Filtration apparatus, apparatus for manufacturing display glass substrates, filtration method, and method for manufacturing display glass substrates

Abstract

To provide a technique improving the accuracy of determining the presence of abnormality in a filter.SOLUTION: The filtration device comprises a filter, an upstream line, a pump, a downstream line, a pressure detector, and a determination unit. The filter filtrates raw water to produce permeation water. The pump installed in the upstream line, delivers the raw water to the filter. The downstream line allows the permeation water passing through the filter to flow. The pressure detector detects the pressure of the permeation water in the downstream line. The determination unit determines the presence of first abnormality when the pressure detector's detected value continuously stays below a first threshold for the duration of a first period during the operation of the pump. The determination unit determines the presence of second abnormality when the number of times of the pressure-detector's detected value falling below a second threshold for the duration of a second period during the operation of the pump is not less than the number of settings. The second threshold is higher than the first threshold, and the number of settings is multiple times.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to a filtration apparatus, a manufacturing apparatus for glass substrates for displays, a filtration method, and a method for manufacturing glass substrates for displays. [Background technology]

[0002] The filtration system comprises a filter, an upstream line, a pump, a downstream line, various detectors, and a control unit. The filter produces permeate by purifying raw water. The upstream line supplies raw water to the filter. The pump pumps raw water from the upstream line towards the filter. The downstream line allows the permeate that has passed through the filter to flow. The various detectors detect physical quantities (e.g., pressure, flow rate, or temperature) of the raw water or permeate in the upstream or downstream line. The control unit controls the pump and other components.

[0003] Patent Document 1 describes a method for determining abnormalities in a filter, specifically clogging or deterioration of the reverse osmosis membrane that constitutes the filter. The method in Patent Document 1 calculates the flow flux of the permeate water based on the detected values ​​of a flow sensor, a temperature sensor, and a pressure sensor, and determines clogging or deterioration of the reverse osmosis membrane by comparing the calculated permeate flux with the initial permeate flux. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2005-288220 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] One aspect of this disclosure provides a technology for improving the accuracy of detecting abnormalities in filters. [Means for solving the problem]

[0006] A filtration apparatus according to one aspect of the present disclosure comprises a filter, an upstream line, a pump, a downstream line, a pressure detector, and a determination unit. The filter produces permeate by filtering raw water. The upstream line supplies the raw water to the filter. The pump sends the raw water towards the filter in the upstream line. The downstream line allows the permeate that has passed through the filter to flow. The pressure detector detects the pressure of the permeate in the downstream line. The determination unit determines that there is a first abnormality if the value detected by the pressure detector during the operation of the pump is below a first threshold for a first consecutive period. The determination unit determines that there is a second abnormality if the number of times the value detected by the pressure detector during the operation of the pump falls below a second threshold within a second period is greater than or equal to a set number. The second threshold is higher than the first threshold, and the set number is multiple times. [Effects of the Invention]

[0007] According to one aspect of this disclosure, it is possible to determine the presence or absence of an anomaly by eliminating fluctuations in the detected value caused by disturbances, thereby improving the accuracy of anomaly detection. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 shows a manufacturing apparatus for display glass substrates according to one embodiment. [Figure 2] Figure 2 shows an example of the change over time in the detected value of the second pressure detector while the second pump is in operation. [Figure 3] Figure 3 is an enlarged view of a portion of Figure 2. [Modes for carrying out the invention]

[0009] The embodiments for implementing this disclosure will be described below with reference to the drawings. In each drawing, the same or corresponding components will be denoted by the same reference numeral, and their descriptions may be omitted.

[0010] Referring to FIG. 1, a manufacturing apparatus 1 for a glass substrate for a display according to an embodiment will be described. In FIG. 1, "P" represents a pump, "PD" represents a pressure detector, and "FD" represents a flow rate detector.

[0011] The manufacturing apparatus 1 includes a filtration apparatus 2, a cleaning apparatus 3, and a polishing apparatus 4. The filtration apparatus 2 generates permeated water by filtering raw water. The permeated water has a lower impurity concentration than the raw water. The permeated water is used, for example, in the cleaning apparatus 3 or the polishing apparatus 4. The cleaning apparatus 3 cleans the glass substrate for a display using the permeated water. The polishing apparatus 4 polishes the glass substrate for a display using the permeated water.

[0012] For example, a TFT (Thin Film Transistor) or a color filter is formed on the glass substrate for a display. High quality is stably required for the glass substrate for a display. Therefore, high quality is also stably required for the permeated water. Note that the use of the filtration apparatus 2 is not limited to the manufacturing apparatus 1 for the glass substrate for a display.

[0013] The filtration apparatus 2 includes, for example, a raw water tank 11, a first line 12, a security filter 13, a second line 14, a first filter 15, a third line 16, a second filter 17, a fourth line 18, and a permeated water tank 19 in this order from the upstream side to the downstream side.

[0014] The raw water tank 11 stores raw water containing impurities. The permeated water tank 19 stores the permeated water that has passed through the security filter 13, the first filter 15, and the second filter 17 in this order. The security filter 13 collects solid particles and the like upstream of the first filter 15 in order to suppress clogging of the first filter 15. The first filter 15 and the second filter 17 are, for example, reverse osmosis (RO) membranes and have a large number of water passing holes slightly larger than water molecules. The RO membrane can also remove solutes dissolved in water.

[0015] Instead of using a reverse osmosis (RO) membrane, it is also possible to use a nanofiltration (NF) membrane. The RO membrane and the NF membrane separate raw water into permeate water and concentrated water. The permeate water has a lower impurity concentration than the raw water. The concentrated water has a higher impurity concentration than the raw water. The concentrated water is discharged outside the filtration device 2. A part of the concentrated water may be refluxed to the raw water tank 11.

[0016] The first line 12 connects the raw water tank 11 and the security filter 13. The second line 14 connects the security filter 13 and the first filter 15. The third line 16 connects the first filter 15 and the second filter 17. The fourth line 18 connects the second filter 17 and the permeate water tank 19. The permeate water tank 19 has a liquid level detector 19a. The liquid level detector 19a detects the water storage capacity of the permeate water tank 19 and transmits a signal indicating the detected value to the control unit 90.

[0017] The filtration device 2 includes a control unit 90. The control unit 90 is, for example, a computer and includes an arithmetic unit such as a CPU (Central Processing Unit) and a storage unit such as a memory. A program for controlling various processes executed in the filtration device 2 is stored in the storage unit. The control unit 90 controls the operation of the filtration device 2 by causing the arithmetic unit to execute the program stored in the storage unit.

[0018] When the detected value of the liquid level detector 19a is below the lower limit value, the control unit 90 operates the first pump 21, the second pump 22, and the third pump 23 to increase the water storage capacity of the permeate water. The first pump 21 sends water toward the security filter 13 in the first line 12. The second pump 22 sends water toward the first filter 15 in the second line 14. The third pump 23 sends water toward the second filter 17 in the third line 16.

[0019] As described above, the control unit 90 activates the first pump 21, the second pump 22, and the third pump 23 when the detected value of the liquid level detector 19a falls below the lower limit. This maintains the amount of permeate stored above a certain level, enabling a stable supply of permeate. The control unit 90 stops the first pump 21, the second pump 22, and the third pump 23 when the detected value of the liquid level detector 19a exceeds the upper limit. This prevents permeate overflow.

[0020] The filtration device 2 includes, for example, a first inverter 31, a second inverter 32, and a third inverter 33. The first inverter 31 supplies an alternating current to the first pump 21 at a frequency corresponding to a control signal sent from the control unit 90. The rotational speed of the first pump 21 is controlled by the frequency of the alternating current supplied to the first pump 21.

[0021] Similarly, the second inverter 32 supplies alternating current to the second pump 22 at a frequency corresponding to the control signal sent from the control unit 90. The rotational speed of the second pump 22 is controlled by the frequency of the alternating current supplied to the second pump 22. The third inverter 33 supplies alternating current to the third pump 23 at a frequency corresponding to the control signal sent from the control unit 90. The rotational speed of the third pump 23 is controlled by the frequency of the alternating current supplied to the third pump 23.

[0022] Incidentally, over time, the first filter 15 becomes clogged. As the first filter 15 becomes clogged, the flow rate of the permeate produced by the first filter 15 decreases. As the flow rate of the permeate decreases, the pressure of the permeate also decreases. Therefore, the filtration device 2 is equipped with at least one pressure detector and a flow rate detector on the upstream or downstream side of the first filter 15 in order to determine the degree of clogging of the first filter 15.

[0023] The first pressure detector 41 is located in the second line 14, between the second pump 22 and the first filter 15. The second line 14 is an upstream line located upstream of the first filter 15. The second line 14 supplies raw water to the first filter 15. The first pressure detector 41 detects the supply pressure of raw water to the first filter 15 and transmits a signal indicating the detected value to the control unit 90.

[0024] The second pressure detector 42 is located in the third line 16, between the first filter 15 and the third pump 23. The third line 16 is a downstream line located downstream of the first filter 15. The third line 16 carries the permeate water that has passed through the first filter 15. The second pressure detector 42 detects the pressure of the permeate water that has passed through the first filter 15 and transmits a signal indicating the detected value to the control unit 90.

[0025] The first flow detector 51 is installed in the third line 16 between the first filter 15 and the third pump 23. The first flow detector 51 detects the flow rate of the permeate water that has passed through the first filter 15 and transmits a signal indicating the detected value to the control unit 90.

[0026] The control unit 90 also functions as a determination unit that determines whether or not there is an abnormality in the first filter 15 based on the detected values ​​of the pressure sensor or flow sensor while the second pump 22 is operating. An abnormality in the first filter 15 includes clogging of the first filter 15. The control unit 90 may evaluate the degree of clogging in stages. The control unit 90 and the determination unit may be provided separately and may send and receive various signals from each other.

[0027] The control unit 90 uses the detected values ​​from the pressure sensor or flow rate sensor while the second pump 22 is operating to determine whether there is an abnormality. The control unit 90 does not use the detected values ​​from the pressure sensor or flow rate sensor while the second pump 22 is stopped to determine whether there is an abnormality. This is because when the second pump 22 is stopped, no permeate water is generated, and the detected values ​​will indicate an abnormality. The second pump 22 is stopped as described above when the detected value from the liquid level sensor 19a of the permeate water tank 19 exceeds the upper limit.

[0028] Figure 2 shows an example of the change over time in the detected value of the second pressure detector 42 while the second pump 22 is operating. As time passes, the first filter 15 becomes clogged. As the clogging of the first filter 15 progresses, the flow rate of the permeate produced by the first filter 15 decreases, and the detected value of the second pressure detector 42 decreases.

[0029] The control unit 90 acquires the detected value of the second pressure detector 42 at set time intervals while the second pump 22 is operating.

[0030] The control unit 90 determines that the value detected by the second pressure detector 42 during the operation of the second pump 22 is the first threshold P TH1 A first abnormality is determined to exist if the value remains below the first threshold P for the first period consecutively. TH1 The first period is set according to the type of first anomaly, for example, the response of the control unit 90 when it is determined that a first anomaly exists. TH1 The first period is set based on the results of experiments conducted in advance and stored in the memory unit of the control unit 90.

[0031] During the operation of the second pump 22, the value detected by the second pressure detector 42 is the first threshold P TH1 If the value falls below the first threshold P, the control unit 90 measures the elapsed time using a timer, and when the elapsed time reaches the first period, the control unit 90 determines that there is a first abnormality. Before the elapsed time reaches the first period, the value detected by the second pressure detector 42 is the first threshold P. TH1 When this is achieved, the control unit 90 determines that there is no first abnormality. By eliminating fluctuations in the detected value caused by disturbances such as pulsation of the second pump 22, the presence or absence of the first abnormality can be determined, and the accuracy of the first abnormality determination can be improved.

[0032] The control unit 90 determines that the value detected by the second pressure detector 42 during the operation of the second pump 22 is within the second period if the second threshold P TH2 A second abnormality is determined to exist if the number of times the value falls below a certain threshold is greater than or equal to the set number of times. Second threshold P TH2The second period is set according to, for example, the type of the second abnormality and the response of the control unit 90 when it is determined that there is the second abnormality. The second threshold value P TH2 and the second period are set based on, for example, the results of experiments conducted in advance and are stored in the storage unit of the control unit 90.

[0033] The second threshold value P TH2 is higher than the first threshold value P TH1 Therefore, the number of times the detected value is below the second threshold value P TH2 is likely to be affected by disturbances. Therefore, the second period may be set longer than the first period. The second period is not particularly limited, but is, for example, selected from 1 hour, 1 day, and 1 month.

[0034] The set number of times used for determining the presence or absence of the second abnormality is set according to the second period. The shorter the second period, the fewer the set number of times. The set number of times may be a plurality of times. If the set number of times is a plurality of times, fluctuations in the detected value caused by disturbances such as the pulsation of the second pump 22 can be excluded to determine the presence or absence of the second abnormality, and the determination accuracy of the second abnormality can be improved.

[0035] Next, the response when it is determined that there is the first abnormality or the second abnormality will be described. In the present embodiment, different responses are performed when it is determined that there is the first abnormality and when it is determined that there is the second abnormality. Note that the same response may be performed when it is determined that there is the first abnormality and when it is determined that there is the second abnormality.

[0036] When the control unit 90 determines that there is the first abnormality, for example, it performs control to prohibit the operation of the second pump 22 in order to prohibit the operation of the filtration device 2. When the control unit 90 prohibits the operation of the filtration device 2, it performs control to prohibit the operation of not only the second pump 22 but also the first pump 21 and the third pump 23. In this case, even if the detected value of the liquid level detector 19a of the permeate water tank 19 is below the lower limit value, each pump remains stopped.

[0037] Furthermore, the control unit 90 also performs control to issue an alarm if it determines that a first abnormality has occurred. The alarm is issued using an alarm device 61. The alarm device 61 is, for example, a display device, a warning light, or a buzzer. The alarm issued when a first abnormality has been determined to occur is, for example, an alarm that prompts an increase in the rotational speed of the second pump 22.

[0038] Upon receiving an alarm, the manager of the filtration system 2 decides whether or not to actually increase the set rotation speed of the second pump 22. Factors used in this decision include, for example, the current set rotation speed of the second pump 22, the time elapsed since the first filter 15 was replaced, or the amount of permeate generated since the first filter 15 was replaced.

[0039] When the administrator of the filtration device 2 determines that the set rotation speed of the second pump 22 should be increased, they input the new set rotation speed to the control unit 90 and also input a command to the control unit 90 to release the prohibition on the operation of the filtration device 2. Subsequently, the control unit 90 controls the second pump 22 to rotate at the input new set rotation speed.

[0040] If the control unit 90 determines that a second abnormality exists, unlike when it determines that a first abnormality exists, it does not prohibit the operation of the filtration device 2 (i.e., the operation of the second pump 22) but allows the operation of the second pump 22. Also, if the control unit 90 determines that a second abnormality exists, it performs control to issue an alarm, similar to when it determines that a first abnormality exists.

[0041] As shown in Figure 2, the second threshold P TH2 is the first threshold P TH1 It is higher than that. Therefore, a second abnormality is usually detected before a first abnormality is detected. An alarm can be issued before the operation of the filtration device 2 is prohibited, prompting the administrator of the filtration device 2 to take action (for example, increasing the set rotation speed of the second pump 22).

[0042] As shown in Figure 2, when the set rotational speed of the second pump 22 is increased at time t1, the flow rate of the permeate generated by the first filter 15 increases, and the detected value of the second pressure detector 42 increases. In this way, by increasing the set rotational speed of the second pump 22, the flow rate of the permeate can be secured without replacing the first filter 15.

[0043] If the operation of filtration device 2 is prohibited, the production of permeate water will stop, and the supply of permeate water to washing device 3 and polishing device 4 will also stop. By prompting the manager of filtration device 2 to take action before prohibiting its operation, a stable supply of permeate water can be ensured.

[0044] It should be noted that a first abnormality may be detected before a second abnormality is detected. For example, in cases where the raw water has a high concentration of impurities, the first filter 15 may become clogged rapidly in a short period of time. Since the first period is shorter than the second period, an abnormality can be detected even if the clogging progresses rapidly in a short period of time.

[0045] The control unit 90 performs control to sound an alarm prompting the replacement of the first filter 15 when the number of times it has determined that at least one of the first and second abnormalities is present reaches a set number (n times) within a predetermined period. The frequency of abnormalities is high, and the degree of clogging is severe. Therefore, an alarm prompting the replacement of the first filter 15 is sounded. n may be an integer of 2 or more. The predetermined period is set to be longer than the first and second periods.

[0046] The detection value of the first flow detector 51 can also be used to determine whether or not a first abnormality or a second abnormality has occurred. The control unit 90 acquires the detection value of the first flow detector 51 at set time intervals while the second pump 22 is operating. As the clogging of the first filter 15 progresses, the flow rate of the permeate generated by the first filter 15 decreases, and the detection value of the first flow detector 51 decreases.

[0047] The control unit 90 determines the value detected by the first flow detector 51 during the operation of the second pump 22 to be the first threshold F. TH1If the value detected by the second pressure detector 42 during the operation of the second pump 22 falls below the second threshold F for the first period, the control unit 90 determines that there is a first abnormality. TH2 A second abnormality is determined to exist if the number of times the value falls below the specified threshold is greater than or equal to the set number of times. Second threshold F TH2 The first threshold F TH1 It is higher than that, and the number of settings is multiple.

[0048] Alternatively, the difference D (>0) between the detected value of the first pressure detector 41 and the detected value of the second pressure detector 42 may be used to determine whether or not a first abnormality or a second abnormality has occurred. While the second pump 22 is operating, the detected value of the first pressure detector 41 is greater than the detected value of the second pressure detector 42. The control unit 90 acquires the difference D at set time intervals while the second pump 22 is operating. As the clogging of the first filter 15 progresses, the flow rate of the permeate water generated by the first filter 15 decreases, and the difference D becomes larger.

[0049] The control unit 90 determines that the difference D during the operation of the second pump 22 is the first threshold D TH1 If the value exceeds the second threshold D for the first period consecutively, the control unit 90 determines that there is a first abnormality. The control unit 90 determines that if the difference D during the operation of the second pump 22 exceeds the second threshold D within the second period TH2 A second abnormality is determined to exist if the number of times exceeding the specified threshold is greater than or equal to the set number of times. Second threshold D TH2 The first threshold D TH1 It is smaller than that, and the number of settings is multiple.

[0050] The determination of whether or not a first abnormality or a second abnormality exists may be made using a combination of two or more factors selected from (1) the detected value of the second pressure detector 42, (2) the detected value of the first flow detector 51, and (3) the difference D (>0) between the detected value of the first pressure detector 41 and the detected value of the second pressure detector 42. The combination is arbitrary.

[0051] The content of the present invention can also be applied to determining whether or not there is an abnormality in the second filter 17. To determine whether or not there is an abnormality in the second filter 17, one or more of the following are used: (1) the detected value of the fourth pressure detector 44, (2) the detected value of the second flow detector 52, and (3) the difference (>0) between the detected value of the third pressure detector 43 and the detected value of the fourth pressure detector 44.

[0052] The third pressure detector 43 is located in the third line 16, between the third pump 23 and the second filter 17. The third line 16 is an upstream line located upstream of the second filter 17. The third pressure detector 43 detects the supply pressure of raw water (permeate that has passed through the first filter 15) to the second filter 17 and transmits a signal indicating the detected value to the control unit 90. While the third pump 23 is operating, the detected value of the third pressure detector 43 is greater than the detected value of the fourth pressure detector 44.

[0053] The fourth pressure detector 44 is located in the fourth line 18. The fourth line 18 is a downstream line located downstream of the second filter 17. The fourth line 18 carries the permeate water that has passed through the second filter 17. The fourth pressure detector 44 detects the pressure of the permeate water that has passed through the second filter 17 and transmits a signal indicating the detected value to the control unit 90.

[0054] The second flow detector 52 is installed in the fourth line 18. The second flow detector 52 detects the flow rate of the permeate water that has passed through the second filter 17 and transmits a signal indicating the detected value to the control unit 90.

[0055] Furthermore, the content of the present invention can also be applied to determining whether or not there is an abnormality in the safety filter 13.

[0056] The above describes the filtration apparatus, the apparatus for manufacturing display glass substrates, the filtration method, and the method for manufacturing display glass substrates related to this disclosure. However, this disclosure is not limited to the embodiments described above. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. These also naturally fall within the technical scope of this disclosure. [Explanation of symbols]

[0057] 2. Filtration device 14. Second line (upstream line) 15. First filter (filter) 16. Third line (downstream line) 22. Second pump (pump) 41. First pressure detector 42. Second pressure detector 51 First flow detector 90 Control Unit (Determination Unit)

Claims

1. A filter that produces permeate water by filtering raw water, An upstream line that supplies the raw water to the filter, In the upstream line, a pump sends the raw water toward the filter, A downstream line through which the permeate water that has passed through the filter flows, A pressure detector for detecting the pressure of the permeate in the downstream line, A determination unit for determining whether or not there is an abnormality in the filter, Equipped with, The determination unit determines that there is a first abnormality if the value detected by the pressure detector during the operation of the pump falls below a first threshold for a first period of time, and determines that there is a second abnormality if the number of times the value detected by the pressure detector during the operation of the pump falls below a second threshold within a second period is equal to or greater than a set number of times. A filtration device in which the second threshold is higher than the first threshold, and the number of settings is multiple.

2. A filter that produces permeate water by filtering raw water, An upstream line that supplies the raw water to the filter, In the upstream line, a pump sends the raw water toward the filter, A downstream line through which the permeate water that has passed through the filter flows, A flow detector for detecting the flow rate of the permeate in the downstream line, A determination unit for determining whether or not there is an abnormality in the filter, Equipped with, The determination unit determines that there is a first abnormality if the detected value of the flow detector during the operation of the pump falls below a first threshold for a first period of time, and determines that there is a second abnormality if the number of times the detected value of the flow detector during the operation of the pump falls below a second threshold within a second period is equal to or greater than a set number of times. A filtration device in which the second threshold is higher than the first threshold, and the number of settings is multiple.

3. A filter that produces permeate water by filtering raw water, An upstream line that supplies the raw water to the filter, A first pressure detector for detecting the pressure of the raw water in the upstream line, In the upstream line, a pump sends the raw water toward the filter, A downstream line through which the permeate water that has passed through the filter flows, A second pressure detector for detecting the pressure of the permeate in the downstream line, A determination unit for determining whether or not there is an abnormality in the filter, Equipped with, The determination unit determines that there is a first abnormality if the difference (>0) between the detected value of the first pressure detector and the detected value of the second pressure detector during the operation of the pump exceeds a first threshold for a first period of time, and determines that there is a second abnormality if the number of times the difference exceeds a second threshold during the operation of the pump within a second period is greater than or equal to a set number of times. A filtration device in which the second threshold is smaller than the first threshold, and the number of settings is multiple.

4. The filtration apparatus according to any one of claims 1 to 3, wherein the determination unit controls the operation of the pump and issues an alarm when it determines that there is a first abnormality, and controls the operation of the pump and issues an alarm when it determines that there is a second abnormality.

5. The filtration apparatus according to any one of claims 1 to 3, wherein the second period is set to be longer than the first period.

6. The filtration apparatus according to any one of claims 1 to 3, wherein the determination unit performs control to issue an alarm prompting replacement of the filter when the number of times it has determined that at least one of the first abnormality and the second abnormality exists reaches a set number of times within a predetermined period.

7. A manufacturing apparatus for display glass substrates, comprising a filtration device according to any one of claims 1 to 3.

8. A filtration method comprising filtering raw water using a filtration device, The filtration device comprises a filter that generates permeate by filtering the raw water, an upstream line that supplies the raw water to the filter, a pump that sends the raw water towards the filter in the upstream line, a downstream line through which the permeate that has passed through the filter flows, and a pressure detector that detects the pressure of the permeate in the downstream line. The filtration method includes determining that a first abnormality exists if the value detected by the pressure detector during the operation of the pump falls below a first threshold for a first consecutive period, and determining that a second abnormality exists if the number of times the value detected by the pressure detector during the operation of the pump falls below a second threshold within a second period is equal to or greater than a set number. A filtration method wherein the second threshold is higher than the first threshold, and the number of settings is multiple.

9. A filtration method comprising filtering raw water using a filtration device, The filtration device comprises a filter that generates permeate by filtering the raw water, an upstream line that supplies the raw water to the filter, a pump that sends the raw water towards the filter in the upstream line, a downstream line through which the permeate that has passed through the filter flows, and a flow detector that detects the flow rate of the permeate in the downstream line. The filtration method includes determining that a first abnormality exists if the detected value of the flow rate detector during the operation of the pump falls below a first threshold for a first consecutive period, and determining that a second abnormality exists if the number of times the detected value of the flow rate detector falls below a second threshold within a second period is equal to or greater than a set number of times. A filtration method wherein the second threshold is higher than the first threshold, and the number of settings is multiple.

10. A filtration method comprising filtering raw water using a filtration device, The filtration device comprises a filter that generates permeate by filtering the raw water, an upstream line that supplies the raw water to the filter, a first pressure detector that detects the pressure of the raw water in the upstream line, a pump that sends the raw water toward the filter in the upstream line, a downstream line through which the permeate that has passed through the filter flows, and a second pressure detector that detects the pressure of the permeate in the downstream line. The filtration method includes determining that a first abnormality exists if the difference (>0) between the detected value of the first pressure detector and the detected value of the second pressure detector during the operation of the pump exceeds a first threshold for a first period of time, and determining that a second abnormality exists if the number of times the difference exceeds a second threshold within a second period during the operation of the pump is greater than or equal to a set number of times. A filtration method wherein the second threshold is smaller than the first threshold, and the number of settings is multiple.

11. A filtration method according to any one of claims 8 to 10, comprising: prohibiting the operation of the pump and issuing an alarm when it is determined that the first abnormality exists; and allowing the operation of the pump and issuing an alarm when it is determined that the second abnormality exists.

12. The filtration method according to any one of claims 8 to 10, wherein the second period is set to be longer than the first period.

13. The filtration method according to any one of claims 8 to 10, further comprising issuing an alarm prompting replacement of the filter when the number of times at least one of the first abnormality and the second abnormality is determined to be present reaches a set number of times within a predetermined period.

14. A method for manufacturing a display glass substrate, comprising manufacturing a display glass substrate using the permeate water obtained by the filtration method described in any one of claims 8 to 10.

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