Transcript for The Story of Hoover Dam, segment 07 of 12


Hoover Dam's penstock system called for pipes of unprecedented size, ranging from eight and one-half to thirty feet in diameter and five-eighths to two and three-quarters inches in thickness. As it was not possible to ship units of this size across country, steel plate was brought from eastern rolling mills. A steel fabrication plant erected especially for this job near the dam site rolled and assembled the nearly three miles of pipe installed in the canyon wall tunnels. As in all unprecedented phases of Hoover Dam's construction, fabrication of the pipe sections required special machinery and equipment. Edges of the dimension plates were shaped on a planing machine to insure precision and accuracy of later steps in their manufacture. Then they were bent on a giant press and rolled into circular form. One such plate equaled one-third the complete circumference of a finished pipe.

Three of the largest curved plates welded together formed a ring thirty feet in diameter and eleven feet long. Two of these rings joined made up a section weighing one hundred fifty to one hundred eighty-four tons. A vertical lathe machined the edges so the sections would fit precisely when joined into continuous penstocks inside the canyon walls. A train passing through one of the thirty foot sections reveals their comparative size.

When the intake towers and their connected tunnels were ready to receive the penstocks, a specially designed trailer hauled the sections one at a time to the dam site. At the canyon rim a one hundred fifty ton cableway relieved the trailer of its tremendous burdens, swung the pipe sections out over the gorge, and lowered them under absolute control.

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Trailers waiting at portals of the access tunnels carried them to their permanent connections inside the main tunnels. The pipe sections were hoisted into location with cables and joined end to end with pressure pins to form continuous conduits between the intake towers, turbines, and outlet valves.