BE1021893B1 - PUMPING UNIT, PUMPING STATION, PUMPING AREA AND METHOD FOR PUMPING A LIQUID. - Google Patents

Abstract

Pumping unit (1) for pumping liquid from a waste liquid line (10) comprising a waste liquid inlet (1 Oin) and a waste liquid outlet (10out) and configured so that said liquid is suitable flowing from said waste liquid inlet (1 Oin) to said waste liquid outlet (10out) by gravity, said pumping unit (1) comprising: a first self-priming pump (501) comprising an inlet (501 in ) and an outlet (501 out), a junction line (15) connected to said inlet (501 in) of said first pump (501) and a coupling means (20) for connecting said junction line (15) to said used liquid outlet (10out).

Description

FIELD OF THE INVENTION The invention relates to the technical field of groups and pumping areas for liquid. More precisely, according to a first aspect, the invention relates to a pumping unit, according to a second aspect, to a pumping station, according to a third aspect, to a pumping area and according to a fourth aspect, to a method to pump liquid. State of the art [0002] FR2837244 describes a pumping unit that can be used in a pumping area, for example for pumping or raising sewage from harvested underground pipes to the soil surface. This pumping unit comprises one (or more) pump (s) which is (are) housed in a tank. This tank comprises an inlet opening into which is introduced an inlet pipe (or channeling spent liquid) carrying for example wastewater from a gravity network. The wastewater leaving the inlet pipe flows into a main pipe towards the pump (or pumps) which can direct these waters by pumping to an outlet pipe.

The pumping unit of FR2837244 has certain disadvantages. Its use is quite complex; its integration into a pumping area is also quite complex; finally, its integration into a pumping area is expensive. SUMMARY OF THE INVENTION [0004] According to a first aspect, one of the aims of the present invention is to provide a pumping unit whose use is simpler and whose integration into a pumping area is simpler and less expensive. . To this end, the inventors propose a pumping unit for pumping liquid from a spent liquid pipe comprising a spent liquid inlet and a spent liquid outlet and configured so that said liquid is capable of flowing from said waste fluid inlet to said gravity-worn liquid outlet, said pump unit comprising: - a first pump for pumping said liquid, comprising a liquid inlet to be pumped and a pumped liquid outlet; a junction pipe mechanically coupled to said inlet of said first pump; a coupling means mechanically coupled to said junction pipe and making it possible to mechanically couple said junction pipe to said spent liquid outlet of said spent liquid pipe;

The pumping unit of the invention is characterized in that said first pump is a self-priming pump.

The first pump of the pumping unit of the invention is a pump for self-priming liquid. Preferably, this first pump is a self-priming centrifugal pump. This makes it possible to have high pumping rates which is often required for sewage lifting. A self-priming centrifugal pump is also less expensive than other types of self-priming pumps, which reduces costs. Another example of a first self-priming pump is a self-priming volumetric pump. Preferably, said first pump is then a peristaltic pump or a lobe pump.

[0006] A self-priming pump is different from the pumps in charge such as that described in FR2837244. A self-priming pump is equipped with an automatic mechanism that makes it possible to automatically prime the pump. Examples of self-priming pumps are wet priming centrifugal pumps and dry priming centrifugal pumps. Commercial examples of self-priming pumps are the 'Redi-prime' and 'venturi-prime' brand CORNELL, the 'dri-prime' brand Godwin or the 'priming assist' brand Gorman-Rupp . For wet priming centrifugal pumps, the pump volute is surrounded by an outer casing that serves as a liquid reservoir. There is a passage between the volute and the liquid tank that will serve to create the vacuum in the suction pipe. For centrifugal dry priming pumps, the liquid centrifugal pump is coupled with a vacuum pump which allows the suction pipe to be emptied, thus allowing the liquid pump to be primed.

The priming of a pump for liquid is a concept known to those skilled in the art. Priming is necessary to allow pumping of liquid through a liquid pump. It refers to the filling of a pump by the liquid to be pumped after removal of air in the body of the pump and in the upstream piping (or suction line) which must bring the liquid to pump to the pump. A pump without automatic priming can not evacuate air from the suction line alone.

The pump FR2837244 is not self-priming. Indeed, in line 11 of page 12, it can be read: the priming of the pumps takes place automatically as soon as the liquid / gas mixture reaches a sufficient density, thanks to degassing chambers, not shown, located behind the impellers. Thus, it is necessary that the liquid / gas mixture reaches a density sufficient for the priming of the pump FR2837244 which is not the case with the first self-priming pump of the pumping unit of the invention. By using the pumping unit of the invention, there is no need for degassing chambers because the first pump is a self-priming pump. Thus, the use of the pumping unit of the invention is simpler.

The first pump of the pumping unit of the invention is self-priming. A priming is possible even if it is at a level higher than the level of liquid to be pumped. This is not possible with the pump of FR2837244 which is a dry dock pump, not self-priming. This explains the fact that the pump FR2837244 is housed in a lower portion of a tank to allow to create the conditions necessary for the priming of the pump, namely that the water level in the suction manifold of the FR2837244 pump wheel is higher than the level where the centrifugal impeller of the pump is located. In particular, this document teaches us to place the pump in the lower part of said tank (which could also be called dry dock), at the inlet opening through which the arrival pipe arrives and thus the liquid to pump. Thus, under normal conditions of use, the priming of the pump is possible due to the weight exerted by the water column upstream of the pump. Normal conditions of use means conditions corresponding to the case where water flows from the inlet pipe to the tank by gravity.

The priming of the first pump of the pumping unit of the invention being possible even if the latter is at a higher level than the level of liquid to be pumped, the integration of the pumping unit in an area of pumping is simplified: the constraint on the vertical positioning of the pumps of FR2837244 is removed (the pumps of FR2837244 must be under the water level to be pumped to allow their priming). In addition, it is possible to position the first pump of the pumping unit of the invention on the soil surface even if the spent liquid line is underground (which is generally the case). This also facilitates integration of the pumping unit into a pumping area; it is no longer necessary to plan and build a tank or dry dock to house the pump or pumps. It follows a significant reduction in costs because this civil engineering work is no longer necessary (this tank can be removed what is not mentioned in FR2837244 because the group described there does not include a self-priming pump the tank is therefore necessary). On the other hand, the maintenance of the pumping unit of the invention is easier when it is integrated in a pumping area 'above ground' because it is more accessible if it is on the surface of the soil (in comparison with a pumping unit whose pump must be in a tank). Maintenance costs are therefore also reduced. In particular, it is not necessary to provide a ladder to descend to the bottom of such a tank and it is not necessary to go down to the bottom of a tank to inspect the state of the pump (s) . In some places (for example, very rocky places), digging such a tank can be particularly complicated and expensive.

By using a self-priming pump such as the first pump of the pumping unit of the invention, it is also possible to position the pump further from the spent liquid outlet of the spent liquid line (pipe of arrival of FR2837244). The FR2837244 pump should be positioned as close as possible to the inlet opening into which the inlet pipe is introduced. This constraint is removed with the pumping unit of the invention. This aspect also facilitates its integration into a pumping area.

The junction pipe may consist of a single part, for example a pipe. In another preferred version, the junction pipe comprises several parts, for example several pipes.

The pumping unit of the invention has other advantages. Through the junction pipe and the coupling means, it is possible to connect the inlet of the first pump to the waste liquid outlet of the spent liquid line. This allows the passage of spent liquid from said waste liquid outlet to the inlet of the first pump without going through a wet sump. This peculiarity is quite original and goes against the usual practice that has been followed in the field of pumping areas for many years.

A wet sump is known to those skilled in the art: it refers to a well in which is stored spent liquid (such as waste water) before pumping to the soil surface. Generally, a wet sump has a cylindrical shape whose diameter is generally between 1.5 and 5 meters, and whose height (or depth) is generally between two and eight meters. A wet sump can also be in the form of a hollow prism with a square or rectangular base.

The pumping unit of the invention makes it possible to remove a wet sump from a pumping area. The result is different benefits. The integration of the pumping unit in a pumping area and the construction of a pumping area employing the pumping unit of the invention are easier because it is not necessary to predict and create this civil engineering work. The costs associated with the integration of the pumping unit into a pumping area and the construction of a pumping area employing the pumping unit of the invention are therefore reduced. The absence of a wet sump in which stagnant wastewater such as wastewater also makes it possible to reduce foul smells that rise to the surface. The comfort of the residents can therefore be improved by the pumping unit of the invention. Since there is no longer a need for a wet sump in a pumping area using the pumping unit of the invention, it is no longer necessary to provide a ladder (or trapillons) to access it. It also leads to a reduction in costs. The absence of a wet sump also makes it possible to increase the number of sites likely to be able to accommodate a pumping area: the constraints on the ground to accommodate the pumping area are reduced. In the same vein, it is possible, thanks to the pumping group of the invention, to provide for the construction of a pumping area even in tight places which is not possible with a pumping area requiring a wet sump.

Preferably, the pumping unit comprises: a second self-priming pump for pumping said liquid, comprising an inlet for liquid to be pumped and an outlet for pumped liquid; a junction pipe mechanically coupled to said inlet of said second pump; coupling means mechanically coupled to said junction pipe for mechanically coupling said junction pipe to said spent liquid outlet of said spent liquid pipe.

In this preferred embodiment, the pumping unit thus comprises two self-priming pumps. Thus, the maximum pumping capacity, i.e., the maximum volume of liquid that can be pumped per unit time, is greater using the same type of self-priming pump. This is particularly useful when pumping large amounts of liquid or when pumping liquid at a high flow rate. This preferred embodiment has other advantages. In particular, it can be ensured the pumping capacity of the pumping unit even if a pump is stopped. One of the two pumps can be stopped for various reasons, for example: maintenance service of said pump requiring its shutdown; stopping because of failure of said pump or associated auxiliary services (for example, breaking of the power supply of said pump). Using two pumps instead of one also increases the life of the pumps because they can be operated alternately, reducing the strain on the pumps. For this purpose, the pumping unit of the invention preferably comprises a control system for alternating the operation of the first and second pumps. Operating the first and second pumps alternately also allows them to be used in a substantially similar manner (they turn in the end for substantially equivalent times) which also facilitates the maintenance management of the pumps. When operating the first and second pumps alternately, there are significant peaks or gradients in the speed of rotation of the pumps. These speed peaks make it possible to have sufficient velocities (preferably greater than 0.6 m / s) in the discharge pipework (that is to say the piping connected to the outlets for liquid pumped from the pumps) to carry the sand and the like. solid particles. Thus, the alternating operation of the pumps allows cleaning of the pipes.

Preferably, the junction pipe has a length of between two and nine meters. More preferably, it has a length of between four and six meters. Even more preferably, it is seven meters long. By using a length greater than or equal to two meters for the junction pipe, it is possible to reduce the risks associated with cavitation, or even to eliminate them. By using a length greater than or equal to two meters for the junction pipe, it is also possible to deport the pump (s) at relatively large distances from the spent liquid outlet of the spent liquid pipe. This allows the pump (s) to be placed in easily accessible locations making maintenance of the pumping unit even easier. In particular, with such lengths for the junction pipe, it is generally possible to place the pump (s) on the surface while ensuring a connection between it (s) and where the effluents arrive. Preferably, the junction pipe is vertical.

Preferably, the pumping unit comprises a control system for controlling the operation of said first pump in the following manner: when a level of liquid to be pumped is equal to or greater than h1, said regulation system is capable of starting said first pump and imposing on it a pumping speed v1; when said liquid level is greater than h2 <h1 but less than or equal to h1, said control system is able to impose on said first pump said pumping speed v1 when it is in operation; when said liquid level reaches h2 <h1, said control system is able to impose a pumping rate v2 on said first pump such that v2 <v1 during a time interval ΔΤ so that said liquid level is kept constant; after said time interval ΔΤ, said control system is able to impose a pumping rate v3 on said first pump so that said liquid level reaches a value h3 <h2; - When said liquid level reaches h3 <h2, said control system is able to stop the first pump.

With this preferred embodiment, it is possible to ensure self-cleaning or self-cleaning of said waste liquid line, in particular when it is inclined with respect to a horizontal plane so that the liquid inlet worn at a higher level than the spent liquid outlet along a vertical direction. With this preferred embodiment, it is indeed possible to carry floating and settling residues outside said pipe of spent liquid. Stopping the first pump at level h3 makes it possible to avoid introducing air during pumping, which is harmful to the pumps mechanically and hydraulically (because air bells can form in the discharge pipe), this will lead to the formation of water hammers (pressure shock when stopping pumps). Preferably, v1 and v3 are equal to the maximum pumping rate of said first pump.

Preferably, the pumping unit comprises a bypass duct coupled to said first pump to allow cleaning of a region located in said waste liquid duct by deflecting at least a portion of liquid pumped by said pump. first pump to said region.

The advantages of using such a bypass pipe are various. Said bypass pipe may first serve as an air outlet when the first pump starts. On the other hand, said bypass line may be used to clean an inner region of the spent liquid line by placing one of its ends in said region; the cleaning is provided by deflecting at least a portion of liquid pumped by the first pump by said bypass pipe. Finally, when the first pump is stopped, the bypass line can be opened by a user to drain the entire delivery column to, for example, perform a maintenance intervention on the discharge pipe (which can sometimes to do several kilometers). The discharge line is positioned downstream of the first pump (i.e., connected to the pumped liquid outlet of the first pump) and serves to evacuate the pumped liquid.

Preferably, the pumping unit comprises a level sensor for measuring a liquid level. Preferably, this liquid level is a level of liquid in the spent liquid line. In another preferred variant, the liquid level could be a level of liquid in a well (for example a pebble trap) located upstream of the spent liquid line. By using such a level sensor, it is possible to regulate the pump (s) knowing such a level and to make a closed-loop regulation. Preferably, said level sensor is a bubbling level sensor comprising a bubbling rod.

By controlling the level of liquid to be pumped, for example in the spent liquid line, it is possible to avoid pumping air by stopping the operation of any self-priming pump when said level falls below a certain low threshold. which is to be determined.

According to a second aspect, the invention relates to a pumping station comprising a pumping unit as described above and said spent liquid pipe connected to said connecting pipe by said coupling means, allowing a flow of liquid. used the spent liquid inlet of said waste liquid channel to its spent liquid outlet and then to said junction pipe and then to said liquid inlet to pump from said first pump when the latter operates.

This pump station may comprise any preferred embodiment of the pumping unit of the first aspect of the invention which has been described above.

In general, the advantages mentioned in connection with the pumping unit of the first aspect of the invention also apply to the pumping station. In particular, the pumping station of the invention is easier to use and easier to maintain. Since the first pump is a self-priming pump, it is not necessary to place it at the bottom of a tank or dry dock. It can be placed on the surface, which facilitates the use and maintenance of the pumping station. Since it is not necessary to provide a tank or dry dock, the pumping station of the invention is also less expensive. This pumping station does not require the presence of a wet sump because the first pump is in direct contact with the spent liquid outlet of the spent liquid line. The cost associated with the pumping station can therefore also be reduced for this reason, as explained above. The absence of a wet sump also reduces the amount of nauseating odors. The advantages of the preferred embodiments of the pumping unit of the first aspect of the invention also exist for pumping stations comprising such preferred pumping units.

[0027] Preferably, the pumping station comprises at least two pipes of spent liquid. Said first pump can then be connected to each of the spent liquid outlets of said spent liquid lines.

In an embodiment corresponding to the case where there are first and second self-priming pumps and two spent fluid lines, it is preferred to connect each of said first and second pumps to a spent liquid line.

Preferably, the spent liquid pipe has a mean inclination of between 10 ° and 50 ° with respect to a horizontal plane so that said used liquid inlet is situated at a higher level with respect to said spent liquid outlet. along a vertical direction. Preferably, the spent liquid line has a mean inclination of 30 ° to 45 ° with respect to a horizontal plane so that said spent liquid inlet is located at a higher level than said spent liquid outlet along the a vertical direction.

By imposing such inclinations to the spent liquid line, problems of settling of solid particles present in the liquid to be pumped can be reduced or even avoided. When the used liquid line is horizontal, there is a risk of settling, especially when the pump (s) is at a standstill. These settling problems reduce the pumping capacity and may, in the long run, block the spent liquid line, thereby preventing any pumping of liquid. By imposing an inclination of said used liquid pipe greater than or equal to 10 °, and preferably greater than 25 °, it is possible to reduce such risks and to ensure what the inventors call a self-cleaning of the pumping station. . Imposing such an inclination of said waste liquid pipe also makes it possible to increase the reliability of a liquid level regulation.

Preferably, said used liquid pipeline is underground and the pump (s) found (s) on the surface of the ground. Access to the pump (s) is then easier while having a pumping station to pump water flowing underground.

The liquid flow velocity in the spent liquid pipe is preferably greater than or equal to 0.4 m / s, more preferably greater than or equal to 0.6 m / s and even more preferably greater than or equal to 0.6 m / s. equal to 1 m / s. With these three preferred variants, the risk of settling in the spent liquid line is reduced and this especially as said liquid flow rate is large. Such liquid flow rates can be obtained in the spent liquid line by imposing a certain inclination with respect to a horizontal plane, see above. Generally, it is necessary to impose an inclination greater than or equal to 30 ° with respect to a horizontal plane to ensure that the flow velocity of liquid in the spent liquid pipe is at least equal to 0.4 m / s.

According to a third aspect, the invention relates to a pumping area comprising a pumping station as described above. This pumping area may comprise any preferred embodiment of the pumping station of the second aspect of the invention which has been described above. Preferably, this pumping area comprises a well communicating with the used liquid pipe via its spent liquid inlet.

In general, the advantages mentioned in connection with the pumping unit of the first aspect of the invention and the pumping station of the second aspect of the invention also apply to the pumping area. In particular, the pumping area of the invention is easier to use and easier to maintain. Since the first pump is a self-priming pump, it is not necessary to place it at the bottom of a tank or dry dock. It can be placed on the surface, which facilitates the use and maintenance of the pumping area. Since it is not necessary to provide a tank or dry dock, the pumping area of the invention is also less expensive. This pumping area does not require the presence of a wet sump as the first pump is in direct contact with the spent liquid outlet of the spent liquid line. The cost associated with the pumping area can therefore also be reduced for this reason, as explained above. The absence of a wet sump also reduces the amount of nauseating odors. The advantages related to the preferred embodiments of the pumping unit of the first aspect of the invention and the pumping area of the second aspect of the invention also exist for pumping areas comprising such preferred pumping groups and such favorite pumping stations.

With the pumping unit, the pumping station or the pumping area of the invention, a screening basket is no longer necessary. In preferred variants of the pumping group, the pumping station or the pumping area, one could nevertheless integrate one. A screening basket is known to those skilled in the art. It allows to retain and thus filter objects that float on the surface of the liquid to be pumped, for example pieces of wood.

According to a fourth aspect, the invention relates to a method for pumping liquid from a spent liquid line comprising a spent liquid inlet and a liquid outlet used and configured so that said liquid is suitable. flowing from said spent fluid inlet to said gravity-worn liquid outlet, said method comprising the steps of: - providing a first pump for pumping said liquid, comprising a liquid inlet to be pumped and a pumped liquid outlet; providing a junction pipe including first and second ends; mechanically coupling said first end of said junction pipe to said inlet of said first pump and mechanically coupling said second end of said junction pipe to said spent liquid outlet of said spent liquid pipe so that said inlet of said first pump is connected to said waste liquid line via said junction pipe; said method being characterized in that said first pump is a self-priming pump.

In general, the advantages mentioned in connection with the pumping unit of the first aspect of the invention also apply to the method in connection with the fourth aspect of the invention. In particular, by following this method, the use and maintenance of both a pumping group and a pumping station comprising a pumping group are simpler. Since the first pump is a self-priming pump, it is not necessary to place it at the bottom of a tank or dry dock. It can be placed on the surface, which facilitates the use and maintenance of a pumping station or pumping unit. As it is not necessary to provide a tank or dry dock, the costs are reduced. Thanks to the method of the invention, it is not necessary to provide a wet sump because the first pump is in direct contact with the spent liquid outlet of the spent liquid line. The associated cost can therefore also be reduced, as has been explained above in connection with the first aspect of the invention. The absence of a wet sump also reduces the amount of nauseating odors.

Preferably, said waste liquid pipe is a sub-ground pipe. Preferably, said underground waste liquid pipe is a waste liquid discharge pipe of a well. Preferably, said well is a pebble trap. Preferably, said first pump is controlled in the following manner: when a level of liquid to be pumped is equal to or greater than h1, start said first pump and impose on it a pumping speed v1 ^ 0; - If said liquid level is greater than h2 <h1 but less than or equal to h1, impose said pumping rate v1 to said first pump if the latter is in operation; when said liquid level reaches h2 <h1, impose a pumping speed v2 <v1 on said first pump during a time interval ΔΤ, so that said liquid level is kept constant; after said time interval ΔΤ, imposing a pumping speed v3 on said first pump so that said liquid level reaches a value h3 <h2; when said liquid level reaches h3 <h2, stop the first pump.

For the four aspects of the invention, said channel of spent liquid can be connected to a recovery line without using a well such a pebble trap. Liquid can therefore pass from said recovery line to said waste liquid line without passing through such a well. The associated costs are then all the more reduced. Thus, according to this preferred variant, the invention relates to a configuration comprising the pumping unit of the invention, the spent liquid pipe, a recovery pipe and a coupling means for coupling said spent liquid pipe and said pipe. recovery.

BRIEF DESCRIPTION OF THE DRAWINGS [0039] These aspects as well as other aspects of the invention will be clarified in the detailed description of particular embodiments of the invention, reference being made to the drawings of the figures, in which:

Fig.1 shows the pumping unit of the invention integrated in a pumping area;

Fig.2 shows an example of possible configuration for the spent liquid pipeline;

Fig. 3 shows a preferred embodiment of junction piping when the pump unit comprises two pumps;

Fig. 4 shows an example of pump operation mode when the pump unit comprises two pumps;

Fig. 5 shows a part of a preferred embodiment of the pumping unit of the invention;

Fig.6 shows a part of a preferred embodiment of the pumping unit of the invention;

Fig.7 shows a part of a preferred embodiment of the pumping unit of the invention;

Fig.8 shows a part of a preferred embodiment of the pumping unit of the invention;

Fig.9 shows a part of a preferred embodiment of the pumping unit of the invention;

Fig. 10 shows an example of a spent liquid pipeline having a non-zero average inclination with respect to a horizontal plane.

The figures are not scaled or proportioned. Generally, similar elements are denoted by similar references in the figures.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION [0040] FIG. 1 shows a preferred version of the pumping unit 1 according to a first aspect of the invention, integrated in a pumping area 8. This pumping area 8 comprises a well 4 like a pebble trap. A pebble trap is known to those skilled in the art. It is generally a cylindrical cavity whose diameter is generally between 50 cm and 2 meters (with a preferred value of 1 meter) and whose height is generally between 50 cm and 9 meters (with a preferred value of 5 meters). Waste liquid (for example wastewater) is generally brought to a pebble trap 4 by one or more recovery lines 40. Preferably, the bottom of the pebble trap 4 is located about 1 meter below. the arrival of said recovery line 40 located at said pebble trap 4. Used liquid can carry stones, pebbles or particles whose density is higher than the liquid that carries them. When this spent liquid reaches the pebble trap 4, these particles of higher density tend to fall to the bottom by gravity. The function of the pebble trap 4 is therefore to remove the high density particles from the spent liquid. In general, an overflow pipe 30 is present to allow liquid to be evacuated from the well 4 in the event of an overflow.

A used liquid pipe 10 allows the liquid to be discharged from the well 4. Preferably, this used liquid pipe 10 is a sewage pipe. It comprises a spent liquid inlet 10in which communicates with the interior of the well 4 and a spent liquid outlet 10out. The spent liquid line 10 is configured so that liquid is able to flow from the spent liquid inlet 10in to the spent liquid outlet by gravity. In the example shown in Figure 1, this is possible since the spent liquid outlet 10out is lower than the used liquid inlet 10in. This is not necessary, however. FIG. 2 shows a case where the used liquid channel 10 is configured so that liquid is able to flow from the spent liquid inlet 10in towards the used liquid outlet 10out by gravity without the output of waste liquid 10out is lower than the spent liquid inlet 10in. In this case, liquid will flow from the spent liquid inlet 10in to the spent liquid outlet 10out per communicating vessel. The arrows indicate the direction of flow of the liquid in the configuration shown in FIG. 2. The force of gravity exerted on the liquid present in the well 4 forces it to flow according to the arrows shown in FIG. This waste fluid line 10 is thus also configured to allow liquid flow from the spent liquid inlet 10in to the spent liquid outlet by gravity.

The pumping unit 1 of the invention comprises a first self-priming pump 501. The latter comprises an inlet 501 in for liquid to be pumped and an outlet 501 out for pumped liquid. The pumping unit 1 of the invention also comprises a junction line 15 comprising a first 15a and a second 15b ends. The connecting pipe 15 is mechanically coupled (preferably fixed) to the liquid inlet 501 for pumping the first pump 501 through its first end 15a. A coupling means 20 makes it possible to mechanically couple (or connect) said junction conduit 15 to the spent liquid outlet 10out of the used liquid pipe 10 by its second end 15b. Examples of coupling means 20 are: glue, flange, elbow (example shown in FIG. 1), a collar, or any adapter piece making it possible to connect a free end of the junction pipe. 15 to the spent liquid outlet 10out of the spent liquid line 10. With this coupling means 20, liquid can pass from the spent liquid outlet 10out of the used liquid line 10 to the inlet 501 in for liquid to pump the first pump 501 without going through a wet sump. Preferably, the junction pipe 15 has a length of between two and nine meters. An example of internal diameter for the junction pipe is 150 mm. Other values of internal diameter such as 80 mm to 300 mm could nevertheless be chosen.

As illustrated in Figure 1, the pumping area 8 preferably comprises a stabilized 85 to support the spent liquid outlet 10out of the used liquid pipe 10. Preferably, this stabilized 85 is concrete. In general, the pumped liquid outlet 501 of the first pump 501 is connected to a discharge pipe 45 for discharging the pumped liquid. Preferably, this discharge pipe 45 is partly underground. As illustrated in Figure 1, the first pump 501 is preferably housed in a chamber such as a house.

In a preferred embodiment, the pumping unit 1 comprises a first 501 and a second 502 pumps. A connecting pipe 15 makes it possible to connect the inlet of the second pump 502 to the used liquid outlet 10out of the spent liquid pipe 10. It may be the same connecting pipe 15 as that used to connect the pipe. input 501 in from the first pump 501 to the spent liquid outlet 10out of the spent liquid line 10. In another preferred embodiment, each of the first 501 and second 502 pumps is instead connected to the spent liquid outlet 10 out of the channel of waste liquid 10 by a different connecting pipe (151, 152): see Figure 3. Preferably, these two connecting pipes (151, 152) are then housed in the same outer pipe 16. A coupling means 20 such a bend for example makes it possible to connect each connecting pipe (151, 152) to the used liquid outlet 10out of the spent liquid pipe 10. It is possible to use a single coupling means 20 to achieve these connect them or use two different coupling means to connect the two connecting pipes (151, 152) to the spent liquid outlet 10out of the used liquid pipe 10.

Preferably, the pumping unit 1 of the invention comprises a regulation system 70 (an automaton for example) for alternating the operation of the first 501 and second 502 self-priming pumps when said pumping group 1 comprises two such pumps (501, 502). This mode of operation is illustrated in FIG. 4. This figure shows a time evolution of the state 100 of the first and second pumps (501, 502) according to this preferred mode of operation. The state of the first pump 501 (respectively second pump 502) is drawn in dotted lines (respectively in solid lines). During an alternating period 5f, the first pump 501 is in operation (state 100 at level 1) while the second pump 502 is at a standstill (state 100 at level 0). Then, it's the opposite.

In a preferred embodiment, the pumping unit 1 of the invention comprises a regulation system 70 (an automaton for example) to impose the following operation of the first pump 501 (it can be the same system 70 than that described previously or another). When a liquid level to be pumped is equal to or greater than h1, said control system 70 starts said first pump 501 and imposes on it a pumping speed v1. The first pump 501 will therefore trigger when the liquid level is h1 and will then operate at the pump speed (or rotational speed of a centrifugal pump) v1, the time for the first pump 501 to start and then to cause the liquid level to decrease to h2 <h1. Preferably, this pumping speed v1 represents the maximum pumping speed (or maximum flow rate) of the first pump 501. An example of speed v1 is 1500 rpm. The time for said liquid level to change from h1 to h2 depends on a part of the priming time (which depends on the speed of the first pump 501) and the flow of liquid arrival at that time. Preferably, said liquid level represents the level of liquid in well 4 (which is preferably a pebble trap). This is illustrated in FIG. 5 which shows two two-dimensional cuts of the pumping unit of the invention according to a preferred embodiment in combination with a spent liquid line 10 and a well 4. Preferably, said level of liquid is measured using a level sensor such as a bubbling sensor (example shown in Figure 5). In this case, the level sensor comprises a bubbling rod 61 whose end 61a is preferably located close to the spent liquid outlet 10out in the used liquid pipe 10. Preferably, a zero liquid level then corresponds to at a liquid level which is at the same height as said end 61a of the bubble rod 61. A positive liquid level then corresponds to a liquid level located above said end 61a of the bubbling rod 61; in other words and from a general point of view, a zero liquid level corresponds to a level of liquid at the same height as where the level is measured by the level sensor. The dimensions mentioned in FIG. 5 and the following figures are purely illustrative for certain examples of preferred embodiments. Other dimensions can be used.

When said liquid level reaches h2 <h1 (see FIG. 6), the regulation system 70 imposes on the first pump 501 a speed such that said liquid level is kept constant (thus at h2) during a time interval. ΔΤ, with measurement errors and with a liquid level indication tolerance which is preferably between +/- 5%. Preferably, ΔΤ is five minutes. The variation in pumping speed of the first pump 501 is preferably made possible by the use of one or more frequency variators. Preferably, such a frequency converter is installed in a control box on the surface of the ground. During ΔΤ, the flow rate of the first pump 501 is equal to the flow of arrival of effluents.

Once the time interval ΔΤ has been completed, the regulation system 70 imposes a pumping speed v3 on the first pump 501. Preferably, v3 is equal to the maximum pumping speed of the first pump 501. This will allow at the first pump 501 to exceed the flow rate of arrival of the effluent and empty an inclined waste liquid pipe 10 as shown in Figure 7 to a level h3. When said liquid level reaches h3, the control system 70 stops the first pump 501 (h3 = 0 in FIG. 7). Subsequently, the spent liquid line 10 will refill to level h1 following the arrival of effluent or liquid.

The sequence of operations of the first pump 501 imposed by the control system 70 which has just been described in connection with FIGS. 5 to 7 allows the self-cleaning of an inclined waste liquid pipe 10 while taking away floats and settling. Stopping the first pump 501 at level h3 prevents the introduction of air during pumping, which is detrimental to the pumps. The pumping of liquid and air triggers significant vibrations of the pump and can produce premature mechanical failures of bearings and mechanical seals. At the end of the sequence of operations of the first pump 501, we said that the spent liquid line 10 will refill to level h1 following the arrival of effluent or liquid. It is then possible to repeat this sequence of operations. In another preferred embodiment, this sequence will rather be imposed on a second pump 502 when the pumping unit 1 comprises at least two pumps. This will then do the same cycle of operations as previously described. This makes it possible to use the first 501 and second 502 pumps in the same way. This results in ease of pump maintenance planning.

Preferably, the following procedure is chosen for monitoring the malfunction of the first 501 and second 502 pumps when the pumping group 1 comprises two such pumps. This monitoring procedure may be applied by a control system 70, for example, the same as that described above with respect to FIGS. 5 to 7. In this procedure, there are two additional thresholds for the liquid level, which Preferably, it represents a level of liquid in a well 4 upstream of the used liquid line 10 (see above): h4 and h5. The threshold h4 is such that h4> h1 along a vertical direction upwards. Preferably, h4 is located at a vertical distance of h1 between 20 and 80 cm. More preferably, h4 = h1 + 40 cm. To illustrate the monitoring procedure for which the associated liquid levels are shown in FIGS. 8 and 9, assume that the first pump 501 is in operation to pump liquid but that the second pump 502 is at a standstill (the procedure However, in the case of surveillance, this applies mutatis mutandis). When a liquid level reaches h4, the second pump 502 is started while the first pump 501 is stopped. This procedure is followed because if a level h4 is reached, it means that the first pump 501 does not give its nominal flow. Simultaneously with the stopping of the first pump 501, an alarm is triggered. Subsequently, the second pump 502 is the only one to work while waiting for the intervention of a maintenance department which will have to intervene on the first pump 501 to restore it. It is possible that the first 501 and second 502 pumps are both damaged. In this case, the fluid level will continue to rise to a high general alarm level called h5. Preferably, this level h5 corresponds to the level too full of a well 4. When the liquid reaches this level of overflow, the liquid can preferably flow through an overflow pipe 30, see for example in Figure 9 Preferably, an alarm is generated when the liquid level reaches h5. Thus, users can be notified.

Preferably, the pumping unit 1 comprises a bypass duct 50 (see FIGS. 5 to 9). The by-pass line 50 may for example be a DN50, DN65 or DN80 tube (DN denotes the nominal diameter which is a notion known to those skilled in the art). The choice of a particular type will depend on the size and pumping power of the first pump 501. This bypass line 50 is mechanically coupled to the first pump 501. Specifically, the bypass line 50 is connected to the pumped liquid outlet 501 out of the first pump 501. In a preferred embodiment comprising two pumps, the bypass pipe 50 is preferably connected to the two pumps: in this preferred embodiment, there is therefore a pipe by-pass 50 for both pumps. It is however possible to provide two bypass lines 50, one for each pump (501, 502).

In the following description of the preferred embodiment comprising a bypass line 50, we will assume that there is only one pump called the first pump 501. The elements described below s' nevertheless apply to a preferred embodiment comprising two pumps (501, 502). Preferably, a valve is inserted between the pumped liquid outlet 501 out of the first pump 501 and the bypass line 50. The latter can have three functions.

The bypass duct 50 may serve to evacuate the air when the first 501 self-priming pump starts. Indeed, when the first pump 501 evacuates in the suction pipe (that is to say in particular the junction pipe 15) so that the atmospheric pressure can then push the liquid to be pumped into the suction pipe , the sucked air must be evacuated. By-pass pipe 50 may be used to evacuate this air sucked during priming.

On the other hand, the bypass pipe 50 can be used to clean a part of the liquid circuit, for example an internal region of the spent liquid pipe 10. During normal use of the first pump 501 , the valve located between the pumped liquid outlet 501 out of the first pump 501 and the bypass pipe 50 is closed preventing the passage of liquid in this pipe. When the user desires, he can open this valve while the first pump 501 is running. At least a portion of pumped liquid that is under pressure is out of the pumped liquid outlet 501 out is then diverted to this bypass line 50 and is driven to where the end of the bypass line is located. 50 which is not connected to the first pump 501. This place corresponds, for example, to an internal region of the used liquid pipe 10, close to the spent liquid outlet 10out (that is to say in a region located at a distance less than 35 cm from said used liquid outlet 10out along the main axis of the used liquid pipe 10). The sands and settled particles can be resuspended while still pumping. This function is very effective since it takes its source immediately to the discharge (or the exit) of the pumps (where the pressure is maximum). The valve located between the pumped liquid outlet 501 out of the first pump 501 and the bypass pipe 50 can be manual or automatic electric for example. An automatic electric valve can be opened via a control system 70 or control such as an automaton for example. Such an automaton can be housed in the electrical box which is on the surface of the ground, close to the pump or pumps (501, 502). Preferably, the valve is open for two minutes every hour.

Finally, when the pump (s) are stopped, the bypass pipe 50 can be opened (via the valve described above for example) by the user to empty the entire column. discharge (located downstream of the pumped liquid outlet 501 of the pumps) to, for example, make a maintenance intervention on the discharge pipe (which can sometimes be several kilometers long).

Preferably, the pumping unit 1 of the invention comprises a discharge check valve between the pumped liquid outlet 501 of the pump (s) and the discharge line (s) where is evacuated the pumped liquid. Such a valve avoids on the one hand the water hammers and on the other hand that the discharge column does not empty when the pump (s) are stopped.

Preferably, the pumping unit 1 of the invention comprises an air flush valve between the pump (s) (501, 502) and said nonreturn check valve. This flush valve closes automatically when the pump (s) (501, 502) is primed by the pressure exerted by the pumped liquid at that level.

Preferably, the end 50a of the bypass pipe 50 which is not connected to a pumped liquid outlet 501 out of a pump is immersed in a lower part of the used liquid pipe 10 which generally comprises liquid: see for example Figures 5 to 9. This avoids the defusing of the pump (s) once stopped (s). Indeed, since this pipe is immersed, air can not enter. On the other hand, the discharge check valve also prevents the entry of air into the piping.

Preferably, the pumping unit 1 comprises a level sensor for measuring a liquid level. Preferably, this level of liquid represents a level of liquid in the spent liquid line 10. It may also be in another preferred variant of a level of liquid in a well 4 (for example a pebble trap) in upstream of the spent liquid line 10. It is then possible to regulate the pump (s) knowing such a level and to make a closed-loop regulation. Preferably, said level sensor is a bubble level sensor comprising a bubbling rod 61. This type of sensor is known to those skilled in the art. Preferably, the bubbling stick 61 is a DN25 pipe.

Preferably, two level sensors such as two bubbling sensors are used to increase the reliability of the liquid level measurement. Compressed air is injected into the bubbling cane (s) 61 (for example at a rate of one bubble per second) by means of a bubbler which is preferably situated on the surface of the ground, for example on the ground. inside a cabin housing the pump (s) (501, 502). One end of the bubbling cane (s) 61 is preferably positioned in the used liquid pipe 10 as illustrated in FIGS. 5 to 9, preferably at a distance of less than 35 cm from the used liquid outlet 10out of said spent liquid line 10. This distance is preferably measured along the main axis of the spent liquid line 10. When said spent liquid line 10 has the shape of a hollow cylinder, this main axis corresponds to the axis of revolution of said hollow cylinder. Preferably, the bubbling rod (s) 61 are terminated by bubbling bells at the end located in the used liquid pipe 10.

In a second aspect, the invention relates to a pumping station 3 (see Figure 1). This pumping station 3 comprises a pumping unit 1 as described above and a spent liquid pipe 10. Various preferred embodiments of the pumping station 3 correspond to different preferred embodiments of the pumping group 1 as described previously. . The spent liquid line 10 is generally in the form of a hollow cylinder. Preferably, the used liquid channel 10 is connected to a well 4 such as a pebble trap (see FIG. 1). In another preferred embodiment, the used liquid line 10 is connected to the recovery line 40. In this case, the use of a well 4 such as a pebble trap is not necessary.

Preferably, the used liquid channel 10 has a mean inclination 11 of between 10 ° and 50 ° (with a still more preferred value of 45 °) with respect to a horizontal plane so that said used liquid inlet 10in is located at a higher level (or higher) than the spent liquid outlet 10out along a vertical direction. This is illustrated in Figure 10 for a preferred embodiment where the spent liquid line 10 has a hollow cylinder shape. In such a case, the corresponding axis of revolution (in broken lines in FIG. 5) has an inclination 11 of between 10 ° and 50 ° (with a still more preferred value of 45 °) with respect to a horizontal plane in this mode. preferred embodiment. In FIGS. 5 to 9, the used liquid channel 10 has an average inclination 11 of 30 ° with respect to a horizontal plane.

Preferably, the used liquid pipe 10 is underground and allows to discharge by gravity water from a well 4 (pebble trap for example). Preferably, the pump (s) are on the surface which allows easy access, which makes their maintenance easier. These preferred variants are illustrated in Figure 1 where the reference sign 2 represents the ground.

Preferably, when the pumping station 3 comprises a first 501 and a second 502 pumps, they are able to operate alternately with an alternation frequency 5f between four and six minutes, a still preferred value is five minutes. To this end, the pumping station 3 preferably comprises a control system 70 as described in connection with the first aspect of the invention, for controlling said first 501 and a second 502 pumps of the kind.

Preferably, the pumping station 3 comprises a bypass line 50 as described in connection with the first aspect of the invention. This bypass pipe 50 is connected to the first pump 501 by one of its ends. The other end of the bypass line 50 is preferably located in the spent liquid line 10, preferably at a distance less than 35 cm from the spent liquid outlet 10out. This distance is preferably measured along the main axis of the used liquid pipe 10. When the used liquid pipe 10 has the shape of a hollow cylinder, its main axis corresponds to the axis of revolution of the hollow cylinder .

Preferably, the pumping station 3 comprises a level sensor for measuring a liquid level. Preferably, this level of liquid is the level of liquid in a well 4 such as a pebble trap to which is connected the spent liquid inlet 10in of the used liquid pipe 10. Preferably, this level sensor is a sensor of bubbling level as described for the first aspect of the invention. In this preferred embodiment, the bubbling rod 61 is preferably positioned in the spent liquid pipe 10 so that one of its ends is located near the used liquid outlet 10 of the used liquid pipe 10, by example less than 35 cm from said used liquid outlet 10out. This distance is preferably measured along the main axis of the used liquid pipe 10. When the used liquid pipe 10 has the shape of a hollow cylinder, its main axis corresponds to the axis of revolution of the hollow cylinder .

According to a third aspect, the invention relates to a pumping area 8 comprising a pumping station 3 as described above. This pumping area 8 can include any preferred embodiment of the pumping station 3 described above. An example of a pumping area 8 according to this third aspect of the invention is illustrated in FIG. 1. In another preferred example, the pumping area 8 does not include wells 4 such as a pebble trap. In this case, the used liquid pipe 10 is connected directly to the recovery pipe 40. This reduces the bulk and manufacturing costs. Such a pumping area 8 is also simpler to build and can be built in more different places because there is no need to provide space for such a well 4.

According to a fourth aspect, the invention relates to a method for pumping liquid from a used liquid line 10 as described above. The inventors propose to mechanically couple (or fix, connect), for example by means of glue or a collar, a junction pipe 15 between the spent liquid outlet 10out of said used liquid pipe 10 and the inlet for liquid to be pumped 501 in from a first self-priming pump 501. This allows a passage to be formed for liquid to be pumped from the used liquid line 10 to the liquid inlet to be pumped 501 in from the first pump 501 without having to go through a wet sump.

The preferred embodiments described in connection with the pumping unit of the first aspect of the invention apply to the method of the invention, mutatis mutandis. This results in the same advantages for the method of the invention. Thus, it is for example possible to connect a first 501 and a second 502 self-priming pumps to the spent liquid outlet 10out of a used liquid pipe 10 by using one or more connecting pipe (s) (15; 151,152 ).

The present invention has been described in relation to specific embodiments, which have a purely illustrative value and should not be considered as limiting. In general, it will be apparent to those skilled in the art that the present invention is not limited to the examples illustrated and / or described above. The presence of reference numbers in the drawings can not be considered as limiting, even when these numbers are indicated in the claims. The use of the verbs "to understand", "to include", "to include", or any other variant, as well as their conjugations, can in no way exclude the presence of elements other than those mentioned. The use of the indefinite article "a", "an", or the definite article "the", "the" or "Γ", to introduce an element does not exclude the presence of a plurality of these elements.

The invention may also be described as follows. Pumping unit 1 for pumping liquid from a spent liquid line 10 comprising a spent liquid inlet 10in and a spent liquid outlet 10out and configured so that said liquid is able to flow from said liquid inlet used 10in towards said waste liquid outlet 10out by gravity, said pumping unit 1 comprising: a first self-priming pump 501 comprising an inlet 501 in and an outlet 501 out, a connecting pipe 15 connected to said inlet 501 in of said first pump 501 and a coupling means 20 for connecting said junction conduit 15 to said used liquid outlet 10out.

Claims (20)

claims A pumping unit (1) for pumping liquid from a spent liquid line (10) comprising a spent liquid inlet (10in) and a spent liquid outlet (10out) and configured so that said liquid is adapted to flow from said waste liquid inlet (10in) to said waste liquid outlet (10out) by gravity, said pump unit (1) comprising: - a first pump (501) for pumping said liquid, comprising an inlet (501 in) for liquid to be pumped and an outlet (501 out) for pumped liquid; a junction conduit (15; 151) mechanically coupled to said inlet (501 in) of said first pump (501); a coupling means (20) mechanically coupled to said junction pipe (15; 151) and capable of mechanically coupling said junction pipe (15; 151) to said spent liquid outlet (10out) of said spent liquid pipe ( 10); characterized in that said first pump (501) is a self-priming pump. 2. Pumping unit (1) according to the preceding claim characterized in that said pumping group (1) comprises: - a second self-priming pump (502) for pumping said liquid, comprising an inlet (502in) for liquid to be pumped and an outlet (502out) for pumped liquid; - a junction pipe (15; 152) mechanically coupled to said inlet (502in) of said second pump (502); - coupling means (20) mechanically coupled to said junction conduit (15; 151) and adapted to mechanically couple said junction conduit (15; 152) to said spent liquid outlet (10out) of said spent liquid line ( 10). 3. Pumping unit (1) according to the preceding claim characterized in that it comprises a control system (70) for alternating the operation of said first and second pumps (501,502). 4. Pumping unit (1) according to any one of the preceding claims characterized in that said connecting pipe (15; 151; 152) has a length of between two and nine meters. 5. pumping unit (1) according to any one of the preceding claims characterized in that it comprises a control system (70) for controlling the operation of said first pump (501) as follows: - when a level of liquid to be pumped is h1 or higher, said control system (70) is adapted to start said first pump (501) and to impose a pumping rate v1; when said liquid level is greater than h2 <h1 but less than or equal to h1, said control system (70) is able to impose on said first pump (501) said pumping speed v1; when said liquid level reaches h 2 <h 1, said control system (70) is able to impose a pumping rate v 2 on said first pump (501) such that v 2 <v 1 during a time interval ΔΤ so that said level liquid is kept constant; after said time interval ΔΤ, said control system (70) is able to impose a pumping rate v3 on said first pump (501) so that said liquid level reaches a value h3 <h2; - When said liquid level reaches h3 <h2, said control system (70) is able to stop the first pump (501). 6. pumping unit (1) according to the preceding claim characterized in that said pumping speeds v1 and v3 are equal to the maximum pumping speed of said first pump (501). 7. pumping unit (1) according to any one of the preceding claims characterized in that it comprises a bypass pipe (50) coupled to said first pump (501) to allow cleaning of a region located in said waste liquid line (10) by deflecting at least a portion of liquid pumped by said first pump (501) to said region. 8. Pump unit (1) according to any one of the preceding claims characterized in that it comprises a level sensor for measuring a liquid level. 9. Pumping unit (1) according to the preceding claim characterized in that said level sensor is a bubble level sensor comprising a bubbling rod (61). A pumping station (3) comprising a pumping unit (1) according to any one of the preceding claims and said waste liquid channel (10) connected to said connecting pipe (15; 151) by said coupling means ( 20), allowing a waste liquid flow from the spent liquid inlet (1 Oin) of said spent liquid line (10) to its spent liquid outlet (10out) and then to said joint line (15; 151) and then to said liquid inlet (501 in) to be pumped from said first pump (501) when the latter operates. 11. Pump station (3) according to the preceding claim characterized in that the used liquid pipe (10) has a mean inclination of between 10 ° and 50 ° with respect to a horizontal plane so that said spent liquid inlet ( 1 Oin) is located at a higher level than said spent liquid outlet (10out) along a vertical direction. Pump station (3) according to any one of Claims 10 to 11, characterized in that the spent liquid pipe (10) has a mean inclination of between 30 ° and 45 ° with respect to a horizontal plane so that said spent fluid inlet (10in) is located at a higher level than said spent liquid outlet (10out) along a vertical direction. 13. Pumping station (3) according to any one of claims 10 to 12 characterized in that: - said waste liquid pipe (10) is underground, and in that - said first pump (501) is found on the surface of the soil. A pumping area (8) comprising a pumping station (3) according to any one of claims 10 to 13 and a well (4), said spent liquid inlet (10in) of said spent liquid line (10). being in communication with the interior of said well (4). 15. A pumping area (8) according to the preceding claim characterized in that said well (4) is a pebble trap. 16. A method for pumping liquid from a spent liquid line (10) comprising a spent liquid inlet (10in) and a spent liquid outlet (10out) and configured so that said liquid is flowable said waste fluid inlet (10in) to said waste liquid outlet (10out) by gravity, said method comprising the steps of: - providing a first pump (501) for pumping said liquid, comprising a liquid inlet (501 in) to pump and an outlet (501 out) for pumped liquid; providing a junction conduit (15) comprising a first (15a) and a second (15b) end; - mechanically coupling said first end (15a) of said junction pipe (15) to said inlet (501 in) of said first pump (501) and mechanically coupling said second end (15b) of said junction pipe (15) to said discharging spent liquid (1 Oout) from said waste liquid line (10) so that said liquid inlet (501 in) to be pumped from said first pump (501) is connected to said spent liquid line (10) by intermediate of said junction pipe (15); said method being characterized in that said first pump (501) is a self-priming pump. 17. Method according to the preceding claim characterized in that said channel of spent liquid (10) is a subterranean pipe. 18. Method according to the preceding claim characterized in that said pipeline of waste liquid (10) underground is a channel for discharging spent liquid from a well (4). 19. Method according to the preceding claim characterized in that said well (4) is a pebble trap. 20. Method according to any one of claims 16 to 19 characterized in that said first pump (501) is controlled in the following manner: - when a liquid level to be pumped is equal to or greater than h1, start said first pump ( 501) and impose a pumping speed v1 ^ 0; - If said liquid level is greater than h2 <h1 but less than or equal to h1, impose said pump speed v1 to said first pump (501) if the latter is in operation; when said liquid level reaches h2 <h1, imposing a pumping rate v2 <v1 on said first pump (501) during a time interval ΔΤ, so that said liquid level is kept constant; after said time interval ΔΤ, imposing a pumping rate v3 on said first pump (501) so that said liquid level reaches a value h3 <h2; when said liquid level reaches h3 <h2, stop the first pump (501).