_A hydraulic ram or water-ram is a substitute for a pump_ for 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-pipe or 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 of
_Montgolfier’s hydraulic ram_, and Boulton added to it a number of
ingenious modifications, which were the basis of his patent.
[Illustration: 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, _a_ and _b_ the valves, C the air-chamber, and D the
discharge. Water first flows out in quantity through the valve _a_, 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 valve _b_, raises this valve, and a quantity of water
passes into the air-chamber shutting off air and compressing it in the
space above the mouth _d_ of the discharge D. This air by its electric
force closes the valve _b_, 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 valve _a_ again falls by its own weight, the flow
begins afresh, and when it has acquired sufficient velocity the valve
_b_ again closes, and the whole process is repeated.
_The efficiency of hydraulic rams_ has 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 × H
E = -----
g × h
where 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 Table_ given on page 174 is from the _American 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 efficiency_ or per cent., is ·3282. (_Example_) of 100
gallons 32-82/100 gallons would be delivered.
[Illustration: FIG. 151.]
_The double hydraulic ram_ is 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 at _H_, Fig. 152, to be closed, the valve
_B_ being 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 at _B_ until 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 at _C_, 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 a ^U^ shaped tube. The instant the column of water in the
drive pipe comes to rest, and the air pressure being 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 valve _C_ a 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 chamber _D_, 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.
[Illustration: 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 ports and 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 to _H_, the engine is called
_double acting_; spring water, or that which is purer than the water
used to drive the engine, may then be supplied through the supplemental
drive pipe _I_, 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 is _the 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 20-3/4 cubic 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, 7-1/2 feet.
_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.
[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.