The Water System Improvement project includes more than 80 projects from San Francisco to Central Valley and is expected to be completed near the end of 2010.
The pipe connections are AWWA C207 ductile iron Class D flat face flanges, ranging from 24" to 108" and are buried in underground tunnels. Due to the size of the lines, cranes are required to maneuver many of the flanges into place. The gasket will either sit on or hang on the bolts while the flanges are being brought together. The flanges may bang or hit the gasket yet the gasket must maintain its upright position and still be capable of creating a seal. As the crane brings together and aligns two flanges it is crucial to have a gasket that will stay in place and maintain its form during this sometimes bumpy process.
Rubber gaskets are compressible and easy to seal, yet they are not very crush resistant. Large rubber gaskets can sometimes be hard to hold in place because they lack rigidity. Also rubber sheet typically comes in rolls that are 36" or 48" wide. Gaskets with diameters larger than the roll width are dovetailed to join two or more arcs with interlocking puzzle-piece-like ends to form a full gasket.
During one phase of the San Francisco project, an EPDM rubber gasket made in 6 segments was used on a 96" pipe. The gasket segments were put together and placed on the bolts of one vertical flange. The crane bringing the two 96" flanges together was not able to align the flanges faces perfectly. When the faces made contact the rubber gasket crushed causing the dovetails to come apart.
Because of this experience, the San Francisco Public Utility Commission decided to specify a one-piece gasket. After trying other options, the utility finally selected a gasket system from Garlock.