Shasta Dam Penstock Coaster Gate Project
Tri Tool Inc., was contracted by a local California contractor to bid on a project at the Bureau of Reclamation, Shasta Dam Power Plant. An engineering change to the Penstock Coaster Gate required modifications to the existing five gates for the installation of two Monovar control valves to be used for discharge applications. The new design would allow the plant to replace an old piping system that had experienced cavitation and erosion-corrosion problems, a large portion of which was encapsulated in concrete.
Scope of Work
The Coaster Gates are constructed with 1-1/4" thick steel skin plates riveted to 36" I-Beams. Two 1-5/8" thick spacer plates approximately 12" wide by 36" long were welded between the beams, each 6 feet from centerline of the gate. A 12" flange was then welded to spacer plate and I-Beam. To finish the process a through bore along with a transfer of the bolt circle pattern was needed to attach the new valves. In addition it was discovered that a noticeable distortion occurred to the flange after the welding process.
Trepan 12" hole(left) Boring hole to size(right)
Tri Tool's Service Solution...
A special fixture was designed by Tri Tool to mount on a 1" centerline hole that was transferred from the back spacer plate. This fixture served as a template for drilling the bolt circle pattern, and was then later used to support the clamshell during the boring process. A 212B trepan machine was used to remove the bulk of the material by cutting 12" disks from the gate skin plate and through the newly added spacer plate. After the disks were removed the bore was taken to within 1/8" of final dimension and vee groves for welding were added between the plates and the flange. Once the I.D. welding was completed, the 612SB Clamshell, boring attachment and mounting fixture were bolted in place and the bore was machined to specified tolerances. The final operation consisted of resurfacing the flange to allow a proper seal for the valve gasket.
Finish Bore(left)
