Backwash pool sand filter

By absorbing particles and contaminated materials and keeping them on their silica surface, sand filters lose their filtration ability over time and need to be restored and cleaned. Cleaning the sand surface of the filter is very simple and it is enough to reverse the direction of the water flow (backwash) and direct the pollution to the sewage.

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In metal sand filters, this is done by the valves installed in the water inlet and outlet. Four valves are considered for easy backwashing of the pool sand filter, which are:

Water inlet valve from the pool to the sand filter
Water outlet valve from the filter to the pool
Sand filter outlet valve to sewage
Pool water inlet valve to the lower part

Pool sand filter backwash time

In calculating the sand filter, the backwash time is considered once after 15 to 20 return cycles. But this time is only theoretical and can be changed based on the amount of water pollution and the amount of pollution.
The best criterion for backwash time is the pressure drop of the sand filter. For this purpose, at the time of setting up the sand filter of the pool, by installing a pressure gauge (pressure display corresponding to the pressure of the pumps and the filtration system) and measuring the pressure in the clean state of the filter, it is possible to obtain the sand filter's working time. By increasing the pressure of the sand filter, which indicates an increase in its pressure drop and clogging of the surface of the sand filter, it is necessary to backwash the sand filter.
During normal operation and filtration of pool water, water enters the upper part of the filter and after passing through the sand bed of the filter, it leaves the lower part of the filter and is directed to the pool.

In general, the following steps should be taken to perform the test correctly:

First, the pool water purification pump must be turned off (the pump that circulates the water in the sand filter of the pool).
Close the outlet valve to the pool and the inlet valve to the filter from the top, and open the filter valve to the sewer and the pool water valve to the lower part of the filter.
Turn on the purification pump. The flow rate for metal filters (closed pool sand filter) can be up to three times the flow rate during filtration. So, if the pool filtration system is equipped with a reserve pump, it is recommended to turn on this reserve pump as well.
In addition, please note that the exit of silica grains from the sand filter in the backwash mode can be due to two reasons:

Too much silica and sand in the filter
Excessive discharge of the pumps in the idle mode
The water coming out of the sand filter of the pool is checked and after making sure that the filter is clean and the clean water comes out of the drain pipe, the purification pump is turned off.
It should be noted that after turning on the pump in flush mode and water exiting the sewer, no pollution may be removed. For this reason, wait at least 1 to 2 minutes during the cooking time and then, if there is no contamination, turn off the pump and perform other steps. Note that in low-water areas or industries, air may be used instead of water to wash the pool sand filter. The steps of backwashing with air are similar to backwashing with water, with the difference that during backwash, an air blower enters the circuit instead of a water pump.
When the pump is off, close the inlet valve to the lower part of the filter and the outlet valve of the water from the sand filter of the pool to the sewer, the inlet valve of the pool water to the upper part of the sand filter of the pool and the drain valve of the sand filter should also be opened.
Turn on the pump for 30 to 90 seconds.
Turn off the pump and return the valves to filtration mode.
Turn on the purification pump again.

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The steps of the fiberglass sand filter (FRP) swimming pool

In the fiberglass pool sand filter, due to the use of a multi-way valve, these steps are much easier and faster. In order to better understand the backwash steps of the pool sand filter, it will also be explained:

1. Turn off the pump (in the fiberglass pool sand filter, to change the valve state, the pump must be turned off, otherwise the valve will be damaged)

2. Placing the valve handle in backwash mode to wash the filter

Pool filter

3. Turn on the pump and check the water coming out of the sand filter of the fiberglass pool (in the sand filter of the fiberglass pool, a glass site is installed in the sewage water path for ease of checking)

4. After making sure that the filter is clean, turn off the pump.

5. Put the valve in rinse mode to drain the dirty water inside the filter after backwashing and turn on the pump for 30 to 60 seconds, then turn it off.

Pool sand filter backwash

Back to the pool sand filter circuit

Put the valve on the filter mode ready to purify the pool water and turn on the pump.

Of course, on the multi-mode valve, there is the Waste option, to completely drain the pool water without filtering, and the Recirculate mode to circulate the water when the pool is not in use, using the gravitational force of the water (when the pump is off), and the Closed mode to remove the filter from the system. There is also pool water purification.

final word

On the website of the specialized collection of Dematehez, the technical information of dozens of sand filter models, from reputable brands with original warranties, has been presented, so that you, dear ones, can enjoy the good feeling of an optimal and smart purchase.