Hydraulics Facilitate Repairs on 12,000-Ton Movable Roof
The ten 22-foot long bogies on which the five movable sections of the 12,000 ton roof of the Miller Park stadium are carried had to be replaced. The original-equipment bogies proved inadequate. When a bogie guide roller shattered the roof had to be left partially open. The new bogies are 24 feet long and each weighs either 49 or 66 tons. The replacement of each bogie was a straightforward job. The roof had to be lifted, the old bogie removed, the new bogie positioned and the roof had to be lowered. Jacking brackets to lift against had to be designed separately. The stadium roof sections were jacked in ten separate lifts, one for each bogie replacement. Each time, the roof was lifted 4–6 inches, the old bogie driven out under its own power, a new bogie rolled in, and the roof lowered back into place on a spindle bearing.
The weight lifted ranged up to 800 tons, so a capacity safety margin was provided by using four Enerpac 300-ton, 10,000 psi, 12-inch stroke cylinders for each lift. The cylinders were connected to a common manifold fed by an Enerpac 12.5 hp, 10,000 psi electric pump. The 300-ton jacks were a single-acting load-return type. To provide positive pull-down, the Enerpac pump setup included a valve with a venturi feature to deliver negative pressure when needed.
