Sand Filter Backwashing  

by Pool Builders on 01-25-2012 in Articles

The purpose of your swimming pool filter is to remove suspended solids from the water. Good filtration along with the correct chemical treatment should give you a sparkling, clean and safe pool in which to swim.

Backwashing and rinsing of the filter are important steps to remember when vacuuming your pool. As the name implies, sand filters trap dust and dirt in a bed of sand. The small particles that are removed from the water gradually block up the tiny spaces between the grains of sand, resulting in loss of efficiency of the filter and an increase in internal pressure. Backwashing a filter involves reversing the flow of water, sending it backwards through the filter, flushing out the previously trapped dirt and debris. After backwashing, you will notice a decrease in return pressure to the pool, and if you have a pressure gauge, you should notice a decrease of at least 0.5 bar. Backwashing a sand filter is required when the pressure is 8-10 psi above the standard operating pressure, or at least once every 10 days. For standard filter operating pressures see you filter details.

Step By Step Backwashing.

Please note: Before moving the handle on your multiport valve, the pump must be switched off.

1. Turn the pump off at the electric mains.

2. Switch the handle on the multiport valve from "filter" to "backwash".

3. Open the pump, remove the strainer basket, clean it and replace.

4.Turn the pump back on and backwash for 2-3 minutes. Some filters have a sight glass, if this is the case then run the pump until the cloudy water runs clear.

5. When you have finished backwashing turn the pump off.

6. Turn the handle on the multiport valve from "backwash" to "rinse". This cleans out the pipes and prevents any dirt from returning to the pool. Rinsing also helps to settle the sand which has been disturbed by the backwashing.

7.Turn the pump on and rinse for 20-30 seconds.

8.Turn the pool pump off.

9. Change the setting on the multiport valve from "rinse" to "filter".

10.Open the leaf trap near the pump, remove the basket and clean out all the leaves, twigs and rubbish it may have collected, then replace.

11.Turn the pump on and operate as normal.

As the backwashing process removes water to waste, away from the pool. It may be necessary to top up the water level in the pool.

If using sand as the filter media it should be replaced every 4-5 years. The sand gradually breaks down, becoming finer and finer, and will eventually create a solid block, with no gaps to trap the dirt.

When you are doing a filter sand change, be very careful not to damage the laterals which are at the bottom of the filter. Cracked or broken laterals will result in sand entering the pool.

If using sand use either special filter sand or washed sharp sand 0.3mm - 0.5mm grade.

An alternative to sand is Durafilter Glass Filter Media, which is longer lasting and can last up to 10 years, in addition to which it also removes finer particles and requires 10% less volume than sand.

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