A sand filter backwash cleanses the filter by reversing the normal water flow. This process effectively removes trapped dirt and debris from the sand bed, restoring the filter's cleaning power.
The Backwash Process: A Step-by-Step Explanation
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Reverse Water Flow: The backwash cycle reverses the direction of water flow within the filter. Instead of water entering from the top and filtering down through the sand, it flows from the bottom to the top. This upward flow is crucial for lifting the accumulated debris. ([Backwashing reverses the flow of water, lifts up and flushes the sand, and then expels the dirty water via a waste line into the ground or drain](Multiple Sources)).
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Sand Agitation and Cleaning: The upward rush of water dislodges and suspends the dirt and debris trapped within the sand. The sand itself becomes agitated, helping to scrub away the contaminants. ([During backwashing, the water flows in reverse, from bottom to top, out of the laterals and up thru the sand, to flush out the trapped dirt from the sand bed,](Pettis Pools))
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Wastewater Removal: The dirty water, now carrying the dislodged debris, is expelled through a dedicated waste line. This line typically leads to a drain or directly into the ground. ([Backwashing reverses the flow of water, lifts up and flushes the sand, and then expels the dirty water via a waste line into the ground or drain](Multiple Sources)).
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Rinse Cycle (Optional but Recommended): After the backwash, a rinse cycle is often used to remove any remaining loose particles from the sand bed. This cycle uses the normal water flow direction (top to bottom) and helps to ensure clear filtered water. ([Typically doing 1 min backwash, 30second rinse, but check the clarity to confirm.](Reddit r/pools)) The rinse water is typically returned to the pool.
Knowing When to Backwash
You should backwash your filter when the pressure gauge shows a significant increase (usually 7-10 PSI above the starting pressure). Cloudy pool water is another indication. ([After "How do I backwash my pool filter?", the most common question we hear regarding backwashing is "When do I know when to backwash my](YouTube - How To Backwash A Pool Sand Filter and When To Do It)).
Duration of the Backwash Cycle
The duration of the backwash cycle varies depending on filter size and the amount of debris accumulated. Visual inspection is key – the backwash is complete when the expelled water runs clear. ([You have to backwash for as long as it takes for the water to run almost clear in the “window”. It could take almost a minute or more.](Reddit r/pools))
