how to choose a sand filter for swimming pool

Fiberglass Sand Filters' working theory: 

Sand filter is used to eliminate the small dirt in the pool. The filter sand, as the medium to remove the dirt, is filled in the cavity of the filter. When the control valve is turned to the "filter" position, the pool water containing suspended dirt particles is pumped into the filter pipeline, and then led to the water outlet of the filter. The pool water passes through the filter, and the tiny dirt is collected and filtered  by the sand bed. The filtered clear water is returned to the swimming pool by the pipe at the bottom of the filter. The whole program is continuous and automatic, and provides a complete circulation process for the pool filter and piping system.

After a period of use, the accumulated dirt blocks the water flow and weakens it. Clean the filter at this time. For example, when the valve of  filter  is turned to the "backwash" position, the water flow will turn into the reverse flow, and the water flow will directly reach the bottom of the filter chamber, and then it will be recoiled through the sand layer, and the previously collected dirt and residue will be flushed out from the drain outlet. After each backwashing, the valve should be turned to the "rinse" position, open Turn on the water pump for 0.5 to 1 minute, then turn it to the "filter" position, and restart the normal filtration.

Multi way valve function description:

1. Filter (normal filtration)

2. Backwash (back wash, discharge the dirt in the filter)

3. Rinse (after backwashing, the waste discharged into the sewage pipe)

4. Waste (direct drainage without filter)

5. Recycle (without filter circulation)

6. Closed (turn off filter device)

The final flow of the filter sand cylinder is related to the following factors:

1、 The flow rate of the pressurized water pump (which plays a decisive role);

2、 Filtering area (the larger the filtering area and the smaller the relative resistance, the finer sand can be put to improve the filtering accuracy);

3、 The thickness of sand layer (the greater the thickness of sand layer, the higher the filtration);

4、 The diameter of the pipe (the larger the diameter, the smaller the relative resistance and the larger the flow).

It can be concluded from the above that the deep filtering sand tank can greatly improve the filtering accuracy if not pursuing the flow. 

 As a whole, the flow rate is inversely proportional to the filtering accuracy.  In fact, the flow parameters of the filtering sand tanks are the maximum values that can be achieved in an ideal state (no sand layer resistance), generally larger than the actual flow. If users want to get a larger flow, they should choose a larger sand filter. Only in this way can we avoid the waste caused by the flow mismatch with the pump.