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CHAPTER XIV.

TURBINES.

THESE Useful water-wheels, for such they really are, may be divided into three classes, viz.: those through which the flow of water is

(1) Parallel. (2) Inward. (3) Outward.

In the first the water flows through the turbine in a direction parallel to its rotating axis, acting upon curved inclined blades. The Jonval is the best known form of this type.

In the second the water acts at a tangent upon vanes in the plane of rotation, but from the circumference inward. Of such are those known as centre-vent patterns-the Trent, the "Hercules," the Rodney, the Victor, and many others, such as the New Victor, the Schiell, the Climax, etc., while the Girard is made both in this form and the succeeding.

In the third the water acts tangentially upon vanes in the plane of rotation, as in the inward form; but in this case the water introduced at the centre flows outward to the circumference. The Fourneyron and the Girard are made on this principle.

All these types have their respective merits; all can claim to have done good work under certain circumstances. The most convenient general form is undoubtedly the second, though there are cases where the first and third may be found more advantageous.

Compared with water-wheels turbines have a great advantage in economical working, and especially in their high speed of rotation, by which large gearing is done away with and simple direct driving may be employed.

This is particularly advantageous in electric - dynamo

driving, the speeds of which approximate those of turbines, and may by proper choice of powers and proportions be made equal.

A horizontal turbine may then be employed coupled direct to the shaft of the dynamo. Such installations are numerous and successful. An excellent sample has been driving the electric plant in the Genoa railway terminus for many years past.

We are not here concerned with the actual construction of the turbine, rules for which may be found in Molesworth's Pocket-Book of Engineering Formulæ, and various treatises on that special subject. But we are concerned with the practical question of which is the best turbine to suit given conditions of water-supply. For this purpose we may arrange the special merits of the well-known form of turbines upon the market somewhat as follows:

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The above dissection must not by any means be taken as conclusive or authoritative, but merely suggestive. If a choice is to lie among the various excellent types of turbines on the American and English markets, and of which some such as the Samson, the Leffel, the Swain, the Houston and the Waverley have not been dealt with in detail, it

must be made on the merits of their manufacture and their actual performances.

Then, too, the claims made by different makers as to their machines' performances and efficiencies are so wide that a whole volume would be needed for their dissection and comparison. It suffices to say that responsible makers of any of these machines will, on being informed of the conditions, offer what their experience has told them to be the best form of turbine to suit the requirements.

Useful Effect.-Performances as high as 88 and 89 per cent. of useful effect have been recorded with a turbine, but an average would not exceed 80 per cent. Therefore, for the purposes of calculation, an average of 75 per cent. of the work in the fall and weight of water is a safe assumption.

As, however, the recorded figures may give strength to this conclusion, I append the record of a test made by Mr. Herschel, engineer to the Holyoke Water Power Company:

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In the Turbine Reporter, Mr. Emerson gives the following record:

Head in Feet. Revolutions. Horse-power. Cubic Feet Water. Percentage.

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It would therefore appear that the assumed useful effect of 75 per cent. is well within the mark of a good machine, and the power obtainable by a turbine from a given fall and quantity of water will run as follows:

Cubic feet per minute × 62.35 × fall in feet

33,000

effective horse-power of the turbine.

X .75

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Upon which basis the following useful table by Mr. Hett is calculated.

Quantity of Water per Horse-power.-The following table shows the quantity of water required for each horse-power, when acting under different falls.

TABLE GIVING THE NUMBER OF CUBIC FEET REQUIRED PER HORSEPOWER PER MINUTE AT 75 PER CENT. EFFICIENCY.

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Head in Feet.

10 ft. 20 ft. 30 ft. 40 ft. 50 ft. 60 ft. 70 ft. 80 ft. 90 ft.

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