3 Types of Hardness Leakage in Softeners
Hardness leakage in softeners can happen for a few different reasons. In today’s short post we’ll cover some fundamental reasons why hardness could find its way to the outlet of your softeners. Let’s be clear here: we’re talking about “modern” softeners using ion exchange resin, not hot lime softeners or other technologies used to remove hardness from water.
Some leakage is normal!
Most people don’t realize that it’s normal to have some leakage coming out of their softeners. Of course it’s possible to design softeners such that their leakage levels will be below detectable limits. In critical applications where softeners are protecting expensive equipment like boilers you’ll want to have your water treatment partner size and configure softeners for minimal leakage.
Leakage type 1: Poor design, configuration or bypass leakage
Ok, so this category is a bit of a cop out. I’ll be the first to admit it. If your regeneration cycle isn’t well configured, if some part of the system design is wrong or if there is a bypass in the system where untreated water can make its way to the outlet, you can (and usually will) end up with hardness leakage.
I’ll write a basic softener troubleshooting guide in an upcoming post, but here are the basics. You need to make sure that:
- Your flow rates are correct for bed volume and cross-sectional area. 1-5 gpm per cubic foot of resin and 4-20 gpm per square foot of cross-sectional area are good numbers to use for service flow rates. Aim for the middle of the range.
- Your regeneration cycle achieves correct salt concentration for correct time, as per target leakage. Generally people use 10% brine (by weight) for 30 minutes as a rule of thumb.
- There are no bypasses in the system. Typically in smaller systems with risers (centre tubes) we find leakage possibilities where the riser meets the control head. Every now and then a defective control head or other valve issues cause hardness bypass.
Leakage type 2: Kinetic leakage
Kinetic leakage is leakage caused by water (and the harness it’s carrying) moving through the resin bed too quickly for all the hardness ions to find and stick to an exchange site. If you’re getting kinetic leakage you’ve got two options: make the water move through the bed slower (reduce velocity) or increase bed depth so that hardness will have more time to “find a seat”.
To reduce velocity you have two options: get vessels with a wider diameter or reduce flow rates. Either way, you’ll need to make sure your flow rates meet the design guidelines discussed above.
To increase bed depth you can either add resin to existing vessels or add more vessels in series. Adding resin comes with the complication of needing to leave headroom in your vessel if you need to backwash your softener (as most do).
Leakage type 3: Equilibrium leakage
Equilibrium leakage is one that most people don’t think much about. It’s what happens when flow through the softener is stopped for some time. Hardness already trapped on the resin beads slowly leaches out into the surrounding water, moving towards equilibrium of concentration. It also happens when resin becomes exhausted near the end of a cycle or near the end of its useful life.
Equilibrium leakage is a problem mostly in very sensitive applications. Some industrial applications have a very low tolerance for hardness downstream of their softeners. This type of leakage can be addressed by keeping resin well regenerated, using Purolite SST resins, diverting flow to drain for the first few minutes of service and/or recirculating water through softeners while they are in standby.