to a conventional motor as exemplified by prior art references 20 0B24625392 and 0B2506280.

A traditional brushed or brushless electric motor may run at 12V DC at 3A, providing (for example) 60mNm of output torque at 6000 rpm (628 rad/s). This may be referred to as original motor A "OM-A". The present invention replaces the single 0M-A motor, referenced above, with two smaller motor units 29 with the aim of producing the same or similar overall mechanical output. For example, each of the two smaller motor units 29 could comprise motors operating at 30mNm at 6000 rpm (one-half of the output torque at the same speed). By summing the output torques at the same speed, the same overall output as the original single motor system 0M-A described above, would be provided.

It will be noted that each new smaller sub-motor (which will be referred to as NM-1 to NM-2) will each only be required to carry one-half of the current, that is 1.5A at 12V DC. It will also be noted that the rotor wire needs only to be one-half of the thickness in order to carry this smaller current. As such, the amount of wire mass required for the two individual motor units 29 compared with the original motor 0M-A is approximately 37% less (Figure 7), which is a considerable useful but unexpected improvement.

Because the power requirement of each motor unit 29 is half of the equivalent prior art motor 0M-A, the magnetic flux across the motor unit stator coils is also lower than the equivalent prior art motor 0M-A. In other words, each of NM-1 to NM2 requires one half of the flux (and thus one had of the magnetized material).

In addition, the rotors of NM-1 and NM-2 can be made smaller than 0M-A. Therefore, the gap required between the stators in order to surround the rotor of each motor unit 29 is reduced. As well as requiring one half of the flux, each motor of the motor units 29 only requires it to be established across a smaller gap. This leads to a further benefit, by an inverse square law relative to the amount of magnetic material required. Therefore, each of NM-1 and NM-2 actually requires less than one-half of the magnetic material in 0M-A. In reality, the approximate size and weight reduction of the total magnet mass is approximately 26% (Figure 7). In a similar system which utilizes electro-magnets to establish the magnetic field of the stator, a similar power reduction into the stator coils would also he realized. This is because the strength of the magnetic field is dependent upon the power within the electromagnetic coil, and the air gap, both of which can be reduced for smaller motors.

Turning to Figure 7, various combinations of motors are shown in tabular form. The columns are as follows: Column A Number of sub-motors Column B Potential difference across each sub-motor input Column C Current used per sub-motor Column D Output torque per sub-motor Column E Summed output torque Column F Percentage copper saving on rotor wire material Column G Percentage saving on magnetic material in stators.

Because the diameter of the rotor wire decreases the smaller the rotor is, the cross-sectional area also decreases and hence the amount of copper required.

The total torque output is always 60Nrn (at the same speed for each arrangement). With the reduction in current comes the associated reduction in core wire diameter, and an associated reduction in cross sectional area in n11112 (which is proportional to the copper mass used). The final column represents the reduction in copper material required. The present example uses 2 motors and as such realizes a reduction of about 26%.

In one embodiment, the twin ended pump for the apparatus in accordance with the invention comprises a housing; the first pump arranged at one end of the housing, said first electric motor having a rotor for driving said impeller to cause the heated fluid to flow out of the pump chamber of the first pump to the mixing chamber, said first electric motor including a stator for driving said rotor, wherein said rotor is arranged on a pump chamber side of a fluid-sealed boundary separating said pump chamber from the stator; and the second pump arranged at an opposing end of the housing, said second electric motor having a rotor for driving said impeller to cause an unheated fluid to flow out of the pump chamber of the second pump to said mixing chamber, said second electric motor including a stator for driving said rotor, wherein said rotor is arranged on a pump chamber side of a fluid-sealed boundary separating said pump chamber from the stator.

Preferably, the first electric motor of the first pump does not have a motor shaft extending through said fluid-sealed boundary separating said pump chamber from the stator. Preferably also, the fluid-sealed boundary separating said pump chamber from the 20 stator of said first pump is defined by a pump chamber inner end plate, the pump chamber inner end plate being substantially cup-shaped about a rotational axis of the rotor. A cup part of the pump chamber inner end plate may extend into the housing by an amount sufficient to mount the motor stator around an exterior cylindrical face of said cup part.

The rotor of the first motor may accommodated within an interior volume of the cup part of the pump chamber inner end plate such that the rotor is positioned concentrically with the stator for rotation within the cup part when driven by the stator.

In another embodiment, the twin ended pump for the apparatus in accordance with the invention comprises the first pump having a rotor for driving impeller of said first pump to cause a heated fluid to flow out of the pump chamber of the first pump to the mixing chamber, said first electric motor including a stator for driving said rotor, wherein said rotor is arranged on a pump chamber side of a fluid-sealed boundary separating said pump chamber from the stator; and the second pump having a rotor for driving the impeller of the second pump to cause an unheated fluid to flow out of the pump chamber of the second pump to said mixing chamber, said second electric motor including a stator for driving said rotor, wherein said rotor is arranged on a pump chamber side of a fluid-sealed boundary separating said pump chamber from the stator.

While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only exemplary embodiments have been shown and described and do not limit the scope of the invention in any manner. It can be appreciated that any of the features described herein may be used with any embodiment. The illustrative embodiments are not exclusive of each other or of other embodiments not recited herein. Accordingly, the invention also provides embodiments that comprise combinations of one or more of the illustrative embodiments described above. Modifications and variations of the invention as herein set forth can be made without departing from the spirit and scope thereof, and, therefore, only such limitations should be imposed as are indicated by the appended claims.

In the claims hereof, any element expressed as a means for performing a specified function is intended to encompass any way of performing that function including, for example, a) a combination of circuit elements that performs that function or b) software in any form, including, therefore, firmware, microcode, or the like, combined with appropriate circuitry for executing that software to perform the function. The invention as defined by such claims resides in the fact that the functionalities provided by the various recited means are combined and brought together in the manner which the claims call for. It is thus regarded that any means that can provide those functionalities are equivalent to those shown herein.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as -comprises" or "comprising" is used in an inclusive sense, i.e., to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

It is to he understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art.

Claims

Claims.1 An apparatus for mixing hot and cold fluid flows, the apparatus comprising: a fluid mixing chamber; a first pump comprising an impeller provided in a pump chamber of said first pump, and a first electric motor for driving said impeller to cause a heated fluid to flow out of the pump chamber of the first pump to the mixing chamber; and a second pump comprising an impeller provided in a pump chamber of said second pump, and a second electric motor for driving said impeller to cause an unheated fluid to flow out of the pump chamber of the second pump to said mixing chamber; wherein the first pump and the second pump are controlled separately of each other by one or more motor controllers to thereby control at least one of a first set pressure and/or a first set temperature of a mixed fluid flowing from the mixing chamber resulting from mixing of the heated fluid flow from the first pump with the unheated fluid flow from the second pump.IS
2. The apparatus of claim I, wherein the separately controlled operating speed of each of the first and second pumps is changed in tandem to reach a second set pressure of the mixed fluid flowing from the mixing chamber.
3. The apparatus of claim 1, wherein the separately controlled operating speed of each of the first and second pumps is changed in tandem to reach a second set pressure of the mixed fluid flowing from the mixing chamber at said first set temperature.
4. The apparatus of claim 1, wherein the separately controlled operating speed of each pump is changed differentially to reach a second set temperature of the mixed fluid flowing from the mixing chamber.
5. The apparatus of claim 1, wherein the separately controlled operating speed of each pump is changed differentially to reach a second set temperature of the mixed fluid flowing from the mixing chamber at said first set pressure.
6. The apparatus of claim I, wherein each of the first and second pumps comprises a brushless direct current (BLDC) motor unit.
7. The apparatus of claim 1, wherein the first pump has a first drive controller and the second pump has a second drive controller.
8. A method of operating an apparatus according to any one of claims 1 to 7, comprising the steps of: mixing a pumped heated fluid flow from the first pump with a pumped cold fluid flow 10 from the second pump; separately controlling operation of the first pump and the second pump to control at least one of a set pressure and/or a set temperature of a resulting mixed fluid flow.
9. The method of claim 8 including differentially controlling the first and second pumps I 5 to obtain a set temperature of the resulting mixed fluid flow.
10. The method of claim 8 including controlling the first and second pumps in tandem to obtain a set pressure of the resulting mixed fluid flow.