EP3475579B1

EP3475579B1 - Electric pump with explosion-proof leak detector

Info

Publication number: EP3475579B1
Application number: EP17751833.9A
Authority: EP
Inventors: Antonio Gambigliani Zoccoli; Christian Muzzioli
Original assignee: Caprari SpA
Current assignee: Caprari SpA
Priority date: 2016-06-24
Filing date: 2017-06-26
Publication date: 2020-03-18
Anticipated expiration: 2037-06-26
Also published as: DK3475579T3; EP3475579A1; WO2017221217A1; ITUA20164654A1

Description

Technical Field

The present invention concerns an electric pump.

Background Art

It has been known that for transporting fluids from a first height to a second height, higher than the first, pump members are used, of the centrifugal pump type. Centrifugal pumps usually comprise one or more pump stages predisposed to be traversed by the fluid to be transported, each comprising an impeller and a diffuser member suitably mounted on a shaft, so-called "pump shaft", and inserted inside a containment cover.
In particular, it is known the use of centrifugal pumps for transporting waste fluids, such as sewage, waste water or industrial fluids, which are usually dispersions of a solid part, for example sand or scraps, in a liquid part, generally aqueous.
This type of centrifugal pumps is generally installed in wells or collection tanks, totally or partially immersed, so as to automatically activate when the liquid reaches a certain level.
Thus, such pumping members, which are usually installed with the longitudinal axis oriented vertically, have a suction portion arranged at the bottom, not flanged, and a discharge portion arranged peripherally, provided with a flange for connection with the discharge or conveying pipes.
In particular, such pumping members or electric pumps are provided with an electric part comprising a motor member, usually in air, of a hydraulic part comprising at least one pumping stage, and an oil chamber, for example interposed between the electric part and the hydraulic part, for cooling in particular the motor assembly.
For the safety of the operation of such electric pumps, it is important to preserve the motor member from the risk of pumping liquid leakage coming from the hydraulic part. To this end, the electric pumps usually provide for the installation of a pair of sealing means, preferably mechanic, each comprising respective sliding surfaces, interposed between components being in relative motion. More precisely, first sealing means are arranged between the hydraulic part and the above-mentioned oil chamber, while second sealing means are provided between the same chamber and the electric part.
In order to ensure the safety of the pump and to signal any faults of the sealing means, which may cause a pumping fluid leakage towards the electric part, the electric pumps generally include a detection probe, powered by a specific power supply member, preferably a low-voltage one, inserted in a respective electric circuit.
The aforesaid detection device is intended to signal the presence of water, generally present in the pumping liquid, or, more precisely, of the salts contained therein. The detection probe is preferably, where possible, inserted inside the oil chamber, to allow signalling the possible fault of the first sealing means and thus preventing the fault, more critical, of the second sealing means.
In practice, after exceeding a certain concentration value of the pumping liquid salts, inside the oil chamber, the cooling fluid becomes conductive, thereby activating the detection member, which detects the presence of an electric current in the circuit in which it is inserted.
The onset of an electric current detected by the detection member is therefore indicative of a fault at the first sealing means. The subsequent signal therefore enables an effective maintenance of the failing sealing means before the pumped fluid arrives inside the motor assembly, due to the presence of the second sealing means.
A detection member is for example illustrated in U.S. patent No. 3,949,389 , which describes a moisture detector device that is present in an insulating medium. A sensor containing two electrodes, the first of which has a flat surface, and the second of which has a cone-shaped surface with the vertex directed towards the flat surface, is immersed in an emulsion of water and oil. A pulsating voltage is applied to the first electrode, thus producing a static electrical load that rejects the insulating medium while having no effect on the conductive medium, causing migration and accumulation of drops of the conductive medium towards the area interposed between the electrodes. When a sufficient number of liquid drops are accumulated, a conductive path is formed between the electrodes, causing the output of an alarm signal by the probe.
However, in some applications, the positioning of the aforesaid detection probe inside the oil chamber, which is very advantageous for the pump safety as it allows for preventive maintenance, has considerable risks. This is the case, for example, wherein the pumping liquid has a high concentration of potentially explosive gas, such as biogas, and there is therefore a risk that an explosive phenomenon may be triggered by the generation of sparks in the well or collection tank where the electric pump is installed.
In such cases, a specific type of explosion-proof pump design must be provided, which means that in the event of a spark ignition, the confinement of the explosion inside the pump is ensured.
Pumps operating under such conditions must pass certain tests to be explosion-proof certified. Such tests must be able to ascertain that, in the presence of sparks, which may be generated, in particular, in the detection probe area, the casing may control propagation of the explosive phenomenon, by extinguishing it.
To ensure an explosion-proof behaviour, the known solutions currently provide for arranging, more prudently, the detection probe beyond the second sealing means, thus directly within the portion of casing containing the motor member. This arrangement thus does not allow signalling in advance any malfunctioning of the first sealing means, but can only signal possible leakage of the pumped liquid when this, as it is already present in the chamber containing the electric motor member, can actually damage it.
Therefore, the known explosion-proof solutions do not actually allow pre-maintenance of the sealing system, but can only intervene when the first damages on the electrical part have already been produced.
Patent application DE 19711185 discloses an electric pump in which a leakage monitoring system is provided, comprising a pair of electrodes inserted inside a seat obtained in a wall separating the motor housing from the lubricant liquid chamber. A membrane filled with an electrolyte defines a chamber placed in communication, through a plurality of holes acting as flame arresters, with said electrode housing seat.
EP 2489880 discloses an explosion-proof, pressure-tight connector, applicable to a pump of the so-called "canned" type, through an attachment that can be arranged outside the pump body.
Known solutions, however, do not fully meet the needs of the field, to ensure an effective explosion-proof behaviour in any condition of use.
In addition, such known solutions represent very complex and expensive systems.

Disclosure

The task of the present invention is to solve the aforementioned problems, devising an electric pump having reliable functioning, allowing a reliable pre-maintenance of the sealing system in any installation environment.
Within such task, it is a further scope of the present invention to provide an electric pump provided with effective explosion-proof behaviour.
A further scope of the invention is to provide an electric pump with a simple constructive and functional design, provided with surely reliable functioning, as well as relatively economic cost.
The cited scopes are reached, according to the present invention, by the electric pump according to claim 1.
The electric pump according to the invention comprises a motor shaft, also called pump shaft, having a longitudinal axis, a motor member contained inside a chamber in air and fixed to the above-mentioned pump shaft, to drive in rotation the same motor shaft about the cited longitudinal axis. The electric pump comprises at least one pumping stage comprising an impeller fixed to the pump shaft and a diffuser member fixed relative to the impeller, to pump a pumping liquid from a suction portion to a discharge portion of the electric pump.
The electric pump comprises as well a collection chamber, for collecting possible leakage coming from the pumping stage, as well as a detection device inserted inside the above-mentioned collection chamber, for detecting the presence of such possible leakage of pumping liquid.
The collection chamber is interposed between the hydraulic assembly, comprising at least one pumping stage of the pump, and the electric actuation assembly, comprising the motor member.
A feature of the invention is that the detection assembly comprises a detection device for detecting the presence of the pumping liquid and a protection device, associated with the aforesaid detection device, resistant to flame propagation, predisposed to ensure an explosion-proof behaviour, thus retaining a possible flame front, which could develop at the detection device, inside the collection chamber.
In other words, the protection device is able of limit any combustion process occurring accidentally inside the collection chamber, thus extinguishing the flames that can be generated after the trigger of a first spark. This trigger phenomenon can occur when the environment of the collection chamber becomes conductive, for example if a given concentration of salts is reached in the collected liquid in the collection chamber, and an electrical current is generated being detectable by the detection device.
In practice, the above-mentioned protection device preferably comprises at least one flame arrester element, capable of causing a flame front to be switched off.
The flame arrester element is therefore an effective barrier to the propagation of a fire that can be developed within a pump, and therefore to the development of an explosion.
The flame arrester element is advantageously made up of a body that is capable of stopping the propagation of a possible fire.
The flame arrester element is advantageously permeable to the liquid to be detected, so as to permit direct detection by the detection device.
Such flame arrester element is preferably made up of one or more portions of metal net or suitably sintered and/or pressed powder, shaping in its inside a plurality of discontinuous ducts, having a relatively reduced cross-section, thereby hindering the propagation of a possible flame front, gradually lowering the temperature thereof. Such thermal effect effectively stops the flame front, slowing down it and preventing its propagation beyond the flame arrester element itself.
Preferably, the detection device is a conductivity probe of known type inserted inside a suitable seat in the collection chamber.
Advantageously, the collection chamber in which the detection device is inserted is the same containment chamber of the cooling liquid, provided in the electric pump.
In this case, the detection assembly according to the invention enables the carry out the pre-maintenance of the sealing system of the electric pump with a high degree of safety, even in potentially explosive environments. In fact, the assembly can then signal the fault of the sealing means placed immediately downstream of the hydraulic part, which constitute the first safety barrier of the electric part. In particular, it can signal such a fault before the possible fault of the barriers, that is, of the sealing means, placed immediately upstream of the electric part, that means in a most critical position for the safety of the electric pump.
According to a particular aspect of the invention, it is possible to provide for said probe to be arranged in said seat by interposing a respective perforated cap, predisposed to reduce the cross-section of the seat itself and hence the passage of a possible flame front.
The flame arrester element can advantageously and easily be inserted inside a detection duct.
The detection duct can be usefully obtained in the collection chamber so as to be arranged in communication with the sensitive portion of the detection device, on one side, and, on the other side with the inside of the same collection chamber, in such a way as to circumscribe as much as possible the detection circuit of the detection device, which represents the area being most at risk of explosion.
The functionality of the detection device is made possible by the fact that the flame arrester element is permeable both to a possible flame front, and to the pumping liquid and eventually to the mixture of pump liquid and cooling fluid.
The detection duct is preferably obtained in a cooling fin provided by the containment box of the cooling fluid.
The protection device may comprise a plurality of flame arrester elements, preferably a pair, arranged in series in said detection duct.

Description of Drawings

Details of the invention shall be more apparent from the detailed description of a preferred embodiment of the electric pump according to the invention, illustrated for indicative purposes in the attached drawings, wherein:

Figure 1 shows a cross-sectional axial view of an electric pump according to the invention;
Figures 2 and 3 respectively show a cross-sectional axial and perspective view of a portion of the same electric pump;
Figures 4 and 5 respectively show a cross-sectional axial and perspective view of a component used in the electric pump according to the invention.

Best Mode

With particular reference to such Figures, the electric pump predisposed to pump a pumping liquid, for example an industrial liquid or waste water, from an inlet or suction portion 2 to an outlet or discharge portion 3 through at least one pumping stage 4, is indicated in its entirety with 1.
The electric pump 1 has a longitudinal axis A that, in the case shown for indicative purpose, is predisposed for a vertical installation. As an alternative, the electric pump 1 can be installed with longitudinal, horizontal or differently inclined axis A.
The electric pump 1 is provided with an electric actuation assembly 5 comprising a motor member 6, and a hydraulic assembly 7, comprising the cited pumping stage 4, the suction portion 2 and the discharge portion 3 of the pumped liquid. The motor member 6 comprises a motor shaft also called pump shaft 8 arranged according the longitudinal axis A to operate the pumping stage 4. In particular, the pumping stage 4 comprises an impeller 9 fixed to the pump shaft 8 for transferring the pumping liquid aspirated from the suction portion 2 to the discharge portion 3.
The actuation assembly 5 comprises a casing 51 inside which the motor member 6 is contained, arranged according to the longitudinal axis A.
The hydraulic assembly 7 comprises a fixed body 71 shaping the diffuser member, inside which the impeller 9 is housed, to perform the transfer of the pumping liquid.
The electric pump 1 also comprises a containment body 10 for a cooling fluid, for example oil, predisposed to be conveyed to the actuation assembly 5, through a suitable circuit 11, to ensure the continuous cooling thereof during functioning.
The electric pump 1 further comprises a sealing system 20, intended to prevent the pumping liquid to reach the inside of the casing 51 containing the motor member 6 and a detection assembly 30 intended to detect possible faults of the sealing system 20.
The sealing system 20 preferably comprises first sealing means 21, for example of mechanic type, interposed between the hydraulic assembly 7 and the containment body 10, and second sealing means 22, also for example of mechanic type, interposed between the containment body 10 and the motor assembly 5.
In addition to the cited first and second sealing means, the sealing system 20 can comprise further sealing means to optimize the barrier function against pump fluid leakage that can reach the motor member 6.
The detection assembly 30 comprises a detection device 31, arranged inside a detection chamber, preferably coinciding with the same containment body 10 of the cooling fluid, and a protection device 32 associated with the detection device 31, to ensure, in particular to the detection assembly 30, an explosion-proof behaviour.
As an alternative, the detection device 31 can be arranged inside a separated collection chamber, for example, superimposed to the containment body 10 and normally empty, thus a "dry" installation, instead of, as in the case of installation inside the containment body 10, usually filled, at least partially, with cooling fluid.
More precisely, the detection device 31 is preferably made up of a conductivity sensitive probe. The probe 31 is fed by an electric supply member, preferably a low-voltage one, for simplicity not shown in the figures, and inserted inside an electric circuit, connected preferably with the grounding system of the same electric pump 1.
Therefore, in the event that, due to fault of the sealing system 20, the pumping fluid, which generally includes water, reaches the inside of the detection chamber 10, the sealing member 31 registers the conductivity acquired by the collected liquid and reports the fault of the control unit of the electric pump 1, thus allowing the maintenance required to restore the functionality.
The probe 31 is advantageously arranged inside the containment body 10, so that it is able to signal a fault of the first sealing means 21, while the second sealing means 22, or the sealing means arranged upstream of the actuation assembly 5, are supposedly functioning and not yet reached by considerable flow of pumping liquid from the hydraulic part (see Figure 1).
Moreover, the probe 31 is preferably axially inserted inside a respective seat 33 obtained in the collection chamber, i.e., in the non-limiting example illustrated is obtained in the containment body 10.
For example, the containment body 10 can comprise a plurality of radial fins 34 predisposed to ease the cooling of the same body, in which it is possible to realize the above-mentioned seat 33, preferably in the thickness of a respective fin 34 (see Figures 2 and 3).
Moreover, it is possible to provide a perforated cap 35 for insertion of the probe 31, interposed between the probe 31 itself and the seat 33 (see Figures 4 and 5). The cap 35 serves to reduce the probe 31 insertion space, which also represents the passage portion for a possible flame front.
The protection device 32 is made up of a flame arrester or filter element, which is able to stop, if any, a flame front.
The filter 32 is preferably made up of one or more portions of metal net or suitably sintered and/or pressed powder portions, for example cylindrical, so as to shape in its inside a plurality of discontinuous ducts, having a relatively small cross-section, which hinder the propagation of a possible flame front, gradually lowering the temperature. This thermal effect stops the flame front, preventing its propagation beyond the flame arrester element itself, thus acting as an effective explosion-proof barrier.
The filter 32 is preferably inserted inside a detection duct 36 communicating with the collection chamber 10 on one side and with the sensitive portion of the probe 31 (see, in particular, Figure 2), so as to further circumscribe the detection circuit of the probe 31, which represents the area with increased risk of explosion. This is made possible by the fact that the flame arrester element 32 inserted in the duct 36 is permeable not only to a possible flame front, with the extinguishing effect mentioned above, but also to the pumping liquid or to the mixture of the same liquid with the cooling fluid.
Preferably, the detection duct 36 is in communication with the sensitive portion of the probe 31, for example through a respective branch connected to the seat 33.
Preferably, the duct 36 is provided inside the collection chamber 10, radially along one or more fins 34 of the containment body 10.
It is also possible to advantageously provide a plurality of flame arrester elements or filters 32, for example a pair of filters 32, arranged in series inside the duct 36, to amplify the stopping action of such protection devices.
The functioning of the electric pump according to the invention can be understood from the preceding description.
At an initial stage, the electric pump 1 is started, this latter being installed in a collection tank to pump a pumping liquid, for example waste waters, through the operation of the motor member 6. The electric pump 1 can be installed with longitudinal, vertical or horizontal axis A, or otherwise, indifferently.
During operation of the electric pump 1, the motor member 6 is continuously cooled by the circulation of the cooling fluid present in the containment body 10.
In particular, during the normal operation, the electric pump 1 is capable of pumping the pumping liquid, from the suction portion 2 to the delivery portion 3, without the fluid reaching the motor member 6, due to the presence of the sealing system 20.
However, if a fault of the sealing system 20, in particular of the first sealing means 21, occurs, there is leakage of pumping liquid inside the containment body 10, which the detection assembly 30 is capable of detecting, before the fault causes damage to the motor assembly 5.
More specifically, the detection device 31 of the detection assembly 30, which can be advantageously inserted inside the same containment body 10 due to the presence of the protection device 32, can effectively detect the presence of pumping liquid, at the fault, preferably, of the first sealing means 21, which represent the first barrier of the motor assembly 6.
Upon the occurrence of the fault, the detection device 31 emits an alarm signal to the control unit of the electric pump 1 to indicate the need for preventive maintenance.
It is important to note that the presence of the protection device 32 allows, even in explosive environments, to place the detection device 31 between the hydraulic assembly 7 and the motor assembly 5 so as to permit timely detection of any faults of the sealing system 20, in particular the first sealing means 21, when further barriers are still presumed to be located upstream of the casing 51 containing the motor member 6.
In particular, while carrying out the tests imposed by the regulations in force to certify the explosion-proof behaviour of the electric pump 1, the at least one flame arrester or filter element 32 effectively acts as a barrier against propagation of a flame, intentionally developed inside the containment body 10.
In this condition, in fact, the filter 32 prevents propagation of the combustion reaction of explosive gas inside the body 10, gradually lowering the temperature until complete extinction.
In practice, the used materials as well as the size and shape may vary according to the needs.
The invention is defined by the appended claims. Should the technical characteristics mentioned in the claims be followed by reference signs, such reference signs were included for the sole purpose of increasing the understanding of the claims and thus they shall not be deemed limiting the scope of the element identified by such reference signs by way of example.

Claims

Electric pump comprising an electric actuation assembly (5), having an electric motor member (6) arranged inside a casing (51) and fixed to a motor shaft (8) having a longitudinal axis (A), to drive in rotation the same motor shaft (8) about said longitudinal axis (A), a hydraulic assembly (7), having at least one pumping stage (4) provided with an impeller (9) fixed to said motor shaft (8) and a fixed body shaping a diffuser member (71) fixed with respect to said impeller (9), to pump a pumping liquid from a suction portion (2) to a discharge portion (3) of said electric pump, a sealing system (20) interposed between said hydraulic assembly (7) and said electric actuation assembly (5) to prevent the suction of said pumping liquid inside said electric actuation assembly (5), further comprising a detection assembly (30) intended to detect possible faults of said sealing system (20), said detection assembly (30) comprising a detection device (31), placed inside a collection chamber (10) interposed between said hydraulic assembly (7) and said electric actuation assembly (5), predisposed to collect possible leakage of said pumping liquid coming from said hydraulic assembly (7), a protection device (32) associated with said detection device (31), comprising at least one flame arrester element (32) to ensure, in particular to said detection assembly (30) of said electric pump (1), an explosion-proof behaviour, and a detection duct (36) arranged in communication with the inside of said collection chamber (10) and with said detection device (31), said flame arrester element (32) shaping a body inserted inside said detection duct (36) between said inside of said collection chamber (10) and said detection device (31), said at least one flame arrester element (32) inserted in said detection duct (36) being permeable to said pumping liquid, so as to ensure direct detection of possible leakage of said pumping liquid from said hydraulic assembly (7) to said collection camber (10).
Electric pump according to claim 1, characterized in that said collection chamber (10) inside which is arranged said detection assembly (30) is predisposed between said hydraulic assembly (7) and said electric actuation assembly (5), to contain a cooling and/or lubricating fluid.
Electric pump according to claim 2, characterized in that said at least one flame arrester element (32) is of the type made by portions of metal net or pressed and/or sintered powder.
Electric pump according to claim 3, characterized in that said protection device (32) comprises a plurality of flame arrester elements (32) arranged in series inside said detection duct (36).
Electric pump according to one of claims 2 to 4, characterized in that said collection chamber (10) comprises at least one radial cooling fin (34) and in that said detection duct (36) in which said protection device (32) is inserted, is obtained in the thickness of said fin (34).
Electric pump according to claim 5, characterized in that said detection duct (36) extends, at least partially, in radial direction in said thickness of said at least one fin (34) of said collection chamber (10) predisposed to contain said cooling and/or lubricating fluid.
Electric pump according to one of the preceding claims, characterized in that said detection device (31) is inserted inside a seat (33) obtained in said collection chamber (10), through interposition of a respective perforated cap (35), to reduce the insertion cross-section of said detection device (31).
Electric pump according to claim 7, characterized in that said detection duct (36) is in communication with a sensitive portion of said detection device (31) through a respective branch connected with said seat (33).
Electric pump according to one of the preceding claims, characterized in that said detection device (31) is a conductivity probe.