Abstract:
A water circulation unit includes an ejector ( 142 ), a convergent, and a pipe ( 146 ) which is arranged in the extension of the convergent. The ejection axis practically merges with the symmetry axis of the convergent, the two axes forming a common axis of the unit, and the distance between the water outlet of the ejector ( 142 ) and the downstream section of the convergent is between 0.4 and 1.6 times the length of the convergent. A guiding region is located just upstream of the upstream section of the convergent following the common axis, at least up to the water outlet of the ejector ( 142 ) when the outlet is located outside the convergent, the region ensuring that the water is essentially symmetrically guided around the common axis during the operation of the ejector. In a filter unit, a cartridge ( 154 ) is arranged around the water circulation unit.

Description:
The present invention relates to a flow-multiplier water circulation assembly for a swimming pool, in particular for use in a swimming pool filter and maintenance group that is movable or a fixture, the invention also relates to a swimming pool maintenance and cleaner head, and even to a swimming pool cleaner robot. 
   To multiply flow rate, the invention essentially makes use of a system in which an ejector projects a flow of water into a converging portion. 
   BACKGROUND OF THE INVENTION  
   Attempts have already been made to use a flow-multiplier effect by projecting a flow of water directed towards a nozzle, an orifice, or a cone for the purpose of entraining water and thus obtaining a high flow rate for water circulation. 
   Thus, document U.S. Pat. No. 4,501,659 describes an appliance for circulating water in a swimming pool so as to enable the water to be filtered. As shown in accompanying  FIG. 1 , which reproduces a figure of that document, the top portion of the appliance comprises a filter and the bottom portion of the appliance is connected to a supply of water under pressure and includes a nozzle assembly directed towards an outlet opening in a facing wall. A converging portion or spout may be placed facing the ejector. It is located towards the bottom of the appliance. Water that has passed through the filter approaches the ejector from one side thereof and changes in direction in order to pass into the spout. The flow-multiplication factor that is obtained is relatively small, and it never exceeds 2.5. 
   Document U.S. Pat. No. 4,826,591 also describes a swimming pool filter installation, as shown in accompanying  FIG. 2 , which reproduces a figure of that document, in which installation a pump causes a flow of swimming pool water to circulate through a filter. Before returning to the swimming pool, the water passes through an ejector or restricted nozzle placed in front of a converging portion or entrainment nozzle so that the water which has come through a basket connected to a skimmer is sucked in by the converging portion. In that system, the flow obtained by multiplication is not used for circulation through a filter, but only through a basket for stopping debris such as leaves. As in the preceding document, the ejector and the converging portion are placed close to a bottom surface of a space whose top portion houses the basket. As indicated by arrows, the water moves down towards the inlet of a converging portion disposed horizontally, where it changes direction. Although the body of that document does not specify the multiplication ratio obtained with such a system, the values given for the various dimensions correspond to a multiplication factor that is small, certainly not exceeding 2.5. 
   Document U.S. Pat. No. 5,785,846 also describes an installation, as shown in accompanying  FIG. 3 , which reproduces a figure of that document, in which installation a pump feeds an ejector that projects a flow of water towards a duct facing it and in alignment therewith and disposed in a chamber that defines a rounded converging portion leading to the inlet of the duct. The suction effect created by the ejector in the converging portion is used for sucking in water that has passed through a filter and that arrives via a duct opening out into the side of the chamber surrounding the ejector. As shown in that figure, the flow of water coming from the filter arrives on one side of the ejector and is subjected to a change in direction through 90° in order to be entrained towards the outlet duct. Although the document gives no value for the flow-multiplication factor, the highly asymmetrical water inlet certainly puts a limit on the flow-multiplication factor at well below 2.5. 
   Document WO 02/086259 describes a flow-multiplier water circulation assembly, part of which is shown in accompanying  FIG. 4  which reproduces one of the figures of that document, which assembly gives a multiplication factor greater than 2.5, and that can even exceed 3. That flow-multiplier assembly comprises a converging portion, a throat, and a diverging portion, and water under pressure is injected in a direction that is parallel to the inside surface of the throat through a slot disposed at the periphery of the throat. That system is limited to injecting water into the throat, and given the great length of the slot formed around the throat, the slot must be very narrow; in practice, it is found that it is easily clogged, unless appropriate precautions are taken to ensure that it does not become clogged. 
   Document WO 03/062561 which in the context of the present invention should be taken into consideration only under EPC Article 54(3) [prior filing date], describes an improvement to the system disclosed in the preceding document. As shown in accompanying  FIG. 5 , which reproduces one of the figures of document WO 03/062561, that system comprises an assembly having a converging portion, a throat, and a diverging portion including a first ejector disposed at the inlet to the converging portion, and a second ejector disposed in the throat. That system thus combines two injections, firstly via an ejector on the axis of the converging portion, the throat, and the diverging portion, and subsequently by the throat ejector. In addition, that document states that the upstream ejector placed on the axis of the converging portion may be located inside a Kaplan bend so as to enable a high flow-multiplication ratio to be obtained. As indicated in the figure, a flow at a rate of 10 cubic meters per hour (m 3 /h) inserted half into the upstream ejector and half into the throat ejector gives an outlet flow at a rate of 30 m 3 /h, i.e. that the flow-multiplication ratio is equal to 3. 
   SUMMARY OF THE INVENTION 
   It has been found that in the application to which the above-cited document relates, i.e. circulating water with flow-multiplication for a swimming pool, it is possible to obtain flow-multiplication ratios that are much greater than 3, being of the order of 10 or even more, by using technical means that are particularly simple. 
   There follows a description with reference to  FIGS. 6A to 6D  of experiments that have been carried out to demonstrate the effectiveness of the simple technical means implemented in the invention. 
   An ejector  110  was placed inside a swimming pool at a distance from its surface, bottom, and walls, the ejector  110  serving to direct water horizontally at a flow rate of 2 m 3 /h at a pressure of 2 bar. The speed of the water at the outlet form the ejector was about 1.7 meters per second (m/s). In the horizontal position, centered on the axis  112  of the ejector, there was disposed an element constituted by a converging portion  114  and a cylindrical duct  116 . The section of the converging portion and the section of the duct were circular, going from an upstream section of the converging portion to a downstream section thereof and on to an outlet section of the duct, such that the assembly formed a surface of revolution. The outlet orifice from the ejector was placed in the plane of the upstream section of the converging portion. 
   In the experiment shown in  FIG. 6A , the duct  116  connected to the converging portion  114  had a length equal to 40% of the length of the converging portion  114 . In the experiment of  FIG. 6B , the duct portion  116  was doubled in length and extended by a diverging portion, such that the duct  118  had a length equal to 1.75 times the length of the converging portion  114 . Finally, in the experiment of  FIG. 6C , the  FIG. 6B  duct  118  was extended by a cylindrical duct of length equal to 1.25 times the length of the converging portion, such that the duct  120  had a total length equal to about 3 times the length of the converging portion  114 . The section of the smallest section portion, i.e. in the cylindrical duct portion  116  was 57 square centimeters (cm 2 ). 
   The ejector  110  was fed with water at a rate of 2 m 3 /h at a pressure of 2 bar, and the flow rate and the speed were measured at the outlet from the duct  116 ,  118 , or  120 . It was found that with the setup of  FIG. 6A , a flow rate of 12 m 3 /h was obtained, with the setup of  FIG. 6B , a flow rate of 21 m 3 /h was obtained, and with the setup of  FIG. 6B , a flow rate of 24 m 3 /h was obtained. It can thus be seen that respective multiplication factors of 6, 10.5, and 12 were obtained. These factors are much greater than those obtained with the devices of the prior art. 
   To obtain more precise results, experiments were performed as shown diagrammatically in  FIG. 6D . The device was analogous to that of  FIG. 6B , but the ejector  110  was placed in three positions  110 A,  110 B, and  110 C, with the position  110 B corresponding to the position shown in  FIG. 6B , the position  110 A being outside the converging portion, at a distance equal to 45% of the length of the converging portion, and the position  110 C corresponding to a position inside the converging portion, at 45% of the length of said converging portion. 
   In all three cases, to within the accuracy of measurement, a multiplication factor was obtained that was practically unchanged, lying in the range 10 to 11. 
   It can thus be seen that with the extremely sample means as shown, it is possible firstly to obtain very high flow-multiplication factors, and secondly to obtain such high factors in a manner that leaves a broad margin for adjusting the positions of the elements used in the longitudinal direction. 
   Additional experiments were then performed to determine why it is not possible to obtain high multiplication factors in the prior art devices. It was then found that when the axis of the ejector is not in alignment with the axis of the converging portion and of the duct, then the multiplication factor is greatly reduced. It was also found that any asymmetrical disposition at the inlet to the converging portion leads to a great reduction in the multiplication factor. 
   Thus, in the operating conditions of the swimming pools taken into consideration (volume lying in the range about 20 cubic meters (m 3 ) to 200 m 3 ), i.e. under conditions in which it is necessary to obtain a relatively high flow rate of several cubic meters to several tens of cubic meters per hour (e.g. in the range 5 m 3 /h to 50 m 3 /h) at a water speed that is relatively high (e.g. 0.1 m/s to 2 m/s), a fundamental factor in obtaining a high multiplication factor is a symmetrical flow of water at the outlet from the ejector and at the inlet of the converging portion. 
   In the experiments described with reference to  FIGS. 6A to 6D , precautions were taken for the setup to be located within a large mass of water so as to make it possible to consider that mass as being infinite around the ejector at the inlet of the converging portion. The water could therefore behave in perfectly symmetrical manner around the ejector and the converging portion. As soon as any asymmetry was introduced, the flow of water was greatly disturbed and the kinetic energy of the flow projected by the ejector dissipated rapidly on entering the converging portion, and even sooner by disturbance to the flow of water. 
   Amongst all of the documents cited above, only the fifth corresponds in part to the conditions of the invention. According to that document WO 03/062561, one ejector is disposed upstream from a converging portion, and at the inlet to the converging portion and also around the ejector, good water flow symmetry is obtained by using a Kaplan bend. However, the device described in that document does not suggest the invention, firstly since there is still fluid injection into the throat, and secondly since the alignment of the ejector on the axis of the converging portion, the throat, and the diverging portion was not properly understood, as can be seen from the results obtained (multiplication factor limited to 3). 
   An object of the invention is to implement the above characteristics to obtain a high multiplication ratio; it makes it possible to use low flow rate pumps to obtain simultaneously a large circulation flow rate, filtering of a large volume of water, and sufficient stirring of the water in a swimming pool to ensure that particles do not become deposited, so that the bottom of the swimming pool remains clean and the amount of cleaning it requires is greatly reduced. 
   More precisely, the invention provides a flow-multiplier water circulation assembly for a swimming pool, of the type that includes a water inlet, the assembly comprising: 
   an ejector connected to the water inlet and having a water outlet for projecting water along an ejection axis; 
   a converging portion having an axis of symmetry and a section perpendicular to said axis that decreases from an upstream section to a downstream section, and presenting a length between the upstream and downstream sections; 
   a duct disposed in line with the converging portion to which it is connected without internal discontinuity at the downstream section of the converging portion, the duct presenting a length between the downstream section of the converging portion and an outlet, the section of the duct not decreasing in practice along its length, and the length of the duct being not less than one-third the length of the converging portion; 
   the ejection axis practically coinciding with the axis of symmetry of the converging portion, and the two axes together forming a common axis of the assembly; 
   the distance between the water outlet of the ejector and the downstream section of the converging portion lying in the range 0.4 times to 1.6 times the length of the converging portion; and 
   a guide space disposed immediately upstream from the upstream section of the converging portion on the common axis, and at least as far as the water outlet from the ejector when the outlet is outside the converging portion, said space serving to guide water in practically symmetrical manner around the common axis. 
   Preferably, the axis of symmetry of the converging portion is an axis of circular symmetry. In an advantageous embodiment, the common axis is an axis of circular symmetry of the converging portion and of the duct. 
   In a particularly advantageous embodiment, the converging portion is a truncated cone having a circular section and having a generator line that makes an angle relative to the axis lying in the range 10° to 15°. 
   Preferably, the duct is of a length that is greater than 1.7 times the length of the converging portion and preferably greater than 3 times said length. 
   In a variant, the duct also includes a diverging portion. 
   It is advantageous for the outlet section of the duct to have a value such that the mean water outlet speed from the duct is greater than 0.1 m/s, in particular greater than 0.3 m/s, and preferably lying in the range 0.5 m/s to 2 m/s. 
   Preferably, the water inlet flow rate is greater than 1 m 3 /h. 
   In an embodiment, the assembly further comprises a pump for feeding the water inlet. 
   The invention also provides a filter and maintenance group for a swimming pool, the group comprising a water circulation assembly in accordance with the preceding paragraphs, and a filter device. 
   In a first embodiment, the filter and maintenance group is designed to constitute a fixture in a swimming pool installation. 
   Above-cited document WO 02/086259 describes a filter method in which a flow-multiplier is incorporated in a pump assembly disposed downstream from the filter assembly. In that way, the filter assembly operates in suction, unlike a sand filter, which operates in pressure. 
   In that embodiment, valves and pipes connected to the pump assembly make it possible to use a robot for swimming pool maintenance, i.e. a tool that requires a low flow rate at high pressure, and also a cleaner head for collecting debris and dirt. 
   The use of a cleaner head for cleaning a swimming pool by suction in prior art systems requires the filter and pump circuit to be closed by operating at least one valve, and requires a cleaner-head circuit to be opened by opening at least one other valve. However, the cleaner head is not a simple device since it needs to include an assembly for retaining the collected debris and dirt so that they do not reach the assembly associated with pumping. Drawbacks associated with the pumping system becoming unprimed are also known due to the almost inevitable inflow of air when the cleaner head is put into operation. 
   It is therefore relatively inconvenient to use such a cleaner head in a swimming pool since it requires operations that are relatively complex and quite a large amount of specialist equipment. 
   In the first embodiment, the invention provides a swimming pool filter and maintenance group in which it is extremely simple to use a cleaner head. It does not require any valve to be operated and can be provided merely by using an accessory that is simple to make, by making use of the resources of a filter group that has special characteristics. 
   More precisely, in the first embodiment, the filter and maintenance group for constituting a fixture in a swimming pool installation comprises a pump assembly itself including a circulation assembly of the invention that is disposed between an inlet opening placed partially above and partially below the nominal filling level of the swimming pool, and an outlet opening disposed at the nominal level or close thereto, together with a filter assembly disposed between the inlet opening and the pump assembly. 
   Preferably, the guide space of the circulation assembly is defined by a Kaplan bend that is connected without discontinuity to the inlet of the converging portion. 
   In an embodiment of the filter group suitable for use with a suction device used as a cleaner head, the group further comprises: a shutter and coupling element, the shutter-forming portion being for placing upstream from the filter assembly to prevent direct communication between the inlet opening and the filter assembly, and the coupling-forming portion serving to provide direct communication between a flexible hose and the filter assembly; and a bypass duct coupling a first location disposed upstream from at least a fraction of the filter assembly to a second location disposed downstream from the filter assembly but upstream from at least a fraction of the pump assembly, and at which suction exists; the flexible hose being of a length that is sufficient for its end remote from the end coupled to the shutter and coupling element to be capable of being moved to any point in the swimming pool, and of a section that is sufficient to suck up the debris and dirt that is present, possibly also sucking in a large quantity of air without that leading to malfunction. 
   It is then advantageous for the filter assembly to comprise at least two stages: a coarse first filter stage; and a fine second filter stage; for the shutter and coupling element to be placed upstream from the coarse filter stage, and for the first location to which the bypass duct is coupled to be located between the two stages. Preferably, the first filter stage is constituted by a removable basket having a large working area with orifices of dimension lying in the range 0.1 mm to 0.5 mm. Also preferably, the section of the bypass duct is much less than the inlet section of the converging nozzle of the circulation assembly. 
   Preferably, the bypass duct is coupled to the filter assembly and to the pump assembly close to the nominal filling level of the swimming pool, and the pump assembly sucks in water coming from the filter assembly at a level that is well below the nominal filling level of the swimming pool. 
   Preferably, the filter group further comprises a duct having a first end for connection to a swimming pool drain plug, and a second end coupled upstream from the circulation assembly, the duct being provided with a valve disposed close to its second end. 
   Preferably, the filter group further comprises a shutter for shutting the inlet opening that enables all of the water to be emptied from the filter and maintenance group by the pump assembly, so as to put the group into an over-wintering condition. 
   Preferably, the pump assembly that sucks in the water leaving the filter assembly comprises a dual pump driven by a single electric motor, comprising a low pressure and high flow rate pump, and a high pressure and low flow rate pump. 
   Preferably, the outlet opening disposed at the nominal water level or close thereto has an axis that slopes relative to a normal to the swimming pool wall where it is located so that the water it projects has a component that leads to rotating circulation in the swimming pool. 
   In a second embodiment, the filter and maintenance group is designed to constitute a movable filter group for a swimming pool installation, in which the filter device is a filter that is practically centered on the common axis. 
   In a variant, the filter is cylindrical and is in the form of a cartridge surrounding the guide space of the circulation assembly, and the converging portion and the duct are placed essentially in line with the cartridge. 
   In another variant, the filter is cylindrical and is in the form of a cartridge placed essentially around the guide space, the converging portion, and the duct. 
   In a third embodiment, the filter and maintenance group is for constituting a movable filter group for a swimming pool installation, in which the filter device and the circulation assembly are disposed in a structure provided with a device enabling it to be secured temporarily to a swimming pool wall. 
   In a first variant, the group includes a water inlet pipe coupling for coupling to a water supply. 
   In a second variant, the group includes an electric pump feeding the ejector. 
   Preferably, the entire group is ballasted so as to enable it to float in an orientation such that the water inlet orifice and a water outlet orifice are close to the surface on which the movable group is floating. 
   In a fourth embodiment, the filter and maintenance group is for constituting a swimming pool cleaner head. 
   For cleaning swimming pools, both robots and cleaner heads are already known. The term “robot” is used to designate a cleaner appliance that can operate without the presence of any operator, while the term “cleaner head” is used for an appliance that is moved by an operator. A robot differs from a cleaner head in that it includes displacement means enabling it to move over the bottom of a swimming pool. 
   A cleaner head, sometimes referred to as a “leaf-collector”, comprises a body fitted with a long handle, usually a telescopic pole, that is manipulated by an operator from the edge. Such a cleaner head includes a body having a bottom portion that is close to the pool bottom, a suction device possessing an inlet for water under pressure, and a vertical duct going perpendicularly from the center of the body and defining at its bottom end a water inlet, and at its top end a water outlet, with a filter fixed to the top end serving to receive contaminating material, essentially leaves. 
   A cleaner robot comprises a body fitted with propulsion means (wheels, chains, crawler tracks, belts, water jets, etc.). The propulsion means are driven by a motor device to move the body over the bottom of the swimming pool, with the ability to change direction at the edges of the bottom. The body includes a suction device possessing an inlet for water under pressure and a vertical duct, sometimes in the form of a Venturi, into which water under pressure is injected so as to cause an upward flow of swimming pool water directed towards the filter which is fixed at the top end of the duct. Such a robot also includes a cleaner accessory formed by a flexible hose fitted with a body for rubbing against the bottom of the swimming pool in order to detach contaminating matter. 
   To feed the pressurized water inlet of a robot or of a cleaner head, and sometimes of other accessories, swimming pool installations deliver a flow of water at moderate pressure (about 0.3 m 3 /h to 0.5 m 3 /h at a pressure of 1 bar to 5 bar, usually 2 bar to 3 bar, with the flow rate of a given pump decreasing as its pressure increases). 
   A cleaner head can make use of all of this power, which is of the order of 100 watts (W), solely for suction purposes. A robot has the same power made available to it, but in a robot the flow of water is shared in substantially equal quantities between the functions of propelling the robot, of creating an upflow in the vertical duct, and of driving the cleaner accessory. It can thus be seen that the function of creating an upflow is not very powerful. That is why cleaning a swimming pool requires the robot to operate for many hours, and why it is often performed at night. Since feeding the robot with water requires at least one pump to be used, that can give rise to a noise problem. Above all, this low level of power available for the upflow does not deliver a speed that is sufficient for detaching contaminating material that is firmly stuck to the swimming pool, which is why the cleaner accessory is needed. 
   It can thus be understood that a cleaner head presents advantages of simplicity, effectiveness, and speed in comparison with a robot. Nevertheless, prior art cleaner heads suffer from a certain number of problems. 
   Firstly, prior art cleaner heads are not very stable. In order to avoid unduly tiring the operator, they have bodies that are relatively lightweight. As soon as the filter, which is in a high position, begins to fill up with leaves, they tend to make the filter lean over and tilt to one side. Even when the weight of collected material is not very great, the filter tends to cause the cleaner head to tilt towards the side where the bag is located. If this tilting tendency is directed along the axis of the telescopic pole handle, then only moderate effort is required on the part of the operator to compensate the observed effect. However, if the bag tends to tilt sideways relative to the handle axis, then the operator needs to exert greater and greater twisting forces on the handle, which is tiring. Indeed some telescopic poles are incapable of transmitting such a twisting torque, which means that the cleaner head needs to be extracted from the pool very often in order to empty out the bag. 
   Another drawback of such cleaner heads is that when the bottom of the swimming pool presents a convex shape, it is the central portion of the cleaner head that tends to press against the convex shape which means that strong forces need to be exerted in order to shift the cleaner head. It happens frequently that swimming pool bottoms possess such convex shapes, particularly at the transitions between portions of the swimming pool bottom that are at different depths. 
   Another drawback of such cleaner heads is that they include a duct that is relatively ineffective in forming the cleaning upflow of water, so their cleaning effect is not very powerful. 
   In this fourth embodiment of the invention, the cleaner head is very powerful, highly mobile, and very stable. 
   High power is obtained by a combination of characteristics, firstly with the high flow-multiplication factor obtained by the water circulation assembly of the invention, secondly with the large area over which a fast flow of water travels over the bottom of the swimming pool, said fast flow of water being obtained by forming a thin layer of liquid in the guide space at the bottom surface of the cleaner head, and thirdly with the formation of a peripheral skirt that defines the zone in which the current that is formed acts powerfully. 
   Great mobility is obtained by using wheels that are placed in such a manner as to avoid any direct contact between the body and the bottom of the swimming pool on a convex portion thereof. 
   Great stability is obtained by the center of gravity of the cleaner head being lowered by causing the collected contaminated matter to accumulate in a low position of the cleaner head, either directly on the base of the body, or close to the bottom portion of the cleaner head. 
   More precisely, in the fourth embodiment, the filter and maintenance group is designed to constitute a pool-cleaner head; in which case, the guide space of the circulation assembly is defined by a plane extending substantially perpendicularly to the common axis passing through the upstream section of the converging portion, and by a surface that is substantially parallel to said plane and disposed further upstream. 
   In an embodiment, the group comprises a body having a base with a bottom surface that is intended to be close to the bottom of a swimming pool constituting a plane that is practically perpendicular to the common axis which is intended to be placed practically vertically, an endpiece for fastening a pole handle to the body, and a filter device surrounding the top portion of the circulation assembly, and the filter device is fastened to the body at the bottom portion thereof. 
   Preferably, the filter device is fastened to the base. 
   In a first variant, the filter device is a filter bag having orifices of a size greater than 40 μm, and preferably of about 60 μm. 
   In a second variant, the filter device is a filter cartridge. 
   Preferably, the filter device possesses a valve for evacuating air from its top portion. 
   In an advantageous example, the bottom surface of the base has two substantially parallel sides that are provided with wheels. Preferably, the wheels are disposed in two parallel lines, and each line includes at least three wheels. 
   Preferably, the space extending between the edges of the base and the inlet of the circulation assembly at the bottom surface is large in area and small in height. 
   Preferably, the edges of the bottom surface of the base are provided with a skirt, and the skirt is advantageously formed by a member selected from a flexible flap and bristles. 

   
     Other characteristics and advantages of the invention will be better understood on reading the following description of embodiments given with reference to the accompanying drawings, in which: 
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1 to 5  are merely reproductions of a key figure in each of the five above-mentioned prior art documents, and they are described above; 
       FIGS. 6A to 6D  are diagrams that are described above when explaining the means of the invention; 
       FIG. 7  is a diagram of a filter fixture for a swimming pool implementing the principles of the invention; 
       FIG. 8  shows an example of the  FIG. 7  filter group being used in an application as a pool-cleaner head; 
       FIG. 9  is a perspective view of an assembly as shown in  FIG. 7 ; 
       FIG. 10  is a fragmentary section of a pool-cleaner head comprising a flow-multiplier water circulation assembly of the invention; 
       FIG. 11  is a perspective view from below of the  FIG. 10  cleaner head; 
       FIG. 12  is a perspective view from above of the cleaner head shown in  FIGS. 10 and 11 ; 
       FIG. 13  is a perspective view from above of a movable filter group comprising a water circulation assembly of the invention; 
       FIG. 14  is a perspective view from behind of the  FIG. 13  group; 
       FIG. 15  is a partially cut-away view of the group of  FIGS. 13 and 14 , showing how the invention is implemented in a movable assembly; and 
       FIG. 16  is a section view of a movable filter group of the invention that is particularly simple and efficient. 
       FIG. 17  shows the cleaner head of  FIGS. 10 to 12  turned upside down. 
   

   The essential characteristics of the operation of the flow-multiplier water circulation assembly of the invention are described above with reference to  FIGS. 6A to 6D . 
   DETAILED DESCRIPTION OF THE INVENTION 
   There follows a description of embodiments corresponding successively to the first, fourth, third, and second embodiments, the description being given with reference to  FIGS. 7 to 9 ,  10  to  12 ,  13  to  15 , and  16  respectively. 
     FIG. 7  is a general view of a filter and maintenance group for a swimming pool constituting the first embodiment of the invention. This group  10  is designed essentially to be placed beneath the nominal level of water in the swimming pool, with this level being identified by reference  12  in  FIGS. 7 and 8 . 
   The main elements of this filter group comprise firstly a filter assembly  14 , and secondly a pump assembly  16 . 
   More precisely, the top portion of the filter assembly  14  is connected to a space that opens out into the pool via an inlet opening  18  formed by an element known in the art as a skimmer and which may be closed by a plug or a shutter (not shown). The top space also has a top opening  20  that is normally at the level of the ground around the swimming pool, and that is closed by a hatch. 
   The filter assembly  14  preferably comprises at least two stages, a first stage  22  for coarse filtering, and a second stage  24  for fine filtering. 
   Preferably, the coarse filter stage  22  allows particles to pass through that are of a dimension smaller than a fraction of a millimeter, and it operates on the principle of a screen filter. For example, this first filter stage  22  is constituted by a basket advantageously formed by a web having orifices of 0.1 mm to 0.5 mm, e.g. 0.3 mm, injection-molded between ribs of plastics material. 
   The fine second filter stage  24  comprises a cylindrical filter constituted by a non-woven sheet folded concertina-like that is held between two circular end plates and surrounded in one variant by an external non-woven fabric. This second filter stage  24  in this variant constitutes a dual stage formed firstly by the outer non-woven fabric acting as a deep filter and secondly by the concertina-folded non-woven fabric that acts as a surface filter, with filtering fineness that is much greater than that of the outer non-woven fabric. 
   An advantageous characteristic of the filter assembly shown in  FIG. 7  is that the outlet from the filter  24  is at the lowest point of the group and is connected by a duct  26  that is connected to a duct  26  that rises to the nominal water level in the swimming pool. 
   The pump assembly  16  comprises a pump  28  and a flow-multiplier assembly  30 . The pump  28  is advantageously of the type described in general manner by French patent application No. 02/13384. The pump comprises a motor  32 , advantageously an electric motor, driving the rotor of a first pump  34  that operates at a high rate (e.g. 14 m 3 /h) and at low pressure (e.g. 1.4 bar) having its inlet connected to the duct  26  at the lowest portion of the filter group, i.e. close to the outlet from the filter assembly  14 . The total flow rate through the pump  34  (e.g. 14 m 3 /h) is shared between a first outlet  36  (e.g. 12 m 3 /h) which is connected to the flow-multiplier assembly  30 , and a second outlet  38  (e.g. 2 m 3 /h) which is connected to the second pump  40 . This pump  40  raises the pressure of the liquid it receives (e.g. from 1.4 bar), and feeds a pipe  42  that makes it possible to operate a cleaner head or a cleaner robot (e.g. operating at 2.5 bar). 
   The outlet  38  shown in the form of a separate pipe is nevertheless preferably constituted by an assembly placed all around the electric motor  32  in order to cool it. 
   The flow-multiplier assembly  30  comprises a converging nozzle followed by a diverging nozzle and an ejector  44  placed immediately upstream from the converging nozzle. Thus, for a flow rate of 12 m 3 /h of a pressure of 1.4 bar transmitted by the ejector  44 , the flow rate at the outlet from the flow-multiplier assembly  30  is of the order of 36 m 3 /h, this flow being transmitted to the pool via the outlet opening  48 . When the ejector  44  is adapted to the flow rate and to the pressure of the second pump  40  for a flow rate of 2 m 3 /h at a pressure of 2.5 bar transmitted by the ejector  44 , the flow rate at the outlet from the flow-multiplier assembly  30  is about 30 m 3 /h, with this flow being transmitted to the pool via the outlet opening  48 . 
     FIG. 8  shows the same filter group, but provided with a shutter and coupling element  50  of the invention. 
   The element  50  comprises firstly a shutter-forming portion  52  and secondly a coupler-forming portion  54 . This coupler-forming portion is for coupling to a flexible hose  56  used as a cleaner head for the swimming pool. 
   The shutter-forming portion  52  is preferably applied upstream from the filter assembly, and in particular from the first stage  22 . For example, this shutter-forming portion  52  is a circular plate provided with tabs enabling it to be blocked by means of a bayonet effect on being turned. Consequently, the major fraction of the suction to the pump  28  passes through the flexible hose  56 . While the hose is essentially sucking in water, leaves, and other debris, the water flows normally through the filter, while the leaves and the other debris that have been sucked in are stopped by the basket  22  forming the first filter stage. While the cleaner head is in operation, it serves essentially to suck in water. 
   According to a characteristic of this embodiment of the invention, when air manages to enter into the filter assembly, via the shutter and coupling element, this air can flow only through the coarse filter portion  22  and not through the fine filter portion  24 . A small-section bypass duct  58  is placed between the filter assembly at a location lying between the two filter stages, and the duct  26  leading to the flow-multiplier assembly. 
   By means of the bypass duct  58 , the air sucked in by the flexible tube  58  is prevented from flowing through the fine filter stage  54 , but passes via the duct  58  as is exhausted directly by the flow-multiplier assembly. 
   In the extreme, if the flow rate of the water passing through the filter assembly  24  is less than the nominal flow rate of the pump  28 , then the filter group is almost certain to become unprimed. 
   The bypass duct  58  thus presents the essential advantage of enabling the operation of the cleaner head to be switched on and off merely by installing the shutter and coupling element  50  of the invention. More precisely, the use of the “cleaner head” function given by the hose  56  merely requires the removal of the hatch closing the opening  20  and the installation of the shutter  52  on the filter assembly. From then on, suction is ensured via the flexible hose  56  and continues until the element  50  is removed. At this moment, the filter group starts operating normally again, with flow-multiplication. 
   The bypass duct  58  presents the auxiliary advantage of enabling a filter basket  22  to be used for retaining debris and dirt without disturbing the fine filter stage  24 . 
   The filter group  10  shown in  FIGS. 7 and 8  present numerous other advantages. 
   Firstly the inlet opening  18  and the outlet opening  48  are located very close to the nominal water level  12  in the swimming pool. 
   Another advantage of the filter group is that the pump assembly is connected to the bottom portion of the filter assembly, at the lowest point of the installation. Consequently, when the inlet opening  18  is suitably plugged, the pump assembly enables the group to be emptied, e.g. for over-wintering. 
   The section of the bypass duct is very small compared with the section of the duct  26 . In this way, in normal operation, the flow rate of the water passing along the bypass duct and that has been subjected to primary filtering only is very small when it comprises water. The ratio of the sections of the ducts  58  and  26  is preferably less than 1/15, e.g. about 1/25. 
   According to an advantageous characteristic of the invention, the outlet  48  which leads to the swimming pool, either directly or via an endpiece, has an axis that is preferably sloped in a horizontal plane relative to a normal to the wall of the swimming pool. This slope of the outlet axis  48  of the flow of water is shown in  FIG. 9 . In this way, the high-rate flow of water also possesses a large amount of kinetic energy, which is transmitted to the water of the swimming pool with a component that encourages flow in a closed loop at the surface of the swimming pool, and that also encourages stirring of the entire volume of the pool. This closed-loop flow serves to set debris and dirt into motion, thus making them easier to capture by being sucked in through the opening  18  of the skimmer. 
   The large amount of energy that is transmitted to the water in the pool, creating a flow component causing rotating flow, presents the advantage of ensuring that the water in the pool is stirred thoroughly, and thereby limits or even eliminates zones of stagnation. 
   This stirring effect is revealed by tests for determining cloudiness. In such tests, extremely fine clay is introduced into the water of the swimming pool, at a concentration of 50 grams per cubic meter of water. This makes the water extremely cloudy. The test consists in determining the effectiveness of filtering by determining the length of time needed for the water to return to a clarity threshold that corresponds to the cloudiness index being reduced by a factor of 4 or even 12 as determined by a turbidity meter. 
   It is thus found that a return to an acceptable threshold of cloudiness requires less than one day, generally about ten hours, whereas several days are usually required with conventional filtering, and ignoring the formation of a large amount of deposit. This result is achieved firstly because of the high flow rate obtained with the flow-multiplier assembly, for a moderate level of pump power, and secondly by the stirring effect obtained by the turning motion induced by the resultant of the outlet water flow and by its direction, e.g. at 20° relative to the normal to the wall of the swimming pool. 
     FIG. 9  shows the major fraction of a filter group of the invention as a perspective view, together with various advantageous characteristics. In particular, it can be seen that the housing containing the filter assembly and the duct  26  is constituted by an assembly made by a blow-molding technique, the body containing the filter being preferably ribbed in order to give it good mechanical strength. 
   In  FIG. 9 , there can be seen an improvement whereby a duct  60  has a top end opening out firstly to the atmosphere and coupled secondly via a valve  62  to a location situated upstream from the flow-multiplier assembly. Its bottom end is for connection to a drain plug at the bottom of the swimming pool. In this way, it is possible to cause water to flow by suction in this duct at a rate of about 4 m 3 /h, thus obtaining flow through a drain plug of the swimming pool. 
   Although it is stated that the bypass duct is connected between the first and second filter stages, it could also be placed entirely downstream from said filter assembly. Under such circumstances, debris can pass via the bypass duct, but since the debris is of small section, it is not very harmful, providing it does not block this duct. Any appropriate device can thus be used for preventing the bypass duct being blocked. In addition, the second end of the duct may be connected to any location where there is suction, e.g. at any point upstream from the converging nozzle of the flow-multiplier assembly. 
   The filter group of  FIGS. 7 to 9  is entirely suitable for swimming pools having a volume of water of the order of 100 m 3  to 200 m 3 . When the volume is greater, a plurality of groups can be used and certain elements can be shared between them, e.g. a pump. When the volume is smaller, it is advantageous to use a group of the movable type, as described below in the present description. 
   In the fourth embodiment, the filter and maintenance groups comprising the circulation assembly of the invention is intended to constitute a pool-cleaner head.  FIGS. 10 to 12  are various views of this embodiment of the pool-cleaner head of the invention. 
   As shown clearly in  FIG. 12 , the cleaner head essentially comprises a body  210  and a filter  212  shown in the form of a bag in order to simplify the drawing, but which could be a filter cartridge. 
   The body comprises a base  214  and a duct  216  extending perpendicularly to the base  214 . The duct forms part of the water circulation assembly of the invention. The base  214  has wheels  218  organized as two rows of three wheels each in the embodiment shown. A skirt  220 , e.g. made of rubber or elastomer, but which could also be made of bristles, is disposed around the entire bottom periphery of the base  214 . The duct  216  has a converging portion inlet  222  level with the bottom surface of the base, and has an outlet  224  at its top end. Under such circumstances, the duct  216  is formed by a converging portion, a central portion  226  that is cylindrical, followed by a diverging portion. 
   A tube  228  is terminated level with the inlet  222  to the converging portion by an ejector  230  for projecting an upward flow of water under pressure as transmitted via an inlet coupling  232 . The coupling  232  is for coupling via a flexible hose to a supply of water under pressure as is usually located beside a swimming pool, delivering flow at a rate of about 2 m 3 /h at a pressure of 1 bar to 5 bar, e.g. in the range 2 bar to 3 bar. 
   At its top end, the base possesses a collar  236  for retaining a retaining cord  234  located at the opening of the filter bag  212  of the cleaner head. 
   As shown in  FIG. 12 , an endpiece  238  having a hinged rod  240  serves for connection to a telescopic pole handle. 
   Finally, it should be observed that there is a valve  242  at the top portion of the filter bag  212 . 
   In  FIGS. 10 and 11 , it can be seen that the base  214  co-operates with the surface on which the cleaner head is standing to define a broad and shallow guide space for the circulation assembly that is symmetrical about the inlet to the converging portion (see the large area of the base surrounding the inlet  222  in  FIG. 11 ). It should also be observed that the skirt  220  leaves only a small gap for passing water between the base and the bottom of the pool. 
   Given that all of the flow of water under pressure (2 m 3 /h at a pressure of 1 bar to 5 bar) is transmitted to the ejector  230 , and given that it is based at the inlet to the converging portion, the suction effect created by the circulation assembly is very large. The sucked-in flow of water begins by flowing in the broad and shallow guide space formed between the bottom surface of the base and the bottom of the swimming pool prior to reaching the converging portion. Since this space is shallow, water flows through it at high speed, thereby producing a significant cleaning effect. This effect is further reinforced at the edges of the cleaner head since the skirt defines a space that is locally very small and thus causes the water to accelerate and take on a high level of kinetic energy against the bottom of the swimming pool. 
   This very powerful suction effect is easily demonstrated: removing several kilograms of earth thrown into the bottom of a swimming pool requires only a few tens of seconds, and the appliance enables pebbles weighing several tens of grams to be sucked up. 
   Another characteristic of the cleaner head shown in  FIGS. 10 to 12  is that it is highly mobile. The wheels  218  are mounted on ball bearings, preferably stainless bearings, and since they are organized in two rows (extending parallel to the direction of the telescopic pole handle secured to the rod  240  of the endpiece  238 ), the base itself does not come directly into contact with a convex surface since the wheels in the middle of each row come into contact with convex surfaces and make movement easy. 
   A very important characteristic of the cleaner head shown in  FIGS. 10 to 12  is that it is highly stable. Although its body is made of lightweight plastics material and weighs little, and although the filter bag  212  that is fixed via a cord  234  at its bottom opening around the collar  236  on the base of the body is likewise light in weight, when the sucked-in contaminating material escapes via the outlet  224 , it drops back around the duct  216  and accumulates on the base all around the duct. Since the outlet flow of water is directed upwards, it tends to center the top portion of the bag, such that leaves and other waste can fall all around the duct onto the base. The weight of the collected contaminating matter thus constitutes a kind of ballast that increases the stability of the cleaner head. In practice, the accumulation of contaminated matter can be as high as the outlet  224 . 
   Another advantageous characteristic of the invention is that the filter bag  212  is preferably made of a fabric having a mesh size that is greater than 40 μm and preferably equal to about 60 μm. Such a mesh size serves to retain contaminating material even when small, such as small particles of earth, thereby enabling the swimming pool to be cleaned quickly. However, a mesh of this size is so small that air cannot escape from the bag through the fabric; a fabric with a mesh size this small therefore cannot be used with a conventional cleaner head. In the invention, when the filter bag  212  is made using such a fabric, it has an air exhaust valve  242 . 
   Although this characteristic is not shown, the cleaner head may also include, in conventional manner, a cleaning accessory in the form of a flexible tube providing with members for scraping against the bottom of the swimming pool in order to remove matter that is stuck thereto. Such an accessory can easily be mounted on the coupling  232  or on some other location of the tube  228 . Nevertheless, such an accessory is generally not needed, unless the pool has not been used for a very long time without being cleaned, so that particularly troublesome dirt has become stuck to the bottom of the swimming pool. 
   The base is described having a collar  236  for retaining the cord  234  at the opening of the filter bag  212 , the collar could be located on the duct close to the inlet, so that contaminating matter constitutes ballast. 
   Although a filter bag  212  is described above, the bag could advantageously be replaced by a filter cartridge, preferably a cartridge secured to the base and thus increasing its stability, as shown in  FIG. 17 , described below. 
   The above-described cleaner head, when provided with a filter cartridge  250  as shown in  FIG. 17 , can also be used as a filter and maintenance group including a circulation assembly of the invention and serving to constitute a movable or independent group for swimming pool filtering and maintenance.  FIG. 17  shows the cleaner head of  FIGS. 10 to 12  turned upside-down through 180° and placed in a box  244  having a water inlet  246  level with the pool surface and a water outlet  248 . The bag is replaced by a filter cartridge  250  and the assembly constitutes a movable or independent filter group. 
   Thus, the same combined appliance can be used either as a cleaner head, or as a filter group. 
   The invention also provides other movable filter groups, as shown in  FIGS. 13 to 16 . 
     FIG. 13  shows the top of a portion of a swimming pool wall  122  supporting two hooks  124  that carry the body  126  of a movable filter group. 
   The movable filter group has a skimmer opening  128  that feeds a vertically-extending filter body  130 . Between the bottom portion of the filter  130  and an opening  132  for exhausting water from the filter group, there is disposed a rising duct whose vertical portion includes a converging portion  134  followed by a duct  136  which in the embodiment shown includes a diverging portion. An ejector  138  of the circulation assembly of the invention is disposed on the axis and on the axis of the duct portion  136  practically at the inlet to the converging portion  134 . In the example shown, the ejector  138  is fed by a water supply  140  made available in the swimming pool wall. 
   A bottom orifice  135  enables the group to be emptied so as to make it easy to remove from a swimming pool. 
   When the wall of the swimming pool has a plurality of water supply points, the movable filter group can be positioned in a variety of locations. In a first variant, one of the hooks  124  (or a swimming pool ladder) can be used for supplying water (or in the variant supplied below for supplying electricity). In this other variant, the group includes a low flow rate and high pressure pump (e.g. at 2 bar or more) e.g. of the electrical type, that is mounted on the body  126  and that sucks water in directly from the pool: no water supply connection is then required. 
   In  FIG. 15 , reference  141  designates a three-port valve enabling water to be fed either to the multiplier assembly (ejector  138 ), or to a pressurized water supply point  139  for feeding an accessory such as a cleaner head. 
   This movable group presents the advantage of being capable of being moved and of being capable of being used in particular with pools standing on the ground which are generally of smaller volumes than pools dug in the ground. It is made up of solely of elements that are lightweight and inexpensive, and it is easily moved, in particular by using its handles. In addition, it can easily be made in a floating form, and it is preferably ballasted so as to enable it to float with an orientation such that a water inlet orifice and a water outlet orifice are close to the surface of the water on which the movable group is floating. 
   In the third embodiment, the filter and maintenance group including the circulation assembly of the invention is also intended to constitute a movable or independent swimming pool filter and maintenance group, but it is even more simple than the group constituting the second embodiment.  FIG. 16  shows such a movable filter group. 
   The appliance of  FIG. 16  comprises an ejector  142  aligned on an axis and connected to a coupling  144  enabling it to be coupled to a water feed pipe. A duct  146  having a converging portion beside the ejector is placed on the axis of the ejector and is connected thereto by a small number of thin arms  148  serving to support the converging portion and disturbing the flow of water between the ejector and the inlet to the converging portion as little as possible. The ejector and the duct  146  are held by two cheek plates  150  and  152  which also support a cylindrical filter cartridge  154 . The cartridge is advantageously held on the inside by a grid  156 , e.g. made of plastics material, and another grid  158  is advantageously disposed on the outside so that objects of large size, such as leaves, do not come directly into contact with the filter  154 . 
   While the appliance of  FIG. 16  is in operation, as soon as the ejector  142  projects a flow of water along the axis of the duct  146 , the water located all around the appliance passes through the grid  158  and the filter  154  and enters into the space that exists between the filter  154  and the duct  146 . This water is sucked towards the converging portion from which it flows into the inside of the duct  146 . 
   In testing, the appliance shown in  FIG. 16  has been used with pressure at the outlet from the ejector lying in the range 1 bar to 3 bar, and with a flow rate varying over the range 0.5 m 3 /h to 3 m 3 /h. The speed obtained at the outlet from the duct was always greater than 0.2 m/s, and the multiplication factor was always greater than 10. 
   This movable group presents not only the advantage of being capable of being moved and of being capable of being used in particular in above-ground swimming pools which are generally of smaller volume than pools dug in the ground, like the group in the second embodiment, but it is also lighter in weight, less expensive, and very effective. 
   The advantages of the movable filter groups of the two last-described embodiments are clear. Thus, a group can be located close to the portion of the swimming pool that is the dirtiest or that is the easiest to access. The group can be inserted into the swimming pool only when necessary. For example, a single group can be used and transported to filter the water in a plurality of swimming pools consecutively. No special apparatus is required other than a water supply or an electricity supply, in particular there is no need for a closed protective space. In addition, because each group is light in weight, a plurality of groups can be located simultaneously in a single pool of large dimensions for the time required to perform filtering. Finally, when the group can float, there is no need for any anchoring device.