A closed loop water system is one in which the water is recirculated in a closed loop without evaporation or exposure to the atmosphere. The only make-up water normally needed is replace water loss from leakage at pump seals, expansion tank overflow, or surface evaporation from system vents. Many times, these systems are neglected since leaks take time to develop. Heat transfer efficiency is not always easy to monitor and the internal system itself is not visible. With proper pre-cleaning and initial treatment, a new system can continue to give good service decades after it is installed. An existing system, dirty due to negligence, can often be restored to an acceptable working condition that is relatively problem free with minimal effort and expense.
A preoperational cleaning is recommended to remove contaminants before start-up. With all areas open to flow, an alkaline solution should circulate for 24 to 48 hours to remove cutting oils and greases. The system should then be flushed. An appropriate inhibitor such as nitrite or molybdate should be added to sufficient levels to maintain corrosion protection. If the new system contains excessive amounts of mill scale and acid-based cleaner should follow the alkaline cleaning.
An analysis should be performed to identify existing or future or problems within the system. This analysis should include pH, conductivity, alkalinity, hardness, and iron. If a freeze protection solution such as glycol is incorporated, freeze protection point and percentage glycol should be performed. With this information a sound recommendation can be made as to the best course of action to prevent future problems or correct existing problems before they reach the point of failure. After chemical treatment is added to a system a water analysis should be performed. From then on , routine tests include pH, iron, and chemical residuals. By performing these tests on a routine basis many problems can be identified long before they progress to the point of failure. Any closed system has the potential to become contaminated with microbes. These microbes can be introduced to the system in many ways. Microbiological corrosion in a closed loop system can become a serious problem in a very short time and should be addressed immediately. Various microbes will produce acidic by-products that will suppress pH and increase corrosion. Others can produce ammonia which will increase pH and cause corrosion. By establishing baseline data as previously mentioned, a determination can be made with good assurance as to the exact process taking place; thereby allowing proper adjustments in the treatment of the system to be made.
If a system becomes contaminated with microbes the system should be sanitized with a biocide. Quaternary Ammonium/Tin biocides have been shown to control most types of microorganisms found in closed loop systems. However, the use of these products may result in foaming problems unless an anti-foam is used along with them. Carbamates and Isothiazolinone based biocides have proven to be effective in closed systems and are not prone to foaming. Sometimes it might be necessary to change treatment programs to help reduce microbial problems, i.e., replacing nitrite with molybdate to alleviate nitrifying bacteria problems.