The principles of siphonic filters and microporous filters

In short: a siphonic filter, also known as a valveless filter tank, is widely used for filtering surface water. As the raw water passes through the filter layer, resistance increases and the liquid level rises; the liquid level in the siphon tube also increases. When it reaches a certain height, a siphon effect is created, which enables backwashing to clean the filter layer and restore its filtering efficiency. This process repeats itself continuously. In the design of siphon filters, factors such as flow rate, media, and backwashing time need to be considered. A microporous tubular filter is a filter that uses microporous tubes as the filtering material; it is widely used for filtering various liquids. Different materials can be chosen as the filtering medium depending on the type of liquid. The filtering precision is at the micron level – as the liquid passes through the microporous tubes, impurities are trapped, while the pure liquid is discharged through the outlet pipe. This type of filter can be backwashed and regenerated using compressed air.

Working principle and operation process of Type A siphonic filter: The body of the Type A filter is divided into three sections by a conical partition and a support mesh, namely the flushing water tank, the filtration area, and the water collection area. At the start of filtration, the naturally clarified water enters the filter through the inlet pipe from the high-level tank; after impurities are trapped by the filter medium, the clean water moves into the collection area and then reaches the flushing water tank via the connecting pipes. When the liquid level reaches point a, it flows out from the outlet to the clean water tank. Due to the need to overcome the resistance of the filter layer, the water inlet level must be higher than point c; thus, the liquid level in the siphon tube is at point b. During the filtration process, as the resistance of the filter layer increases, the liquid level in the siphon tube rises continuously. As the liquid level in the siphon tube gradually rises to point c, water flows down through the siphon auxiliary tube; this is due to the vortex-induced suction at the point where water enters the auxiliary tube, as well as the entrainment of air by the water flow passing through the auxiliary expansion tube. The air in the siphon tube is carried by the water flow through the exhaust pipe to the water seal where it escapes, thereby creating a negative pressure in the siphon tube. Finally, when the negative pressure in the siphon reaches a certain level, siphoning occurs. The clean water stored in the flushing tank flows through the connecting pipes and the collection area to flush the filter media layer, while the flushing water is discharged from the water seal via the siphon rising pipe and the siphon descending pipe. In this way, it automatically transitions from the filtration cycle to the backwashing cycle, as shown in Figure 2. At this point, the liquid level in the rinse water tank begins to drop. When it drops to point e, the opening of the siphon failure tube emerges above the liquid surface; air is drawn in, causing the siphoning effect to cease, and the backwashing cycle stops automatically, entering the second filtration cycle. As can be seen from the operation process, the amount of flushing water depends on the volume of the flushing water tank, while the intensity of the flushing water depends on the average height difference between levels a and e, as well as the drop in level from d, plus the resistance encountered by the water flow during backwashing. The intensity of the flushing can also be controlled by the flushing intensity regulator at the end of the siphon downpipe. Therefore, the flushing of the siphon filter can be strictly controlled according to actual needs. Moreover, once the design parameters are determined, no significant deviations occur during operation, thereby avoiding the problems of insufficient or excessive flushing. Working principle of Type B siphonic filter: The main body of the Type B siphonic filter is divided into a flushing water tank and a filtration area by a support mesh. No conical baffle and collection area. The auxiliary equipment includes a high-level water tank for inflow and a backwash water seal. Pipes that enable automatic operation include siphons, siphon assist pipes, exhaust pipes, and siphon break pipes, as shown in Figure 1. The operating principle of the Type B filter is roughly the same as that of the Type A filter: the liquid to be treated flows from a high-level tank (through natural sedimentation), passes through the filtering layer, and reaches the wash water tank. When the liquid level reaches point a, it flows out from the outlet into the clean water tank. Due to the need to overcome the resistance of the filter layer, the water level at the inlet will be higher than point a; thus, the liquid level in the siphon tube is at point b. During the filtration process, as the resistance of the filter layer increases, the liquid level in the siphon tube continues to rise. As the liquid level in the siphon tube gradually rises to point c, water flows down through the siphon auxiliary tube. Due to the vortex-induced suction at the entrance to the siphon auxiliary tube and the entrainment of air by the water flowing through the auxiliary expansion tube, the air in the siphon tube is carried by the water flow through the exhaust pipe and released into the water seal. and creates a negative pressure in the siphon tube. Finally, when the negative pressure in the siphon reaches a certain level, siphoning occurs. The clean water stored in the flushing tank passes through the filter media layer, into the siphon rise pipe and the siphon drop pipe, and is discharged from the water seal; thus, the system automatically transitions from the filtration cycle to the backwashing cycle, as shown in Figure 2. At this point, the liquid level in the rinse water tank begins to drop. When it drops to point e, the opening of the siphon failure pipe emerges above the liquid surface; air is drawn in, causing the siphoning effect to cease, and the backwashing cycle stops automatically, thereby entering the second filtration cycle. During operation, the amount of flushing water used still depends on the volume of the flushing water tank, while the intensity of the flushing water depends on the average height difference between levels a and e, the height difference between level d, and the resistance encountered by the water flow during backwashing. The intensity of the flushing can also be controlled through the flushing intensity regulator at the end of the siphon downpipe. The Type B filter uses polystyrene plastic foam beads with extremely low specific gravity as the filtering media; these media remain suspended in water. During filtration and backwashing, the direction of water flow is opposite to that in the Type A filter. Due to the absence of a water collection area, connecting pipes, and conical partitions, it features a simple structure, reduced resistance, and easy addition and replacement of filter media – these are the unique advantages of the Type B filter.