Fitz Water Wheels
General Information About Overshoot Water Wheels
The Overshoot Wheel derives its power directly from the force of gravity. The illustration shows the principle upon which it works. The weight of the water which is admitted to the buckets, loads one side of the wheel, causing it to revolve.
The water should be applied to the top of the wheel at a point about ten inches back of the vertical center line, so that the buckets will fill up just as they pass over the topmost point of the wheel.
The diameter of an overshoot wheel should be from 2 ½ to 3 ft. less than the total fall available. By total fall, we mean the vertical distance from the surface of the water in the forebay or “tank " above the top of the wheel, down to the surface of the water in tail race or discharge canal, below the bottom of the water wheel.
Wheels of all these types were formerly built of wood. Many picturesque examples of this method of construction are still to be found in rural districts. The overshoot wheel possessed so many advantages that it soon displaced the other early types of water wheels. Even with all its crude design and ill-suited material, the wood overshoot still persists as a strong competitor of the modern small turbine.
The field of the Overshoot Wheel lies in the development of small powers. It is not suitable for use in very large developments on account of the increase in size and weight of the wheel as the head and discharge are increased beyond certain limits. It can be built in any diameter needed up to 60 ft. and in any width desired up to a capacity of 3,000 cubic feet per minute in single units.
The power of an overshoot wheel depends upon both the diameter of the wheel and the width of the wheel. The larger the diameter of an overshoot wheel, the more power it will develop with the same amount of water. The wider the wheel is made, the more water it will accommodate. The relative power of two wheels of the same diameter is of course in direct proportion to the amount of water each wheel is capable of using, if other conditions are equal. The question of determining the proper size wheel to use for any particular location is one which should usually be left to the judgment of the builder of the wheel. We do not publish any list of sizes of wheels in this booklet for the reason that we prefer to have our customer give us the data asked for on page 62, so that we, ourselves, can select the size of wheel he ought to have.
For any location within the range of its capacity, the overshoot type of wheel possesses certain decided advantages over all other types of water wheels, viz.:
The extent to which any overshoot wheel makes use of these advantages depends largely upon the design of the wheel, its accuracy of construction and the material of which it is made. The Fitz Steel Overshoot Water Wheel makes use of the same basic principles as the old wood overshot, but its superior design enables the Fitz Wheel to develop more than 90% efficiency as compared with the 60% to 70% efficiency of the wood wheel. The reasons for this are set forth in detail later on in this booklet under the heading “Comparison with wood wheels." The efficiency of the Fitz Wheel is not a matter of opinion or guess work. Our wheels are rated according to the results shown by rigid tests in Hydraulic Testing Flumes.
Developing an efficiency of 90% or more, the Fitz Steel Over shoot is vastly more efficient than any other type of water wheel known. In the smaller installations especially, where the overshoot most frequently competes with a turbine, it is doubtful whether the turbines ever operate with efficiency higher than 70%. It is true that many turbine builders claim high efficiencies for their wheels, but every experienced turbine user has good reason to know how far the turbines themselves fall short of their makers' claims when confronted with actual running conditions. In every case, where the amount of fall and quantity of flow is suitable for our type of wheel, a Fitz Overshoot will develop at least one-third more power than any turbine working under similar conditions, or 25% more than the best new wood wheel that can be built.
The above statements are made without prejudice to the turbine type of water wheel, for we build a turbine wheel ourselves that ranks fully equal to the best on the market. We are just as glad to sell a turbine wheel as we are to sell an overshoot where the conditions are suitable for a wheel of that type, but we will not furnish either kind for a location where we know that our customers' interests require the other.
From the Library of Robert Vitale (Fitz Bulletin #70)