HYDRAULIC RAM.

A hydraulic ram or water-ram is a substitute for a pumpfor raising water by means of the energy of the moving water, of which a portion is to be raised. It was considered a notable discovery when it was demonstrated by Daniel Bernovilli, in the beginning of the 18th century,that water flowing through a pipe, and arriving at a part in which the pipe is suddenly contracted, would have its velocity at first very greatly increased.

The hydraulic ram owes its efficacy to the fact that when a flow of water in a pipe is suddenly stopped, a considerable force is generated by the momentum of the water, by its change from a state of motion to a state of rest. In practice, the pipe conveying water from the reservoir or head, connects with a chamber which has a valve opening downward, or outlet valve, allowing the current of water to pass on or escape when the valve is open; but on flowing the current in the pipe acquires sufficient force to close this valve, which checks the flow in the pipe.

The current is thus suddenly stopped; this causes a reaction, which produces pressure sufficient to open another valve (inlet valve) between the current-pipe and an air chamber, and a portion of water enters by means of the force of the current, but by so doing the current has spent its force; the outlet valve at the end of the chamber falls by its own weight, and the pressure in the pipe ceasing, the inlet valve in the air-chamber falls and closes the opening. The condition of things is then restored; the water then acquires a momentum which closes the outlet valve and forces more water again into the chamber. A very slight descending column is capable of raising one ascending very high. In all cases the drive-pipeor inlet pipe must be sufficiently long to prevent water being forced back into the reservoir. The air-chamber serves to keep up a steady supply from the reservoir, preventing spasmodic action. To prevent admixture of air with the water in the air chamber, which is caused by pressure of water when raised to a great height, a small hole should be made on the upper side of the inlet pipe, immediately in front of the same. By the action of the ram at each stroke, a partial vacuum is formed below the air chamber, and the air rushing through the small hole in the inlet pipe, passes into the air chamber, making good that which the water absorbs.

Note.—In 1797 Matthew Boulton (manufacturer and practical engineer, and in later life a partner of Jas. Watt, the Father of the steam engine) obtained a patent for a mode of raising water by impulse. The apparatus had excited much attention in France, under the name ofMontgolfier’s hydraulic ram, and Boulton added to it a number of ingenious modifications, which were the basis of his patent.

Fig. 150.

Fig. 150 shows in section the construction of the ram in its simplest form in which E is the reservoir, A the pipe in which the water falls, B the channel,aandbthe valves, C the air-chamber, and D the discharge. Water first flows out in quantity through the valvea, and as soon as it has acquired a certain velocity it raises that valve, closing the aperture. The impact thus produced, acting on the sides of the pipe and the valveb, raises this valve, and a quantity of water passes into the air-chamber shutting off air and compressing it in the space above the mouthdof the discharge D. This air by its electric force closes the valveb, and the water which has entered is raised in the discharge D.

As soon as the impulsive action is over, and the water in the channel A comes to rest, the valveaagain falls by its own weight, the flow begins afresh, and when it has acquired sufficient velocity the valvebagain closes, and the whole process is repeated.

The efficiency of hydraulic ramshas been much discussed; exhaustive practical tests have been made and the results have been reduced to formulas. Whittaker’s Mechanical Engineer’s Pocket Book gives the following:

G × HE = ——–g × hwhere E = the efficiency;G = gallons of drive water used;g = gallons of water raised;H = height of fall, in feet;h = height to which the water is raised, in feet.

The Tablegiven onpage 174is from theAmerican Engineer. Its use is apparent, thus: when the height of fall in feet is, say 12 feet, and the elevation of discharge above the delivery valve of ram, in feet, is 30 feet,the efficiencyor per cent., is ·3282. (Example) of 100 gallons 3282⁄100gallons would be delivered.

Fig. 151.

The double hydraulic ramis shown in Fig. 151. A sectional view of the same device is shown in Fig. 152, the cuts represent the Rife hydraulic engine, or ram,—a so-called double acting or double supply type of the water ram. It is more clearly described by considering it, first, as a single machine by disregarding its double supply feature.

First, suppose the opening atH, Fig. 152, to be closed, the valveBbeing open, the water from the source of supply from more or less elevation above the machine flows down the drive pipe,A, and escapes through the opening atBuntil the pressure due to the increasing velocity of the water is sufficient to close the valve, B. When the flow through this valve ceases, the inertia of the moving column of water produces a reaction, called the ramming stroke, which opens the valve atC, and compresses the air in the air chamber,D, until the pressure of the air plus the pressure due to the head of the water in the main, is sufficient to overcome the inertia of the moving column of water in the drive pipe. This motion may be likened to the oscillation of water in aUshaped tube. The instant the column of water in the drive pipe comes to rest, and the air pressurebeing greater than the static head alone, the motion of the moving column is reversed, and the valve,C, closes. The water in the drive pipe then moves backward, and with the closing of valveCa partial vacuum is formed at the base of the drive pipe. This negative pressure causes the valve,B, to open again, and completes the cycle of operations. At the moment negative pressure appears the little snifting valve,E, admits a small quantity of air, and at the following stroke this air rises into the air chamberD, which would otherwise gradually fill with water, or the air is gradually absorbed by the water.

In this machine the valve,B, is made as light as is consistent with the necessary strength, and the negative pressure at the completion of the stroke opens the valve. In the largest size of these machines this valve is 18 inches in diameter, with a head of 8 feet, which is a common head for use with hydraulic rams; the static pressure on the under side of this valve is 883 pounds; it is seen that so great a shock in a valve of this weight would rapidly destroy both valve and seat.

Fig. 152.

The waste in a mechanism of the Rife engine consists of a large port with ample opening and a large rubber valve or overflow with a balance counterweight and spring seat, which removes almost entirely the jar of closing. The valve,C, in the air chamber consists of a rubber disc with gridiron portsand convex seats fastened at the center and lips around its circumference. The object of this arrangement is to transfer the shock from the power of the driving water to the air cushion with the smallest possible friction and vibration.

After the valve,C, closes, the pressure in the air chamber forces the water in the air chamber out into the delivery pipes. The Rife engine is claimed to elevate water 30 feet for each foot of fall in the driving head; the machine is built in sizes to elevate as much as 150,000 gallons per day, the efficiency being about 82 per cent.

When a water supply pipe is attached toH, the engine is calleddouble acting; spring water, or that which is purer than the water used to drive the engine, may then be supplied through the supplemental drive pipeI, and by a proper adjustment of the relative flow of the impure driving water, and that of the pure supply, the engine may be made to deliver only the pure water into the mains. This method is employed where the supply of pure water is limited.

The most important detail in which the Rife engine differs from the ordinary hydraulic ram isthe waste valve. It will be seen in the engraving that the counterweight on the projecting arm of this valve permits the adjustment of this valve to suit varying heads and lengths of drive pipe. By adjusting the counterweight so that the valve is nearly balanced, the valve comes to its seat very quickly after the flow past it begins. The result is that the ram makes a great number of short, quick strokes, which are much easier on the valves and seats than slower and heavier strokes. The stroke must be sufficiently powerful to act efficiently in overcoming the head in the delivery pipe. The adjustable weight permits this to be effected with great nicety.

Note.—The engine illustrated weighs approximately 2,800 pounds; the capacity of the air chamber is 203⁄4cubic feet; diameter of drive pipe, 8 inches; diameter of the waste valve, 18 inches; weight of waste valve, 50 pounds; diameter of delivery pipe, 4 inches; height to top of air chamber, 71⁄2feet.

Lifts and Cranes.These, as hydraulic machines, are adapted to very many places where other power apparatus is too slow; they operate on the same principle as the hydraulic press; having a cylinder and a ram: they have chain wheels attached to the outer end of the ram, as shown in the illustration.

crane

As the ram advances the chain is shortened and when it recedes the chain is lengthened, thus, the weight attached to the end of the chain is raised and lowered. The hydraulic “lift” in passenger elevators operates upon the same principle and this gives an idea of the rapid motion capable of being imparted to the load. It is by the adaptation of hydraulic lifts and cranes in steel mills that such economical results have been attained.

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