EP0390627A1 - Motor-pump unit with pressure and flow sensors - Google Patents

Abstract

A pump (1) with delivery pipework (2), a variable speed gear (4) causing the pump (1) to rotate and a start-stop circuit (7) for the variable speed gear (4), together with an analog pressure transducer (6) controlling the variable speed gear (4) and a flow transducer (5) controlling the start-stop circuit (7). <IMAGE>

Description

The present invention relates to pump units, whether intended to be immersed in a deep well or in a borehole or to be used at the surface.

In either case, the depth reached can be very large, a few meters for surface pumps to more than 150 meters in boreholes.

The height of the water in these wells and boreholes is very variable. It can rise to the surface in certain periods and descend again in others, practically at the level of the strainer of the pump. These variations can come from different origins: fluctuation of the water table or pump flow higher than the borehole supply. In any event, this variation, called tablecloth drawdown, poses difficulties in the operation of the submersible pump: discomfort in use and safety (risk of bursting of the devices), because this pressure induced by the rising phenomenon of water table is added to the pressure given by the pump.

This variation in pressure is very damaging for the user, because it imposes the need to provide pipes making it possible to accept these variations in pressure or even to use devices to reduce the pressure to a value compatible with its installation, which , in any case, is very expensive. In addition, operating a submersible pump generally requires a slaving device ensuring the starting and stopping of the group as needed.

In order to overcome the effects of rising groundwater in the borehole, different principles can be used.

- The simplest, if the rise in the water table is not very significant (a few meters to ten meters), is to provide an installation capable of withstanding the overpressure generated. This results in an additional cost of the installation and a lack of comfort in terms of use.

- For larger variations, it is possible to mount a pressure regulator at the drilling head which, by a hydraulic device, keeps the pressure close to a predetermined value. The device becomes particularly expensive when the flow rates to be checked are high. This device, using mechanical parts moving in the fluid, presents risks of deterioration or malfunction in the presence of sand in the water.

- Another solution still used consists in placing a discharge valve at the discharge of the pump which opens in the event of the pressure being exceeded, beyond a predefined point. This solution leads to a drop in the yield of the installation (part of the water being returned to the borehole), resulting in a significant energy expenditure.

- It is possible to limit the pressure at the installation level by using a regulating device consisting of a pressure tank installed on the discharge, associated with a regulating pressure switch. The pressure switch starts and stops the pump as needed. In this type of hydropneumatic operation, the stop of the pump is controlled by a pressure switch as soon as the predetermined pressure is reached, the restarting being done by the same pressure switch at a lower pressure.

• 1. Il nécessite un réservoir de forte capacité avec tampon d'air sous pression de manière à restituer automati­quement de l'eau, en cas de besoin, pour empêcher des batte­ments dommageables pour la pompe et qui sont dus au mode de fonctionnement suivant : si le débit d'utilisation devient inférieur à un débit minimum correspondant à une pression maximum détectée par le pressostat et à partir de laquelle il arrête la pompe, la durée pendant laquelle la pompe reste à l'arrêt est directement proportionnelle au volume du réser­voir. Si celui-ci est trop faible, la pression redevient très rapidement inférieure au seuil de mise en marche, ce qui crée des battements.
• 2. Il nécessite un contrôle fréquent des points de consigne du pressostat et dégonflage du tampon d'air. Si les points de consigne du pressostat deviennent trop proches, il se produit des battements. S'ils sont trop éloignés, la pompe ne s'arrête plus. Si la pression de gonflage de la réserve d'air, fournissant la pression nécessaire à l'expulsion de l'eau du réservoir, diminue, cela se traduit par une diminu­tion de la quantité d'eau restituée, qui devient insuffi­sante, tandis que si la pression augmente trop, il n'y a même plus de réserve d'eau.
• 3. La pression dans l'installation oscille entre deux valeurs, de sorte que l'utilisateur ressent, même en fonctionnement normal, des variations de pression qui sont désagréables, notamment dans les douches.

This device has three main drawbacks:

• 1. It requires a high capacity tank with a pressurized air buffer so as to automatically restore water, if necessary, to prevent beats damaging to the pump and which are due to the following operating mode: if the flow of use becomes lower than a minimum flow corresponding to a maximum pressure detected by the pressure switch and from which it stops the pump, the duration during which the pump remains stopped is directly proportional to the volume of the tank. If it is too low, the pressure very quickly falls back below the start threshold, which creates beats.
• 2. It requires frequent checking of the pressure switch set points and deflating the air buffer. If the pressure switch setpoints get too close, beats occur. If they are too far apart, the pump does not stop. If the inflation pressure of the air reserve, supplying the pressure necessary to expel water from the reservoir, decreases, this results in a reduction in the quantity of water returned, which becomes insufficient, while if the pressure increases too much, there is even no more water reserve.
• 3. The pressure in the installation oscillates between two values, so that the user feels, even in normal operation, pressure variations which are unpleasant, especially in showers.

The most rational solution consists in modifying the characteristics of the pump according to various parameters: (pressure, level, flow).

To modify the characteristics of the pump, it suffices to vary its rotation speed; for this, the motor is supplied by an electronic device making it possible to modify either the frequency of the current (in the case of a frequency variation), or the supply voltage (in the case of a dimmer). To do this, an analog pressure sensor (whose output signal varies proportionally with the pressure) detects the pressure in the pump discharge line and compares it to a set point. In the case where the value detected by the sensor is different from the reference value, a so-called PID processing circuit modifies the speed of the motor, in order to permanently return to the reference setpoint. In this principle, standard devices are used (frequency converter, analog sensor, PID measurement center) but which are very expensive and require great skill, because they are difficult to adjust. (Pumps, Pompes, Pumpen n ° 10 October 1984 Morden GB p 361 to 366; E Stygar: the use of electronics in centrifugal pumps). A motor inverter is not started there when the flow exceeds a given threshold.

U.S. 2,741,986 describes the commissioning of multiple cascade pumps. It is a mano-flow regulation, where the commissioning of an additional pump by flow is controlled. It is not a question of protecting the pump against operation at zero flow (without water).

The invention overcomes these drawbacks by a pump unit which, without maintaining the pressure in the constant installation, keeps it at a sufficiently low value so as not to damage it even in the case of a rise in the water table, without oversizing. of the installation, without loss of efficiency, without using complicated and mobile equipment, difficult to operate and maintain and liable to cause unpleasant beats and pressure variations.

The subject of the invention is therefore a motor pump group comprising a pump with discharge pipe, a variable speed drive driving the pump an on-off circuit of the variable speed drive, an analog pressure sensor, detecting the pressure prevailing in the discharge pipe and com controlling the variable speed drive as a function of this pressure and a flow sensor. According to the invention, the flow sensor is arranged to detect a minimum threshold for the flow of the fluid passing through the discharge piping and to control the on-off circuit so as to put it in the on position only when the flow becomes above this threshold.

If the pressure in the discharge piping increases, for example following a rise in the water table, the analog pressure sensor controls Consequently, the variable speed drive and, by decreasing the speed of rotation of the pump, tends to decrease the pressure. However, since the on-off circuit is controlled by the flow sensor, the beats are eliminated. In addition, the flow sensor and analog pressure sensor do not have to be set to very strict set points. A drift in time of these devices only results in an insignificant displacement of the operating point of the pump set, without bringing any discomfort to the user.

According to an advantageous embodiment, the analog pressure sensor controls the variable speed drive via a pressure-voltage or pressure-current transducer, transforming the pressure characteristic into a transformed characteristic, in voltage or in current, according to a law of prescribed processing, which is not proportional. In particular, the transformed characteristic corresponds to a pressure-flow characteristic of the pump set passing, on the one hand, through the point of the operated part of the actual pressure-flow characteristic of the pump group having the lowest pressure and, from on the other hand, by the point of zero flow having the same ordinate as the point of the operated part of the real pressure-flow characteristic of the pump unit having the higher pressure. Thanks to this transform, it is possible to get rid of the real pressure-flow curve of the pump, at least to carry out the control of the variable speed drive, and to substitute for this real curve an artificial curve which one conforms as best as possible. which is desired for operation. In particular, it is easy to give this transformed curve extreme ordinates of pressure value in the graph representing the variations of the pressure as a function of the flow rate, less distant than before, so that the user feels less variations in pressure. It is also possible to give the initial part of the characteristic curve from the ordinate axis a sensi completely parallel to the flow axis, so that, at the start when you open a tap, you very quickly obtain a large variation in flow for practically the same pressure, whereas it was there precisely, before, that the variations pressure were felt most.

According to one embodiment, the pressure sensor controls, by means of a pressure-voltage or pressure-current transducer, called a low pressure transducer and transforming a pressure below a first given threshold into a temporary signal, the on-off so as to put it in the on position when the pressure drops below this first given threshold.

The pressure sensor can also control, via a pressure-voltage or pressure-current transducer called overpressure transducer, and transforming a pressure above a second given threshold into a permanent signal, the on-off circuit, so as to put it in the stop position when the pressure becomes greater than this second given threshold, called the overpressure threshold. This provides security in the event of accidental overpressure.

According to a preferred embodiment, the output of the low pressure transducer is connected to the first input of an OR gate, the other input of which is connected to the output of a flow-current or flow-voltage transducer of the flow sensor and whose output is connected to the first input of an OU.EX gate whose second input is connected to the output of the overpressure transducer and whose output is connected to the on-off circuit. Protection against an incident is thus advantageously combined with the normal operating mode.

Preferably, a timer is inserted between the output of the low pressure transducer and the first input of the OR gate so that the pump has time to ensure a flow rate. Otherwise, there is an anomaly and the on-off circuit of the pump stops the pump. We also provides a timer interposed between the output of the transducer of the flow sensor and the second input of the OR gate, so as to ensure a certain duration of operation of the engine and to prevent beating. Even if the pressurized water reserve system deregulates, this timer limits the beating.

• la figure 1 est une schéma synoptique du groupe motopompe suivant l'invention ;
• la figure 2 est une graphique représentant la courbe réelle de la pompe (courbe I) et la courbe transformée (courbe II), les débits en m³ à l'heure étant portés en abs­cisses et les hauteurs manométriques totales en mètre étant portées en ordonnées ;
• la figure 3 est un graphique représentant la varia­tion de la tension de sortie du capteur analogique de pres­sion, en fonction de la pression régnant dans la tuyauterie de refoulement ; et
• la figure 4 est un graphique représentant la varia­tion de la tension à la sortie de l'amplificateur de bande proportionnelle en fonction de la pression régnant dans la tuyauterie de refoulement.

In the attached drawing, given solely by way of example:

• Figure 1 is a block diagram of the pump unit according to the invention;
• FIG. 2 is a graph representing the real curve of the pump (curve I) and the transformed curve (curve II), the flow rates in m³ per hour being plotted on the abscissa and the total head in meters being plotted on the ordinate;
• FIG. 3 is a graph showing the variation of the output voltage of the analog pressure sensor, as a function of the pressure prevailing in the discharge pipe; and
• FIG. 4 is a graph showing the variation of the voltage at the output of the proportional band amplifier as a function of the pressure prevailing in the discharge pipe.

Referring to Figure 1, a centrifugal pump 1 has a discharge line 2 comprising a bypass a buffer tank 3. The pump 1 is rotated by a variable speed drive 4. On the discharge line 2 is mounted a sensor flow 5 and an analog pressure sensor 6. The variable speed drive 5 is started or stopped by an on-off circuit 7.

The analog pressure sensor 6 is connected to a proportional band amplifier 8 by a conductor 9, to a low pressure transducer 10, by means of a conductor 11, and to an overpressure transducer 12 by a conductor 13. The propor band amplifier output tional 8 is connected by a conductor 14 to the variable speed drive 4. The output of the low pressure transducer 10 is connected, via a conductor 15 and a timer 16, to the first input 17 of an OR gate 18. The output 19 of the OR gate is connected, by a conductor 20, to a first input 21 of an OU.EX gate 22. The output 23 of the OU.EX gate is connected, by a conductor 24, to the control circuit on / off 7.

The flow sensor 5 comprises a transducer 25, the output of which is connected by a conductor 26 and by a timer 27 to the second input 28 of the OR gate 18.

The output of the overpressure transducer 12 is connected by a conductor 29 to the second input 30 of the OU.EX gate 22.

The operation of the pump set according to the invention will now be described, first assuming that the valve 31 mounted at the end of the discharge pipe 2 is closed. The pressure prevailing in this discharge pipe 2 is equal to Ho on the graph in FIG. 2. The pump 1 is stopped.

The tap 31 is opened. The capacity 3 of very small volume, for example of a volume of 1 liter, and which is intended simply to ensure that the outlet valve of the pump 1 is kept closed, restores a very small volume of water in the discharge pipe 2. The pressure in the discharge pipe 2 drops to the value H1 in FIG. 2 which constitutes a low pressure threshold. The pressure sensor 6 detects the pressure prevailing in the discharge pipe 2 and transforms it into an electrical voltage, in accordance with the curve in FIG. 3. Via the conductor 11, this voltage is sent to the low pressure transducer 10 which emits a signal limited in time by the timer 16 and entering the OR gate 18 by the input 17. This signal puts at state 1, by the conductor 20, the input 21 of the gate OU.EX 22 and, as entrance 30 from the door OU.EX 22 is in the zero state, the output 23 of the OU.EX 22 gate is in the state 1 and transmits the signal to the on-off circuit 7, by the driver 24. The on-off circuit controls the start-up of the variable speed drive 4 and therefore of the pump 1. Water arrives in the discharge pipe 2. The flow sensor 5 detects that the flow exceeds a given threshold. By its transducer 25, the conductor 26 and the timer 27, it sends a signal to the input 28 of the OR gate. This signal arrives, passing through the output 19, the conductor 20, the input 21, the output 23 and the conductor 24, to the on-off circuit 7. This therefore keeps the variable speed drive 4 in operation, the signal arriving at input 28 of OR gate 18 thus taking over from the temporary signal arriving at input 17 of OR gate 18. At the same time, the pressure sensor 6 detects a new higher pressure in the discharge piping 2. Via the conductor 9, it sends this voltage to the input of the proportional band amplifier 8, which outputs a voltage in accordance with the curve in FIG. 4. It will be noted that the curve in FIG. 4 is the curve transformed from that of FIG. 3, according to a law which is not proportional and in particular that it comprises an initial plateau A between 0 and 3 bar and a terminal plateau B between 6 and 10 bar, with a proportional variation between the two trays. This transformed voltage is sent, by the conductor 14, to the variable speed drive 4 which thus sees not a voltage proportional to the pressure detected by the pressure sensor 6, but a transformed voltage corresponding to the pressure which it is desired to obtain in the discharge pipe 2. The variable speed drive 4 consequently controls the speed of rotation of the pump 1 and thus establishes an HF pressure in FIG. 2 corresponding to an operating point at the intersection E of the transformed curve II and of the pressure drop curve III of the installation.

We now assume that we close the tap 31. The pressure in the discharge pipe 2 increases along the curve E Ho in Figure 2. When we reach the intersection, in Figure 2, of the curve EHo and the minimum flow threshold represented by the right X, X ′ in FIG. 2 and detected by the flow sensor 5, this will send by its transducer 25, by the conductor 26 and by the timer 27, a stop signal putting the input 28 of the door OR 18 in the zero state, provided that the delay time defined by the timer 27 has elapsed in order to avoid beating. As the temporary signal has disappeared and input 17 is at zero state, and since input 28 is at zero state, output 20 of OR gate 18 is at zero state. This state is transmitted to the input 21 of the OU.EX gate 22. As this same state prevails at the input 30 of the gate 22, the zero state reigns at the output 23 of the OU.EX gate 22 and the start-stop circuit 7 gives a stop command to the variable speed drive 4. Pump 1 stops. We found the initial state.

We now assume that tap 31 is opened again, but then the water table has risen. It is seen that due to the proportional band amplifier 8, the pressure prevailing in the discharge pipe 2, will always be governed by the transformed curve of FIG. 4 and may never exceed a prescribed limit.

We now assume that there is an accidental overpressure in the discharge pipe 2 due for example to a water hammer. The pressure sensor 6 detects this pressure and transforms it into a voltage which is conveyed, by the conductor 13, to the overpressure transducer 12 which, by the conductor 29, puts the input 30 of the OU.EX gate 22 to the state 1. If, at this instant, the pump 1 is operating, the input 21 of the gate OU.EX 22 is also in state 1. Like the two inputs 21 and 30 of the gate OU.EX 22 are both in state 1, the door 22 is not passing and controls, by the driver 24, the on-off circuit 7 so that the latter stops the variable speed drive 4, and therefore pump 1.

It is now assumed that, by accident, the pump 1 operates, while the valve 31 is open, but that the pump does not deliver water. The flow sensor 5 finds that the flow, in the discharge piping 2, is less than the only one defined by XX ′ in FIG. 2. By the transducer 25, the conductor 26 and the timer 27, it puts the input 28 of the OR gate 18 in the zero state and therefore does not validate the temporary start command issued by the transducer 10. The input 21 of the OU.EX gate 22 is thus set to the zero state by the conductor 20. Since the input 30 is also in the zero state since there is no overpressure, the OU.EX gate 22 is not passing. The on-off circuit 7 is not energized and gives a stop command to the variable speed drive 4. The pump 1 stops.

Claims (8)

1. Pump unit comprising a pump (1) with discharge piping (2), a variable speed drive (4) driving the pump (1), an on-off circuit (7) of the variable speed drive (4), an analog pressure sensor (6) detecting the pressure prevailing in the discharge pipe (2) and controlling the variable speed drive (4) as a function of this pressure, and a flow sensor (5), because in that the flow sensor (5) is arranged to detect a minimum threshold for the flow of the fluid passing through the discharge pipe (2) and to control the on-off circuit (7) so as to put it in the on position only when the flow becomes greater than this threshold. 2. Pump unit according to claim 1, characterized in that the analog pressure sensor (6) controls the variable speed drive (4) via a pressure-voltage or pressure-current transducer (8), transforming the characteristic of pressure and a characteristic transformed into voltage or current, according to a prescribed transformation law which is not proportional. 3. Pump unit according to claim 2, characterized in that the transformed characteristic corresponds to a pressure-flow characteristic of the motor-pump group, passing on the one hand through the point of the operated part of the real pressure-flow characteristic of the motor-pump group having the lowest pressure (H1) and, on the other hand, by the point (Ho) of zero flow having the same ordinate as the point of the operated part of the actual pressure-flow characteristic of the pump unit with the highest pressure. 4. Pump unit according to claim 1, 2 or 3, characterized in that the pressure sensor (6) controls, by means of a pressure-voltage or pressure-current transducer (10), designated by transducer low pressure and transforming a pressure below a first given threshold into a temporary signal, the on-off circuit (7), so as to put it in the on position when the pressure becomes lower than this first given threshold. 5. Pump unit according to one of claims 1 to 4, characterized in that the pressure sensor controls, by means of a pressure-voltage or pressure-current transducer (12), designated by overpressure transducer and transforming a pressure greater than a second threshold given as a permanent signal, the on-off circuit (7) so as to put it in the stop position when the pressure becomes greater than this second given threshold. 6. Pump unit according to claim 4, characterized in that the output of the low pressure transducer (10) is connected to the first input (17) of an OR gate (18) whose other input (28) is connected to the output of a flow-current or flow-voltage transducer (25) of the flow sensor (5), and the output (19) of which is connected to the first input (21) of an OU.EX gate (22) whose second input (30) is connected to the output of the overpressure transducer (12) and whose output (23) is connected to the on-off circuit (7). 7. Pump unit according to one of claims 4 to 6, characterized by a timer (16) interposed between the output of the low pressure transducer (10) and the first input (17) of the OR gate (18). 8. Group according to one of claims 4 to 7, characterized in that the pressure sensor controls, by means of a pressure-tension transducer (12) or pressure-current designated by overpressure transducer, and transforming a pressure above a second given threshold into a permanent signal, the on-off circuit (7) so as to put it in the stop position when the pressure becomes higher than this second threshold given.

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