Is salt bridging mostly theoretical?

Discussion in 'Water Softener Forum, problems, installation and r' started by LLigetfa, May 30, 2012.

  1. LLigetfa

    LLigetfa DIYer, not in the trades

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    I hear so much about it but have never seen it so just trying to understand the physics of it. My take is that in theory, the salt is undermined so that the water meant to dissolve salt into brine doesn't actually touch the salt. In practicality, I cannot see how 200 pounds of salt can hang in the air above the water, supported entirely by friction/adhesion to the sides of the brine tank. If supported by pillars of salt, would not the pillars dissolve and the bridge collapse? Even if there was a cavity formed, would not the brine reach saturation with whatever amount of salt the water is in contact with?

    Last weekend I let the salt level get real low as I intended to empty out the build-up of non-dissolvable material. This got me to wondering if perhaps this material could form pillars to hold up the salt. It never has for me, but it was quite a solid mass that was better not to be there. The mass also caused a dirty silt-like material to get sucked up the intake.

    Anyway... this is the second time in 14 years that I cleaned out the brine tank.
  2. Tom Sawyer

    Tom Sawyer In the Trades

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    Happens all the time, especially with pellets and a humid environment.
  3. Chad Schloss

    Chad Schloss Member

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    it has happened to me twice in 10 years. two different softeners, two different houses.
  4. LLigetfa

    LLigetfa DIYer, not in the trades

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    So what holds the salt up? Are you talking those big box store softeners that have a tank-in-tank design? I can see where those have so much surface area that a mass of salt could fuse around the resin tank.
  5. ditttohead

    ditttohead Water systems designer, R&D

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    There are a lot of ideas about salt bridging, all of them are prtially right and wrong.

    1: Systems that regenerate infrequently tend to bridge more than systems that regenerate regularly... I have seen bridging in systems that regenerate 4 times per day, twin alternating 9000's in commercial applications, so that idea is not accurate,

    2: It only happens in humid environments... partially true, but is also happens in So Cal, we rarely see a day over 30% humidity in the inland areas, humidity does tend to increase the likelihood.

    3: Potassium Chloride is more prone to bridging... yes, definetly true, we see it all the time in areas where the temperature changes dramatically between night and day and when the systems are installed in locations that subject the brine tank to these changes. But... this is easily fixed by simply programming the valve to "brine fill first" one or two hours before regeneration

    4: Pellets bridge worse than salt... unknown, I have seen both bridge, and I have not found any good reasons for why one would, and the other would not.

    Like Tom said, it is not theortical, I have broken bridges in 60" diameter brine tanks, and took a shower as the bridge collapsed into the water below. When servicing commercial and residential systems, the first troubleshooting item is to kick the brine tank down low and hit it up high. If the plastic brine tank is empty on the bottom, and feels like a piece of granite up top, you likely have a bridge. it is easy to tell as your next test is to tast the water in the brine well, a micro drop on your tounge is all it takes to know if the water is making contact with the salt.

    To answer your question, salt bridging is not overly common, but I used to service approximately 10 units per day, every day for 10 years, so bridging was found on a regular basis.

    If you are servicing systems only occassionally, you may never see a bridge.
  6. LLigetfa

    LLigetfa DIYer, not in the trades

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    Rather than keep the salt topped up all the time, I tend to let it get down below the water level before topping it back up. I figured if it was topped up, the 200 pounds of weight would collapse most bridges but with less weight on top I thought there might be a greater propensity to bridge. I've just never seen it.

    Is there any downside to letting the salt get down below the water level? I figure the brine will reach saturation regardless and I can skim off any crud that may float. Also, I get to see the brine level.

    I would also wait until the tank was almost empty to do a manual Iron Out cleaning and watch the brine level drop and refill. Then I would top it back up with 4 bags of salt and repeat when it empties.
  7. ditttohead

    ditttohead Water systems designer, R&D

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    On a system that has a timed refill, not a float refill, the salt level does not matter as saturation will occur so long as there is undissolved salt in the tank. Float refilled systems, you will regenerate the systems with more than the normal amount of salt, this does not hurt, it is simply wasteful. Some systems that regenerate with extremely low amounts of water can get salty water to the house sonce they do not have any buffer built into their regeneration to accomodate a variable like this.

    I do the same, I let the salt run very low, clean the scum off the top, and then fill the tank to the max and ignore it for about 6-8 months. The second filling, about avery 1 months, I will let the salt run very low, and then completely clean and sanitize the brine tank.
  8. LLigetfa

    LLigetfa DIYer, not in the trades

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    One reason I was asking about bridging is that some folk advise against using pellets stating that they have a propensity to bridge. I've been using nature's own water softener potassium pellets for decades and it has never bridged. I have seen the "binder" accumulation in the bottom of the tank though.

    Anyway... I got tired of having to do the manual Iron Out cleaning which always only seemed to give me marginal improvement so decided to try switching to morton system saver II pellets. Again, they are pellets and searching this forum returns warnings about bridging... 10 days and counting... still no bridging.

    So, I've only had a few regens since switching but it has made a world of difference. I don't know how much to attribute to the switch to salt and how much to attribute to the resin cleaning formula. The wife was given quite a potassium "sales pitch" decades ago and so would not consider switching to salt. She was out of town and so I took the opportunity to make the switch and was trying to think about how I was going to break the news to her. She is so impressed with the improvement that it is a non issue.
  9. Tom Sawyer

    Tom Sawyer In the Trades

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    You may never experience bridging with pellets. It's fairly common but on the low end of the common scale.
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