The cast iron water turbine is a key element of the waterpower system of the Ledyard mill which consists of the watershed and Lee’s Brook, a holding pond created by a dam, a headgate controlling water flow through the dam and into the mill penstock (water tank), and then via another control gate into the turbine which directly powers the mill gears and driveshaft. ( for terms see Water Turbine Glossary )

The watershed for Lee’s Brook above the two acre millpond covers about 800 acres. The waterflow is highly variable across seasons, and responds rapidly to rainfall which has resulted in breaching of the dam three or four times in the past 20 years. Dry spells and winter ice limit the power that can be generated and, therefore, limit the times during the year when the mill can be operated.

The turbine receives water through a direct attachment to the bottom of the penstock tank. A wheel near the saw on the main level controls the gate on the turbine, effectively acting as an on-off switch for the sawmill. The top of the turbine can be viewed from the lower level of the mill since it is usually just above or below the surface of the water in the turbine pit. The turbine vanes (blades) cannot be seen moving when it is operating, although the movement is readily inferred from rotation of the vertical shaft rising from the center of the turbine and terminating in a bevel gear. The opening of the turbine gate results in an immediate rush of water out the bottom of the tank and through the turbine, and the resulting turbulence of the water in the pit is obvious. Water flows out of the mill through the tailrace which joins into Lee Brook a couple hundred feet downstream

During the restoration of the mill in the 1970s, the turbine was dug out the accumulated mud and debris of 30-plus years of freshets and dam breaches. The turbine was removed and re-set, and has been the power source of the sawmill since 1975 when the mill reopened. At that time, and in the subsequent years, several generations of volunteers have operated the mill which relied on the turbine for power, but very little specific information was known about the turbine since there are not any manufacturing marks or castings that might indicate what specific type of turbine it is.

Why was a turbine installed at the Ledyard mill instead of a waterwheel? By 1870s-1880s, turbines had evolved from the crude reaction-type wheels of the early 19th century into readily available modern power sources that could be ordered in a size suited for the specific mill seat and head, and with shafting and gears easily customized to specific mill equipment configurations. Turbines often are not as susceptible to reduced flow when the water levels in the tailrace are high (backwater). Perhaps best of all, turbines were iron and therefore did not require constant repair of a complicated waterwheel with wood components that began to rot from intermittent soaking even before installation was complete.

How much power is generated by the 30-inch cast iron Tyler turbine?

Information from turbine testing in the 1860s by the manufacturer showed that under ideal conditions a 30-inch Tyler turbine could generate 7-13 HP with an 8-9 head of water (similar to the distance between the top of the pond and the turbine when the pond is full). We speculate that in its well-used condition with several leaks and some damaged parts, the Tyler turbine in Ledyard can perhaps generate 5-10 HP when the pond is full.

Whatever the actual power, the turbine uses a lot of water. Sawing for three hours can drop the level of the two-acre pond 6-12 inches (depending on pond refilling from the rate of inflow from Lee’s Brook).

Learn more about Tyler turbines