With an average annual rainfall of just seven inches, water is an important commodity in Phoenix, Ariz.
Visitors to the city's water service department website will find links to information on "Phoenix in Drought," "Water Conservation Literature," "Water Conservation Plan" and a section entitled "Water: Use It Wisely," which includes "100 Ways to Save Water."
Lack of water also can be an issue in Phoenix - or any municipality - when water pipeline repairs require a shutdown of water delivery to municipal customers. The inconvenience to residents, businesses, and hospitals, as well as the potential loss of fire protection alone makes such outages one of a municipal manager's biggest capital equipment repair concerns.
Combined with the potential for back siphonage, contamination, legally required boil water orders and lost revenue resulting from repair work, a shutdown can become a costly public safety and public relations nightmare.
So, when critical control valves in one of the city of Phoenix's large 60-in. pre-stressed concrete water mains were not working and needed to be replaced, the city's water service department looked for an alternative to a total system shutdown.
A critical stage
The size of the valves and of the pipes was a major issue; cutting out and replacing 60-in. control valves is not a procedure that can be done quickly. Such change-outs can take several days - even a week or more. If that wasn't enough, the situation had reached, according to the water service department, "the critical stage," and the project was given a three-week deadline for completion.
"What made this situation unique was the size of the water main and the number of people it serves," said Jim Sterne, acting assistant water distribution superintendent. "We needed to keep water flowing during the repairs; otherwise, a large portion of south Phoenix would have been without water for a significant period of time."
After considering a number of options, Western Water Works, the general contractor working with the water service department, decided to use the Hydra-Stopper system from Severn Trent Services.
The Hydra-Stopping procedure is a means of temporarily plugging a pressurized pipe without disrupting pressure or service upstream of the repair area, eliminating complete water system shutdowns that create major service disruptions while needed repair or replacement work is being done. Rated at 250 PSI, the system guarantees 95% to 100% stoppage of flow from point of repair. The equipment is available to service pipes ranging from ?- to 60-in.
No interruption of service
Hydra-Stopper eliminates the need to employ obsolete and costly methods of dealing with valve and hydrant problems used in general maintenance of water or other liquid distribution systems by municipalities and industrial plant networks.
The procedure took 10 days, with no interruption of water service to Phoenix residents.
First, a temporary bypass pipe measuring 36-in. was laid to allow a constant flow of water during the repair work. The line stop fitting was then bolted and grouted onto the pipe, support concrete was poured around the fitting then the tapping gate valve and tapping machine were bolted to the fitting. Hydra-Tapper operates from an air or hydraulic drive and is available to perform pressure taps thru 60-in. It works on steel, cast and ductile iron, AC. PVC or HDPE.
With the gate valve opened, a diamond cutter tapped a hole into the pipe. The cutter was then retracted, pulling a pipe "coupon." The line tapping machine was removed and the line stopping machine was bolted to the temporary gate valve and with the gate opened, a folding head stopper was inserted into the pipe to stop flow, diverting it into the temporary pipe. Three old valves were removed and the new valves installed.
Lastly, the line stopping machines, temporary valves and bypass piping were removed.
Although this project was on a tight schedule, it was completed on time. The repair provided the control over the water supply that the water service department needed while improving the infrastructure that routs it through the city of Phoenix - all without a service interruption.