GB2204153A

GB2204153A - Automatic water supplying device

Info

Publication number: GB2204153A
Application number: GB08807901A
Authority: GB
Inventors: Yasushi Shinko
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1987-04-06
Filing date: 1988-04-05
Publication date: 1988-11-02
Anticipated expiration: 2008-04-05
Also published as: HK51391A; GB2204153B; KR920003111B1; JPS63248997A; CN88101956A; KR880012895A; GB8807901D0; CN1012514B

Abstract

The device comprises a plurality of parallel-connected pumps (1). each having a motor (1a), pressure detecting means consisting of a high pressure tank (8) and a pressure switch (7), disposed on one of the pumps (1) on the discharging side thereof; a controlling section (9), which controls the drive of the pumps, receiving signals coming from this pressure detecting means (7, 8), and motor rotation detecting means (10), which detects the drive state of the motors (1a); and in which section (9) comprises a calculating portion (11a), which uses signals from means (10) immediately after the beginning of the single drive of the pumps (1) to form a parallel drive controlling value to obtain a constant quantity of supplied water; and a comparing portion (11b), which compares the signals from means (10) with the parallel drive controlling value to control the parallel drive of the pumps (1). <IMAGE>

Description

AUTOMATIC WATER SUPPLYING DEVICE AND METHOD FOR CONTROLLING SAME This invention relates to an automatic water supplying device and a method for controlling same and in particular to an automatic water supplying device, in which a plurality of pumps are connected in parallel, and a method for controlling same.

In this kind of prior art automatic water supplvina novices as shown jn Fia. 11 putts 1', eacb of which has a motor la', are connected in parallel; -a pressure tank 8' 5s connected with the pumps 1' on the discharaina sie t:-.- eof; pressure switches 7' are disposed on their discharging side; and a control section 9' is disposed, which section controls the start and the stop of the drive of te pumps, receiving signals from these pressure switches 7.

The operation of this automatic water supplying device will be explained, referring to Fig. 12. Fig. 12 is a graph showing pumping characteristics, in which the abscissa represents the quantity of supplied water Q and the ordinate the pressure H. H1 is a quantity of supplied water-pressure curve at the single drive, while H 1' is a quantity of supplied water-pressure curve at the parallel drive of the pumps 1. R1' and rl' are load curves of the pumps 1' at the parallel drive and the single drive, respectively.

When both of the pumps 1' in the figure are in the stopped state and water supply begins through cocks 6a', the pressure in the high pressure tank 8' is lowered to the single drive starting pressure Pon (point a' of H1'). At this time the pressure switch 7' is closed and the No. 1 pump 1' is driven alone. When the quantity of supplied water is reduced after the beginning of the drive and the pressure H1 rises to the single drive stopping pressure Poff (point b' of H1), the No. 1 pump 1' is stopped. When the quantity of supplied water increases after the beginning of the drive of the No. 1 pump 1' stated above and the pressure H1 is lowered to the parallel drive starting pressure Pon' (point c' of H1) for the motor la' of the No. 1 pump 1', the No. 2 pump 1' begins to be driven, following the first.The parallel drive of the pumps 1' is peffond at the intersection d' of their load curve R1' with the quantity of supplied waterpressure curve H, ' . In this state, when the quantity of supplied water Q through the cocks 6a' decreases and the pressure is lowered to the parallel drive removing pressure pouf', the drive of one of the pumps 1' is stopped and the single drive is performed (point f' of H11). Further e.g. JP-B-59-720 can be cited as a publication relating to this kind of devices.

However, by such a prior art automatic water supplying device and a method for controlling it, since the pressure on the discharging side of each of the pumps 1' was detected by a pressure switch 7' and the parallel drive was controlled by this pressure switch 7', it was not possible to control them, corresponding to the quantity of supplied water with a high precision. That is, immediately after the drive of the pumps 1' has been begun, the pressure on the discharging side of the pumps 1' can not follow variations in the real quantity of supplied water and it may be excessively reduced temporarily. Such a temporary pressure drop is apt to be produced, in particular in the case where the size of the high pressure tank 8' is reduced.When this temporary pressure drop is produced and the pressure is lowered to the parallel drive starting pressure Pox', the parallel drive of the pumps 1' is started. However, in reality, since no quantity of supplied water, which is so great that the parallel drive is required, is needed, the pressure reaches immediately to the parallel drive removing pressure Poff' and one of the pumps 1' is stopped. Thus the single drive is performed thereafter. In this single drive, if the quantity of supplied water remains as it is, the pressure drop is newly produced and the following pump 1' is driven. This operation is repeated, which produces chattering phenomena.

Further, in such an automatic water supplying device, no attention was pair for making the drive time of different pumps 1' uniform, when the parallel drive and the single drive of the pumps 1' are alternately repeated.

In addition, such an automatic water supplying device had another problem that the number of rotations varied because of variations in the voltage applied to the pump 1', which varied the quantity of supplied water.

A first automatic water supplying device according to this invention, in which a plurality of pumps, each of which has a motor, are connected in parallel; a high pressure tank is connected with the pumps on their discharging side; pressure detecting means is disposed on one of the pumps on the discharging side thereof; and further a controlling section is disposed, which section controls the drive of the pumps, receiving signals coming from this pressure detecting means; is characterized in that there is disposed motor detecting means, which detects the drive state of the motor; and the controlling section corpises a calculating portion, which carries out operations by using signals coming from the notor rotation detecting means immediately after the beginning of the single drive of the pumps to form a parallel drive controlling value; and a comparing portion, which compares the signals coming from the motor rotation detecting means with the parallel drive controlling value to control the parallel drive of the pumps.

A method for controlling an automatic water supplying device comprising a plurality of pumps, each of which has a motor, connected in parallel; a high pressure tank connected with the pumps on the discharging side thereof; pressure detecting means disposed on one of the pumps on their discharging side; motor rotation detecting means, which detects the drive state of the motor; and further a controlling section, which controls the drive of the pumps, receiving signals coming from this pressure detecting means; is characterized in that a parallel drive controlling value is calculated by using signals coming from the motor rotation detecting means immediately after having effected the beginning of the single drive of the pumps, receiving signals therefrom; and thereafter the parallel drive of the pumps is started, when a predetermined signals is obtained, comparing the signals coming from the motor rotation detecting means with the parallel drive controlling value without interruption.

A second automatic water supplying device according to this invention, which comprises a plurality of pumps, each of which has a motor, connected in parallel; a high pressure tank connected with the pumps on their discharging side; pressure detecting means disposed on one of the pumps on the discharging side thereof; and further a controlling section, which controls the drive of the pumps, receiving signals coming from this pressure detecting means; is characterized in that there is disposed motor rotation detecting means, which detects the drive state of the motor; and the controlling section comprises a calculating portion, which carries out operations by using signals coming from the motor rotation detecting means immediately after the beginning of the single drive of the pumps to form a parallel drive controlling value; a comparing portion, which compares the signals coming from the motor rotation detecting means with the parallel drive controlling value to control the parallel drive of the pumps; and a positioning portion, which controls the pumps so that they are used alternately at the single drive, when the single drive and the parallel drive of the pumps are repeated.

A third automatic water supplying device according to this invention, which comprises a plurality of pumps, each of which has a motor, connected in parallel; a high pressure tank connected with the pumps on their discharging side; pressure detecting means disposed on one of the pumps on the discharging side thereof; and further a controlling section, which controls the drive of the pumps, receiving signals coming from this pressure detecting means; is characterized in that there is disposed motor rotation detecting means, which detects the drive state of the motor; and the controlling section comprises a calculating portion, which carries out operations by using signals coming from the motor rotation detecting means immediately after the -beginning of the single drive of the pumps to form a parallel drive controlling value to obtain a constant quantity of supplied water; and a comparing portion, which compares the signals coming from the motor rotation detecting means with the parallel drive controlling value to control the parallel drive of the pumps.

According to such an automatic water supplying device and a controlling method therefor, the reference signal is constituted by a signal coming from the motor rotation detecting means responding with a higher precision to the quantity of supplied water with respect to the pressure and further the parallel drive controlling value calculated by using the signal from the motor rotation detecting means doesn't depend directly on the pressure on the discharging side of the pumps, but it can be set, corresponding to the quantity of supplied water.

In this way it is possible to control the parallel drive surely with a high precision, corresponding to the quantity of supplied water. Even if the size of the high pressure tank is reduced and a pressure drop, which doesn't correspond to the quantity of supplied water, is temporarily produced, the parallel drive of the pumps is not started.

Further, by using such an automatic water supplying device, since the pumps are used alternately at the single drive, when the parallel drive and the single drive are repeated, the operation time and the number of operations of the pumps are made uniform.

In addition, by using such an automatic water supplying device, since, even if the voltage applied to the motors of the pumps varies and as the result the number of rotations thereof varies, it is possible to maintain the quantity of supplied water constant, a stable quantity of supplied water can be obtained.

The invention will be described in detail with reference to the accompanying drawings, in which: Fig. 1 is a scheme illustrating the construction of an automatic water supplying device according to this invention; Fig. 2 is a circuit diagram of motor rotation detecting means used in the automatic water supplying device; Fig. 3 is a circuit diagram of an instruction controlling device used in the automatic water supplying device; Fig. 4 is a graph showing characteristics of the automatic water supplying device; Fig. 5 is a flow chart indicating the main routine of a method for controlling the automatic water supplying device; Fig. 6 is a flow chart indicating a working subroutine in the main routine; Fig. 7 is a flow chart indicating a parallel control subroutine in the main routine; Fig. 8 is a time chart indicating drive states of the automatic water supplying device;; Fig. 9 shows pumping characteristics for explaining the variation of the number of rotations of the pumps in the automatic water supplying device; Fig. 10 shows characteristics of the electric power at the parallel drive control in the pumping characteristics; Fig. 11 is a scheme illustrating the construction of a prior art automatic water supplying device; and Fig. 12 shows pumping characteristics of the automatic water supplying device indicated in Fig. 11.

Hereinbelow an embodiment of this invention will be explained, referring to Figs. 1 to 10. In Fig. 1, each of pumps 1 is constructed by coupling directly the rotating axis of a motor la with a rotor wheel (not shown in the figure) of the pumping portion ib. A sucking tube 4 is connected with the pump 1 on the sucking side. The lower extremity of this sucking tube 4 is dipped in water in a tank 3. The water in the tank 3 is separated from the water supply and stored in the tank 3. A discharging tube 5 is connected with the pump 1 on the discharging side. A valve 5a is disposed on the discharging tube 5.

Discharging tubes 5 are connected to a common tube 6. The extremity of the common tube 6 is divided into a plurality of tubes and a plurality of cocks 6a are mounted thereon (only 2 are indicated in Fig. 1). 2 pumps 1, each of which has a sucking tube 4 and a discharging tube 5, are mounted between the water in the tank 3 and the common tube 6 in parallel. The pumps 1 are driven either by the single drive or by the parallel drive, depending on the quantity of supplied water. A pressure switch 7 and a high pressure tank 8 constituting pressure detecting means are mounted on the discharging tube 5 of one of the pumps 1. The pressure detecting means may be a pressure sensor instead of the pressure switch 7.When water begins to be supplied through the cock 6a and water in the high pressure tank 8 is supplied, the pressure in the high pressure tank 8 is lowered and the pressure switch 7 is closed. The signal coming the pressure switch 7 is inputted in an instruction controlling portion 11 in a controlling section 9. The controlling section 9 includes an electric power detecting portion 10 constituting motor rotation detecting means, which detects the drive state of the motor la. This electric power detecting portion 10 detects the electric power of each of the motors la and the signal thus obtained is outputted to the instruction controlling portion 11.The instruction controlling section 11 is provided with a calculating portion lla effecting operations on the basis of a signal coming from the electric power detecting portion 10 immediately after the beginning the single drive of the pumps 1 to form a parallel drive controlling value, a comparing portion 10b comparing the parallel drive controlling value stated above with the signal coming from the electric power detecting portion 10 to control the parallel drive of the pumps 1, and a positioning portion llc controlling the pumps 1 so as to drive them alternately at the single drive, when the single drive and the parallel drive of the pumps are repeated. Signals from the instruction controlling section 11 are outputted to each of the motors la. The motor rotation detecting means may be a current detecting portion or a portion detecting the number of rotations instead of the electric power detecting portion 10.

In Fig. 2 the motors la are connected with a power source. 12 in parallel. Each of them is connected therewith through an electromagnetic contactor 13, 14. An electric power detecting section 10 is connected to each of the circuits between the electromagnetic contactor 13 and 14 and the power source 12. The electric power detecting portion 10 consists of a coil 15 connected in series to the power source circuit, a Hall element 16 connected in parallel thereto, and a rectifying-smoothing circuit 17 connected with the output of the Hall element 16. In this way an arbitrary electric power can be measured in the form of a DC voltage representing the electric power by using the multiplying effect of the Hall element 16. The outputs of two rectifying-smoothing circuits 17 are indicated by 0 and in Fig. 2.These and means that they are connected with and , , respectively, in Fig. 3. Each of the motors la includes a phase advancing condenser 18. Furthermore the electric power detecting portion 10 may be a current detecting portion.

In Fig. 3 an instruction controlling section 11 is constituted by an instruction controlling element 19 such as a microcomputer as the central element. The electric power source 12 is connected with VDD and Vss ports of the instruction controlling element 19 through a power transformer 20, a rectifying-smoothing circuit 21 and a constant voltage circuit 22. A clock circuit 23 forming a reference timer for the instruction controlling element 19 is connected therewith.

Coils 24 and 25 for opening and closing the electromagnetic contactor 13 and 14, respectively, are connected with the power source 12 through a l-circuit-3 contact switch 26 and one 7a of the contactors of the pressure switch 7.

The input to the instruction controlling element 19 is effected through ports Pl0, P40 and P41. The circuit including the other contactor 7b of the pressure switch 7 is connected with the port Pl0. The outputs ((awl and &commat; ) of the electric power detecting portions 10 of the motors are connected with the ports P40 and P41 through comparators 27 and 28, respectively. A D/A converter 29 converts digital values at port P30, P31, P32 and P33 into analogue values and generates voltages corresponding to electric powers to be judged, which are inputted in the comparators 27 and 28. The comparators 27 and 28 judge whether the outputs of the electric pover detecting portions of the motors la have arrived to predetermined values or not and input the results in ports P40 and P41, respectively.

The - side of a zero cross timing input circuit 30 is connected with the secondary side of the power transformer 20 and the other side is connected with a port INT of the instruction controlling element 19. Signals are outputted by the timing of the zero cross through the ports P20 and P21 in the instruction controlling element 19, which are connected with phototriacs 31 and 32. These phototriacs 31 and 32 drive triacs 33 and 34 serving as switching elements. The triacs 33 and 34 are connected with the contactors of the l-circuit-3-contact switch 26, to which the coils 24 and 25 are connected, respectively, in parallel thereto.By switching over the l-circuit-3contact switch 26, switching on and off of the coils 24 and 25 can be effected by opening and closing one 7a of the contactors in the pressure switch 7, independently of the instruction controlling signal coming from the instruction controlling element or even if there is no instruction controlling signal because of a trouble, etc.

The start and the stop of the pumps 1 are effected in this way.

The outline of the operation of such an automatic water supplying device will be explained below, referring to Fig. 4. Fig. 4 is a graph showing pumping characteristics, in which the abscissa represents the quantity of supplied water Q and the ordinate the pressure H and the electric power W. H1 is a quantity of supplied water-pressure curve at the single drive of the pumps 1, while H1, is a quantity of supplied water-pressure curve at the parallel drive of the pumps l. W1 is a quantity of supplied water-electric power curve of one of the pumps 1. R1 and rl are load curves of the pumps 1 at the parallel drive and at the single drive, respectively.

When both the pumps 1 are in the stopped state and water supply begins through the cocks 6a, the pressure in the high pressure tank 8 is lowered to the single drive starting pressure Pon (point a of H1). At this time the pressure switch 7 is closed and the No. l pump 1 is driven alone. When the quantity of supplied water is reduced after the beginning of the drive and the pressure H1 rises to the single drive stopping pressure Poff (point b of Hl), the No. l pump 1 is stopped.When the quantity of supplied water increases after the beginning of the drive of the No. l pump 1 stated above and the pressure H1 is lowered to the parallel drive starting pressure P on (point c of Hl) for the motor la of the No. 1 pump 1, the No. 2 pump 1 begins to be driven, following the first.The parallel drive of the pumps l is performed at the intersection of their load curve R1 with the quantity of supplied water-pressure curve H In this state, when the quantity of supplied water Q through the cocks 6a decreases and the electric power consumed by the motors la of the pumps 1 is lowered to the parallel drive removing pressure Pa NZoff, the drive of the preceding No. 1 pump l is stopped and the single drive is performed (point f of H1) by the No. 2 pump 1 alone.

Now a method for controlling such an automatic water supplying device will be explained, referring to Figs. 5 to 7. Fig. 5 shows the main routine. The procedure is started by switching-on the power source 12 and the initial setting is effected at first (Step 500).

This initial setting is effected by securing areas for parameters F, S and J in a random access memory on the instruction controlling element 19 and by setting F = 1, S = 0 and J = 0. F is a parameter for controlling the No. 1 pump; S is one for controlling the Lilo. 2 pump; and J is one for judging the parallel drive. Then, waiting that the pressure reaches the pressure Pon for the pressure switch 7 (Step 510), the procedure proceeds to a subroutine for driving the pumps 1 at that time (Step 520).

Fig. 6 shows the working subroutine. In the working subroutine it is judged at first whether the parameter F is equal to 1 (Step 600). In the case where F = 1, the No. l pump l is driven, preceding the other (Step 610). If F # 1, the No. 2 pump 1 is driven, preceding the other (Step 620). Immediately thereafter the electric power Sl consumed by the motor la of the driven pump 1 is detected (Step 630).The parallel drive starting electric power Won and the parallel drive removing electric power Woff are obtained by calculation on the basis of the electric power Wsl thus detected (Step 640) and the procedure returns to the main routine. It proceeds to the subroutine for the parallel drive (Step 530), after having returned once to the main routine.

Fig. 7 shows the parallel drive controlling subroutine. In the parallel drive subroutine the electric power W1 consumed by the motor la of the driven pump 1 is detected (Step 710). This electric power W1 is compared with the parallel drive starting electric power Won (Step 720). If Wl h Won, the pump 1 driven alone, preceding the other, is judged by using the parameter F (Step 730).

If the parameter F = 1, the No. 2 pump 1, which was not driven, is driven, following the other (Step 740). If F Z 1, the No. 1 pump 1, which was not driven, is driven, following the other (Step 750). After that, the parameter J is set to J = 1 (Step 760) in order to indicate that the pumps are in course of the parallel drive, and the procedure returns to the main routine. The detected electric power W5 of the motor la described above is compared with the set electric power Won (Step 720). If WS < Won, it is judged whether the parameter F = 1 or not. If J # 1 (in course of the single drive), the procedure returns to the main routine. If J = 1 (in course of the parallel drive), the detected electric power W1 is compared with the parallel drive removing electric power Woff (Step 771).If Wl > Woff, the procedure returns to the main routine and if W1 - Wofft the parameter F is judged (Step 772). If the parameter F = 1, the No. 1 pump 1, which was driven, preceding the other, is stopped (Step 773!. If F # 1, the No. 2 pump 1, which was driven, preceding the other, is stopped (Step 774). Next the state of the parameter F and the state of the parameter S are interchanged ("1" and "0" are inverted), i.e. the preceding and the following positionings are interchanged (Step 775). After that, the parameter J is set to J = 1, which indicates the parallel drive removing (Step 776), and the procedure returns to the main routine.

Then, in the main routine, waiting for the pressure Poff of the pressure switch 7 (Step 540), the procedure repeats the parallel drive controlling subroutine, until the pressure increases to Pouf. When the pressure reaches Pouf, the pump 1, which was in course of the drive, is stopped (Step 550). Next the state of the parameter F and the state of the parameter S are interchanged ("l" and "0" are inverted), i.e. the preceding and the following positionings are interchanged (Step 560). Thereafter the procedure waits for the pressure Pon of the pressure switch 70 (Step 510).

Fig. 8 is a time chart showing an example of the drive state of such an automatic water supplying device.

As it can be seen clearly from this figure, the drive time of the No. l pump and that of the No. 2 pump are well balanced.

By such a controlling method it will be explained, referring to Figs. 9 and 10, that the control is possible, even if the number of rotations of the motor la of the pump 1 varies. Fig. 9 is a graph showing pumping characteristics, in the case where the number of rotations of the motor la of the pump 1 varies, in which the abscissa indicates the quantity of supplied water Q and the ordinate represents the pressure H and the electric power W.H1 to H3 are quantity of supplied water-pressure characteristic curves for the single drive of the pumps 1, whose variation ratios of the number of rotations are nln, "0.95" and we.9", respectively, H1' to H3, are quantity of supplied water-pressure characteristic curves for the parallel drive of the pumps 1, whose variation ratios of the number of rotations are "1", "0.95" and no.9", respectively. W1 to W are quantity of supplied 3 water-electric power characteristic curves of the pumps 1, whose variation ratios of the number of rotations are "1", "0.95" and "0.9", respectively.R to R3 are load curves for which variation ratios of the number of rotation are nln, "0.95" and "0.9", respectively. rl is a load curve. It is supposed that the parallel drive starting electric power and the parallel drive removing electric power are represented by Wonl and Woffl, respectively, which can be obtained on the basis of the detected electric power Wsl, Wsl being the electric power of the motor la of the pump 1 immediately after the pump 1 has begun to be driven alone, when the pressure has been lowered to the single drive starting pressure Pon and the pressure switch 7 has been closed.The quantities of supplied water corresponding to these points be QS1' Qon and Toff. The parallel drive starting electric powers of W2 and W3 at a parallel drive starting quantity of supplied water Qon1 be Won2 and Won3, respec- tively, and the parallel drive removing electric powers of W2 and W3 at a parallel drive removing quantity of supplied water Qoff1 be Woff2 and Woff3, respectively.

Further the single drive starting electric powers of the pumps 1 at H2 and H3 be W52 and Ws3 respectively.

The relations between the detected electric powers Wsl, W52 and W53 of the motors la of the pumps 1 immediately after the single drive and the parallel drive starting electric powers Wool, WOn2 and or the parallel drive removing electric powers Woff1, Woff2 and Woof3 are linear, as indicated in Fig. 10, and they can be represented by the following equations: Won l S 2K2 ..... (1) Wolf= K3}ls + K4 (2) (K1 to K4 are constants) Consequently the parallel drive starting electric power Won and the parallel drive removing electric power Woff can be easily calculated by using the detected electric power Ws.

According to such an automatic water supplying device and such a method for controlling it, the reference signal is formed by the detected electric power W5 corresponding to the quantity of supplied water Q with a higher precision than the pressure, and in addition, the parallel drive starting electric power Won or the parallel drive removing electric power Vloff calculated by using this detected electric power W5 have no direct relation with the pressure on the discharging side, but they can be set, corresponding to the quantity of supplied water. In this way it is possible to control the start and the stop of the parallel drive surely with a high precision, corresponding to the quantity of supplied water Q. Even if the size of the high pressure tank 8 is reduced and pressure drop, which doesn't correspond to the quantity of supplied water, is produced temporarily, the parallel drive of the pumps 1 is not started.

Furthermore, according to such an automatic water supplying device, when the parallel drive and the single drive of the pumps 1 are repeated, since the two pumps 1 are driven alternately at the single drive, the drive time and the number of drives of the pumps 1 are made uniform.

Still further, according to such an automatic water supplying device, even if the voltage applied to the motors la of the pumps 1 varies and the number of rotations thereof, etc. change, since the quantity of supplied water by the pumps 1 can be maintained constant, it is possible to obtain a stable quantity of supplied water.

According to this invention, firstly it is possible to obtain an automatic water supplying device and a method for controlling it, which can control the parallel drive surely with a high precision, corresponding to the quantity of supplied water. Secondly it is possible to obtain an automatic water supplying device, which can further make the drive time and the number of drives of pumps uniform. Thirdly it is possible to obtain an automatic water supplying device capable of supply a more stable quantity of water.

Claims

CLAIMS:

1. An automatic water supplying device comprising: a plurality of pumps, each of which has a motor, connected in parallel; a high pressure tank connected with the pumps on their discharging side; pressure detecting means disposed on one of the pumps on the discharging side thereof; a controlling section, which controls the drive of the pumps, receiving signals coming from said pressure detecting means; and motor rotation detecting means, which detects the drive state of the motor; wherein said controlling section includes a calculating portion, which carries out operations by using signals coming from the motor rotation detecting means immediately after the beginning of the single drive of the pumps to form a parallel drive controlling value, and a comparing portion, which compares the signals coming from the motor rotation detecting means with the parallel drive controlling value to control the parallel drive of the pumps.

2. An automatic water supplying device according to Claim 1, wherein said pressure detecting means is constituted by a pressure switch.

3. An automatic water supplying device according to Claim 1, wherein said motor rotation detecting means is an electric power detecting portion, which detects the electric power consumed by said motor.

4. An automatic water supplying device according to Claim 1, wherein said controlling section includes a microcomputer.

5. An automatic water supplying device according to Claim 1, wherein said parallel drive controlling value is a parallel drive starting value.

6. An automatic water supplying device according to Claim 1, wherein said parallel drive controlling value consists of a parallel drive starting value and a parallel drive removing value.

7. An automatic water supplying device according to Claim 5 or 6, wherein said parallel drive starting value is a value corresponding to a quantity of supplied water, which is greater than that for the beginning of the single drive.

8. A method for controlling an automatic water supplying device consisting of a plurality of pumps, each of which has a motor, connected in parallel; a high pressure tank connected with the pumps on their discharging side; pressure detecting means disposed on one of the pumps on the discharging side thereof; motor rotation detecting means, which detects the drive state of the motor; and further a controlling section, which controls the drive of the pumps, receiving signals coming from this pressure detecting means; comprising the following steps of: calculating a parallel drive controlling value by using signals coming from the motor rotation detecting means immediately after having effected the beginning of the single drive of the pumps, receiving signals therefrom; and starting thereafter the parallel drive of the pumps, when a predetermined signal is obtained, comparing the signals coming from the motor rotation detecting means with the parallel drive controlling value without interruption.

9. An automatic water supplying device comprising: a plurality of pumps, each of which has a motor, connected in parallel; a high pressure tank connected with the pumps on their discharging side; pressure detecting means disposed on one of the pumps on the discharging side thereof; a controlling section, which controls the drive of the pumps, receiving signals coming from said pressure detecting means; and motor rotat-ion detecting means, which detects the drive state of the motor; wherein said controlling section includes a calculating portion, which carries out operations by using signals coming from the motor rotation detecting means immediately after the beginning of the single drive of the pumps to form a parallel drive controlling value, a comparing portion, which compares the signals coming from the motor rotation detecting means with the parallel drive controlling value to control the parallel drive of the pumps, and a positioning portion, which controls the pumps so that they are used alternately at the single drive, when the single drive and the parallel drive of the pumps are repeated.

10. An automatic water supplying device comprising: a plurality of pumps, each of which has a motor, connected in parallel; a high pressure tank connected with the pumps on their discharging side; pressure detecting means disposed on one of the pumps on the discharging side thereof; a controlling section, which controls the drive of the pumps, receiving signals coming from said pressure detecting means; and motor rotation detecting means, which detects the drive state of the motor; wherein said controlling section includes a calculating portion, which carries out operations by using signals coming from the motor rotation detecting means immediately after the beginning of the single drive of the pumps to form a parallel drive controlling value, to obtain a constant quantity of supplied water; and a comparing portion, which compares the signals coming from the motor rotation detecting means with the parallel drive controlling value to control the parallel drive of the pumps.