Siphon filter is one of the fast filter forms which uses siphon instead of inlet and outlet valves. Each cell of the filter is connected with each other, and the backwash water is supplied by other filter water. Each filter cell operates under the condition of constant filter speed and variable water level. Siphon filter is a form of fast filter. Its characteristic is to use siphon principle to enter and discharge sand washing water, so two gates are saved. In addition, it uses the water distribution system with small resistance and the water level of the pool itself to carry out backwashing, and does not need to set another flushing water tank or pump. In addition, it is easy to use hydraulic power to automatically control the operation of the pool, so it has been widely used.
Structure and working principle
Siphon filter is a form of fast filter. Its characteristic is to use siphon principle to enter and discharge sand washing water, so two gates are saved. In addition, it uses the water distribution system with small resistance and the water level of the pool itself to carry out backwashing, and does not need to set another flushing water tank or pump. In addition, it is easy to use hydraulic power to automatically control the operation of the pool, so it has been widely used.
Siphon filter is composed of 6-8 unit filters. The shape of the filter is mainly rectangular, and it can also be round when the water volume is small. The central part of the filter is equivalent to the pipe gallery of the ordinary fast filter, and the inlet water and flushing water of the filter are discharged by siphons. The upper part of the pipe gallery is provided with a vacuum control system 14.
The clarified water flows from the water inlet tank 1 to the distribution tank 2 at the upper part of the filter. The water flows into the water inlet tank 4 of the unit filter through the siphon 3, and then into the filter through the water inlet weir 5 (regulating the water inflow of the unit filter) and the water distribution pipe 6. The water flows into the clean water tank 9 through the filter layer 7 and the water distribution system 8, and then flows into the water outlet well 11 through the outlet pipe 10, and flows out of the filter through the control weir.
In the process of filter, the pollutant content of filter layer is increasing and the head loss is increasing. In order to maintain the water level on the outlet weir 12, that is to maintain a certain filtering speed, the water level in the filter should be rising continuously to overcome the head loss of filter layer growth. When the water level in the filter rises to a predetermined height, the head loss reaches a large allowable value (generally 1.5-2.0m) and the filter layer needs to be washed.
When the siphon filter is filtering, because the water level after filtering is always higher than the filter layer and the positive water head is maintained for filtering, no negative water head phenomenon will occur. The water level in each unit filter varies with the head loss through the filter.
The water distribution system of the filter must adopt a small resistance water distribution system. Therefore, the filter water level (water level in clean water tank) of the filter itself can be used for flushing.
When the filter is washed: first, the vacuum of the inlet siphon 3 is destroyed, then the water in the distribution tank 2 will not enter the filter, and the filter will continue to filter. At first, the water level in the filter tank drops rapidly, but soon there is no significant drop. At this time, flushing can be started. The air in the flushing siphon 15 is extracted by the vacuum system 14 to form a siphon, and the water stored in the filter tank is pumped to the lower part of the tank center through the flushing siphon 15, and then discharged by the flushing drainage pipe 16. At this time, the water level in the filter tank decreases. When the water level in the clean water tank and the water level in the tank form a certain water level difference, the flushing work starts formally. The process of flushing water is similar to that of ordinary fast filter. When the filter material is washed clean, the vacuum of flushing siphon 15 will be damaged, and the flushing will be stopped immediately. Then, start siphon 3, and the filter can be filtered again.
Generally, the flushing head is 1.1-1.3m. It is controlled by the water level difference between the clean water tank 9 and the top of the flushing drainage tank. The average flushing intensity of the filter is generally 10-15 L / s · m2, and the flushing duration is 5-6 minutes. When one unit filter is flushing, other filters will automatically adjust and increase the filtration rate to keep the total treatment water volume unchanged. As the flushing water of the filter is directly supplied by the clean water tank 9, the total water output of other filter units must meet the requirements of flushing water volume when one filter unit is flushed.
The washing strength of the supply unit filter depends on the number of units used, and their relationship can be expressed as follows:
q=nQ/F（3.38）
Where Q -- flushing strength (L / s · m2);
N - number of unit filter;
Q - filtering water volume of unit filter (H / s);
F -- area of unit filter (M2).
The above formula can also be expressed by filtration rate:
n≥3.6q/v（3.39）
Where V - filtration speed (M / h).
When the washing intensity is 10-15 L / s · m2; and the filtration rate is 8 m / h. Using the above formula, it can be calculated that the filter needs at least 5-7 units. If the filter speed is higher, the number of filter cells needed can be less.
The construction of circular or polygonal siphon filter is complex. The plane of the cell pool is fan-shaped or trapezoid. When flushing, there will be mud deposition due to the distance from the drain tank along the pool wall, so the flushing is not clean. At present, the standard drawing adopts rectangular plane. The water treatment capacity is 160m3 / H ~ 2400m3; the siphon filter at / h can be selected according to the national standard drawing.
