This blog explores some common mistakes made in the application of de-ionization hardware. Although a properly engineered and installed de-ionization system will prevent these potential mistakes at the start, post-installation modifications by those less knowledgeable about de-ionizing technology don’t always respect good design practices.
Temperature Limits –
In general, de-ionization systems are not intended to be used to process water at temperatures exceeding 120°F without special consideration. Once the water temperature exceeds 120 degrees, the de-ionizing resins rapidly degrade or fail completely as they potentially melt and fuse. The canisters containing the resins, normally made of fiberglass, also have a high temperature limit of 120°F. De-ionization at temperatures exceeding 120°F may be accomplished in some cases through the use of special resins and stainless steel canisters but this should only be done under the direction of someone knowledgeable about high temperature de-ionization hardware.
The fact that de-ionization hardware has temperature limits basically rules out re-circulating de-ionized water rinses. If the temperature of the rinse exceeds 120°F the water must be cooled before it enters the de-ionization system only to be re-heated once it is returned to the rinse.
Flow Direction –
The direction of flow through the resin canisters is critical. Although inlet and outlet connections are usually labeled, it is easy to install a canister so that the flow is opposite to that intended. In some cases inlet and outlet connections use plumbing fittings that help prevent improper connections. Any plumbing modifications should respect the proper flow direction through the canister(s).
If a canister is installed so that the flow is in the wrong direction, the result will be an extremely short canister life as the resins inside will not be totally utilized. When water is flowing in the proper direction through the canister, water contact with the resin is maximized. Usually, incoming water is introduced at the bottom of the canister and flows upward to the outlet. In this configuration, no water exits the canister until the resin is totally “flooded” by water. If water is introduced at the top of the canister, it does not fully “flood” the resin resulting in a condition similar to “channeling” which was described in a previous blog.
Since DI canisters look a lot like filters it is easy to mistake them as filters and treat them as filters. In fact, de-ionizing canisters are not intended to provide particle filtration. Filters, of course, have increased resistance to flow as they do their job of removing suspended particles from a liquid. DI canisters, however, do not exhibit reduced flow as they collect ions from water. The flow through a totally spent resin canister will be essentially the same as that through a fresh canister. It can not be assumed that a resin canister is effectively performing its purpose just because water is flowing through it. An indicator light or resistivity meter monitoring the quality of the water exiting the system is the only reliable indicator that the canister is performing properly.
If the flow through a canister diminishes over time it is an indicator that the filter preceding the canister may require replacement. If filter replacement does not restore the expected flow, it can be assumed that the resin canister has been clogged by particles not removed by the pre-filter. This indicates that a better pre-filter is required.
De-ionization is intended to remove electrically charged ions from water. However, there are many other potential contaminants in water that are not electrically charged and require other means for their removal. Subsequent blogs will describe means for removing contaminants that are not electrically charged.
– FJF –
One comment on “Water – De-Ionoized – Right and Wrong”
“The fact that de-ionization hardware has temperature limits basically rules out re-circulating de-ionized water rinses. If the temperature of the rinse exceeds 120°F the water must be cooled before it enters the de-ionization system only to be re-heated once it is returned to the rinse.”
Sounds like a job for a simple counterflow heat exchanger, doesn’t it?