Chapter 7

A description of this work will be of interest in showing the general practice followed in California for carrying water across deep mountain gorges. In order to augment its water supply, the North Bloomfield Gravel Mining Company desired to conduct water from a stream known as Texas Creek, in Nevada County, California, across the Big Cañon branch of the South Yuba River into the main Bloomfield flume or aqueduct, which was located on the side of Big Cañon Creek, at a vertical elevation of 620 feet above the bed of the latter stream. The quantity of water to be carried was about 32 cubic feet a second (1,250 miner's inches), which could be diverted from Texas Creek at a point 480 feet vertical above the Bloomfield flume. An aqueduct about 4,000 feet long, partly of ditch and partly of flume, was needed to bring the water from the catchment dam on the creek to the brow of the gorge. The vertical head for the pipe could therefore be from a maximum of 460 feet down to any lesser head; with a head of 460 feet, the pipe would be 4,790 feet long; and with a head of 220 feet, the length would be 4,290 feet. Assuming a maximum tensile strain upon the iron of 16,500 pounds per square inch, with the formula for the greatest head of about

d = (.359 l/h)^{1/5}, [or, v = 68 (dh/l)^{1/2}, and Q = 32],

and a lower value of the coefficient in the last equation for the lesser heads, it was found, by calculation, that the least cost could be obtained with a head from 300 to 350 feet. The head fixed upon was 303.6 feet, with a length of 4,438.7 feet. A profile of the pipe, with nearly the same horizontal and vertical scales (horizontal scale, showing slope lengths), is given in Fig. 14; details are given in Figs. 15 and 16. The pipe was of double riveted sheet iron, made in lengths of about 20 feet, and of the following thicknesses:

1,349 linear feet, 0.083 inch thick. 220 " 0.095 " 240 " 0.109 " 250 " 0.120 " 320 " 0.134 " 610 " 0.148 " 1,450 " 0.165 "

Some of the iron was of the very poorest quality; the pipe was made by contract in San Francisco, without the supervision of an inspector, as the contractors were a firm of good reputation; the bad quality of the iron was not detected until too late to have it corrected. Since then, the writer has always had such pipes--the mines of which he has been the manager using large quantities--made directly on the ground where they are to be used; the pipe makers, in the latter case, always reject such sheets as are too much below in thickness the standard gauge, and those which show in passing through the rolls the bad quality of iron; tests of each joint by hydrostatic pressure would add too much to the cost.

The maximum tensile strain upon each of the seven thicknesses of iron used was intended to be 16,500 pounds per square inch. Some of the sheets were below the standard gauge, so that, in reality, the tensile strain is sometimes as high as 18,000 pounds. The mean diameter of the pipe was 1.416 feet. The entrance into the pen-stock was tapered, so that the coefficient of contraction was about 0.92. For pressures not exceeding say 380 feet, the joints were put together stove-pipe fashion. For greater pressures, the joints were made by an inner sleeve riveted on one end of the joint, with an outer lap-welded band, as shown by Fig. 15; lead was run into the space between the outer band and the pipe, and then tightly driven up by calking-irons. The pipe was laid under the bed of the Big Cañon Creek, a large stream when in freshet, where the head below the hydraulic grade line was 760 feet. Some of the lead joints leaked slightly at first, but this was soon remedied by more careful calking. No man-holes or escape-gates were used. The pipe for the larger part of the year is not filled at its upper end; when such is the case, the water at the inlet carries down the pipe a great quantity of air, for which escapes must be provided to prevent a jarring or throbbing, which would soon destroy the pipe. The escape air-valves used are shown by Fig. 16. They consist simply of a heavy flap valve of cast-iron, with recess for lead filling to give greater weight set on top the pipe, seating on a vulcanized rubber cushion, and swinging on a loose hinge. When the pipe is only partly filled with water, the valves drop down by their own weight, allowing the air to freely escape; when the water rises above the level of a valve, it is tightly closed by the resulting pressure. There are fourteen of these valves, those on the lower end being designed to allow air to freely enter the pipe in case it should burst in the deeper portion, and thus prevent any collapse from atmospheric pressure. The valves have answered the desired purposes most effectually. The pipe was hauled over a road built to the inlet end, and shot down the mountain side by means of a V-shaped trough of wood. For the lower end, the joints were hauled up the cliff side into place by a crab worked by horse-power. On steep inclinations, the pipe was held firmly in place by wire ropes fastened to iron pins in the solid rock, as shown by the sketch. The covering of earth and stone was 1 foot to 2 feet in depth; with steep slopes, the earth was kept from sliding by rough dry walls, or by cedar plank placed crosswise. The pipe was laid in 1878; the first year it broke twice, owing to the wretched quality of the iron; since then, it has given no trouble, and has required practically no attention. The cost of this work--ditch and flume 4,000 feet, and pipe 4,440 feet--was $23,779.53.

A comparison of the relative values of n, in the formula v = n (r s)^{½}, for the foregoing ditch, flume, and pipe will be instructive. The ditch has a width on the bottom of 3 feet, on the top of 6 feet, with a depth of 3 feet, and an inclination of 20 feet per mile; its sides are rough, being cut in part through the rock and with sharp curves, although fairly regular; with a flow of about 1,300 miner's inches (32.8 cubic feet per second) the ditch runs about full.

Therefore:

6 + 3 a = ----- × 3 = 13.5 ; 2

[TEX: a = \frac{6+3}{2} \times 3 = 13.5;]

a r = ------------- = 1.41 ; 3.3 + 3 + 3.3

[TEX: r = \frac{a}{3.3 + 3 + 3.3} = 1.41;]

20 1 s = ------ = ----- ; 5280 264

[TEX: s = \frac{20}{5280} = \frac{1}{264};]

Q = 32.8, hence

Q v = --- = 2.43; a

[TEX: v = \frac{Q}{a} = 2.43;]

and

/ {½} \ n ( in v = n (r s)^ ) = 33. \ /

[TEX: n\ (\text{in}\ v = n (r s)^\frac{1}{2}) = 33.]

The flume is of unplaned boards, rectangular, 2.67 wide × 2.83 deep, with an inclination of 32 feet per mile. There are sharp curves, although these were made as regular as practicable; the boiling action of the water passing around these curves brought the flow line (Q = 32.8) nearly up to the top of the sides; with a straight flume of the same size, the water would have doubtless stood several inches lower.

Therefore:

a = 2.67 × 2.83 = 7.56 ;

a r = -------------------- = 0.908 ; 2.83 + 2.67 + 2.83

[TEX: r = \frac{a}{2.83 + 2.67 + 2.83} = 0.908;]

32 1 s = ------ = ----- ; 5280 165

[TEX: s = \frac{32}{5280} = \frac{1}{165};]

Q = 32.8, hence

Q v = --- = 4.34; a

[TEX: v = \frac{Q}{a} = 4.34;]

and n = 59.

With the pipe,[6] 1.416 diameter,

d r = --- = 0.354; Q = 31.69; v = 20.13. 4

[TEX: r = \frac{d}{4} = 0.354;\ Q = 31.69;\ v = 20.13.]

[Footnote 6: _Vide_ pages 120-122, Transactions American Society of Civil Engineers for 1883.]

Allowing for loss of head due to imparting velocity to water, and for contraction,

296.1 s= --------; and n = 131. 4438.7

[TEX: s = \frac{296.1}{4438.7};\ \text{and}\ n = 131.]

We hence have the following values of n, in v = n (r s)^{½}, Q being constant:

Rough ditch, with sharp curves. 33 Rectangular flume, with sharp curves. 59 Wrought-iron pipe, with easy curves, coated with asphalt, but with rivet-heads forming noteworthy obstructions (m = 65.5, and 2m = n) 131

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PARACHUTE HYDRAULIC MOTOR.

The very singular and simple hydraulic motor which we illustrate herewith is the invention of a Russian engineer, Mr. Jagn. It is scarcely as yet known in Western Europe, where, however, something will probably be heard of it ere long. Its true field would seem to be Egypt, India, or any country where canals or rivers are used for irrigation, and where it is desired to draw water from them at particular spots in the simplest and cheapest manner. At present in nearly all such cases water is raised by hand or steam power; nevertheless it must be obvious that the current of the canal itself, slow though it may be, is quite sufficient to raise a small portion of the discharge to the very moderate height generally needed to lift it over the banks into the adjoining fields. Why then is it not employed for the purpose? The answer is obvious, when we consider the various hydraulic motors at present in use. Of course, motors worked by water pressure must here be excluded; and we are left with scarcely anything but the undershot wheel, the turbine, and the screw pump. All these require expensive buildings and erections to set them to work, present but a very small fraction of their surface to the water at any one time, and must be very large and costly if they are to draw even a very moderate amount of power from such a source. There is no possibility of adjusting them readily to suit variations in the speed of the current or in the quantity of water required, nor of moving them from place to place should this be convenient.

The motor of Mr. Jagn is on a totally different principle. Its essential features consist, as shown, of an endless rope made of hemp or aloe fiber, which takes a turn or two round a pair of drums mounted on a barge or pontoon, and then passes down the channel to return over a pulley hung from a floating punt, at such a depth that the whole of the rope is immersed in the water. Along this rope are suspended at equal intervals a number of parachutes made of sail cloth. The rope passes through the center of each of these, and to it are attached a series of strings, the other ends of which are connected to the outside edge of the parachute. Thus they act like the spokes of an umbrella to prevent the parachute from opening too far under the pressure of the current. The parachutes must be placed so far apart that the current may act fairly on each, and the sum of the pressures forms the force which draws the rope through the water. The moment, however, that any parachute has passed round the return pulley, the current acts upon it in the opposite direction. It then shuts up like an umbrella, and assumes a volume so small that its resistance on the return journey is insignificant. After passing round the drum at the upper end, it at once opens afresh of its own accord, and once more becomes part of the moving power of the whole system. The parachutes are formed by first cutting out a complete circle of cloth, and then taking from this a sector equal to one-fifth or one-sixth of the total area. Such parachutes are found to keep their form when stretched by the water better than a surface originally spherical, although the latter would be theoretically more correct. The motion of the drum is transmitted by spur, gear, or otherwise as may be required, to give the requisite speed.

It will be seen that the advantages of the system are as follows: First, the facility it offers for obtaining a large working area, which may be increased or diminished at will, according to the requirements of the moment, by lengthening or shortening the rope. Secondly, the ease with which it is erected and set to work. Thirdly, the small part of the river section which it occupies, so as to present no obstacle to navigation. Fourthly, the ease with which it can be mounted on a barge of any kind, and carried wherever it may be needed. Fifthly, it is not stopped, like all other hydraulic motors, by the appearance of ice--it has, in fact, already been worked under ice in the Neva. At the same time, winds and waves have no influence upon it.

The principle of the apparatus is not altogether new. In 1872 there was tried on the Ohio River an arrangement termed the Brooks motor. It was composed of two drums, placed horizontally and parallel to each other. Round these there passed endless chains at equal spaces apart on the length of the drums, and to these chains were fixed wooden blades or arms of a curved form, and so jointed to the frames that they opened when moving in one direction, and closed down on the chain when moving in the other. In this machine the weight of the chains was a serious obstacle to obtaining any large amount of power. The whole apparatus was mounted on a heavy wooden scaffold, which proved an impediment to the flow of the river. Again, the resistance due to the surface of the returning blades and to their stiffness was found to be far from insignificant.

In the present system Mr. Jagn has found, after many experiments, that the best effect was obtained when the parachutes were spaced apart at twice their diameter, and when the rope made an angle of 8 degrees to 10 degrees with the current. It is found that when open and in motion the parachutes never touch the bottom. This was the case with a rope containing 180 parachutes of 4 feet diameter, and working in a depth of only 6 feet. This is easily explained by the fact that the velocity of a current always diminishes as it approaches the bottom. Hence the pressure on the lower part of the parachute will be less than that on the upper part; but the former pressure tends to draw the parachute downward, while the latter tends to raise it to the top of the water. Thus, the latter being the larger, the parachute will always have a tendency to rise. In fact, it is necessary to sink the return pulley sufficiently deep to make sure that the parachutes will not emerge from the surface. For the same reason no intermediate supports are needed over the driving span; if any are needed it is for the return span, on which the parachutes are closed. Of course, if metal were used instead of hemp, the case would be entirely different, and intermediate supports would have to be used for anything but very moderate lengths.

In practice, Mr. Jagn has employed two ropes wound upon the same pair of drums, which are mounted upon a pontoon. The ropes are spread out from each other, as in Fig. 1, making an angle of about 10 degrees. The low specific gravity of the system enables ropes to be employed of as great a length as 450 yards, each of them carrying 350 parachutes of 17.2 square feet area. As half of these are in action at the same time, the total working area for the two cables is 5,860 square feet. This immense area furnishes a considerable amount of power even in a river of feeble current. Comparing this with a floating water wheel of the type sometimes employed, and supposing this to have only 172 square feet of working area, such a wheel must have a length of 46 feet, a diameter of 23 feet, and seventy-two floats, each 2½ feet wide. The enormous dimensions thus required for a comparatively small working area point sufficiently clearly to the advantage which remains on the side of the parachute motor.

The general arrangement of the system is shown in the engraving. Behind the return pulleys, D D, are attached cords, A A, with some parachutes strung upon them. These present their openings to the current and preserve the tension of the connecting ropes. At the further end of each cord is a board, B, which is kept in a vertical plane, but lying at a slight angle to the direction of the current; and this acts to keep the two moving ropes apart from each other. The two return pulleys are, however, connected by a line, E, which can be shortened or lengthened from the pontoon, and in this way the angle of inclination between the two ropes can be varied if required. A grooved pulley presses upon the trailing span at the moment before it reaches the circumference of the drum. It is mounted on a screwed spindle, which is depressed by a nut, and thus makes the wet rope grip the outside of the drum in a thoroughly efficacious manner.

The author has made a theoretical investigation of the power which may be developed by the system, and has worked out tables by which, when the velocity of the current and the other elements of the problem are known, the power developed by any given number of parachutes can be at once determined. We do not reproduce this investigation, which takes account of the resistance of the returning parachutes and other circumstances, but will content ourselves with quoting the final equation, which is as follows: T = 0.328 S V³. Here T is the work done in H.P., S is the total working area in sq. m., and V is the velocity of the current in m. per sec. Taking V = 1, and S = 1 sq. m., which is by no means an impracticable quantity, we have T = 0.328 H.P. per sq. m. We may check this result by the equation given, in English measures, by Rankine--"Applied Mechanics," p. 398--for the pressure of a current upon a solid body immersed in it. This equation, F = 1.8 m A v² / 2g, where m is the weight of a unit of volume of the fluid--say 62 lb.--A is the area exposed, and v the relative velocity of the current. Mr. Jagn finds that the maximum of efficiency is obtained when the rope moves at one-third the velocity of the stream. If this velocity be 3 feet per second, we shall have v = 2. and we then get F = 7 lb. per sq. ft. very nearly. Now 1 sq. meter = 10.76 sq. ft., and a speed of 1 ft. per second (which is that of the rope) is 60 ft. per minute. Hence the H.P. realized in the same case as that taken above will be 7 × 10.76 × 60 / 33,000 = 0.137 H.P. The difference between the two values is very large, but Rankine, of course, depends entirely on the value of the constant 1.8, which is quite empirical, and is for a flat band instead of a hollow parachute. Taking, however, his smaller figure, and an area of 544 square inches, which Mr. Jagn has actually employed, we get a gross power of = 0.137 × 544 = 7.43 H.P. Hence it will be seen that the amount of power which can be realized by the system is far from being inconsiderable.

Lastly, we may point out that the durability of the apparatus will be considerable. There is no wear except at the moment when the rope is passing round the drum, and even then there need be no slipping or grinding. The apparatus worked in the Neva was in very good condition after running for four months day and night. After five months about one-fifth of the parachutes had to be replaced, but after seven months the hemp rope still showed no signs of wear. We think we have said enough to show that for certain purposes, and especially, as we have, already mentioned, for irrigation purposes, the new motor is well worthy of a careful and extended trial. It may be questioned even whether we have not here the germ of an idea which may hereafter enable us to solve one of the most interesting and important of engineering problems, viz., the utilization of the great store of power provided for us twice daily in the ebb and flow of the tide.--_The Engineer._

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IMPROVED SHAFTING LATHE.

Our engraving represents a new departure in shaft turning lathes, and is the result of thirty years' experience in the manufacture of shafting, with many years' study, to perfect a machine of the greatest practical capacity and efficiency.

The principal points of difference from a common engine lathe are readily distinguished, among which may be mentioned the absence of centers and tail stock, a traveling head with hollow driving spindle, and a stationary tool rest and water tank. By dispensing with a tail stock a much shorter bed may be used, and the hollow driving spindle enables any length shaft to be turned, with one setting of the tools. The tool rest is so arranged as to allow of perfect lubrication of the tools, keeping the shaft cool, and at the same time holding it perfectly rigid and strong; the operator is not required to travel the length of the bed, but remains near the driving belt, feed gearing, etc. Power is communicated to the driving spindle by means of a sliding pinion on a splined rod inside the bed, the driving belt and gears being at the end.

The driving head, after having traveled the length of the bed and turned a shaft, is returned by a quick feed, and stops automatically, allowing nearly time enough for the operator to grind tools and be ready with another shaft, thus economizing the time completely.

Wood, Jennison & Co., Worcester, Mass., are the makers, and they say that with a good quality of iron they have turned three hundred feet of two inch iron in ten hours.

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POWER STRAIGHTENING MACHINE.

The machine is provided with a pair of rolls at each end of the bed, which are adjustable for different lengths of shaft, and are made to revolve by power applied through suitable gearing and a splined rod inside the bed; the bar of iron being placed on the periphery of the rolls receives a rotary motion by friction, and shows the crooked places in the same way and with the same ease as though rotating on centers in the usual manner; vertically adjustable blocks are arranged in the base of the press to support the iron; power is applied by means of gearing to a splined rod at the back of the machine, on which is a sliding clutch connecting, at the will of the operator, with an eccentric; the eccentric conveys motion and power through a link to the elbow joint at the front of the press, which forces a plunger down against the iron.

Sufficient adjustment is provided for different sizes of iron by turning a nut at the top of the press.

Any point in the length of the bar can be reached by moving the press on the bed. Any length of iron can be straightened, and the most laborious and disagreeable work in the process of making shafting is rendered easy and rapid. Made by Wood, Jennison & Co., Worcester, Mass.

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HYDRAULIC MINING IN CALIFORNIA.

By GEORGE O'BRIEN.