Water-powered gristmill takes its place in history as an engineering landmark

Henry Baumgartner
ASME NEWS

Colvin Run Mill, an operating gristmill in northern Virginia, will become an ASME Historic Mechanical Engineering Landmark in a ceremony next month at the mill site in Great Falls, Va.

The gristmill, which is now operated as a museum, was built around 1811, on a tract of land that had previously belonged to George Washington — and on which he had planned to build a mill. It was used by local farmers to grind grain into flour.

Products from the mill were sold locally as well as along the Eastern Seaboard, transported via the Leesburg Pike. Power was provided by a waterwheel on Colvin Run, a tributary of a stream called Difficult Run.

Colvin Run Mill is powered by a 20-foot-diameter overshot oak waterwheel that produces up to 26 hp. It was in commercial operation until the mid-1930s and restored in 1972.

The mill was based on the work of Oliver Evans (1755-1819), an important figure in the early history of American inventions. Evans revolutionized the milling business with his ideas for using water power to achieve automated processing of grain. He also patented a high-pressure steam engine, in 1790.

Evans's classic "Young Mill-Wright and Miller's Guide" of 1795 explained how to use elevators, moving belts and screw conveyors to construct an automatic production line. The only labor required of the mill operator was to start, stop and adjust the machinery. Grain was fed in at one end and moved through the mill by gravity and water power.

At Colvin Run Mill, the machinery loads, conveys, sifts, grinds, separates and dries the grain into various desired grades, with each of the building's four floors serving a specific function in the production of flour or cornmeal. The mill contains what may be the only operating example in the United States of Evans's hopper boy, a device to cool and dry flour as it comes from the millstones prior to sifting or bolting.

Visitors may also see a grain elevator, wooden Archimedean screws to push the grain through the chute, a bolting chest and shaker assembly (for sifting), and a beam scale for pricing.

The water to power the mill comes from Difficult Run and is diverted into the millrace to power the 20-foot overshot waterwheel. The waterwheel, turning at a rate of 10 rpm, can produce up to 26 horsepower. This results in a top rate of 100 rpm at the grindstone. The gears and machinery are made almost entirely of wood, as was customary before the introduction of metal fittings around 1850.

The gears were originally attached to the brick walls of the mill, and it is thought that this may have contributed to the collapse of the west wall at the turn of the 20th century.

The cog pit extends the length of the mill along the west wall, and the entire gearing apparatus is contained within a husk framework, which is set on the foundation, unattached to the walls. The greater face gear, 10 feet in diameter, transmits power to the grinding stations and the other machinery through a series of shafts and gears. Two of these gears, called wallowers, or trundle or lantern gears, take their power directly from the greater face gear.

At present, only the middle grinding station is in operation. At each grinding station there is a stone crane, positioned to lift and move the runner stones for cleaning and sharpening.

Colvin Run Mill was in commercial operation until the mid-1930s. It languished until being acquired in 1965 by the Fairfax County Park Authority, which restored it to the original Evans design and reopened it as a historical site in 1972.

The combined lesser face and wallower gears power a vertical metal drive shaft that extends through the ceiling of the cog pit and turns the grinding stone on the floor above. Power is transmitted from the waterwheel to these gears along a horizontal oak shaft.

The original millrace was destroyed by highway construction in the 1950s, so a three-stage electric pumping station was built to direct the water into an underground millrace that flows beneath the road. Clifford Currie, a millwright and engineer, designed and built the restored waterwheel, gearing and other handcrafted fittings. The site now includes four buildings on 36 acres.

At the dedication ceremony, set for May 20 at 1 p.m. in the mill building, ASME International President John R. Parker will speak and present a plaque.

Further information may be obtained from the History and Heritage Division's Web site at www. asme.org/history. Colvin Run Mill also operates its own Web site, at www.fairfax.va.us/parks/crm/. The mill can be reached by phone at (703) 759-2771.

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