The size of the sand filter system

Sand filters are very efficient filters. In particular, due to the density of sand, clear requirements are explicitly made of the size of a sand filter system. Below we explain how you can determine the required size of a sand filter system.

Principle of a sand filter system

Sand filters are filters in which the fluid, in most cases water, is mechanically filtered. Dirt particles stick in the sand while the water seeps back out of the sand. This makes sand filters suitable for a wide variety of applications:

  • Fountain
  • House waterworks and water pump
  • Rain water collection tank
  • Aquarium
  • Swimming pool and any kind of swimming pool
  • sewage treatment plants

Reasons for the high efficiency

The high efficiency of sand as a filter medium is to be found above all in the high density. The spaces between the individual grains of sand are therefore extremely small. Depending on the sand grain, then in principle only water fits through these spaces.

Differences compared to other, conventional filter media

There is also an enormous difference compared to conventional filters such as paper, mat or ceramic filters. For these filters, the size of the surface is important, as the fluid is filtered on the surface. When sand as a filter medium, however, one can speak of a "temporal filtering".

The water should run as long as possible through the sand

That is, the longer the water seeps through a correspondingly high layer of sand, the more efficient filtering becomes. In addition, another effect is added, through which the sand filter not only mechanically filters. The longer the sand flow, the larger an anaerobic area forms in the sand. This means an oxygen-free area.

This creates an important anaerobic climate

Here, anaerobic bacteria settle, for example, completely decompose nitrogen and thus algae deprive the food base. This principle is used specifically for the sand filter for the sewage treatment plant. But even at the swimming pool, for sand filters in aquariums or the garden pond, this property is specifically promoted.

Minimum size depends on the amount of water

But it is true that sand also has its volume. As a result, the size of the sand filter must always follow a minimum dimensioning. Accordingly, the sand filter for the aquarium should have at least 20 percent of the water volume. But it is easier with the calculation, which is used at the swimming pool. This is unsuitable for the aquarium.

Calculate minimum size or volume of the filter sand

Accordingly, the minimum requirement for sand in kilos corresponds to the amount of water in cubic meters. For a pool 5 meters long, 2.50 meters deep and 3 meters wide, that would be 37.5 kilos of sand. But even here is more likely to double to triple the amount to guess. Therefore, you should use at least 75 kg of sand as a filter medium in the mentioned Beckenmaßen.

The layer height

But at least as important is the concrete form. So the surface should make a maximum of a quarter of the height. Although it can be repeatedly heard that a sand filter as a pool filter with a sand layer height of at least 50 cm would be fine. But the fact is that the efficiency of the sand filter increases with the stratification height.

Each sand filter should have at least 1 m

For example, there are DIN regulations (DIN 19643) according to which public sand filter systems must have a minimum height of 1.20 m. In the private environment, these DIN standards have no effect. Nevertheless, a minimum height of 1 m should be kept, because only then can the anaerobic area be correspondingly effective.

Size dependence of throughput

The size of the sand filter is also dependent on the water flow. At the swimming pool, all the water should be filtered within four hours. The total volume of water in the pool must therefore be divided by 4. This water flow must be guaranteed. So the size depends on a few factors:

  • Throughput of the sand filter
  • Size of the pool (sand requirement)
  • Height of the sand layer
  • Requirements for filtration needs (how fast and how often daily)

Under "Designing and planning sand filter systems" you will learn in detail how to calculate a sand filter system accordingly.

Tips & Tricks

We offer a whole range of interesting and useful articles about sand filters and sand filter systems. Within our sand filter series, you will learn everything fundamental to this filter system, so for example, to build and materials of sand filter systems, but also useful instructions on how to build the sand filter itself.

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