Here's a copy from the thread started by AndyC dated 1/15/2006 on the Purolite forum
and his answer to my question saying:
Posted by Gary Schreiber, CWS VI on 01/18/06 at 19:18 from 22.214.171.124
In reply to: Re: Co-current vs counter current regeneration posted by Gary Slusser on 01/18/06 at 11:18
You asked: "My statement "co-current and counter-current are equally salt efficient" is based on both type softeners using the same type resin and the same salt dose. IOWs, the salt efficiency grains/lb will be the same regardless if co-current or counter-current (upflow or downflow) brining is used. Is that true?". Yes.
Prior to that he said:
Posted by Gary Schreiber, CWS VI on 01/15/06 at 18:24 from 126.96.36.199
In reply to: Re: Co-current vs counter current regeneration posted by AndyC on 01/15/06 at 10:03
Regeneration with soft water is better than regenerating with hard water. The obvious "why" of that is the lack of a hardness load on the resin reducing capacity after regeneration. Resin life can, in some cases, be extended by regenerating with soft water. Salt efficiency is not likely affected by a soft water regeneration. Equipment maintenance is likely to be less with soft water regeneration. Produced water quality is not likely to be improved.
The only "out performance" of a single tank over a twin tank system is capital cost is less for a single tank system.
That was in reply to a packed bed and if you look at "The obvious "why" of that is the lack of a hardness load on the resin reducing capacity after regeneration.", if the very slight reduction in capacity allows regenereation to occur prior to the leakage increasing noticably, then there is no advantage to soft water regeneration. Also, "Resin life can, in some cases, be extended by a soft water regeneration.". Do you have any ideas as to what cases he is refering to?
BTW, the efficiency of a twin tank is reduced due to the use of salt to create the capacity used for every soft water regeneration. Which will usually be greater or equal to the two tank type softeners' reserve capacity loss of efficiency the twin tank salesmen claim.
I size all my two tank (regular/normal) softeners to give 0 gpg leakage between regenerations on an 8 day service run. The vast majority of those softeners use fewer than 9 lbs per regeneration and most are around 3-5 lbs total. That's =<9 lbs per 8 days and in the realm of 3333+ grains/lb salt efficiency using sodium chloride. Show me a twin that will do that and use 50-75 total gallons of water on an average 8 day basis with calendar override on day 8 with with a continuous SFR sufficient to produce 0 gpg leakage between co-current (downflow) regenerations.
Now I'd appreciate it if you can prove me wrong. Note there was no mention of damage to resin that are downflow brined...