Ion Exchange Support Bed

[dogbertcountry2]

I am looking for a technical explanation of why the gravel in the bottom of a water softener does not allo ion exchange resin to flow down through the bed. I" realize the difference in the relative size, but is this the only reason that it does not flow down through? It seems as if there would be "some" amount of escape, especially when the bed gets "lifted" during a backwash. I read in some literature from a gravel manufaturer that, "... the material will hydraulically classify during backwash according to granual size, the smallest rising to the top. When water flows downward, the fine particles at the top of the bed do most of the straining...."

Is this really that simple? We have 3 layers of gravel in the softeners, with increasing size as we go lower in the bed. If resin did get through the gravel, it would then have to get through one of the PVC distributor pipe slits to escape. I am not sure that it would fit, unless it was cracked. If resin did get through the gravel but not out of the distibutor, wouldn't it try to rise to to the top during backwash (as the gravel literature suggests about its own hydraulics)?

 

[GarySCWSVI]

The Backwash Flow Rate for a Water Softener that has a gravel underbedding will not disturb the underbedding. That flow rate is designed to only lift the resin bed.

Resin bead particle size is such that it will not penetrate the gravel underbedding during a service run.

Gary Schreiber, CWS VI
The Purolite Co.

 

[bimr]

It is really that simple. The gravel bed functions as a strainer. The gaps between the gravel in each gravel layer get progressively smaller as you move up through the bed.

Cracked and broken resin will either rise to the surface from where the pieces can be periodically scraped off or overflow with the backwash.

 

[Oscar3]

The density on the gravel is greater than the density of the Garnet, Silica sand and Anthracite. Also keep in mind that the back flow is intended to "lift" those three layers and the "cake" formed during the filtration while the gravel will stay at the bottom.

 

[bimr]

Oscar: Garnet, Silica sand and Anthracite are not used for support beds for ion exchange systems.