When disinfecting valves and other parts of equipment with hot water, the water temperature should be _______ with a chlorine solution of _________ concentration.

The correct pairing of water temperature and chlorine concentration for effective disinfection hinges on the relationship between temperature and the efficacy of chlorine as a disinfectant. In practice, warmer temperatures generally enhance the disinfection capabilities of chlorine by facilitating better reaction rates.

At 120 °F, chlorine remains effective enough to facilitate the disinfection process while still being manageable for equipment and material integrity. Maintaining a chlorine concentration of 25 mg/l at this temperature strikes a balance, ensuring that the solution is strong enough to achieve disinfection goals without causing excessive corrosion or damage to the materials being treated.

This combination is important as higher temperatures like 140 °F or 160 °F could potentially damage equipment or cause safety issues, while too low temperatures may not allow the chlorine to be effective enough for adequate disinfection. Therefore, the choice of 120 °F with a chlorine concentration of 25 mg/l is optimal for achieving effective disinfection while also considering safety and material compatibility.