Construction and materials of sand filter systems

Filtering water for different applications often makes use of sand filter systems. But very few people have an idea of ​​building a sand filter system. Therefore, we explain in this guide the structure and the materials used in sand filter systems.

Distinguishing sand filters from sand and filtering sand

First of all, it has to be pointed out that a sand filter in this series on all topics about sand filter systems refers to filters that use sand to mechanically or physically filter a medium (water). So it's not about filters that are supposed to filter sand out of the fluid or medium. This distinction is important because such filters are also referred to as sand filters.

Fields of application for sand filter systems

Sand filter systems can be used for a wide variety of applications:

  • Swimming pools and pools
  • Aquariums (fresh and salt water)
  • Well water (water pumps and domestic waterworks)
  • Wastewater treatment plants (private as well as public)
  • Guards and bunkers
  • Air turbines (aviation)

We do not want to take the design and materials of sand filter systems for aviation, but also for sand filters for sewage treatment plants into closer consideration here. Aerospace sand filters are unlikely to be of any relevance to do-it-yourselfers while you learn all about the sand filter system for wastewater treatment plants by following the link.

Construction of the entire sand filter system

Sand filters for swimming pools, for the filtration of well water, garden ponds, etc. have the widest distribution. In these applications, in principle, sand filter systems with identical materials and the same structure can be used. The sand filter system can be subdivided into various components:

  • Inlet (suction line, at the pool overflow or skimmer)
  • Circulation pump with two directions
  • Pressure gauge (gauge)
  • Multiway valve (mostly four- or six-way valves)
  • filter housing
  • Connections for drain (return and sewage or sewer)

Construction and technology in the filter vessel

The filter housing or the boiler takes up not only the sand, but also further supply and drainage technology. In addition the structure from top to bottom, as it is often usual:

  • water distributor
  • Supply from the multi-way valve (lateral position)
  • underlying supply line from the multiway valve
  • from this supply line to the filter cross with nozzles or candles for water absorption
  • from the filter cross up a vent hose
  • a drain plug on the outside of the filter bowl
  • between water distributor up to the filter cross sand, possibly multi-layered (different grain size)

Functions and connections at the multiway valve

The multi-way valve is basically optional, so it can be a four- or six-way valve. The typical supply lines or outlets would be:

  • from the pool to the sand filter
  • from sand filter to water basin
  • to the water distributor (above in the sand filter)
  • from the filter cross (or the nozzles or candles)
  • from the water pump
  • to the sewage or canal

principle of operation

The water is pumped or sucked in with pressure (different systems). In order for the water to hit the entire surface of the sand evenly, an appropriate water distributor is installed. This ensures that the water can infiltrate evenly over the entire surface of the sand.

Filtering the water

Now the water seeps through the sand. Dirt particles and other particles are deposited in the sand. Now the water reaches the filter cross. These are arranged in a star or cross-shaped hollow tube, which may be slotted or selectively opened. These nozzles or openings are so small that only the water can flow into the tubes.

Return to the multiway valve

Now the filtered and purified water returns to the multi-way valve. Depending on the setting, the water circulates (the valve is set to "filter"), is routed from bottom to top (drains, waste water or flushed from top to bottom to the sewer or waste water connection) when backwashing the sand filter system.

All drains closed at the valve

A final setting, where all outlets are closed, serves to build up the pressure. From this, the water flow through the filter can be deduced, ie the current degree of soiling of the sand. The more the sand is polluted, the worse the throughput. How often this is the case, of course, depends on the general pollution of the water, so is individually very different.

The materials in a sand filter system

The sand

The sand can be a single grain (single-layer sand filter), but also several layers of sand with different grain sizes can be filled on top of each other (multi-layer sand filter). Sand is conventional quartz sand.

While the size of the surface is crucial in the case of a mat, cotton or paper filter, the main concern of the sand filter is how long the water seeps through the sand. Thus, the filling height of the sand is much more important than the surface.

Direct structure and requirements for the filter sand

In the private environment, the filling height should be at least 50 cm, but even better are sand filter systems from a filling height of 1 m. In public areas even minimum filling heights of 1.20 m are mandatory. This level applies to the aquarium as well as the sand filter for a swimming pool.

The filter kettle

The filter vessel can be made of steel, but also of different plastics. Since many sand filter systems also work with relatively high pressures, a steel boiler is generally recommended because it is significantly more durable than all plastic containers.

Tips & Tricks

The multi-way valve, which is already optional equipment, is chosen according to what is required. Therefore, either a four- or six-way valve. In addition, however, could also be done a motor control to which the pump is connected.

For more information about sand filter system control, read our "Sand Filter Series" if you follow the link below. In addition, other items in the series will be displayed on the page you are currently viewing.

Video Board: Bio Sand Water Filter Construction DIY step-by-step