Hydraulic Ram, a machine for raising water by employing its own momentum, acquired by a fall, a portion of the water only being raised. The accompanying diagram, fig. 1, will serve to explain its action. An impulse pipe, II, leads from a cistern or reservoir, C, and has a fall depending on the amount of impulse required, and corresponding with the other parts of the machine, and on the height the water is required to be raised. The lower end of this impulse pipe turns up at A, where there is a large valve, usually conical and opening downward. This valve is of such a weight that the simple pressure of the water in the cistern and pipe, or the head, will not raise it, a certain degree of momentum being required for that purpose. When the valve is open the water rushes through it and soon attains this required momentum, and the valve rises and shuts against its seat. The motion of the water in the end at A is arrested, but not entirely so in that portion of the pipe between H and the cistern, for the impulse opens the valve B and forces water into the bell-shaped chamber D, and eventually into the delivery pipe E. When the impulse of the water flowing through the valve B becomes less than the pressure upon it, the valve closes and prevents the water which has passed through from returning.
The time of this flow is very short, because the arrest of motion of the water in the end of the impulse pipe so reduces the force exerted against the impulse valve that it falls after a brief interval, when the water again rushes out and relieves the pressure at B. But it soon acquires sufficient momentum to again raise the impulse valve, when the shock is repeated, and the acquired momentum again expends itself principally against the valve B, and the water ascends into the air chamber and delivery pipe. The use of the air chamber is obviously to produce a constant pressure in the pipe E, as nearly as practicable, and to relieve it from the sudden shock which would otherwise be caused by the shutting of the valve B.
Fig. 1. - Hydraulic Earn.
The expenditure of force in this machine is obtained by multiplying the amount of water discharged at A into the head, or height of water in the cistern above the valve A. The economy of force is found by multiplying the amount of water delivered by the pipe E into the height to which it is raised. The proportion in good rams is from 60 to 70 per cent. The head of water should be from 4 to 6 ft. for raising water vertically 30 ft. There is a difference of opinion in regard to the proportional increase of head to increase in height of the delivery pipe, and machines of different modes of construction will require variation in this particular. The height of head is, however, practically restricted in consequence of the wear and strain produced by the shock when the head is great. A practical difficulty in the machine is to preserve the necessary quantity of air in the air chamber. This is constantly being absorbed by the water, so that in time its volume becomes too small to yield sufficient elasticity.
The difficulty is obviated to a great degree by the application of what is called a shifting valve, opening inward at G. There is a moment of time after the shutting of the impulse valve when there is in certain parts of the machine a diminution of internal pressure to a degree below that of the pressure of the atmosphere. During this moment a bubble of air will enter at G- and ascend into the air chamber, but it is difficult so to regulate the supply that it will not be necessary to remove the air chamber and introduce a fresh supply of air. In large European machines there is often placed at B an inner air chamber with two valves at its base, suspended by hinges and opening laterally. The impulse pipe may be straight, and inclined as shown in the figure, or have a vertical and a horizontal limb; or it may be curved. There are several practical points in regard to its size and length which should be observed in the erection of the ram. In general, it may be stated that if the impulse pipe is very wide and short, it will not maintain a sufficient impulse to lift the water against great pressure in a long delivery pipe, because of the tendency to a reactionary movement of its contents, which is prevented by the resistance offered by a longer and smaller pipe.
The invention of the hydraulic ram is ascribed to the elder Montgolfier, and its improvements to his son. The principle, however, was previously employed by John Whitehurst of Cheapside in a machine constructed by him in 1772, an account of which was published in the "Philosophical Transactions " in 1775. Fig. 2 is a representation of Whitehurst's machine, and it will be seen that the principal difference between it and Mont-golfier's ram is that it has a stopcock in place of the automatic impulse valve. Leading from the cistern H is a long pipe, A E, much longer in proportion than is represented in the figure, which is the impulse pipe. Its contents receive momentum from the opening of the cock B, which is several feet below E. When sufficient force has been obtained the cock is shut, and the column of water in A B is urged by its momentum along the direct branch of the pipe G, through its depressed extremity D, into the bottom of the air chamber C. This part of the pipe contains a valve opening toward the air chamber, corresponding to the one in Mont-golfier's machine. F is the lower section of the delivery pipe.
The principle of action is precisely the same in the two machines, and the explanation of the ram will answer for that of Whitehurst's machine.
Fig. 2. - Whitehurst's Machine.