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In late 1998, the City of Tulsa, Oklahoma, installed a new block valve in a 16-inch utility water line at the new Mohawk Water Treatment Plant. The line had to be shut down during the installation, which meant the entire operation had to be completed within 4 hours to keep water flowing to Tulsa.
TDW Services, Inc., was contracted to tap and plug the line, while city crews installed the valve. The newly designed Model 860 Tapping Machine was chosen to tap a 12-inch access into the line. A Model 1220 Folding Plugger was used to stop flow in the line, and the SHORTSTOPP® 60 Plugging Machine installed a completion plug in the 12-inch SHORTSTOPP® Fitting to complete the job.
The one-day job was a very small part in the final stages of completing Tulsa's new $75 million water treatment plant, replacing facilities constructed in 1924. Although the task was minor, it was vital, because the 16-inch line provided cooling water to both the raw water pump station and the distribution pump station. Utility water was also essential to the chemical feed facilities. While flow was stopped in the line, one pumping station remained on line but the raw water pumping facility and the chemical facilities were shut down. The water storage facility, feeding the distribution pumps, held enough water to supply the City of Tulsa for a maximum of 4 hours after flow was stopped. During that time the line was drained, a section removed, a new block valve installed, the line filled, pressurized and placed back in service.
After installation of the 12-inch fitting on the pipe, it was blocked in with concrete to prevent movement of the pipe due to line pressure. A 12-inch SHORTCUTT® Valve was installed on the fitting.
Use of the new Model 860 Tapping Machine, designed for size-on-size taps up to 20 inches, was more "horsepower" than necessary on the 12-inch line, but it provided an excellent opportunity TDW Services to collect data on the new machine, its uses, and applications. The 860 is a larger than it predecessor, the Model 760, and is designed with tougher gearing and hydraulics to provide capabilities for up to 20-inch taps.
When crews and equipment were ready, the tapping machine was removed from its cradle atop its diesel power unit and installed on the fitting. The power unit remained on the flatbed truck adjacent to the tapping site. Once started, the tap required only 40 minutes and the coupon was recovered successfully.
Inspecting the coupon provided the actual inside diameter of the pipe, which was slightly smaller than anticipated because of a thin mortar coating on the inside wall. Opening the plugging head inside the line would be a tight fit.
The Model 1220 Plugging Machine with pivoting plugging head was developed in 1979. It uses a folding plugging head which, inserted through a 12-inch fitting, can plug up to a 20-inch line. The system was developed to provide a cost effective alternative that allows the use of smaller-size fittings to plug a larger line.
The plugger was prepared and installed on the SHORTCUTT® Valve. Before lowering the plugging head, TDW Services Technician Jim Treece confirmed that the line was operating at 100 psi. With the "go ahead" from Ron Cass, Principal Engineer for Montgomery Watson, Construction Contract Manager, the plugging operation began. After stopping the flow, the plugging head would have to be retracted within four hours to keep Tulsa's water supply on line.
The SHORTCUTT® Valve was opened and the plugging head lowered hydraulically into the line. Because of the smaller inside diameter, considerable "jockeying" of the control bar tilt mechanism and opening and closing of the plugging head leaves was required to move the plugging head into the sealing position. Checking the pressure downstream confirmed that the plugging head had sealed.
As the water downstream was drained, a City of Tulsa work crew began cutting the pipe 100 feet downstream from the plugging head. Farther downstream, a 3-inch side outlet valve was being replaced also. In less than 90 minutes, the line had been cut, and the new 16-inch valve had been installed using mechanical couplings.
Now, the downstream line had to be filled and pressurized before the plugging head could be withdrawn. Pressure on both sides of the plugging head had to be equal before the seal could be broken and it could be retracted. Efforts to break the seal began when the downstream pressure was 80 psi, 20 psi lower than the upstream side. It would not break loose. The pressure differential and the tight fit held it in place. There was a problem: 80 psi was the highest pressure possible downstream from the plugging head. The solution was to lower the pressure upstream to equalize pressure on both sides. The plugging head was then removed, placing the line back on stream. Completion time was well within the 4-hour "window" available.
After removing the plugger, a SHORTSTOPP® Plugging Machine, with completion plug installed, was placed on the valve. The valve was opened and the completion plug was inserted into the fitting and locked into the neck. Removing the completion plug would permit re-entry into the line at a future date. The completion machine was removed, a blind flange installed on the fitting, and the job was complete.
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