why is sand introduced into the pool after the backwash procedure is complete?

[RENEP]

we have a triton sand filter and we get a little sand residual into the pool for about 4 minutes when we bring the filter back on line.

 

[Denis Mitrowski]

A sand filter has a permeable stone in the bottom of the filter canister. There is a bead of caulking around the stone to seal the stone to the stainless steel (or plastic) canister. The sand is layered on top of the stone. When operating in filter mode,water is forced down through the sand and the stone and returns to the pool. When in backwash mode, water is forced up through the stone and sand which dislodges trash and sends it to the drain. Now -- when you switch back to filter mode and notice some sand being sent to the pool, this indicates that the caulk is not making a good seal or the stone has a crack (not likely) or your sand is composed of very fine particles. The only way to find out for sure is to open up the canister,remove the sand and look at the stone and caulking. If all looks OK, replace the sand with Sharp Pool Filter Sand (not just any old sand). If the water is clean and you have no other problems with your pool you may decide to live with this condition until the end of the season. Just be aware that when you vacuum the pool, the sand will "sand blast" the impeller of your pump and cause damage to it.

 

[ranger_co_1_75]

You are using the wrong grit of sand for the screen in the bottom of your filter. Every sand filter should have a screen in the bottom that the sand rest on. This screen keeps the sand out of the pool. If you use the wrong grit of sand, it will go through the screen and into the pool.

The next time you change the sand, get the correct grit. When you vaccum the sand out of the pool, it will wear down the impellers in the pump and damage the pump.

 

[tercir2006]

I'm no expert, but I can only imagine that when you back-flush, some of the sand gets suspended in the water column. It must be settling somewhere in the pipes, and when you switch back to filtration, that sand is being blown into the pool.

Hope this helps a little.

Good luck.