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Thread: Gravel Bed Question

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  1. #1
    DIY Junior Member benzo's Avatar
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    Default Gravel Bed Question

    I've seen mixed reviews and water softener systems w/ and w/out gravel beds. The folks selling resin tanks w/ gravel beds argue you need it, the ones who don't say its not necessary for softening alone. Care to comment? I'm looking at a 48k grain system for my new home.

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    Underbedding is put in the tank for several reasons. It helps to prevent channeling, keeps resin out of the slats and prevents the baskets from expanding during backwash. I prefer to use underbedding with all my units. I"ve seen unit without it and I've seen units with it. So it will work with it or without.

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    That's all folks! Gary Slusser's Avatar
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    There is no disadvantage to a gravel underbed except the small cost. The primary advantage is a reduction in pressure loss across the softener.

    There is no advantage to not having a gravel underbed.
    Gary Slusser Retired (= out of business)
    Click Here to learn how to correctly size or program a water softener.
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    Master Plumber nhmaster's Avatar
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    Three for gravel under bed.

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    DIY Junior Member pspitael's Avatar
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    Aside from the cost - does adding the 4-6 inches of gravel diminish the required freeboard area above the resin? How does that impact backwash efficiency?

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    Water systems designer, R&D ditttohead's Avatar
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    The gravel cost is minimal, average less than $1 per system. We buy it in bulk, 40,000 pounds a couple times a month.
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    As to calculating water softeners capacities and freeboards etc, industry standards state that only the non domed areas are to be calculated for resin capacity and freeboards. The domed sections are not part of the calculation. The gravel should only fill the domed section in the bottom of the tank. I have attached a picture that shows this.

    Many companies use a smaller tank to save a few dollars, and they do not use a gravel underbed. This is improper, but in all reality, it will work fine. it is bad practice. Other system designs, Vortech tanks, and Turbulator do not use gravel underbedding.

    There is no disadvatage to gravel, other than the slight weight increase for shipping. The units that do not use gravel and claim "incredible performance advantages to systems with gravel" are mostly marketing hype. If the advantages were that amazing, then why is it only used in the most common tank sizes, and not on huge commercial equipment where the advantages would be worth while? These designs are not bad, they are primarily just marketing.
    Last edited by ditttohead; 08-22-2012 at 10:53 AM.

  7. #7
    DIY Junior Member pspitael's Avatar
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    Thanks Dittohead - your picture illustration is helpful

    So a quick follow-up. You state that companies tend to not use gravel and undersize their tanks. From your illustration, seems like the 50% freeboard is 50% of the RESIN volume (not the total TANK volume?). So for instance, a 1.25 cu ft system seems to commonly come in a 10x44" tank - which has a volume of about 2.0 cubic foot. Add 1.25 cu ft resin, and 0.75 cubic foot freeboard - is that sized about right?

    And a related follow-up. If I were to take that same tank (10x44) and add just enough gravel to fill the bottom dome (and most of the distributor?) - that really shouldn't effect the amount of resin needed and the available freeboard, correct? Or would you upsize the tank to a 10x54 (commonly sold for 1.5 cu ft resin?).

    Thanks!

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