JPH0255090B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for starting and stopping a backwash siphon tube of a gravity filtration device.

Conventionally, when starting each siphon tube in a gravity-type filtration device, a vacuum pump or ejector was connected to the top of the siphon tube, and the vacuum pump or ejector reduced the air pressure inside the siphon tube to start the siphon. However, there is a drawback that an expensive vacuum pump or pressure water pump for the ejector must be provided as a power source.

The present invention compensates for these conventional drawbacks and makes it possible to reliably start and stop a backwashing siphon pipe without the need for a special power source, with low production costs and operation management costs, and with simple operation. purpose.

That is, the present invention has a plurality of filter basins 3 which are partitioned by a partition wall 14 into a floor 6 and a backwash wastewater inflow chamber 13, which are adjacent to and separated from the backwash wastewater inflow chamber 13, so that the backwash water of the floor 6 is A common backwash drainage retention conduit 16 that maintains the water level below the overflow water level, and a common backwash drainage retention conduit 16 that communicates with the bottom of the floor 6 and that maintains the water level above the overflow water level of the backwash water of the floor 6. The overwater drain 9, the raw water drain 2 installed above the overwater drain 3, the backwash wastewater retention drain 16, and the overwater drain 9, and the backwash wastewater inflow chamber 13 and the common backwash wastewater retention drain 16, It is composed of at least a plurality of backwashing siphon pipes 5, which are inverted U-shaped pipes having a bent part above the water level of the water tank 3 and communicating with each other, and both ends of which are sealed with water. In a gravity-type filtration device in which the water in the inflow chamber 13 is discharged by a backwashing siphon pipe 5 and the excess water is caused to flow back to the floor 6 by the water head held by the culvert 9, a closed water tank 19 is used. The upper part of the backwashing siphon pipe 5 and the water tank 19 are connected by a communication pipe 20, and an automatic valve V ₁ is provided for each backwashing siphon pipe in the communication pipe 20, and the water tank 19 is installed.
A common siphon stop automatic release valve V ₃ in the upper part of the or in the communication pipe 20 between the water tank 19 and the automatic valve V ₁
In addition, a water suction pipe 21 having an automatic valve _V5 is provided in the water tank 19, and the lower end of the water suction pipe 21 is connected to the raw water conduit 2.
The water is sealed with raw water inside, and an automatic valve V ₂ is installed in water tank 19.
The lower end of the drain pipe 23 is sealed with water from the backwash drainage retention conduit 16, and the water tank 19 is provided with a supply pipe 28 having an inflow valve _V4 consisting of an automatic valve or a manual valve. , and the water surface of the backwash wastewater inflow chamber 13 when trying to start the backwash siphon pipe 5 for the water tank 19 and the backwash siphon pipe 5.
and the distance H ₂ between the low level water level in the water tank 19 and the water seal water level of the drain pipe ₂₃ ,
The relationship H ₁ < H ₂ holds, and the distance between the high level water level in the water tank 19 and the water seal water level of the water suction pipe 21
H ₅ and the distance H ₄ between the upper part of the backwashing siphon pipe 5 and the water surface of the backwashing wastewater retention conduit 16 are installed so that H ₅ <H ₄ , and the water tank 19 has the above-mentioned high level. A water surface detector 25 for detecting the water level is provided, and the water surface detector 25 and the automatic valve _V5 are linked,
The capacity of the water tank 19 is increased by sucking the air present inside the backwashing siphon pipe 5 and the communication pipe 20 when the water in the water tank 19 is discharged from the drain pipe 23 from the high water level to the low water level. By doing so, the water in the backwashing wastewater inflow chamber 13 is sucked up to a capacity that allows the backwashing siphon pipe 5 to start, and when starting and stopping one of the plurality of backwashing siphon pipes 5, the initial When starting the backwashing siphon pipe 5, the automatic valve _V2 is closed, and the siphon stop automatic release valve _V3 ,
Open the inflow valve V ₄ and fill the water tank 19 with water up to the above-mentioned high water level, then close the inflow valve V ₄ and the siphon stop automatic release valve V ₃ to automatically start the backwashing siphon pipe 5. By opening the valve V ₁ and the automatic valve V ₂ and closing the automatic valve V ₁ of the other backwash siphon pipe 5, the water in the water tank 19 is discharged from the drain pipe 23 with a head difference. Start pipe 5, and after starting, the automatic valve
V ₂ is closed, automatic valve V ₅ is opened, and the negative pressure generated in the upper part of the backwashing siphon pipe 5 sucks up the raw water from the raw water conduit 2 through the water suction pipe 21, and when the water level reaches a high level, the automatic valve is activated. Close valve _V5 and open water tank 1
The water in the water tank 19 is used as starting water for the next backwashing siphon pipe 5, and the automatic valve _V1 of the backwashing siphon pipe 5 which is started is used.
Then, open the siphon stop automatic release valve V ₃ to stop the backwashing siphon pipe 5, and when starting the backwash siphon pipe 5 next time, close the siphon stop automatic release valve V ₃ and start it. Automatic valve V ₁ and automatic valve of siphon pipe 5 for backwashing
V ₂ is opened, automatic valve V ₁ of the other backwash siphon pipe 5 is closed, and the water sucked up from the water suction pipe 21 in the water tank 19 is discharged according to the water head difference, thereby starting the backwash siphon pipe 5. After startup, the automatic valve V ₂ is closed and the automatic valve V ₅ is opened, and the negative pressure generated at the top of the backwashing siphon pipe 5 sucks up the raw water in the raw water conduit 2 through the water suction pipe 21, and the water level rises. When the water level reaches the water level, the automatic valve V ₅ is closed to hold the water in the water tank 19, and the water in the water tank 19 is used as starting water for the backwashing siphon pipe 5 from the next time onwards. The present invention relates to a method for starting and stopping a backwashing siphon tube of a gravity-type filtration device, characterized by sequentially repeating the activation of the backwashing siphon tube 5 and the stopping of the backwashing siphon tube 5.

The present invention will be explained in detail below with reference to the drawings.

The drawing is a longitudinal cross-sectional explanatory view showing an example of an embodiment of a gravity-type filtration device using the method for starting and stopping a backwashing siphon pipe of the present invention. A plurality of over ponds 3 are provided in a line, and a raw water conduit 2 common to each over pond 3 is provided above the over ponds 3. In addition, a raw water distribution chamber 4 is provided on the side of the raw water conduit 2 corresponding to each filter pond 3, and a raw water inflow chamber 15 is provided outside of the raw water distribution chamber 4 via a water seal weir 27. The raw water distribution chamber 4 and the raw water conduit 2 are connected via a plurality of water flow siphon pipes 22. (For convenience, only one siphon pipe 22 for water flow is shown in the figure.) In addition, the filter basin 3 is separated by a partition wall 14.
It is divided into chambers, one chamber is designated as a backwash wastewater inflow chamber 13, and each chamber 13 and each raw water inflow chamber 15 are communicated with each other through a plurality of raw water pipes 24. Further, a support bed 7 is provided below the other chamber of each of the overpass ponds 3, and a floor 6 is formed above the support bed 7, and above the bed 6 and opposite to the height of the upper end of the partition wall 14. A plurality of wash drainage gutters 12 are provided, and one end of the backwash drainage gutters 12 on the partition wall 14 side is opened. In addition, an overwater collection chamber 8 is provided below the support bed 7, and this chamber 8 is further connected to a common overwater conduit 9, so that overwater flowing out from each overwater basin 3 is passed through the overwater collection chamber 8 to the common overwater collection chamber 8. It joins the overflow ditch 9. Further, the overwater drain 9 is communicated with the overwater outflow drain 10 via an overflow weir 11, and the overflow weir 11 is provided so as to be higher than the upper end of the backwash drainage gutter 12, so that the water level of the overwater drain 9 is is maintained approximately constant at the height of the overflow weir 11. Also Kagaike 3
A water surface detection meter 26 is attached to the.

In addition, a common backwash wastewater retention conduit 16 is arranged adjacent to and separated from each backwash wastewater inflow chamber 13, and the backwash wastewater retention conduit 16 and the backwash wastewater inflow chamber 13 of each filter basin 3 are connected. The backwashing siphon pipes 5 are connected to each other by a plurality of backwashing siphon pipes 5 which are inverted U-shaped pipes having a bent part above the water level of the water tank 3 and having both ends sealed with water. (Only one unit is shown.) Further, a backwash wastewater outflow culvert 18 is provided further outside the backwash wastewater retention culvert 16, and a water seal weir 17 having a height lower than the partition wall 14 is provided between the backwash wastewater retention culvert 16 and the backwash wastewater outflow culvert 18. The water level of the backwash wastewater retention conduit 16 is kept constant at the height of the water seal weir 17 through communication.

Also, the water surface of the backwash wastewater inflow chamber 13 above the backwash wastewater retention conduit 16 when the backwash siphon pipe 5 is to be started, and the water surface of the backwash wastewater inflow chamber 13 and the backwash siphon pipe 5
and the distance H ₂ between the low-level water level in the water tank 19 and the water seal level in the drain pipe 23, which will be described later _.
becomes the relationship H ₁ < H ₂ , and the water tank 19
The distance _H5 between the high level water level and the water seal water level of the water suction pipe 21, which will be described later, and the distance _H4 between the upper part of the backwashing siphon pipe 5 and the water surface of the backwash wastewater retention conduit 16 are _H5 <
A closed water tank 19 is provided so that the relationship is _H4 . Note that the capacity of the water tank 19 will be described later. Further, a drain pipe 23 having a thickness that allows the water in the water tank 19 to be quickly drained is provided below the water tank 19, and the lower end of the drain pipe 23 is opened below the water surface of the backwash wastewater retention conduit 16. The water is sealed to prevent air from rising up the drain pipe 23 and flowing into the water tank 19. In addition, an automatic valve is installed in the drainage tank 23.
Attach V ₂ . In addition, the water tank 19 and raw water channel 2
and communicate with each other via a water intake pipe 21 having an automatic valve _V5 , and one end of the water intake pipe 21 on the raw water culvert 2 side is opened below the water surface of the raw water culvert 2 to seal the water,
Air is prevented from flowing into the water tank 19 through the water suction pipe 21.

Further, the diameter of the water suction pipe 21 is set to such a thickness that the raw water from the raw water conduit 2 can be sucked up into the water tank 19 in a short time.

Further, one end of a communication pipe 20 is connected to the upper part of the water tank 19, the other end is connected to the upper part of each backwash siphon 5, and an automatic valve V ₁ is provided in the communication pipe 20 for each backwash siphon pipe. . Furthermore, water tank 19 and automatic valve
A common siphon stop automatic release valve _V3 is provided in the communication pipe 20 between the valve _V1 and the valve V3. Note that the siphon stop automatic release valve _V3 may be provided at the upper part of the water tank 19. In addition, the siphon stop automatic release valve V ₃
The communication pipe 20 between the automatic valve V ₁ and each automatic valve V 1 is further branched to each water flow siphon pipe 2 via the automatic valve V ₆ .
It may be connected to the upper part of 2. Further, a supply pipe 28 having an inflow valve V ₄ consisting of an automatic valve or a manual valve is connected to the water tank 19 .

In addition, a water surface detection meter 25 is provided in the water tank 19, and the water surface detection meter 25 and the automatic valve _V5 are linked to absorb raw water from the raw water conduit 2 by the negative pressure generated in the upper part of the backwashing siphon pipe 5, as described later. Water is sucked into the water tank 19 through the pipe 21, and when the water surface of the water tank 19 reaches a high level A, an automatic valve _V5 linked to the water level detector 25 closes, and water suction from the water suction pipe 21 is stopped. do.

Further, the low level water level D of the water tank 19 mentioned above is lower than the high level water level A, and the capacity of the water tank 19 from the water level A to D is the backwashing siphon pipe 5.
It has sufficient capacity to suck and depressurize the air inside and the communication pipe 20, and when the water in the water tank 19 is discharged through the drain pipe 23 with a water head difference, the water level will be from A to The configuration is such that the backwashing siphon pipe 5 is activated while the process reaches D.

When carrying out filtration in such a filtration device 1, first the siphon pipe 22 for water passage is activated, but as shown in the drawing, the other end of the communication pipe 20 is branched and the siphon pipe 22 for water passage is branched through an automatic valve _V6 . siphon tube 22
When the water tank 19 is in communication with the upper part of the water tank 19, the water flow siphon pipe 22 can be started by using the water tank 19 used in the present invention. That is, the siphon stop automatic release valve V ₃ is opened to open the water tank 19 to the atmosphere, and the inflow valve of the supply pipe 28 is opened.
V ₄ is opened and water for miscellaneous purposes is supplied to the water tank 19 as make-up water, for example, by a water supply pump (not shown).
When the water level of the water tank 19 rises to the high water level A, the inflow valve _V4 is closed and the supply of miscellaneous water is stopped.
Also, when the supply of the makeup water is stopped, close the siphon stop automatic release valve _V3 . Next, open automatic valve V ₆ and automatic valve V ₂ of the water flow siphon pipe 22,
The water in the water tank 19 is rapidly drained from the drain pipe 23. As the water level in the water tank 19 decreases, the air in the water siphon pipe 22 is sucked into the water tank 19 through the communication pipe 20, and the water siphon is sealed by the raw water conduit 2 and the raw water distribution chamber 4. The air pressure in the pipe 22 drops rapidly, the water level inside the water-flowing siphon pipe 22 rises, and the siphon is activated. In this way, the raw water in the raw water conduit 2 passes through the water flow siphon pipe 22 to the raw water distribution chamber 4, and then to the raw water inlet chamber 1.
5, and further flows through the raw water pipe 24 into the backwash wastewater inflow chamber 13 of the overwater basin 3, passes over the partition wall 14 and passes through the floor 6 in a downward flow, and the overwater flows into the overwater collection chamber 8 and the overwater collection chamber 8. It flows out through a water drain 9 and an overwater discharge drain 10. As described above, the water flow siphon pipe 22 has a smaller internal air capacity, for example, about 1/12, compared to the backwashing siphon pipe 5, and the inflow when trying to start the water flow siphon pipe 22 is small. The distance H ₃ between the water surface on the side and the top of the siphon pipe 22 for water passage is much smaller than H ₁ in a normal gravity-type filtration device, and the relationship H ₃ <<H ₂ exists. By using the water tank 19, the water in the water tank 19 can be rapidly drained by the above-described operation.
The water flow siphon pipe 22 can be easily activated.

Further, when the water flow siphon pipe 22 is activated, the discharge of water from the drain pipe 23 of the water tank 19 is stopped, and the water level in the water tank 19 becomes constant. Then automatic valve V ₂ ,
Then, close the automatic valve V ₆ , open the siphon stop automatic release valve V ₃ , and open the inflow valve V ₄ to store makeup water in the water tank 19 up to the high water level A as described above, and open the inflow valve V ₄ . Close it and wait for the first activation of the backwashing siphon tube 5.

If such filtration continues, the floor 6 will become clogged, so backwashing is performed. In other words, at the beginning of the overflow period, the water level in the overflow pond 3 is almost the same as the water level in the overflow channel 9, but as the floor 6 becomes clogged, the water level in the overflow pond 3 gradually rises until the water level reaches the water level. It reaches B of the detector 26. Since the siphon stop automatic release valve V ₃ reached in this way is already open, the automatic valve V ₆ is opened to introduce air into the water flow siphon pipe 22 and turn off the siphon, allowing raw water to flow into the filtration pond 3. interrupt. Also,
When the water sampling time set in advance by a timer (not shown) ends, the automatic valve _V6 may be opened to stop the water flow siphon pipe 22. When the inflow of raw water is interrupted, the water in the over pond 3 passes through the floor 6 and flows out from the over water culvert 9, and the water level drops from B to C, which is slightly above the water level in the over water culvert 9. Draining is completed.

A water surface detector (not shown) is used to detect the end of water draining.
may be provided to detect that the water level has fallen to C, or the time for the water level to fall to C may be set in advance and detected using a timer (not shown).

After doing this, the first backwashing siphon tube 5
In this case, close the siphon stop automatic release valve V ₃ and open the automatic valves V ₁ and V ₂ of the backwash siphon pipe 5 to be activated.
Then, the automatic valve V ₁ of the other backwashing siphon pipe 5 is closed, and the water in the water tank 19 is rapidly discharged from the drain pipe 23. As the water level in the water tank 19 decreases, the air in the backwashing siphon pipe 5 flows into the communication pipe 20.
The water level in the backwashing siphon pipe 5, which is sealed by the backwashing wastewater inflow chamber 13 and the backwashing wastewater retention conduit 16, rises and the siphon is activated. In this way, the water in the filter basin 3 is discharged from the backwash wastewater inflow chamber 13 through the backwash siphon pipe 5, the backwash wastewater retention culvert 16, and the backwash wastewater outflow culvert 18, and the water level in the backwash wastewater inflow chamber 13 is reversed. It falls below the washing drainage gutter 12.

Also, during this time, filtration is being carried out in other overwater basins, and the water level in overwater culvert 9 is kept constant at the height of overflow weir 11. Due to the water head difference with the edge, excess water in the excess water channel 9 flows back from the excess water collection chamber 8 to the floor 6.
Backwashing is performed, and the backwash wastewater flows into the backwash wastewater inflow chamber 13 from the backwash drainage gutter 12. In addition, the backwash wastewater flowing into the backwash wastewater inflow chamber 13 passes through the backwash siphon pipe 5, and then flows into the backwash wastewater retention conduit 16 as described above.
and backwash drainage from drain culvert 18, and the corresponding room 1
3 is maintained below the backwash drainage gutter 12 and above the water level of the backwash drainage retention conduit 16, so that the floor 6 is continuously backwashed.

On the other hand, when the backwashing siphon pipe 5 is activated, the discharge of water from the drain pipe 23 of the water tank 19 is stopped, and the water surface in the water tank 19 becomes a low water level D. After that, if automatic valve V ₁ is left open, automatic valve V ₂ is closed, and automatic valve V ₅ is opened, the backwash siphon pipe 5 is started, and a problem occurs in the upper part of the backwash siphon pipe 5. By a negative pressure of, for example, 4 to 5 m·H ₂ O, the air in the water tank 19 is sucked into the backwashing siphon pipe 5 through the communication pipe 20. In addition, as the air is sucked, the raw water in the raw water conduit 2 is sucked up into the water tank 19 through the water suction pipe 21, and the water level in the water tank 19 rises to the high water level A. At this point, the automatic Valve V ₅ closes,
The flow of water into the water tank 19 is stopped. Then, it is placed on standby for the next activation of the backwashing siphon tube 5.

In this way, while the backwashing siphon pipe 5 is activated for the first time, the negative pressure generated at the upper part of the backwashing siphon pipe 5 can be used to suck up the raw water in the raw water conduit 2 into the water tank 19 and fill it. Therefore, it is only necessary to supply make-up water such as miscellaneous water to the water tank 19 when starting the backwashing siphon pipe 5 for the first time, and from then on, each siphon pipe can be started and stopped without operating the inflow valve V ₄ . It can be performed.

Next, after performing backwashing for a predetermined period of time, the backwashing siphon pipe 5 is stopped, but before that, the following operation is performed to start the water flow siphon pipe 22 and start water flow. good. That is, in a normal gravity filtration device, the siphon capacity of the siphon tube for water passage is much smaller than that of the siphon tube for backwashing, and _H3 is much smaller than _H1 . By opening the valve V ₆ , the air in the water flow siphon pipe 22 is simply sucked into the water tank 19, which has the residual negative pressure generated by the activation of the backwash siphon pipe 5, through the communication pipe 20. The siphon can be easily activated by raising the water level of the water passing siphon pipe 22, and the water flow starts. In addition, the water tank 19 and the communication pipe 2 when starting the water flow siphon pipe 22
0 has a residual negative pressure of, for example, 1.5 to 3 m·H ₂ O, so such negative pressure can be sufficient for starting. Furthermore, if the automatic valve _V1 is opened, the negative pressure generated at the upper part of the backwashing siphon pipe 5 is also added, so that the water flow siphon pipe 22 can be started more easily.

In addition, after starting the water flow siphon pipe 22, immediately close the automatic valve _V6 of the water flow siphon pipe 22, and then close the automatic valve V6 of the water flow siphon pipe 5 that is activated.
V ₁ and the siphon stop automatic release valve V ₃ are opened to introduce air into the backwash siphon pipe 5 to stop the siphon and stop the discharge of backwash wastewater.

After a predetermined period of time, backwashing is performed again, but since the siphon stop automatic release valve V ₃ is already open, the automatic valve V ₆ is opened and air is introduced into the siphon pipe 22 for water flow. to stop the siphon and interrupt the inflow of raw water.

The next activation of the backwashing siphon tube 5 is performed as follows.

i.e. close the siphon stop automatic release valve V ₃ ,
Open the automatic valves V ₁ and V ₂ of the backwashing siphon pipe 5 to be activated, close the automatic valve V ₁ of the other backwashing siphon pipe 5, and close the previous backwashing siphon pipe mentioned above. Water tank 1 sucked up when starting up
The water in 9 is discharged by the difference in water head.

As the water level in the water tank 19 decreases, the air in the backwash siphon pipe 5 is sucked into the water tank 19 through the communication pipe 20, and the water is sealed by the backwash wastewater inflow chamber 13 and the backwash wastewater retention conduit 16. The water level in the backwashing siphon pipe 5 rises and the siphon is activated.

In addition, after the siphon is started, in the same way as the above-mentioned activation of the siphon pipe 5 for backwashing for the first time, if automatic valve V ₁ is left open, automatic valve V ₂ is closed, and automatic valve V ₅ is opened, backwashing starts. The raw water in the raw water conduit 2 is sucked up into the water tank 19 through the water suction pipe 21 due to the negative pressure generated in the upper part of the siphon pipe 5 when the siphon pipe 5 is activated.

Further, the water level of the water sucked into the water tank 19 rises to the high water level A, but at this point the automatic valve _V5 is automatically closed and the flow of water into the water tank 19 is stopped. The water sucked into the water tank 19 in this manner can be used as starting water for the backwashing siphon pipe 5 from the next time onwards.

The method for starting and stopping the backwashing siphon pipe of the present invention is to discharge water from the water tank with a water head difference that is larger than the water head difference in the backwashing siphon pipe, and to suck air in the backwashing siphon pipe that communicates with the water tank. The method is to start the siphon, open the siphon stop automatic release valve, introduce air into the backwash siphon pipe, and stop the siphon.
There is no need for a special power source such as a vacuum pump, and the siphon can be reliably started or stopped simply by opening and closing a small-diameter automatic valve, resulting in low production and operation management costs, and simple and reliable operation. can start and stop the siphon.

In addition, the water tank 19 and the raw water conduit 2 are connected through the water suction pipe 21, and the negative pressure generated by the activation of the backwashing siphon pipe 5 is used to suck up and fill the raw water into the water tank 19. In addition to being able to fill water into tank 19, H ₂ can be made considerably larger than H ₁ , so the water in tank 19 can be drained through the drain pipe 23 in a short time, making the siphon even better. Can be started quickly.

Furthermore, when the water flow siphon pipe 22 is communicated with the water tank 19 used in the present invention via the automatic valve _V6 ,
The water flow siphon pipe can be easily started by simply switching the automatic valve _V6 , and
Further, there is no need to separately provide a siphon stop automatic release valve for the water flow siphon pipe, and the siphon can be stopped using the siphon stop automatic release valve _V3 of the backwash siphon pipe 5.

[Brief explanation of the drawing]

The figure is a longitudinal cross-sectional view of a self-cleaning gravity-type filtration device using a method for starting and stopping a backwashing siphon pipe according to an embodiment of the present invention. 1... Gravity type filtration device, 2... Raw water conduit, 3... Filter pond, 4... Raw water distribution room, 5... Backwash siphon pipe,
6...Floor, 7...Support floor, 8...Hyperwater collection room, 9...
Overwater drain, 10... Overflow drain, 11... Overflow weir,
12... Backwash drainage gutter, 13... Backwash drainage inflow chamber, 14
...Partition wall, 15...Raw water inflow chamber, 16...Backwash wastewater retention culvert, 17...Water seal weir, 18...Backwash wastewater outflow culvert, 19
...Water tank, 20...Communication pipe, 21...Water suction pipe, 22...Water flow siphon pipe, 23...Drainage pipe, 24...Raw water pipe, 25...Water surface detection meter, 26...Water surface detection meter, 27
…Water seal weir, V ₁ , V ₂ , V ₅ , V ₆ … automatic valve, V ₃ … siphon stop automatic release valve, V ₄ … inflow valve.

Claims (1)

[Claims] 1 A plurality of filter basins 3 partitioned into a floor 6 and a backwash wastewater inflow chamber 13 by a partition wall 14, which are adjacent to and separated from the backwash wastewater inflow chamber 13, and the backwash water from the floor 6 overflows. A common backwash drainage retention culvert 16 that maintains the water level below the water level, and a common overwater culvert that communicates with the bottom of the floor 6 and maintains the water level above the water level at which the backwash water of the floor 6 overflows. 9, the raw water culvert 2 installed above the overwater basin 3 and the backwash wastewater retention culvert 16 and the overwater culvert 9, and the backwash wastewater inflow chamber 13 and the common backwash wastewater retention culvert 16,
It is composed of at least a plurality of backwashing siphon pipes 5, which are inverted U-shaped pipes having a bent part above the water level of the water tank 3 and communicating with each other, and both ends of which are sealed with water. In a gravity-type filtration device in which the water in the inflow chamber 13 is discharged by a backwashing siphon pipe 5 and the excess water is caused to flow back to the floor 6 by the water head held by the culvert 9, a closed water tank 19 is used. The upper part of the backwashing siphon pipe 5 and the water tank 19 are connected by a communication pipe 20, and the communication pipe 20 is provided with an automatic valve V ₁ for each backwashing siphon pipe, and the upper part of the water tank 19 is connected to the upper part of the water tank 19. Alternatively, a common siphon stop automatic release valve _V3 is provided in the communication pipe 20 between the water tank 19 and the automatic valve _V1 , and a water intake pipe 21 having an automatic valve _V5 is provided in the water tank 19,
The lower end of the water suction pipe 21 is sealed with raw water in the raw water conduit 2, and a drain pipe 23 having an automatic valve _V2 is provided in the water tank 19, and the lower end of the drain pipe 23 is sealed with water from the backwash drainage retention conduit 16. Supply pipe 2 sealed with water and having an inlet valve V ₄ consisting of an automatic valve or a manual valve in the water tank 19
8 is provided, and the water tank 19 is used as the backwash wastewater inflow chamber 13 when starting the backwash siphon pipe 5.
The distance between the water surface and the top of the backwashing siphon pipe 5
H ₁ and the distance H ₂ between the low level water level in the water tank 19 and the water seal water level of the drain pipe 23 have a relationship of H ₁ < H ₂ , and the distance between the high level water level in the water tank 19 and the water seal water level of the water suction pipe 23 is satisfied. It is installed so that the distance H ₅ of the water seal water level of No. 21 and the distance H ₄ between the upper part of the backwash siphon pipe 5 and the water surface of the backwash drainage retention conduit 16 have a relationship of H ₅ < H ₄ , and A water surface detector 25 for detecting the high level water level is provided in the water tank 19, and the water surface detector 25 and the automatic valve _V5 are linked, and the water tank 19
When the water in the water tank 19 is discharged from the drain pipe 23 from its high water level to its low water level, the air contained within the backwashing siphon pipe 5 and the communication pipe 20 is sucked, The water in the backwash wastewater inflow chamber 13 is sucked up to a capacity that allows the backwash siphon pipe 5 to start, and when starting and stopping one of the plurality of backwash siphon pipes 5, the first backwash siphon is used. When starting the pipe 5, close the automatic valve V ₂ and open the siphon stop automatic release valve V ₃ and the inflow valve V ₄ .
The water tank 19 is filled with water up to the high water level, and then the inflow valve V ₄ and the siphon stop automatic release valve V ₃ are closed, and the automatic valves V ₁ and V ₂ of the backwash siphon pipe 5 to be activated are closed. and close the automatic valve V ₁ of the other backwashing siphon pipe 5.
By discharging the water in the water tank 19 from the drain pipe 23 according to the water head difference, the backwash siphon pipe 5 is started, and after starting, the automatic valve V ₂ is closed, the automatic valve V 5 is opened, and the backwash siphon pipe ₅ is started. The raw water in the raw water conduit 2 is sucked up by the water suction pipe 21 due to the negative pressure generated in the upper part of the pipe 5, and when the water level reaches a high level, the automatic valve _V5 is closed to retain the water in the water tank 19, and the water is retained in the water tank 19. The water in the water tank 19 is used as starting water for the next backwashing siphon pipe 5, and the automatic valve V ₁ and siphon stop automatic release valve V ₃ of the activated backwashing siphon pipe 5 are opened for backwashing. When stopping the siphon pipe 5 and starting the next backwashing siphon pipe 5, the siphon stop automatic release valve V ₃ is used.
, open the automatic valves V ₁ and V ₂ of the backwashing siphon pipe 5 to be activated, close the automatic valve V ₁ of the other backwashing siphon pipe 5, and start the water suction pipe 2.
The backwashing siphon pipe 5 is activated by discharging the water sucked up from the water tank 19 from the water tank 19 with the difference in water head, and after activation, the automatic valve V ₂ is closed, the automatic valve V 5 is opened, and the backwashing siphon pipe ₅ is activated. The raw water in the raw water conduit 2 is sucked up from the water suction pipe 21 by the negative pressure generated in the upper part of the pipe 5, and when the water level reaches a high level, the automatic valve _V5 is closed to retain the water in the water tank 19, The water in the water tank 19 is used as starting water for the backwashing siphon pipe 5 from the next time onward, and thereafter, the starting of the next backwashing siphon pipe 5 and the stopping of the backwashing siphon pipe 5 are sequentially repeated. A method for starting and stopping a siphon tube for backwashing in a gravity-type filtration device.