Water Quality for Bird Water-Cooled Loads


Water quality is measured in terms of the solids (of any character) dissolved in the water. The
solids are usually expressed in “parts per million”. (1ppm=1mg per liter). Standards for drinking water
(potable) are established in the U.S. at a maximum of 500 ppm of total dissolved solids. Due to the fact
that this total ppm count could potentially be comprised of many different types of materials, it is
impossible for us to place a specific water conductivity figure on this limit. However, our experience with
the hardness of water refers to the content of calcium and magnesium salts, which may be bicarbonates,
carbonates, sulfates, chlorides or nitrates.

The salts in “hard water” form “deposits” or “scale” as water is heated or evaporated. Therefore, we recommend that the calcium and magnesium salts cannot exceed 75 ppm. Both the electrical and thermal performance of water-cooled Econoloads is affected by these impurities or other chemical additives in the water. The presence of salts in the water definitely make the device unusable because of the rapid increase in VSWR due to the “scale” accumulation on the inside surface of the ceramic tube (the fields still exist inside of the tubular conductor due to the very thin resistive film used in the manufacture of the resistor). These impurities or “scale” also result in the increase of the thermal resistance of the load and in turn causes the load to overheat and fail. Therefore, sea water or silty water should not be used for cooling the loads.

Effects of De-ionized, Demineralized, and Distilled Water
We use a distilled water/ethylene glycol mixture when we need to fill and operate our water-cooled Moduloads. However, our experience has shown use of pure de-ionized water has a tendency to chemically attack brass, copper, silver and aluminum parts in the whole water system and deposit a
percentage of them on the resistor, resulting in degraded performance as the water tends to seek out
ions to combine with.

Soft or demineralized water is acceptable due to the lower amount of dissolved solids and reasons outlined in above. We have not experienced any detrimental effects on the load housings with the use of soft water. We have also not seen a direct relationship between leaks and the use of incorrect water usage, generally the load will fail electrically or thermally sooner than we see leaks due to incorrect water usage.

Mixing Water & Ethylene Glycol
Ethylene Glycol should be added to the potable water to prevent bacterial growth and freezing.
Bird recommends 10-35% ethylene glycol mix in Moduloads and up to 50% in Econoloads. Using at least
10% will protect against bacteria growth and 35% will protect against freezing to –20o
C. Use only industrial grade ethylene glycol. Do not use commercial anti-freeze preparations or automotive antifreeze. Always add water first then ethylene glycol to ensure proper mixing.

Cleaning & Flushing
If necessary, Bird recommends using diluted oxalic acid for cleaning purposes in a 15-30% acid
concentration. This acid (used in dilution) does not harm the substrates or dielectric coatings and is
used for cleaning out mineral deposits & corrosion products. This acid is readily available world-wide and
does not present major shipping concerns.

Please follow these guidelines:
1. Always refer to your operating instructions for the proper flushing procedure
2. Use 15% acid concentration and no more than 30% acid concentration. Higher concentrations could
cause serious damage to the load.
3. Run the solution through for at least 30 mins. If possible, apply one-half (50%) power to
increase the cleaning effectiveness
4. Flush the acid solution out at least twice with clean coolant before refilling with new coolant.

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