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8. A travelling crane is essential. The building should be designed for a 10-ton load at least.

9. Ornamentation is not necessary on the exterior of power stations.

10. The boiler-house would best be paved with brick on edge, and the engine-house with tessellated paving.

A very important observation is not to place flues and economisers below the ground water-level. Water is sure to leak in, with continual reduction of economy.

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With gas engines the best system of ventilation must be provided. It may have to be mechanical.

The gas-producer house should, however, always be separate, and the gas holders outside.

As stated, in country districts, for moderate-sized pumping stations for waterworks (or sewage), gas engines demand much attention.

1. The cost of transport of coal will be reduced.

2. With waterwork engines a steady load will always be obtainable, a fact which at once lends itself to economy in working of gas engines, which are not suited to overloads, nor economical at low ones (that is, lower than their rated capacity).

For small plants of any kind gas engines would at once hold the field, but for larger ones it is a debated question.

For the purpose of demonstrating the economy of gas engines the reader is presented with the curves in figs. 594A and 594B, which represent recent gasengine and producer practice. They are interesting. The engine referred to is a 140 B H.P. gas engine,

B.T.US per Hour in. Gas.

2,500,000

2,000,000

15"x14" 3 CYL Gas Engine

BTUs per BHP

Hour

22,000

20,000

18,000

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10000

3 cylinders, 15 in. x 14 in., made by the Westinghouse Company. A small engine would give about 10 per cent. lower values. Fig. 594A shows some efficiency curves of a gas producer by the same firm. Bituminous coal was used, having a calorific value of 13,000 B.T.U.'s per lb. of coal. It was rated at 170 horse-power.

The practice in Britain at

14000 present in small plants is to use suction producers work14,000 ing on anthracite coal, or 12.000 some form of pressure producer working on similar fuel, like the Dowson producer. In large plants, however, where bituminous slack could be cheaply obtained, and the ammoniacal by-products treated on the process invented by Dr Mond of Northwich, great economy would no doubt result.

Producer gas used in these engines is obtained by

passing air and steam through incandescent fuel. Two simple reactions take place, expressed by

2C+0, 2CO,
C +H,O=CO + H

which is to say that the oxygen of the air combines with the carbon of the fuel to form carbon monoxide; the water splits up to form more CO and H. In addition, a certain amount of CH, and CO2 are formed, so that the ultimate composition of the gas is combustibles ČO1, H2, and CH, diluted with the non-combustibles CO, and N2. For further information on gas engines the reader is referred to standard text-books.

2

CHAPTER XXV.

THE USE OF WATER POWER.

THAT the use of water power in a scientific and economical manner has not had the attention of English engineers that it should have done is beginning to be felt at last. It is to be regretted, perhaps, that while Englishmen have been devoting their time to the perfection of the steam engine, the foreigner has been bringing the use of water power to a fine art. The lack of energy at home in this direction is due, no doubt, to two things

1. Not a large supply of water power to be utilised. 2. A plentiful supply of coal for power purposes.

Therefore it is natural that the Continental engineers, and American ones too, have studiously devoted their energies to perfecting turbines. It is surprising how little consideration some engineers give to the subject at all. We may admit that the output required may be greatly in excess of what could be supplied by water, but why not utilise what there is, and help the engines by daily and hourly reducing the coal bill? Turbines find use in a variety of places, electric generation for large supplies and for country-houses being perhaps of primary importance. There is no doubt, however, pumping machinery could well utilise it. A small stream would work a stonebreaker,

and the surveyor could have all his stones broken for nothing, saving about 1/4 to 1/6 per ton of road metal.

We are not concerned with old-fashioned water-wheels. They gave, no doubt, to their designers much satisfaction; their efficiency, however, was always low, rarely obtaining more than 50 per cent. Besides, they are too cumbersome, slow, and heavy, and are now universally giving way to suitably designed turbines, which will work on almost any fall available; and when the fall is very high, we resort to a very efficient motor, the pelton wheel. Turbines also have the advantage of very little wear and tear, and the necessity of hardly any attention. The turbine is also remarkably steady in running, especially those of the pressure type; water-wheels are just the opposite.

When there is a running stream there will always be a certain amount of power available.

Say, for instance, the engineer gauges a stream in the manner described under Hydraulics, and finds the average flow is 1000 cub. ft. per minute. Between two convenient points on the stream, 1200 ft. apart, by levelling, he ascertains that there is a difference of surface-level of 10 ft. Then if he places a weir at the upstream point and builds a mill race or head race, viz. a canal having only sufficient fall to allow the water having a gentle velocity of about 1 ft. per second (vide Hydraulics), he will have at the point down

=

stream 1000 cub. ft. of water falling 10 ft. 1000 × 62.5 x 10 = 625,000 189 theoretical horse-power; and

foot-lbs. of energy per minute =

625000
33000

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if a turbine of good design is installed which will easily give 80% efficiency, he has

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Of course larger and swifter streams give much larger results. We only give the example to show what can be done.

We said before that we are not going to advise any engineer to instal a water-wheel; at the same time a few words in reference to them will not be out of place. First of all there is the over-shot wheel. It consists of a wooden or iron wheel which has a number of blades, which, together with the inner circumference, form a series of buckets. Into these buckets the water which is led to the top of the wheel by a pentrough (usually of wood supported on steel joists) falls and acts by gravity alone. In the pentrough is the regulating sluice. The buckets are designed to hold the water as long as possible so as to use as much of the power as they can. The inherent velocity of the water assists the process. It is not an efficient motor.

Then there is the breast wheel. There the wheel runs in a sort of masonry casing or "breasting" with very little clearance, the water being admitted about halfway up the wheel. The old breast wheels had ordinary flat radial blades or paddles, and acted by impulse only. A more modern form, much seen at the present day, is Fairbairn's wheel, with curved steel blades, in which the water acted to a great extent by gravity. The buckets usually have no ends, the breasting having a fine clearance. They must, however, be ventilated. Then there is the undershot wheel. Here the water enters by a sliding hatch on the lower circumference of the wheel, and acts by impulse or momentum. A later form, however, has curved blades, introduced by a French engineer, Monsieur Poncelet. The introduction of these blades was at the time considered a great improvement, and the efficiency went up by leaps and bounds to nearly double that of the old wheels. There is no doubt also that Sir William Fairbairn did much to advance the water-wheel, and many are still giving satisfactory results where efficiency has no weight. But there is no doubt that the modern hydraulic motor is the turbine.

We are not going to deal with hydraulic power as applied to cranes, dock machinery, etc., under very high pressures generated by artificial means--it would be out of the scope of the present work; but to those interested I would recommend Mr Croydon Mark's book on Hydraulic Power Engineering. What we have to deal with are natural sources of power. Now the first thing the engineer has to do is to find out if he has water power available. If he has, he will have to find out the total available fall, being the difference between the head and tail water-levels when water is passing.

Then the quantity must be carefully gauged.

He must then consider if it will be economical to store some of the water. For instance, in a small electric generating station the load will only be required for, say, a maximum of 8 hours per day. Then, if the day flow is stored up, he would have something like three times the available energy. But the question arises, Will the outlay warrant the procedure?—another opportunity for his practical experience. Then he will have to consider how the power is to be conveyed. For low falls, the head race or canal constructed

practically level as in fig. 498, the water being diverted and stored up by a weir, is the most usual procedure. Or a circular shaft in mid-stream and a tunnel driven to the turbine may be deemed advisable, although an expensive procedure. For high falls and utilising water from lakes, a pipe line of cast iron or riveted steel is generally adopted. Then he has to consider what horse-power he will require, and if, as is often the case, the new turbine is to replace an old, inefficient water-wheel, what horse-power the wheel gave out, and if the position of the wheel pit is suited to the turbine. Fortunately, turbines are compact machines, and it is usually a matter of no great difficulty to place a turbine in the wheel pit. Then he must decide if a vertical or horizontal spindle is to give the best results; and finally, the direction his turbine is to run in. These particulars are usually required by the manufacturers. Then the first thing to do is to construct the Head Race.

In constructing the head race a very frequent error is committed by failing to give it sufficient capacity. It should be wide and deep, and especially where the race is of a considerable length. As a general rule, the water should not flow faster than from 60 to 120 ft. per minute.

When the water is conveyed to the turbines through iron pipes, the receiving ends should be well submerged, so as to prevent any possibility of their drawing air. The velocity of water through pipes should never be excessive, and should never exceed 4 ft. per second for short pipes; and as the length of pipes increases, the velocity should be reduced. It is, however, often necessary to run the water at a greater velocity than above named.

Secondly, he must design the Tail Race. This also should be wide and deep, and the level of the bottom of the wheel pit should be carried out from 5 to 10 ft. below the end of forebay or flume, and if possible it should be carried out to the bed of the stream. By having the tail race thus constructed, as soon as the water is discharged from the wheel or wheels it will push out or displace the dead water in the race, thus preventing a loss of head.

For instance, suppose the bottom of tail race is on a level with the water in main stream into which tail race discharges, when wheels are started the water in tail race would have to rise in proportion to the width of race and quantity of water flowing therein, and reduce the working head in proportion; while if the race was as first above stated, the water from the wheels would displace the water without rising above the water in the main stream, thus utilising the full amount of head.

And thirdly, the wheel pit. In putting in turbine wheels, whether under high or low heads, the pit must be wide and deep. This is most important where a large wheel is run inside a low head, as under such circumstances every available inch of head must be used. A pit of insufficient size causes the water to react upon the wheel. An additional loss of power is also caused by the fact that a portion of the head is consumed in forcing the water out of the pit when there is not sufficient outlet.

A suitably constructed wheel pit for a turbine having a vertical shaft is shown by fig. 595. It is adapted to a low-fall turbine and has an open flume. The walls would be built of concrete or rubble masonry set in cement mortar. At A is a strainer of the usual pattern made of 2-in. round bars in a frame. It is removable. At B is a wooden sluice, which may be similar to pattern in fig. 490 or fig. 491. It is worked by a hand wheel. At D is a special block of masonry to which the shaft is bolted, while F is a cast-iron ring for a similar purpose. Then there is the ordinary wooden floor at E, through which the turbine shaft passes, and on which will be placed all the regulating gear. For

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