25 May 2005
Table 5-2. Selection Guidelines for Closed System Treatment
High-temperature hot water
Medium-temperature hot water
1. Sulfite-caustic (1)
Low-temperature hot water
Chilled, brine, glycol
Diesel engine jacket
NOTES: (1) Or other oxygen scavenger-caustic.
Table 5-3. Microbiological Control Guidelines for Closed Water Systems
Total aerobic bacteria
< 106 - Undetectable
Sulfite-Caustic (or other Oxygen Scavenger-Caustic) Treatment
Program. This program is required for high- and medium-temperature closed hot water
systems. It is optional for low-temperature water systems. The water is treated with
sodium hydroxide (caustic soda) and with sodium sulfite. This program is suitable for
water systems having temperatures up to 288 C (550 F). This chemical program is
not compatible with ethylene glycol nor propylene glycol. A recommended procedure
for maintenance is described below.
1. Soften makeup water unless the total hardness in the makeup water
supply is less than 10 ppm. The makeup water should be dealkalized if the
makeup's total alkalinity is more than 200 ppm, as CaCO3.
2. Add sodium sulfite to maintain 50 to 100 ppm sulfite (as SO3).
3. Add the appropriate chemical to maintain a pH of 9.0 to 10.0. A pH lower
than 9.0 can be raised by adding sodium hydroxide (caustic soda). A pH
higher than 10.0 can be lowered by adding sodium bisulfite.