Sand filters for swimming pools

A pool sand filter passes water through filter media that retains some of the suspended particles before returning the water to the pool.

The pump pushes the water through the filter, and the circuit is normally controlled by a multiport valve.

Performance depends on the flow rate, filtration area, filtration rate, condition of the media, and correct sizing of the system.

To choose a sand filter, you need to know the pool volume and the flow rate required to recirculate the water properly.

You should also check the flow rate provided by the pump, operating pressure, pipe diameter, and head losses in the system.

It is not advisable to choose the filter solely based on the pool's cubic metres.

The filter diameter is related to its filtration area and the flow rate it can handle.

Two filters with different diameters may offer different capacities and filtration rates even if they are intended for pools of a similar size.

To select the right model, compare the recommended flow rate and the hydraulic specifications provided by the manufacturer.

The pump and sand filter must be sized as a set.

The pump's actual flow rate must not exceed the operating conditions permitted by the filter. An excessively powerful pump can increase the water flow velocity and affect filtration performance.

Always check the flow rate, pressure, connections, and hydraulic characteristics of both pieces of equipment.

Each filter specifies the type, grain size, and amount of filter media to be used.

Silica sand is one of the traditional filter media, although certain filters may accept filter glass or other compatible materials.

Do not use a different grain size without first checking the manufacturer's instructions.

The amount of sand depends on the model, diameter, and internal design of the filter.

Each manufacturer specifies the required load for the equipment to function correctly.

It is not recommended to fill the filter to an approximate height or to calculate the quantity solely based on its outer diameter.

In certain models, filter glass may be used as an alternative to sand, provided that the filter manufacturer allows it.

The required quantity and material characteristics may differ from those of silica sand.

Consult the filter and filter medium specifications before carrying out the replacement.

The multiport valve directs the flow of water through the filter and allows different operations to be performed.

Depending on the model, it may have positions such as filtration, backwashing, rinsing, recirculation, draining, and closed.

The pump should normally be switched off before changing the valve position. Always consult the equipment's specific instructions.

There is no single fixed frequency that applies to all sand filters.

A useful reference is to compare the pressure shown on the pressure gauge with the filter's usual pressure when it is clean. An increase may indicate dirt buildup.

Backwash the filter when appropriate according to the manufacturer's instructions, and then rinse it if the valve has this function.

During backwashing, the water flow is changed to dislodge some of the dirt accumulated in the filter medium and send it to the drain.

Rinsing is carried out afterward in systems that have this function and helps stabilize the filter medium before returning to the filtration position.

Always follow the sequence and duration recommended by the manufacturer.

The increase in pressure may indicate that the filter medium is accumulating dirt and is offering greater resistance to water flow.

Obstructions or problems may also occur in other components of the circuit.

Compare the reading with the usual pressure of the clean system before deciding whether backwashing is necessary.

Sand appearing in the pool may be related to damaged laterals or collectors, problems with the distributor pipe, incorrect grain size, excessive loading, or assembly errors.

If the problem began after replacing the filter media, check the grain size and amount used in particular.

The exact cause will depend on the filter's internal design.

There is no number of years that applies to all sand filters.

Its service life depends on water quality, use, maintenance, treatments applied, and the characteristics of the filter media itself.

If clumping, channeling, or a persistent loss of performance occurs, the media should be inspected and the manufacturer's recommendations consulted.

Poor filtration may be caused by a dirty filter, incorrect flow rate, deteriorated filter media, an incorrectly positioned valve, or circulation problems.

There may also be a chemical imbalance in the water causing cloudiness even if the filter is working correctly.

It is advisable to check the condition of the water, pressure, flow rate, and equipment operation together before attributing the problem solely to the filter.

It may be possible to use a higher-capacity filter as long as it is compatible with the pump and the rest of the installation.

You should check the flow rate, filtration speed, operating pressure, and connection diameter.

Increasing the filter size without reviewing the hydraulic system does not automatically guarantee better performance.

Periodically check the filter pressure, pressure gauge condition, selector valve, seals, and possible leaks.

Backwash when necessary and periodically check the condition of the filter media.

It is also important to keep the pool water properly balanced and follow the manufacturer's maintenance and winterizing instructions.