Pure water production device and method for operating same

Abstract

The objective of this invention is to suppress the temperature rise of pure water due to circulation at a lower cost. A pure water production apparatus 1 includes: a storage tank 2 for storing pure water; a circulation pipeline L1 for circulating the pure water in the storage tank 2; a pump 3 installed in the circulation pipeline L1 to allow the pure water in the storage tank 2 to flow through the circulation pipeline L1; a water supply pipeline L2 downstream of the pump 3, branching off from the circulation pipeline L1 and connected to a point of use 7; and a control mechanism 10 that switches the rotational speed of the pump 3 based on the results of directly or indirectly detecting whether pure water flows through the water supply pipeline L2 or changes in the flow rate of pure water flowing through the water supply pipeline L2.

Description

[Technical Field]

[0001] This invention relates to a pure water manufacturing apparatus and its operation method. [Previous Technology]

[0002] A pure water production device is known to produce pure water (refined water) for pharmaceutical or biochemical analysis and supply it to the point of use. The pure water circulates through a circulation pipeline, and a portion of this pure water is supplied to the point of use as needed (see, for example, Patent Document 1). In cases where the supply of pure water to the point of use is stopped for extended periods, such as at night or on holidays when pure water is not needed, the device continues to circulate the pure water to inhibit the growth of bacteria due to stagnation. [Prior Art Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2006-095479 [Summary of the Invention]

[0004] [The problem the invention aims to solve]

[0005] When pure water circulation continues for an extended period, the temperature of the pure water may rise beyond the appropriate operating temperature (set temperature) at the point of use due to heat generated by pumps or ultraviolet sterilization devices installed in the circulation pipeline. For example, smaller pure water production equipment frequently used in research institutions often employs pumps with a capacity (maximum spray flow rate) relatively large than the maximum storage capacity of the storage tank to accommodate various applications, making such temperature rises significant. As a countermeasure to this temperature rise, as described in Patent Document 1, a cooling mechanism such as a heat exchanger can be installed in the circulation pipeline. However, this is impractical for smaller pure water production equipment due to considerations of equipment size and cost. Furthermore, even in larger pure water production equipment installed in various factories, cooling mechanisms are sometimes not installed in the circulation pipeline from an economic point of view. Therefore, most pure water production equipment sprays out a certain amount of pure water in the circulation and replenishes it in order to lower the temperature of the pure water below the set temperature. However, the useless disposal of this pure water is a significant cause of increased costs and is therefore not ideal.

[0006] Therefore, the object of the present invention is to provide a pure water production apparatus and its operating method, which, at a lower cost, suppresses the temperature rise of pure water due to circulation. [Means for Solving the Problem]

[0007] To achieve the above objective, the pure water manufacturing apparatus of the present invention comprises: a storage tank for storing pure water; a circulation pipeline for circulating the pure water in the storage tank; a pump installed in the circulation pipeline for circulating the pure water in the storage tank through the circulation pipeline; a water supply pipeline branching off from the circulation pipeline downstream of the pump and connected to a point of use; and a control mechanism for switching the pump speed based on the result of directly or indirectly detecting whether pure water is flowing through the water supply pipeline or the change in the flow rate of pure water flowing through the water supply pipeline.

[0008] Furthermore, the operation method of the pure water manufacturing apparatus of the present invention includes the following steps: using a pump installed in the circulation pipeline to circulate pure water stored in the storage tank along the circulation pipeline; transporting the pure water circulating in the circulation pipeline to the point of use via a water delivery pipeline branching off from the circulation pipeline downstream of the pump; and switching the pump speed based on the results obtained by directly or indirectly detecting whether pure water flows through the water delivery pipeline or the change in the flow rate of pure water flowing through the water delivery pipeline.

[0009] According to this pure water production apparatus and its operating method, by switching the pump speed, the temperature rise of the pure water due to circulation can be suppressed, thus preventing the waste of pure water. Furthermore, compared to running the pump at the same speed for an extended period, it also reduces the pump's power consumption and lowers operating costs. [Effects of the Invention]

[0010] As described above, according to the present invention, the temperature rise of pure water due to circulation can be suppressed at a lower cost.

Implementation Method

[0012] The embodiments of the present invention will be described below with reference to the drawings. In this specification, a cabinet-type pure water production apparatus is exemplified as the pure water production apparatus of the present invention, which is appropriately used in research institutions or medical institutions together with analytical instruments such as automated blood analyzers, but the present invention is not limited thereto. As the pure water production apparatus of the present invention, as long as it does not have a mechanism (such as a heat exchanger) for dynamically adjusting the temperature of the circulating pure water, it can also be a large-scale pure water production apparatus installed in various factories.

[0013] (First Embodiment) Figure 1 is a schematic diagram showing the configuration of a pure water production apparatus according to one embodiment of the present invention. Furthermore, the configuration of the pure water production apparatus shown is merely an example and does not limit the scope of the present invention.

[0014] The pure water production apparatus 1 includes: a storage tank 2, a pump 3, an ultraviolet oxidation device 4, an ion exchange device 5, and a separation membrane device 6. These components are housed in a cabinet, forming a secondary pure water system (subsystem) that "produces pure water by sequentially processing the primary pure water produced by the primary pure water system (not shown)," and supplies the pure water to the point of use 7.

[0015] Pump 3, ultraviolet oxidation device 4, ion exchange device 5, and separation membrane device 6 are installed on circulation pipeline L1, with both ends of circulation pipeline L1 connected to storage tank 2. At point of use 7, a water supply pipeline L2 branching from circulation pipeline L1 is connected via solenoid valve V1. Solenoid valve V1 opens and closes according to the command signal (open / close command signal) sent from point of use 7. Furthermore, a primary pure water supply line L3 is connected to storage tank 2. For example, based on the water level in storage tank 2 detected by a water level sensor (not shown), primary pure water is supplied to storage tank 2 from a primary pure water system (not shown). Specifically, when the water level in storage tank 2 is below a predetermined water supply start level, primary pure water is supplied to storage tank 2 via primary pure water supply line L3. When the water level in storage tank 2 reaches a predetermined upper limit level, the supply of primary pure water to storage tank 2 is stopped.

[0016] The primary pure water (treated water) stored in storage tank 2 is supplied to ultraviolet oxidation device 4 by pump 3, where it is irradiated with ultraviolet light with a wavelength of 185nm, and the total organic carbon (TOC) in the treated water is decomposed. Then, the treated water is subjected to ion exchange treatment in ion exchange device 5 to remove metals, etc., and in separation membrane device 6 to remove microparticles, etc. The pure water obtained in this way is returned to storage tank 2 through circulation pipeline L1. However, when solenoid valve V1 is opened due to a water collection request received from point of use 7, part or all of the pure water is supplied to point of use 7 through water supply pipeline L2. Furthermore, a back pressure valve V2, which serves as a back pressure generating mechanism, is provided downstream of the branch point B between circulation pipeline L1 and water supply pipeline L2 when solenoid valve V1 is opened, so that pure water can reliably flow from circulation pipeline L1 to water supply pipeline L2.

[0017] The storage tank 2, pump 3, ultraviolet oxidation device 4, ion exchange device 5, and separation membrane device 6 can be those commonly used in the secondary system of a pure water production system. For example, the ion exchange device 5 can be a non-regenerative mixed-bed ion exchange device (tube-type high-purification device) filled with cation exchange resin and anion exchange resin in a mixed bed configuration. Furthermore, the separation membrane device 6 can include either a microfiltration membrane (MF membrane) or an ultrafiltration membrane (UF membrane). Alternatively, an ultraviolet sterilization device that sterilizes the treated water by irradiation with ultraviolet light at a wavelength of 254 nm can be installed instead of the ultraviolet oxidation device 4, or both can be installed.

[0018] Even when the pure water production apparatus 1 stops water intake (supplying pure water to point 7) for extended periods, such as at night or on holidays when point 7 does not require pure water, the produced pure water is still circulated back to the storage tank 2 to suppress the growth of bacteria due to stagnation. If this pure water circulation continues for a long time, the temperature of the pure water may sometimes rise above the appropriate operating temperature (set temperature) of point 7 due to heat generated by the pump 3 or the ultraviolet oxidation device 4. In particular, if it is a cabinet-type pure water production apparatus as in this embodiment, a pump with a capacity (maximum spray flow rate) relatively large compared to the maximum storage capacity of the storage tank is often used to accommodate various applications, and cooling mechanisms such as heat exchangers are not installed due to considerations of apparatus size or cost. Therefore, such a significant temperature rise is likely to occur, for example, when the purified water is used in analytical instruments such as automated blood analyzers. The temperature of the purified water will exceed 35°C, while the operating temperature at the point of use is 30-35°C.

[0019] Therefore, in this embodiment, in order to suppress the temperature rise of the pure water due to circulation, the pump 3 operates at a lower speed during circulation operation compared to the water intake operation. That is, the pump 3 operates at a first speed during circulation operation, and operates at a second speed higher than the first speed during water intake operation. For this purpose, the pure water production apparatus 1 has a control unit (control mechanism) 10, which includes an inverter (not shown) for controlling the speed of the pump 3. The control unit 10 switches the speed of the pump 3 according to whether pure water flows into the water supply pipeline L2.

[0020] When the control unit 10 receives an opening command signal sent to the solenoid valve V1 from the point of use 7, it indirectly detects that: the solenoid valve V1 opens, and pure water begins to flow in the water supply pipeline L2 (i.e., water extraction operation begins). When the control unit 10 receives a closing command signal sent to the solenoid valve V1 from the point of use 7, it indirectly detects that: the solenoid valve V1 closes, and pure water stops flowing in the water supply pipeline L2 (i.e., water extraction operation stops). Furthermore, when the control unit 10 detects the start of water extraction operation, it switches the speed of the pump 3 from a first speed to a second speed; when it detects the stop of water extraction operation, it switches the speed of the pump 3 from the second speed back to the first speed. Moreover, the speed of the pump 3 can be adjusted by controlling the drive output (motor output) of the pump 3.

[0021] Here, the first rotational speed during circulation is appropriately set according to the actual device configuration and is not particularly limited. However, it is preferable to set the first rotational speed by verifying in advance, through experiments, that the temperature of the pure water in circulation will not rise within a certain range. The results of the actual verification are described later. However, in order to minimize the temperature rise of the pure water caused by circulation, it is preferable to set the drive output of pump 3 corresponding to the first rotational speed to 5W or less per liter of minimum storage water volume in storage tank 2, and preferably 2W or less. The minimum storage water volume referred to here is the storage water volume when the water level in storage tank 2 is at its lowest, that is, the storage water volume at the predetermined water supply start level. Furthermore, the overall volume of the piping constituting the circulation pipeline L1 is not so small as to be negligible compared to the volume of storage tank 2. When setting the drive output of pump 3 corresponding to the first rotational speed, the overall volume of such piping can also be taken into account. In other words, the minimum water storage capacity of storage tank 2 can be set by adding the total volume of the piping to the volume of storage tank 2. On the other hand, the second rotation speed during water intake operation is set appropriately according to the flow rate of pure water required by point 7, and is not particularly limited.

[0022] In this manner, according to this embodiment, the pump speed of 3 is switched based on whether pure water is supplied to the point of use 7 through the water supply pipeline L2, allowing 3 to operate at a relatively low speed during circulation. This suppresses the rise in pure water temperature during circulation without the waste of pure water. Furthermore, compared to operating 3 at the same speed during circulation and water intake, even if the pure water circulates at the same flow rate, the power consumption of 3 and the wear of the ion exchange resin in the ion exchange device 5 can be suppressed, resulting in reduced operating costs. Moreover, assuming it is a cabinet-type pure water production device used in research institutions or medical facilities, where pure water is frequently used for short periods, it is advantageous to have access to pure water at any time if a purging step is not required due to the rise in pure water temperature.

[0023] As described above, the configuration of the pure water production apparatus 1 shown in the figure is merely an example and can be appropriately modified according to the purpose or use of the apparatus and the required performance. In particular, as long as the following components are provided: a storage tank 2 for storing pure water (primary pure water); a circulation pipeline L1 for circulating the pure water in the storage tank 2; a pump 3 for allowing the pure water in the storage tank 2 to flow through the circulation pipeline L1; and a water supply pipeline L2, which branches off from the circulation pipeline L1 downstream of the pump 3 and connects to the point of use 7, one or more of the ultraviolet oxidation device 4, ion exchange device 5, and separation membrane device 6 can be omitted, or all three can be omitted. Regarding the back pressure valve V2, in order to adjust the flow rate of pure water flowing through the water supply pipeline L2 during water collection operation, two or more can be provided, or they can be omitted depending on the situation.

[0024] Here, we will explain the test results obtained by verifying the extent to which the temperature of the pure water circulating in the circulation pipeline rises due to pump heating.

[0025] (Test 1-1) Using a test apparatus simulating the pure water production device shown in Figure 1, pure water was continuously circulated, and the temperature change of the pure water (water temperature) over time was measured. Then, the period with the largest temperature rise after the operation was determined, and the rate of temperature rise (the amount of temperature rise per unit time) was calculated from this period (time) and the amount of temperature rise at this time. This test apparatus has the same structure as the pure water production device shown in Figure 1, except that it does not have an ion exchange device or a separation membrane device (nor a water supply pipeline). A storage tank with a maximum storage capacity of 60L was used, and a magnetic drive gear pump (model: MDG-M4S6A100) manufactured by IWAKI Co., Ltd. was used. The pure water circulation was performed with the pump motor output set to 200W, and the storage tank was filled with 60L of pure water.

[0026] (Test 1-2) Except that the circulation was performed with 40L of pure water in the storage tank, the measurements were performed under the same conditions as in Test 1-1.

[0027] (Test 1-3) The storage tank has a maximum water storage capacity of 20L. The tank is filled with 20L of pure water and the circulation is performed. Otherwise, the measurements are performed under the same conditions as in Test 1-1.

[0028] (Test 2-1) Except for the following points, measurements were performed under the same conditions as in Test 1-1. A turbine pump (model: 15DNL03ZM-V) manufactured by Nikuni Corporation was used, and an inverter (model: FR-D710W-0.75K) manufactured by Mitsubishi Electric Corporation was used for the pump motor drive. The pure water circulation was performed with the pump motor output set to 110W, and the storage tank filled with 60L of pure water.

[0029] (Test 2-2) Except that the motor output was set to 165W and the cycle was performed, the measurement was performed under the same conditions as in Test 2-1.

[0030] (Test 2-3) Except that the motor output was set to 235W and the cycle was performed, the measurement was performed under the same conditions as in Test 2-1.

[0031] (Test 2-4) Except that the circulation was performed with 40L of pure water in the storage tank, the measurements were performed under the same conditions as in Test 2-1.

[0032] (Test 2-5) Except that the circulation was performed with 40L of pure water in the storage tank, the measurements were performed under the same conditions as in Test 2-2.

[0033] Table 1 shows the calculation results of the water temperature rise rate in each test. In addition, for easy reference, Table 1 also shows the water volume of the storage tank, the motor output of the pump, and the motor output of the pump for every 1L of water stored in the storage tank.

[0034] [Table 1] test 1-1 test 1-2 test 1-3 test 2-1 test 2-2 test 2-3 test 2-4 test 2-5 Water temperature rise rate [°C / h] 1.2 1.3 5.5 0.2 1.4 1.3 1.6 1.4 Water storage capacity of the storage tank [L] 60 40 20 60 40 Pump motor output [W] 200 110 165 235 110 165 Motor output [W] per liter of stored water 3.3 5.0 10.0 1.8 2.8 3.9 2.8 4.1

[0035] Except for tests 1-3, in all tests, the rate of water temperature rise was suppressed to below 1.6℃ / h. Among them, test 2-1, in which the pump motor output was the lowest relative to the water volume stored in the storage tank, yielded particularly ideal results. Therefore, from the viewpoint of suppressing the temperature rise of pure water due to circulation, a pump motor output of 5W or less per 1L of water stored in the storage tank is preferable, and 2W or less is even better.

[0036] (Second Embodiment) Figure 2 is a schematic diagram showing the configuration of a pure water production apparatus according to a second embodiment of the present invention. Hereinafter, configurations identical to those in the first embodiment will be labeled with the same symbols, and their descriptions will be omitted; only configurations different from those in the first embodiment will be described.

[0037] As described above, when the solenoid valve V1 opens due to a water sampling request received from the point of use 7, part or all of the pure water flowing through the circulation pipeline L1 is supplied to the point of use 7 via the water supply pipeline L2. At this time, downstream of the branch point B in the circulation pipeline L1, the pressure decreases due to the decrease in the flow rate of pure water. By detecting this pressure decrease, it is possible to indirectly detect that pure water has begun to flow into the water supply pipeline L2. In this embodiment, in order to detect this pressure decrease, a pressure switch 11 is installed downstream of the branch point B in the circulation pipeline L1 and upstream of the back pressure valve V2. The pressure switch 11 outputs a detection signal when the pressure of the pure water flowing downstream of the branch point B in the circulation pipeline L1 is below the set pressure (predetermined value). Then, when the control unit 10 receives this detection signal, it considers the water sampling operation to have started and pure water to have begun to flow into the water supply pipeline L2, and switches the speed of the pump 3 from the first speed to the second speed. Therefore, in this embodiment, the temperature rise of pure water during circulation can be suppressed without the waste pure water being rendered useless, thus reducing operating costs.

[0038] The detection mechanism for indirectly detecting the start of pure water flow in the water supply pipeline L2 is not limited to the pressure switch 11; a pressure sensor may also be used. In other words, as long as the pressure of the pure water flowing downstream of the branch point B in the circulation pipeline L1 can be detected to be below a predetermined value, a pressure sensor can be used instead of the pressure switch 11. Furthermore, in order to reliably detect the start of pure water flow in the water supply pipeline L2, it is preferable to generate a sufficient pressure drop downstream of the branch point B in the circulation pipeline L1. Therefore, in the first embodiment, as described above, it is not necessary to provide a back pressure valve V2, but in this embodiment, it is preferable to provide a back pressure valve V2. Alternatively, other back pressure generating mechanisms such as orifices may be provided to replace the back pressure valve V2.

[0039] (Third Embodiment) Figure 3 is a schematic diagram showing the configuration of a pure water production apparatus according to the third embodiment of the present invention. Hereinafter, configurations identical to those in the above embodiments will be labeled with the same symbols, and their descriptions will be omitted; only configurations different from those in the above embodiments will be described.

[0040] This embodiment is a variation of the second embodiment, and the method for detecting whether pure water flows into the water supply pipeline L2 differs from the second embodiment. Specifically, in the second embodiment, a pressure switch 11 is installed in the circulation pipeline L1 to indirectly detect the start of pure water flow into the water supply pipeline L2. In contrast, in this embodiment, a flow switch 12 is installed in the water supply pipeline L2 to directly detect the start of pure water flow into the water supply pipeline L2. The flow switch 12 outputs a detection signal when the flow rate of pure water flowing through the water supply pipeline L2 is above a set flow rate (predetermined value). Upon receiving this detection signal, the control unit 10 switches the speed of the pump 3 from a first speed to a second speed. Thus, in this embodiment, the rise in pure water temperature during circulation can be suppressed without the waste of pure water, thereby reducing operating costs.

[0041] Furthermore, in the second embodiment, if the pressure loss of the water supply pipeline L2 changes, when pure water begins to flow through the water supply pipeline L2, the pressure downstream of the branch point B in the circulation pipeline L1 may not sometimes drop below the set pressure of the pressure switch 11. Therefore, in the second embodiment, the change in pressure loss of the water supply pipeline L2 must be considered, and the set pressure of the pressure switch 11 must be adjusted accordingly. However, this embodiment does not need to consider such a change in pressure loss, which is advantageous.

[0042] The detection mechanism that directly detects the start of pure water flowing through the water supply pipeline L2 is not limited to the flow switch 12; a flow sensor may also be used. In other words, as long as the flow rate of pure water flowing through the water supply pipeline L2 can be detected to be above a predetermined value, a flow sensor may be used to replace the flow switch 12.

[0043] (Fourth Embodiment) FIG4 is a schematic diagram showing the configuration of a pure water production apparatus according to the fourth embodiment of the present invention. Hereinafter, configurations identical to those in the above embodiments will be labeled with the same symbols, and their descriptions will be omitted; only configurations different from those in the above embodiments will be described.

[0044] In the second embodiment, when a pressure drop in pure water is detected downstream of branch point B in the circulation pipeline L1, the speed of pump 3 is switched. However, this pressure drop in pure water occurs not only when switching from circulation operation to water intake operation and pure water begins to flow in the water supply pipeline L2, but also when the flow rate of pure water flowing through the water supply pipeline L2 increases during water intake operation. Therefore, the speed switching of pump 3 can also be based on the change in the flow rate of pure water flowing through the water supply pipeline L2 during water intake operation, as in this embodiment.

[0045] In this embodiment, the water supply pipeline L2 has multiple branches (three in the illustrated example), each connected to multiple usage points 71-73 via solenoid valves V11-V13. In this case, water intake requests from the multiple usage points 71-73 are made independently. Therefore, even during water intake operation, the flow rate of pure water flowing through the water supply pipeline L2 varies significantly. For example, the flow rate increases significantly when there are simultaneous water intake requests from multiple usage points 71-73 compared to when there are individual water intake requests from each usage point 71-73. To indirectly detect this increase in pure water flow rate, a pressure sensor 13 is installed downstream of branch point B in the circulation pipeline L1 in this embodiment. The pressure sensor 13 outputs a detection signal when the pressure of the pure water flowing downstream of branch point B in the circulation pipeline L1 is below a predetermined set value. Then, upon receiving this detection signal, the control unit 10 assumes that the flow rate of pure water flowing through the water supply pipeline L2 has increased, and switches the speed of pump 3 from the first speed to the second speed. In this way, the speed of pump 3 can be switched according to the required flow rate of pure water at usage points 71-73. In this embodiment, the rise in pure water temperature during circulation can be suppressed without the waste of pure water, thus reducing operating costs.

[0046] The set value (threshold value) of the pressure sensor 13 can be appropriately changed according to the required pure water flow rate of each usage point 71 to 73. For example, the pump speed 3 is switched from the first speed to the second speed only when there is a simultaneous water sampling requirement from some of the multiple usage points 71 to 73. If there is a water sampling requirement from each of the individual usage points 71 to 73, the pump speed 3 is not switched and the first speed is maintained. Furthermore, if the required pure water flow rates of each of the usage points 71 to 73 are different, the pump speed 3 is switched from the first speed to the second speed only when there is a water sampling requirement from the usage point with the larger required flow rate.

[0047] Furthermore, in this embodiment, as in the third embodiment, the increase in the flow rate of pure water flowing through the water supply pipeline L2 can also be directly detected. As a detection mechanism to achieve this purpose, it is preferable to use a flow sensor, which can arbitrarily set the threshold value for switching the speed of pump 3. [Simplified Explanation of the Diagram]

[0011] [Figure 1] is a schematic diagram showing the configuration of a pure water manufacturing apparatus according to a first embodiment of the present invention. [Figure 2] is a schematic diagram showing the configuration of a pure water manufacturing apparatus according to a second embodiment of the present invention. [Figure 3] is a schematic diagram showing the configuration of a pure water manufacturing apparatus according to a third embodiment of the present invention. [Figure 4] is a schematic diagram showing the configuration of a pure water manufacturing apparatus according to a fourth embodiment of the present invention.

Claims

1. A pure water production apparatus, comprising: a storage tank for storing pure water; a circulation pipeline for circulating the pure water in the storage tank; a pump disposed in the circulation pipeline for circulating the pure water in the storage tank through the circulation pipeline; a water delivery pipeline branching off from the circulation pipeline downstream of the pump and connected to a point of use; and a control mechanism for switching the rotational speed of the pump based on the result of directly or indirectly detecting whether pure water flows through the water delivery pipeline or the change in the flow rate of pure water flowing through the water delivery pipeline; the control mechanism indirectly detects whether pure water flows through the water delivery pipeline or the change in the flow rate of pure water flowing through the circulation pipeline downstream of the branch point of the water delivery pipeline by detecting the opening and closing of a solenoid valve disposed in the water delivery pipeline or detecting the pressure change of pure water flowing through the circulation pipeline downstream of the branch point of the water delivery pipeline; When pure water begins to flow through the water supply pipeline, or when the flow rate of pure water flowing through the water supply pipeline increases, the control mechanism switches the pump speed from a first speed to a second speed higher than the first speed. The control mechanism adjusts the pump speed to the first speed by setting the pump drive output to 5W or less per 1L of minimum water volume in the storage tank.

2. The pure water production apparatus of claim 1 further comprises: a detection mechanism that directly or indirectly detects the start of pure water flowing through the water supply pipeline or the increase in the flow rate of pure water flowing through the water supply pipeline, and outputs a detection signal; and a control mechanism that, upon receiving the detection signal, switches the speed of the pump from the first speed to the second speed.

3. The pure water production apparatus of claim 2 further comprises: a back pressure generating mechanism disposed on the downstream side of the branch point of the circulation pipeline and the water supply pipeline; and a detection mechanism that outputs the detection signal when the pressure of the pure water flowing through the downstream side of the branch point in the circulation pipeline is below a predetermined value.

4. The pure water production apparatus as described in claim 3, wherein, The detection mechanism, which is a pressure switch or pressure sensor, is located downstream of the branch point in the circulation pipeline and upstream of the back pressure generating mechanism.

5. The pure water production apparatus as described in claim 2, wherein, The detection device outputs the detection signal when the flow rate of pure water flowing through the water pipeline exceeds a predetermined value.

6. The pure water production apparatus as described in claim 5, wherein, The detection mechanism is a flow switch or flow sensor installed in the water supply pipeline.

7. The pure water production apparatus as described in claim 1, wherein, When the solenoid valve connecting the water supply pipeline to the point of use is opened, the control mechanism switches the pump speed from the first speed to the second speed.

8. A method of operating a pure water production apparatus, comprising the following steps: using a pump installed in a circulation pipeline to circulate pure water stored in a storage tank along the circulation pipeline; transporting the pure water circulating in the circulation pipeline to a point of use via a water delivery pipeline branching off from the circulation pipeline downstream of the pump; and switching the speed of the pump based on the result obtained by directly or indirectly detecting whether pure water flows through the water delivery pipeline or the change in the flow rate of pure water flowing through the water delivery pipeline; the aforementioned step of switching the speed of the pump includes: indirectly detecting whether pure water flows through the water delivery pipeline or the change in the flow rate of pure water flowing through the water delivery pipeline by detecting the opening and closing of a solenoid valve installed in the water delivery pipeline or detecting the pressure change of pure water flowing through the circulation pipeline downstream of the branch point of the water delivery pipeline; When pure water begins to flow through the water supply pipeline, or when the flow rate of pure water flowing through the water supply pipeline increases, the pump speed is switched from a first speed to a second speed higher than the first speed; the pump speed is adjusted to the first speed by setting the pump drive output to 5W or less per 1L of minimum storage water volume in the storage tank.

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