SAND FILTER (RAPID SAND FILTER)

Filtration is used in purification treatments in drinking water treatment plants and tertiary treatments in sewage treatment plants; it can also be used as a pre-irrigation method and in swimming pool cleaning.

A distinction is made between slow filtration, fast filtration, and multi-layer filtration:

Slow filtration:

Used in drinking water treatment to remove suspended matter, where the water is sieved at low speed and regulated by a sand bed formed of pure sand with grains of a certain size. Physical, chemical, and biological processes purify water. A special feature is the formation of a surface layer with strong biological activity, which is essential for the function of the filter.

Rapid filtration:

Rapid filtration is a water treatment method in which, after purification, the water is passed through a layer of sand to remove any remaining particles. The filter can work by gravity or by pressure. The filter must be inverted periodically to remove trapped material and thus prevent clogging.

Multi-Layer Filtration:

Water flows up or down through two or more layers. The top layer consists of large, low-density grains. In the subsequent layers, the grains are smaller, but the density is higher.

Functioning

The operation of a sand filter can be divided into three operations: filtering, washing, and rinsing.

Filtering:

Consists of introducing water until all the air is expelled from the filter; this air leaves the filter through the vent circuit controlled by suction cups at the ends. The dirty water is pumped at a certain pressure according to the filtration flow rate, so it is sent to the top of the filter and distributed thanks to a perforated tube that evenly distributes the liquid according to the flow rate, the filter bed is not removed and preferential flows can arise.

The position of the valve bank for this operation is as follows:
valve A closed
valve B open (an outlet for filtered water)
valve C open (inlet for raw water)
valve D closed

Flushing operation:

Flushing operation at a pressure difference of approx. 12 kg/ cm2 between the manometer at the filter inlet at the top of the filter and the manometer at the filter water outlet at the bottom, the filter must be flushed. This is because the filter bed is loaded with retained suspended particles. Clean water is pumped, the water that remains after filtering. The position of the valves is as follows:
valve A open (rinse water inlet)
valve B closed
valve C closed
valve D open (rinse water outlet)

In this way, the wash water enters the filter from below and reverses the flow. The washing water is pumped through the filter thanks to the pumping device and the air necessary to inflate the bed is introduced without creating preferential flows thanks to the blowing device; The air and water inlets are alternated for about ten minutes until the water is observed to come out clearer in the washroom.

Rinsing process:

As soon as the washing water is recognized as clear, the rinsing process is carried out. With the pumping device, water is taken from the wash tank and fed into the filter circuit for washing. This operation usually takes about five minutes. The position of the valves is as follows:
valve A closed
valve B open (wash water inlet)
valve C open (wash water outlet)
valve D closed

Construction principles of Sand filter :

AQUAGUARD sand or activated carbon filters consists of the following elements:

• pumping and washing systems
  structure
• double bottom
• Pipes

Technical characteristics:

Sand filter or activated carbon filter.
AQUAGAURD manufactures a wide range of SAND OR ACTIVATED CARBON FILTERS in accordance with the requirements of the European Community Machinery Directive 89/395/EEC for pressure vessels and with the modifications and additions under Directives 91/368 and 93/44.

Treatments

Anti-corrosion treatment:

External filter:

• Sandblasting to Sa 2½”, according to Swedish standard SIS 055900.
• Two coats of epoxy tar, every 125 microns.

Internal filter:

• Sandblasting to Sa 2 quality ½”.
• A 30 micron thick chlorinated rubber primer.
• Two coats of chlorinated rubber finish, 35 microns each.

Inspection and maintenance

The maintenance of a pressure sand filter consists of:

• Checking and lubricating the fan and pumps Checking the silencer and the fan filter.
• Check the fan bearings

Acoustic check to replace them if necessary.

• Checking the pulleys and belts

Periodically check whether they are loose or worn.

• Check the coupling of the motor to the pumps.

During maintenance and cleaning work, particular care must be taken to ensure that the machine is switched off and locked in order to avoid accidents.

Quality

The sand filter manufactured by AQUAGAURD has the relevant quality certificates available to any customer upon request.