JP2003176785A - City water liquid supply device and pump control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control pressure fluctuation when a plurality of pumps directly connected to a city water main pipe are operated in parallel. <P>SOLUTION: A plurality of pumps for supplying water sucked from a suction pipe directly connected to a city water main pipe to a demand side are provided and when water supply is to be backed up by starting a free pump 9 replacing a pump 8 which fails during its operation, this backing up is performed by starting the free pump 9 at the running speed of the failed pump 8. Also, when the pump 8 is stopped so as to start the pump 9, the running of the pump 8 is stopped after the pump 9 is started. Preferably, when the pump 8 is to be stopped, the pump 9 is started at a low speed after the running speed of the pump 8 is reduced to the low speed and when water supply pressure reaches a prescribed value, the precedingly running pump 8 is stopped. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water supply system and its pump control method, and more particularly to a water supply system having a plurality of pumps driven by an inverter in parallel and directly connected to a water main. The present invention relates to a device and a pump control method thereof.

[0002]

2. Description of the Related Art A conventional water supply system using an inverter uses a backup system as shown in FIG. 17 because the inverter is expensive. That is, when the pump 8 is driven by the inverter drive, the electromagnetic contactors 1 and 3 are first turned on and the operation and speed command signals are output to the inverter INV to operate. After that, when the pump 9 is operated, the electromagnetic contactor 3 is released, the inverter operation signal and the speed command signal are reset, the electromagnetic contactor 4 is turned on, and the inverter operation signal and the speed command signal are output. To do.

By the way, the inverter may trip in order to protect it from fluctuations in power supply and overload. When the inverter trips, it is disclosed in JP-A-59-18809.
As described in Japanese Patent Laid-Open No. 6, the electromagnetic contactor 2 or 5 of FIG. 17 is turned on and switched to a commercial power source for operation to supply water.

If two pumps are simultaneously operated to increase the amount of water supply, for example, when the pumps 9 are operated in parallel while the pump 8 is being operated by the inverter, the electromagnetic contactor 5 is used. After turning on, the pump 9 is started by a commercial power source to perform parallel operation at a constant speed. Furthermore, when disconnecting the pumps that have been operated in parallel, the constant speed pumps that have been made to follow are stopped. As a conventional technique related to this, Japanese Patent Laid-Open No. 59-511.
There is one disclosed in Japanese Patent No. 93.

[0005]

In the above-mentioned conventional technique, the pump is once stopped when the amount of water used is small, such as at night. However, when the pump is stopped, in the example of the discharge pressure constant control system as shown in FIG. 18, the pressure tank 210 is not filled with water because the pressure is normally constant. Therefore, when it is determined that the amount of water used is small and the control system (not shown) should be stopped, the pressure tank 21
In order to fill 0 with water, NMIN to NST shown in FIG.
The operating speed of the pump is increased until the pump is stopped, but for this reason, the water supply pressure is increased to H4 under the worst condition. Further, when starting / stopping the second constant speed pump, since the parallel starting pressure is H2 and the parallel stopping pressure is H1, pressure fluctuations may occur, which may adversely affect the equipment used. .

In particular, when the water supply device is directly connected to the water mains for operation, the above-mentioned conventional technique cannot be applied as it is. This is because it is necessary to suppress the pressure fluctuation of the water mains when the water supply device for water is operated. Therefore, it is necessary to further suppress the pressure fluctuation when operating a plurality of pumps in parallel as compared with the conventional case. In addition, if the pump is operated with a commercial power source when the inverter trips, it becomes impossible to control the pressure fluctuation to the water main, and a countermeasure against this is also necessary.

It is a first object of the present invention to provide a water supply device which suppresses pressure fluctuations when a plurality of pumps directly connected to a water main are operated in parallel, and a pump control method therefor.

A second object of the present invention is to provide a water supply device which does not require the pump to be operated by a commercial power source even when the inverter trips.

[0009]

[Means for Solving the Problems] The first object is to provide a plurality of pumps in parallel for supplying water to a demand side by sucking water from a suction pipe directly connected to a water main, and when the pump in operation fails. In a water supply apparatus for starting a dormant pump for backup, when the dormant pump is started, it is achieved by starting at the operating speed of the defective pump and backing up.

The first object is also to stop the operation of the pump to be stopped after starting the alternative pump in advance when stopping one of the plurality of pumps to start the alternative pump, To be achieved. Preferably, when the pump is stopped, the speed of the pump in operation is lowered in advance, and then the rest pump is started at the low speed, and when the water supply pressure becomes equal to or higher than a specified value, Stop running pumps.

The first object is also to provide a water supply system for supplying water to the demand side by a plurality of pumps provided in parallel from a suction pipe directly connected to the water main, and This is achieved by starting a stopped pump at a low speed in advance before one pump in operation reaches the maximum speed when water is supplied by the pump.

[0012] The first purpose is also to reduce the number of pumps to be operated in a state where another pump is operated following the pump that is operating in advance and water is being supplied by a plurality of pumps at the same time. This is achieved by continuing the operation control of the following pump and decelerating and stopping the preceding pump.

The first object is also achieved by decelerating the preceding pump when the feed water pressure becomes higher than a specified value in a state where the preceding pump and the following pump are both operating in parallel at the maximum speed. To be done. Preferably, the preceding pump is decelerated each time the water supply pressure becomes higher than a specified value, and when the operation speed of the preceding pump reaches a predetermined low speed, when the water supply pressure still exceeds the specified value, the preceding pump To stop.

The second purpose is to supply water that is connected to the demand side by merging the suction pipe connected to the water mains, a plurality of branch pipes branched from the suction pipe, and the outlet side of each branch pipe. With a tube,
A pump corresponding to the branch pipe provided for each branch pipe and discharging the water sucked from the suction pipe to the water supply pipe side, an electric motor corresponding to the pump driving each pump, and an inverter provided for each electric motor, This is achieved by providing a backup electromagnetic contactor for connecting the controlled motor of the inverter to another inverter when any of the inverters fails.

[0015]

When the plurality of pumps are operated in parallel or backed up, the above-mentioned measures are taken to suppress the pressure fluctuation. Therefore, even if the water supply device is directly connected to the water mains and operated, the pressure on the water mains is less affected. In addition, when one inverter breaks down, it can be operated by connecting another inverter to the pump corresponding to this inverter, so that the pump speed can be controlled at all times instead of directly operating the pump with commercial power. The pressure fluctuation of the main pipe can be suppressed.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 12 are views showing a first embodiment of the present invention. Recently, as shown in FIGS. 1 and 2, a water supply device for water supply (hereinafter, referred to as a water supply device) is being directly connected to a water main and used. In this case, since a large number of water supply devices are directly connected to the water mains, there is a concern that the influence of pressure fluctuations due to pump start / stop of each water supply device may affect the water mains. Therefore, it is necessary for the water supply device directly connected to the water mains to have a minimum pressure fluctuation due to the start / stop of the pump, and the water supply device according to the embodiment of the present invention described below has this pressure. It provides a technology that minimizes fluctuations.

FIG. 1 is an overall schematic configuration diagram of a water supply device according to a first embodiment of the present invention. The two pumps 8 and 9 of this water supply device are stainless steel suction pipes directly connected to the mains of the water via the sluice valve 202.
It is attached to each of the branch pipe portions that are branched into two in the downstream. Check valves 20 are provided downstream of the pumps 8 and 9, respectively.
6, 207 and sluice valves 208, 209 are connected to each other, and the pipe serves as a water supply pipe 213 that is joined downstream thereof and is guided to a consumer. Then, to the water supply pipe 213, a pressure tank (may be a diaphragm tank) 210 having an air reservoir inside, and a pressure sensor 211 that outputs a pressure signal according to the pressure in the water supply pipe 213 are connected.

The pumps 8 and 9 are controlled by the control device 214 and have two inverters for controlling the rotational speeds of the motors IM1 and IM2 for driving the pumps 8 and 9, and a microcomputer for controlling these inverters. A control circuit is built in the control device 214.

FIG. 12 is an external view of the water supply device according to the above embodiment. This water supply device is housed in a compact package and is configured to be easy to handle.

FIG. 3 is a diagram showing a power circuit portion of the control device shown in FIG. 1, where PW is a power source, 401 is a wiring breaker,
402a and 403a are main circuit contacts of the electromagnetic contactors for the first pump 8 and the second pump 9, respectively, 404 and
Similarly, 405 is an inverter for driving and controlling the pumps 8 and 9, and N1 and N2 are inverters 404, which will be described later.
405a, 407 is a signal that commands the speed of 405.
Reference symbol a is a signal for operation command of each inverter 404, 405.

FIG. 4 shows a control circuit of the control device shown in FIG. 1, and 501 is a switch for turning on / off, 502.
Is a stabilized power supply including a transformer, a diode bridge, a regulator, etc., 509 is a power supply terminal for supplying the power supply to a microcomputer (hereinafter, abbreviated as a microcomputer), 503 is electromagnetic contactors 402, 403 and relay 406. , 407 is an interface for controlling opening and closing.

When the electromagnetic contactors 402 and 403 are turned on, their contacts, that is, the contacts 402a and 403 shown in FIG.
a closes. Similarly, when the relays 406 and 407 are excited, their contacts 406a and 407a are closed.

Reference numerals 510 and 511 denote central processing units 51.
3 is an interface for outputting the speed commands N1 and N2 to the inverters 404 and 405 in response to the command No. 3, and is configured by a D / A converter or the like.

As will be described later, reference numeral 518 is a switch for setting a target value, for example, H0, H1 when pressure control is performed in a predetermined relationship, as shown in FIG. It is taken into the CPU 513. Similarly, 519 is a switch for setting a speed point for switching from a speed change command, which is a predetermined command speed, to a fixed speed command or vice versa, and is taken into the CPU 513 via the interface 516. Further, reference numeral 520 denotes an interface for taking in the pressure signal of the water supply pipe detected by the pressure sensor 211, which is taken into the CPU 513 via the port 517. The controller 530 is configured as described above.

FIG. 5 is a diagram exemplifying the operating characteristics of the pump when the constant end pressure control is performed, and the same reference numerals as those in FIG. 18 have the same meaning. Reference numeral 605 is a resistance curve of piping or the like. 601 to 604 set the operating speeds to the maximum speeds Nmax, N1, and Nmi when the amount of water used changes.
The intersection of the Q-H performance curve and the resistance curve when hypothesized as n, ...

The operation of the above-structured one will be described with reference to FIG. In FIGS. 1 and 5, the pressure in the water supply pipe 213 (the pressure tank 210 is approximately the same pressure) is higher than H3 (here, the starting pressure), and the pumps 8 and 9 are It is assumed that both are stopped. At this time, the circuit breaker 401 shown in FIGS. 3 and 4 is turned on, the switch 501 is closed, the control device is activated, and the standby state is assumed. Of course, H0, H1, H
Data such as 3, N1 and N2 are stored in advance in the switch 518,
Read from 519 and stored in memory (701
Step).

When the water tap at the demand end (not shown) is opened, the water supply pressure drops. This is detected by the pressure sensor 211 (step 702). When the pressure detected by the pressure sensor 211 is lower than the starting pressure H3, the control device outputs a signal for turning on the electromagnetic contactor 504 and the relay 506 to the interface 503 through the port 515 and the interface 510, for example. Outputs the speed command signal N1. As a result, one pump 8 is started.

By this start, the pump 8 is moved to the point 6 in FIG.
It will be driven at 04. As the usage increases, the resistance curve 60
5, the operation is continued along the upper direction. On the other hand, when the usage amount decreases, the speed is gradually reduced to continue the low speed NMIN operation (step 703).

If this state is continued for a certain period of time, it shifts to the standby state of the extremely low speed NMIN in step 704.
After that, after timing for a certain period of time in 705 steps, it is confirmed in 706 steps whether the pressure is H0 or less, and if
When it becomes the following, the speed is updated to NMIN (step 707) and the process is executed again from step 703.

If the state is H0 or higher, the controller outputs a signal for turning on the electromagnetic contactor 403 and the relay 507 from the interface 503, and
An extremely low speed signal (speed smaller than NMIN) is output to the inverter 405 as the speed command signal N2. In this state, since the operating characteristic curve of the pump is below the curve 608, the pump does not work and is in idling operation, and the feed water pressure maintains a predetermined pressure (the pressure on the curve 605). After a certain period of time, a signal is output to stop the pump 8 that was operating earlier, and the pump 8 is stopped, and the pump 9 that is to be operated later is subjected to a low-speed standby operation and made to stand by.

When the usage amount increases and the feedwater pressure starts to drop below H0, the pump is sped up to respond to this. When the usage amount is further increased, the pump is further accelerated. Assuming that the pump 8 currently in operation is the pump 8, when the operating speed of the pump 8 reaches a predetermined speed N1, the signals 402, 406, and
510 is output.

Next, the operation at the time of increasing the speed and increasing the number of units is shown in FIG.
Will be explained. 1) The operating speed of the preceding machine increased from Nmin to N1,
And, if the water supply pressure falls below the specified value Hi (to ensure this, it is better to wait for a certain period of time to confirm that it is truly below the specified value before proceeding to the next operation). The acceleration is started toward N and the follower is started at Nmin or less.

2) Thereafter, as the feed water pressure drops below the specified value, the preceding machine continues to accelerate, but the follower machine continues to operate at Nmi.
Maintain n speed. Here, the follower is set to Nmin in order to prevent the water supply pressure from rising above the specified pressure that is the target value.

3) In this way, even if the preceding machine reaches 100% N and the fixed time elapses, the feed water pressure is the specified value H.
When the state becomes lower than 3, the follower is commanded to speed up from Nmin to 100% N so that the feed water pressure becomes the specified value.

Next, the operation during deceleration and reduction of the number of units will be described. 1) When both pumps reach 100% N, fix the operating speed of the follower at 100% N.

2) When the water supply pressure becomes higher than the specified value as the amount of water used decreases, the speed of the preceding machine is changed from 100% N to N.
Instruct to decelerate toward min.

3) Further, if the amount of use becomes small, the speed of the preceding machine reaches Nmin, and the water supply pressure becomes higher than the specified value H4 even after a certain period of time, the speed of the preceding machine is made extremely low, After that, the preceding aircraft is stopped. this is,
This is to eliminate the adverse effect on the inverter due to the transient current at the time of stop.

The above operation will be described in more detail with reference to the flow charts of FIGS. First, in step 801, the water supply pressure is detected, and it is determined whether the water supply pressure is equal to or lower than a specified pressure (step 802). When the pressure is higher than the specified pressure, the deceleration processing is started. When the pressure is lower than the specified pressure, the preceding machine is accelerated (step 803), and at the next step 804, it is determined whether the preceding machine operation speed has reached N1. If the operation speed of the preceding machine is N1 or less, the process returns to step 801, and if it is N1 or more, the process proceeds to the next step 805 to set the follower to Nmin.
Start at the following speeds: And maintain this speed.

Next, in step 806, the waiting time of Δt is processed, and then the water supply pressure is detected (step 807).
It is determined whether this detected pressure is less than or equal to a specified value (step 80).
8). If it is less than the specified value, the process proceeds to step 815, the operating speed of the preceding machine is detected, and in step 816, it is determined whether the operating speed of the preceding machine has reached the maximum speed Nmax. Nmax
If it has reached the maximum speed N, the speed lock of the following machine is released from this point, the speed control is restarted, and the preceding machine is set to the maximum speed N.
Fix at max (step 818). In this state, the operating point of the pump is at the point 602 in FIG. 5, so that pressure fluctuation does not occur. If Nmax has not been reached, the speed of the preceding machine is increased with the speed of the follower machine locked (step 81).
7) and returns to step 806.

If it is determined in step 808 that the operating amount is not greater than the specified value, the operating speed of the preceding machine is detected in step 809, and the operating speed is the minimum speed Nmin. It is determined whether or not (step 810). If Nmin or less, point 604 in FIG.
Since it is in the vicinity, after performing the waiting time process of Δt in step 811, it is determined in step 813 whether the pressure is equal to or higher than the specified pressure, and when it is equal to or higher than the specified pressure, the process proceeds to step 814 and the preceding machine is stopped. Then, the speed lock of the follower is released, the process returns to step 801, and the process is executed again from here. If it is determined in step 810 that it is not Nmin, the preceding machine is decelerated (step 812), and step 8
Return to 06.

After step 818, the routine proceeds to step 819, where the waiting time for Δt is executed and then the water supply pressure is detected (step 820). At the next step 821, it is determined whether or not this pressure detection value is below a specified value. judge. If it is less than the specified value, the routine proceeds to step 822 of FIG. 9A, the operating speed of the follower is detected, and it is determined whether or not this operating speed is the minimum speed Nmin (step 823). Minimum speed Nmin
If it has reached, after executing the waiting time process of Δt in step 825, it is determined in step 826 whether or not the pressure is equal to or higher than the specified pressure H4. As a result of the judgment, if it is H4 or more in FIG. 5, the preceding machine is turned off and the operation speed lock of the follower machine is released in step 827, and the process returns to step 801 and is re-executed. When it is determined in step 823 that Nmin has not been reached, deceleration processing is performed in step 824, and the process returns to step 819.

If it is determined in step 821 that the value is less than or equal to the specified value, the process proceeds to step 828 in FIG. 9B, the operating speed of the follower is detected, and this operating speed is determined to be the maximum speed Nmax in step 829. When the speed reaches the maximum speed Nmax, the speed is not changed (step 831). When the maximum speed Nmax is not reached, the speed-up processing is performed (step 830) and the process returns to step 819.

If pump control is performed as described above,
When the pumps are stopped, the earlier operated pumps can be stopped earlier, so that the operational burdens of a plurality of pumps can be equalized.

FIG. 10 (a) is a diagram showing how the pressure fluctuation is suppressed when the respective pumps are inverter-controlled in the water supply system according to this embodiment described above. In addition, FIG. 10B for comparison is an example in which the pump of the inverter operation and the pump of the rated operation are combined, but a sudden pressure fluctuation is generated when the pump of the rated operation is operated at the time of switching. Shows.

In the present embodiment, as shown in FIG. 11, the pressure of the water mains can be used as compared with the current system using the water receiving tank, so the pressure of the pump can be small and energy saving can be achieved. You can

FIG. 15 is a block diagram of the control circuit of the water supply apparatus according to the second embodiment of the present invention. In this embodiment, the speed command signal to the inverter is one point. Now, it is assumed that the amount of water used is small and the pump 8 is operating under the characteristic curve 609 at the extremely low speed Nmin shown in FIG.

When a state in which the amount of water used is small is detected in this state, the operation signal 407 of the inverter 405 which drives the other pump is turned on, and the same speed command signal N as the preceding inverter is output to output both pumps. Both operate at extremely low speeds. Then, after a certain time, the preceding pump is stopped. Even in this case, since the operation of the pump is switched by wrapping the pressure change, it goes without saying that the pressure does not fluctuate, and further, since the speed command signal only needs to be one point, the control device can be inexpensively constructed.

Next, a third embodiment of the present invention, which will be described with reference to FIGS. 14 and 15, is a water supply device configured to back up when an inverter or a pump fails. 14 shows a configuration in which an electromagnetic contactor contact for switching at the time of backup is added to the configuration of FIG.
5 is provided in order to switch the electromagnetic contactor of FIG.
Further, as a switching circuit, thermal relay contacts 522 and 523 for overload protection of the motor and inverter trip signal contacts 524 and 525 are added. Also, in order to input these failure signals, the controller 508
Is provided with an input port 521.

In the thus-configured device, for example, when the inverters INV1 and IM2 fail, the electromagnetic contactors 402 and 403 are released, the control circuit issues an operation command to INV2, and the inverter INV2 operates IM1. Then back up.

Similarly, when INV2 and IM1 fail, the electromagnetic contactors 402 and 403 are released, INV2 is stopped, electromagnetic contactor 411 is turned on, and the control circuit is INV.
1 is issued to drive IM2 and backup is performed.

In this way, reliability is improved without interruption of water during a failure. Moreover, since the speed is controlled by the backup inverter of the pump, it is possible to suppress the pressure fluctuation to the water mains pressure.

FIG. 16 is a schematic configuration diagram of a water supply device according to the fourth embodiment of the present invention. In this embodiment, a water receiving tank is provided between the water main and the water supply device of the first embodiment,
The other structure is the same as that of the first embodiment. In FIG.
201 is a water receiving tank, 202, 203, 208, 209, 2
12 is a sluice valve, 204 and 205 are pumps driven by inverters respectively, 206 and 207 are check valves, 210
Is a pressure tank (may be a diaphragm tank) having an air reservoir inside, and 211 is a pressure sensor which is provided in the water supply pipe 213 and which issues a pressure signal according to the pressure therein.

As described above, the water supply device according to each of the above-described embodiments is configured to be used by being directly connected to the mains of the water supply, but it is also applicable to a device having a water receiving tank.

[0054]

According to the present invention, it is possible to suppress pressure fluctuations when a plurality of pumps directly connected to a water main are operated in parallel. Further, even when the inverter trips, it is possible to suppress the pressure fluctuation without operating the pump with the commercial power source.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a water supply device according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a water supply system using the water supply device of the present embodiment.

3 is a power circuit diagram of the control device shown in FIG. 1. FIG.

FIG. 4 is a control circuit diagram of the control device shown in FIG.

5 is an operation characteristic diagram when an operation of constant end pressure control is performed by the water supply device shown in FIG.

FIG. 6 is an operation characteristic diagram showing an operation at the time of increasing the speed and increasing the number of vehicles in the first embodiment.

FIG. 7 is a flowchart showing an operating procedure in the first embodiment.

FIG. 8 is a flowchart showing an operating procedure in the first embodiment.

FIG. 9 is a flowchart showing an operating procedure in the first embodiment.

FIG. 10 is a characteristic diagram illustrating a pressure fluctuation suppressing effect in the first embodiment.

FIG. 11 is a diagram showing an energy saving effect in the first embodiment.

FIG. 12 is an external view of the water supply device according to the first embodiment.

FIG. 13 is a power circuit diagram of the water supply device according to the second embodiment of the present invention.

FIG. 14 is a power circuit diagram of the control device for the water supply device according to the third embodiment of the present invention.

FIG. 15 is a control circuit diagram in the third embodiment.

FIG. 16 is a schematic configuration diagram of a water supply device according to a fourth embodiment of the present invention.

FIG. 17 is a power circuit diagram of a control device in a conventional water supply device.

FIG. 18 is an operation characteristic diagram of a conventional water supply device.

[Explanation of symbols]

202, 203 ... Gate valve, 8, 9 ... Pump, IM1,
IM2 ... electric motor, 210 ... pressure tank, 211 ... pressure sensor, 401 ... circuit breaker, 402, 403 ... electromagnetic contactor,
INV1, INV2 ... General-purpose inverter, N1, N2 ... Speed command signal, 406, 407 ... Inverter operation command signal, 501 ... Switch, SW1, SW2, SW3 ... DIP switch, 502 ... Transformer, 508 ... Controller
LA, 503, 510-517 ... Input / output device, 514 ... Memory, 513 ... Central processing unit, 504-507 ... Relay.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 3H045 AA06 AA09 AA16 AA23 BA03                       BA07 BA20 CA03 CA06 CA25                       CA29 DA01 DA32 EA34

Claims (15)

[Claims] 1. A water supply system comprising a plurality of pumps in parallel for sucking water from a suction pipe directly connected to a water mains and supplying it to a demand side, and starting a dormant pump to back up when the pump in operation fails. A method of controlling a pump of a water supply apparatus, comprising: starting a backup pump at the operating speed of the defective pump when starting a pump that is not operating. 2. A pump control method for a water supply device, comprising: a plurality of pumps, which are arranged in parallel to draw water from a suction pipe directly connected to a water mains and supply the demand side, wherein one of the plurality of pumps is used. A pump control method for a water supply device, characterized in that, when stopping and activating the alternative pump, the alternative pump is started in advance and then the operation of the pump to be stopped is stopped. 3. The pump according to claim 2, wherein when stopping the pump, the speed of the operating pump is set to a low speed and then the pause pump is started at the low speed to make the water supply pressure equal to or higher than a specified value. In this case, the pump control method for the water supply device is characterized in that the pump in operation is stopped in advance. 4. A pump control method of a water supply device for supplying water to a demand side by sucking water by a plurality of pumps provided in parallel from a suction pipe directly connected to a water main, wherein the plurality of pumps are used. A pump control method for a water supply device, characterized in that, when water is supplied, a stopped pump is started in advance at a low speed before one pump in operation reaches a maximum speed. 5. A pump control method of a water supply device for supplying water to a demand side by sucking water by a plurality of pumps provided in parallel from a suction pipe directly connected to a water main, which is operated in advance. When reducing the number of operating pumps while operating another pump following another pump and supplying water with multiple pumps at the same time, continue the operation control of the following pumps and decelerate and stop the preceding pumps. A method for controlling a pump of a water supply device characterized by the above. 6. A pump control method of a water supply device for supplying water to a demand side by sucking water by a plurality of pumps provided in parallel from a suction pipe directly connected to a water main, wherein a preceding pump and a following pump are provided. A method for controlling a pump of a water supply device, wherein the preceding pump is decelerated when the water supply pressure becomes higher than a specified value while both are operating in parallel at the maximum speed. 7. The water supply pressure as set forth in claim 6, wherein the feed pump is decelerated each time the feed water pressure becomes higher than a prescribed value, and the feed water pressure is still equal to or higher than a prescribed value even if the operation speed of the lead pump reaches a predetermined low speed. A method of controlling a pump for a water supply device, characterized in that the preceding pump is stopped when it becomes low. 8. A suction pipe connected to a water main, a plurality of branch pipes branched from the suction pipe, a water supply pipe that joins the outlet sides of the branch pipes and is connected to a demand side, and each branch. A pump that is provided for each pipe and that discharges the water sucked from the suction pipe to the water supply pipe side, a pump-compatible electric motor that drives each pump, and an inverter that is installed corresponding to each electric motor. And a control means for starting another inverter at the same speed as the inverter when the inverter trips. 9. A suction pipe connected to a water main, a plurality of branch pipes branched from the suction pipe, a water supply pipe that joins the outlet sides of the branch pipes and is connected to a demand side, and each branch. A pump corresponding to a branch pipe that is provided for each pipe and discharges the water sucked from the suction pipe to the water supply pipe side, an electric motor corresponding to the pump that drives each pump, an inverter provided for each electric motor, and a plurality of units Control means for outputting, to the inverter, a command to stop the operation of the pump to be stopped after starting the alternative pump in advance when stopping one of the pumps to start the alternative pump. A water supply device for water supply. 10. The pump according to claim 9, when the pump is stopped, the speed of the operating pump is set to a low speed, and then the pause pump is started at the low speed to detect the pressure detected by the pressure detecting means. A water supply device, characterized in that the control means is provided with means for outputting to the inverter a command to stop the pump that is operating in advance when the value exceeds a specified value. 11. A suction pipe connected to a water main, a plurality of branch pipes branched from the suction pipe, a water supply pipe that joins the outlet sides of the branch pipes and is connected to a demand side, and each branch. A pump that is provided for each pipe and that discharges the water sucked from the suction pipe to the water supply pipe side, a pump that corresponds to the branch pipe, an electric motor that corresponds to the pump that drives each pump, an inverter that corresponds to each electric motor, and When water is supplied by one pump, a control means for outputting to the inverter a command for starting a stopped pump at a low speed in advance before one pump in operation reaches the maximum speed, A water supply device for water supply. 12. A suction pipe connected to a water main, a plurality of branch pipes branched from the suction pipe, a water supply pipe that joins the outlet sides of the branch pipes and is connected to a demand side, and each branch. A pump that is provided for each pipe and that discharges the water sucked from the suction pipe to the water supply pipe side, a pump that corresponds to a branch pipe, an electric motor that corresponds to a pump that drives each pump, and an inverter that corresponds to each electric motor. When the number of operating pumps is reduced while another pump is operating following another pump and water is being supplied by multiple pumps at the same time, the operation control of the following pump is continued and the preceding pump is decelerated. And a control means for outputting a command to stop the inverter to the inverter. 13. A suction pipe connected to a water main, a plurality of branch pipes branched from the suction pipe, a water supply pipe that joins outlet sides of the branch pipes and is connected to a demand side, and each branch. A pump that is provided for each pipe and that discharges the water sucked from the suction pipe to the water supply pipe side, a pump-compatible electric motor that drives each pump, an inverter that is provided for each electric motor, and the water supply When the pressure detection means for detecting the pressure in the pipe and the preceding pump and the follower pump are operating in parallel at the maximum speed and the pressure detected by the pressure detection means becomes higher than the specified value, the preceding pump is decelerated. And a control means for outputting a command to the inverter to supply water. 14. The control device according to claim 13, wherein the control means decelerates the preceding pump every time the detected pressure becomes higher than a specified value, and the operating speed of the preceding pump reaches a predetermined low speed. A water supply device for water supply, which outputs a command to stop the preceding pump when the detected pressure exceeds a prescribed value. 15. A suction pipe connected to a water main, a plurality of branch pipes branched from the suction pipe, a water supply pipe that joins the outlet sides of the branch pipes and is connected to a demand side, and each branch. One of a pump provided for each pipe, which corresponds to a branch pipe that discharges water sucked from the suction pipe toward the water supply pipe side, an electric motor corresponding to a pump that drives each pump, and an inverter provided for each electric motor. And a backup electromagnetic contactor for connecting the controlled electric motor of the inverter to another inverter when the inverter fails.