Water Wheels, Reaction Wheels, Saw Mill and Grist Mill Basics

Some basic information on Water Wheels and Mills to help us understand what George Lyon's mills and dams might have looked like.

There are 4 basic types of water or impulse wheels:
Pitchback Wheel - requires a minimum water height of 15' to be efficient.  Maximum efficiency is 90% of potential energy.
Overshot Wheel - requires a minimum height of 15' to be efficient.  Maximum efficiency is 70% of potential energy.
Breastshot (or Breast) Wheel - requires a minimum water height of 6'-8' to be efficient.  Maximum efficiency is 50% of potential energy.  George Lyon's lower dam provided 10' of headwater, therefore using a Breastshot Wheel.
Undershot Wheel - is used where there is minimal water height but sufficient water flow to turn the water wheel.  Maximum efficiency is 20% of potential energy. 

The above water wheels derive their power from the momentum/ impact of falling water. 

Cast Iron Reaction Wheels - The 1853 estate sale notices for George Lyon's mills also mention the use of cast-iron reaction wheels to drive some of the mills - three in total. 

Whereas water wheels derive their power from the impact of water falling on open blades or buckets, reaction wheels (sometimes referred to as "turbines") derive their power from both the impact AND pressure of water falling on blades or buckets that are ENTIRELY ENCLOSED in a watertight case of iron or wood.  Unlike water wheels which are open, pressure is obtained by confining the water as it falls over the blades or buckets.  This allows the buckets to be completely filled with water as they rotate, thereby increasing the efficiency of the wheel.

Unlike water wheels which required a large head of water that was constantly flowing, the efficient operation of the reaction wheel only required a large volume of water (cubic feet per minute) and a moderate head of water.  

Reaction wheels consisted of a rotary fan-like iron "runner" which rotated as the momentum and pressure of the water poured over the blades or buckets, thus giving it rotation and thus power.  Wheels were manufactured with cast-iron or wooden enclosures or with the runner alone (set in bearings).  In the latter case, the purchaser had to fabricate an enclosure for the reaction wheel to be effective. 

A 12" diameter reaction wheel could generate about 3 horsepower on a 10' head (fall) of water.  Today's gasoline-powered lawn mower generates about 3 horsepower.  Horsepower could be increased either by using a larger-diameter wheel, a taller head of water, or both.  Reaction wheels could either be vertical or horizontal and could be used with heads (water falls) as low as two (2) feet.

Maximum head was 100' as the speed of the wheel became excessive.  Typically, the head ranged from 5' to 15'.  If the head of water was only 3' but the flow of water was 8,300 cubic feet per minute (cfm), a large reaction wheel could produce 35 horsepower!  It was therefore important for the mill owner to know the flow of water (in terms of volume) throughout the year and the maximum fall of water over the dam. 

While the illustration below is a vertical reaction wheel, we don't know what type of reaction wheels (vertical or horizontal) were installed in George Lyon's mills.  

Technical details can be obtained from the Exege.com website.  Further details can be found on the Old Sturbridge Village website.

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