Why Re-Test?

Re-test programs protect the community water system from a variety of hazards which can develop inside and/or outside the pipes. These drums of highly corrosive and poisonous chemicals served a vital role in maintaining a healthy cooling system in a large plant; but, they posed a serious risk which could strike from inside the pipes if they ever traveled backwards through the pipes. That risk was supposed to be managed; by the installation and maintenance of a high hazard backflow
prevention assembly at the connection to the pipes carrying drinkable water. That assembly was installed when the plant was sold; but, it was not subjected to a re-test requirement. A few years later, the assembly performed as it was designed when a potential backflow condition developed. The tenant below complained about the water which the assembly jettisoned in response to the hazard present at that time. Plant maintenance personnel were directed to the problem, so, they set about becoming hazards outside the pipes ....

They went to the assembly, tucked away
along the back wall, and sawed through the multiple-hundreds-of-dollars
assembly so that they could remove it from the two-inch copper feed-line to
the boiler and chill-water systems....

...then they spliced the copper pipe with black pipe. Black pipe
tends to rust rapidly when it is in a potable system, especially when it is a small section in a large copper system. More important than that, however, is the complete inability to stop backflow which could fly right through the black pipe. This could have turned very bad. Fortunately, the maintenance men did not remove the drip-drain which served the assembly during frequent, yet minor, pressure changes. A knowledgeable person saw the drip-drain and splice, made a report to the appropriate people in the management team at the plant, and then....

... all of the major problems were corrected by the installation of a new assembly, the elimination of the black pipe from the copper system, and the installation of an air-gapped drain large enough to contain
most of the discharge produced by a possible backflow condition.