Question about Backwashing

[squibcakes]

Whrn back washing, why doesn't the sand wash out when doing a back wash?

What speed should I run my VS pump when running backwash? I've read that full speed is required to lift the sand but wouldn't that wash out the sand down the drain?

Squib

 

[JVTrain]

Sand does not go out during a backwash because only the smaller particles filtered by the sand are forced out of the sand, usually upward in the filter, then get suspended in the water above the sand and will then be pushed into the mutliport, then out to waste. You may get some sand coming out backwash on a new fill of sand if some of the sand particles are too small or less dense than the properly sized sand (dust/dirt in the sand). There are also screens on the backwash side of the sand to help prevent this in most newer filter designs.

Even full speed while backwashing on a VS pump will not wash out sand. If the circulation pump is FAR too large for the sand filter, this would be possible, but not probable in pool systems.

 

[duraleigh]

Freeboard....the roughly 1/3 of your filter at the top that contains no sand. During backwash, the sand is certainly displaced but not enough to really suspend it in the "freeboard" area which quickly becomes filled with the tinier, less dense particles of dirt. From there they are whisked out to the multiport and away they go.

 

[PAGirl]

I came to understand this process better when I did a deep clean of my sand two years ago. Even with the hose down in the filter, it was mostly dirt and water then came out the top of the filter opening.. I don't remember seeing any sand exiting. Wet sand is heavy enough to stay at the bottom.

 

[squibcakes]

Ok thanks for the info all.

I just did did a double back wash at full speed. I notice sand particles in the sight glass of the filter during the rinse phase but not in the backwash phase.

i didn't notice any sand around the waste pipe in to the sewer.