Running Gear: Two Francis turbines with induction generators.
Scope: Mechanical design, controls, switchgear, wicket gate operators, automatic trashracks.
PHT designed and built the equipment for a complete redevelopment of this historic grist mill. The mill has been built and rebuilt several times over its history, starting from a land grant from the King of England in the mid-1700s. Prior PHT’s work on the site, it had at one time been an animal feed grist mill, powered by the two turbines through a system of belts and line shafts. In 2009, Leffel rebuilt the turbines, and PHT designed the shafts, bearings, gearboxes and generators to produce electricity at 480v.
The turbines are of the Leffel Samson type, which have a Lignum Vitae thrust bearing under the turbine. As this bearing wears over the years, the turbine and shaft will move down, requiring the guide bearing and shaft coupling to both be expansion types. This allows the shaft to move down without binding the bearing or coupling.
An interesting challenge at this site was installing the new automatic trash racks. The intake is between several grain silos and the river, so it was not possible to directly use a crane or excavator to place the trashracks. Instead, a custom barge was used to float them into place from upstream, where a crane could reach the river. Once the bottoms of the racks were in place, the trash racks were stood up with a chain fall hoist.