Points to Consider When Choosing a Filter
The most important factors to consider when selecting a sand filter are the surface area where the water contacts the sand and the height of the sand layer within the filter. In filters with a swollen (bulged) body and a narrow top, the water flow velocity increases at the top. Additionally, if the filter is short in height, the swollen body diameter loses its significance. To effectively trap particles in the filter, the water velocity through the sand must be kept as low as possible. Low velocity and a sufficiently deep sand layer are essential conditions for good filtration.
For example, in a conical filter with a 1600 mm diameter swollen body and an 800 mm diameter top, the velocity at the wider bottom section may be 50 m³/h, while at the narrower top it can reach 200 m³/h. At this high velocity, particles can no longer be effectively retained, and debris accumulating at the top is pushed toward the sand bed. This creates significant resistance against the water flow, resulting in a notable decrease in flow rate and increasing the water turnover time required for the pool. Therefore, it is more accurate to consider such a filter as an 800 mm diameter filter.
It is a well-known fact that this type of conical filter is not accepted in any developed country and is considered a non-standard product.
