N. Hawkins

Apparatus is another name for machinery but it also carries the particular meaning of a complete collection of instruments or devices prepared for a particular use, hence, hydraulic apparatus may be said to include very many combinations of machines to utilize the pressure or weight of water.

A number of these devices are illustrated in the succeeding pages. It were vain to attempt to describe all.

Knight in his Mechanical Dictionary has grouped some six hundred and seventy five terms and names under the heading of “Hydraulic Engineering and Devices.” In the note are given some terms, the definition of which the student may, perhaps, look up; thus: Gyle (the first term given) is a large cistern or vat. The liquor gyle in a brewery is the water-vat or gyle-tun.

Hydraulic apparatus has been developed mainly from two sources. The “cut and try” method, which of course was the first and second from scientific calculations, based upon both the experiments and upon the mathematics of hydraulics.

It is difficult at this date to say to which procedure the world is the most indebted, but it is plainly discernable that the two methods have been necessary as a check upon each other. Untold thousands of practical experiments and an almost equal number of tables, rules and calculations have been made. The result has been that out of many failures the point of economy and efficiency, aimed at, of hydraulic apparatus is well defined.

Note.—Terms relating to hydraulics named by Edward H. Knight, Civil and Mechanical Engineer, as above. Gyle; Sluice Valve; The Sough; Stade; Worm-safe; Weel; Water-twist; Water-lute; Water-gilding; Vineficatur; Tun; Tide-lock; Tail-bag; Swash-bank; Sump; Stop-plank; Sterhydraulic apparatus; Staith; Rip-rap; Quay; Puffer; Psychrometer; Levee; Leam; Leach; Land tank; Kiddle; Kimelin; Keir; Jetty; Invert Burette; Hydraulic Blower, etc. Some of these terms go “way back,” and the above are a specimen only of the 675 headings.

Fig. 137.
Section of Claw Type Hydraulic Jack.

HYDRAULIC JACK.

A Lifting-Jack is a contrivance for raising great weights by force from below; also called a jack-screw. From its derivation from Jack, equivalent to lad or boy, has arisen its modern use as denoting a contrivance which is subject to rough usage. It is operated by a screw, whereas—a hydraulic jack is a jack or lifting apparatus operated by some liquid, usually oil, acting against a piston or plunger, the pressure on the liquid being produced by a force pump. The hydraulic jack consists of, 1, a cylinder; 2, a ram or plunger; and 3, a pump. One of these machines is shown and described in the Glossary, page 24, another is illustrated by Fig. 138. The Fig. 137 on the opposite page shows the inside view of Fig. 138 but on a different scale. The names of the parts are particularly to be noted.

Fig. 138.

Movable hydraulic, or screw, jacks serve on numerous occasions most effectively for lifting or propping-up of less accessible parts. Eye-bolts and jack-bolts are arranged for, in all parts that are likely to be handled, to facilitate and accelerate the work in necessarily crowded quarters.

The base or foot is usually made of cast iron or cast steel and may be either round or square to suit requirements. The cylinder is bored from a seamless steel ingot and having a thread upon its lower end is screwed into the base.

The ram is also a tube of seamless steel having a thread at the top and is screwed into the head or cap which is made either of cast iron or cast steel. The lower end of the ram has a thread inside to receive the pump plug which contains the delivery valve, while upon its outside is placed the cup leather packing and the ram packing ring. The pump for operating the ram is from five-eighths to three-quarters of an inch in diameter depending upon the capacity of the jack, and has a plunger packed with a cup leather.

A suction valve is contained within the plunger. A short arm is fitted upon a socket which enters through the side of the head or reservoir. This arm is connected by a pin to the pump inside the ram while the outer end of the socket has a tapered rectangular hole through it to receive the jack-lever. A leather collar packing makes the socket tight where it enters the side of the reservoir.

To properly use a hydraulic jack. Place the head under the weight to be raised, be careful to set the jack plumb with a good solid footing; put the lever into the socket with its projection on the bottom side; work the lever until the weight has been raised to the desired height or an escape of liquid blows out of the safety vent. Hold the lever up or raise it to its highest position and remove it from the socket to prevent the valve from opening. In lowering insert the lever in the socket with the projection underneath and then cautiously press it slowly down until it brings up against the stop; remove the lever and turn it over with the projection on top; insert the lever in the socket and gently but firmly press it on the end with the right hand clasping the ram with the fore finger, and thumb of the left hand: thus the workman has full control of the jack and can lower and stop as frequently as may be found necessary.

If from any cause the valves stick a few sharp quick strokes of the lever will usually release it and cause it to work, if not, it should be thoroughly cleaned.

Before shipping the brass filling screw should always be screwed down tight, and before using this screw should always be loosened to let the air out and in.

Note.—A prominent firm making these tools says: “In our Jacks, rams are cut and cylinders bored from solid high carbon steel. We have nearly 300 styles for pushing, pulling or lifting.” This shows the wide use to which hydraulic jacks are put; the style shown in the Glossary with its broad base is to be used when the jack stands upon a light board on the ground and can be placed under the work, or where steadiness is required. Fig. 139 shows a style to be used when there is not room enough to get the head of the jack under the work, and is the style generally used for moving engines, boilers, machinery, etc.

In repairing hydraulic jacks the following points should be carefully observed; before attempting to repair a hydraulic jack the trouble should be definitely located, next:

Put the jack under a weight and attempt to raise it, carefully watching its action. Should the liquid leak out around the lever socket, the gland should be tightened slightly until this leak disappears. If the packing is worn out unscrew the set screw at the back of the head about one-quarter inch, then withdraw the socket not more than one inch, unscrew the gland and put in a new packing of lamp wick braided and well oiled with mineral oil, which is free from gum. Afterwards put the socket back to its former place and tighten the set screw.

When the pump valve leaks the lever can be worked up and down without raising the ram. This is also true when the plunger packing becomes worn. If the trouble is found with the valve it can be ground by taking out the pump plug and unscrewing the brass bonnet which covers the valve.

Fig. 139.

Sometimes the jack will become air bound by reason of the accumulation of dirt around the filling plug; this must be removed before the jack will work. Sometimes the liquid will all have been displaced before the ram is half way up, in this emergency the reservoir must be refilled. It often happens that when the workman stops working the lever it will persist in rising to its highest position. This indicates the presence of dirt under the lower or delivery valve. One or two sharp quick strokes of the lever will generally dislodge such obstructions; if this does not bring relief the valve is probably worn so as to need regrinding. When a jack has been taken apart each part should be thoroughly washed in clean water.

While using, if the liquid escapes over the top of the cylinder the ram packing is too loose, and may be set out by inserting a strip or strips of tin or any sheet metal between the leather and the ram packing ring; all leathers should be kept soft and pliable by saturating with a proper leather dressing such as Frank Miller’s Leather Preservative or Shoemakers’ Dubbing. Castor Oil is excellent as well.

One man can exert upon the lever all the pressure that the jack is capable of raising and this pressure should not exceed 150 lbs. Beyond this the jack will be strained.

To repack the pump remove the pump plug, and unscrew the set screw in the head, then withdraw the socket far enough to permit it to revolve clear of the lug, on the head, which brings the piston head out of the pump.

After the new packing is in place the piston should be worked in and out a few strokes to see if it is right, then replace the plug.

To fill the reservoir remove the filling screw in the top of the head, and fill with a mixture of proof alcohol (95 per cent.), two parts and water three parts for winter use, or for summer use one part alcohol to four parts water.

When not in use the ram in a hydraulic jack should be kept in its lowest position, that is to say, all the way down, or in, as the case may be.

Important.—Jacks should never be filled with kerosene oil, water or wood alcohol, for the following reasons: Kerosene oil destroys the leather packing, water will rust the parts and make them rough, while wood alcohol attacks the smooth steel surfaces, and thus destroys both the cylinder and ram. All liquids should be well strained before putting them into the reservoir and great care should be exercised to prevent any dirt from getting into this reservoir.

The Pulling Jack.—The pulling jack, Fig. 139, is used in connection with travelling cranes over wheel presses, quartering machines, planers, drill presses and lathes. Its operation is the reverse of lifting jacks.

This Jack has an improved force-pump on the outside, worked by a lever, which draws the liquid from the upper end and forces it into the space on the opposite side of the piston. The piston rod has one of the rings attached at the end.

By this operation the rings are drawn together and with them the body to be lifted or moved, for it will be understood that this style of jack works either in a horizontal or vertical position. Hooks are furnished instead of rings when desired.

The liquid is introduced into a hole in the side of cylinder, care, being observed to push the piston into the cylinder. The proportions of filling liquid are proof alcohol two parts and water three parts.

To use this jack extend it as far as it can be pulled apart, first opening the valve in the side of force-pump. Now close this valve and work the pump lever.

This jack appeals particularly to the marine engineer, to be attached to the trolley over the engine for the purpose of raising pistons, rods and lifting various parts of the machinery.

Fig. 140.

Horizontal Jack.—The accompanying engraving, Fig. 140, shows a horizontal type for pulling armatures on to shafts, putting in cranks pins, and marine work. The directions given for the care and handling of the regular hydraulic jack apply also to this as well as other devices of the same description.

This pump has two plungers of different diameters, the small one inside of the large, so that by throwing a clutch, both plungers may work together as one, or they may be separated, and the smaller one used; as for example, in starting, the larger pump is used as far as possible, i.e., until the pressure becomes too great for the large plunger, then the clutch is thrown and the smaller one finishes the work.

The speed of this appliance may be changed to three times greater, and its power reduced to one-third of the maximum by throwing the clutch which brings the large plunger into operation. A rack and pinion with handle is connected with the main ram to cause its return when forced out to its full length. The size shown in Fig. 140 represents a capacity of 200 tons and its approximate weight is 1,200 lbs.

Fig. 141.

The Hydraulic Bolt Extractor.—Much harm is done to coupling bolts in driving them out with a hammer or sledge. The hydraulic bolt extractor shown in Fig. 141 is an admirable device to do this work without injuring the bolts or threads. This same apparatus may be used for other purposes as well as that for which it was designed, as will appear from time to time.

The Hydraulic Punch.—The hydraulic punch has been found of greatest utility in the erection of steel structures, such as buildings, bridges and ship building. It consists of a hydraulic jack attached to a “punching bear” instead of the usual screw to operate the punch. By an ingenious device the punch can be shoved down close upon the work without pumping all the way, as in the earlier styles of hydraulic punches; this means a considerable saving of time and muscle.

Fig. 142.

The construction and operation of working parts of this punch will be easily understood by referring to the engraving, Fig. 142 where 18 represents the body or “punching bear,” 17 the ram, 19 the raising and lowering pinion to move the ram quickly to its work; 20 shows the die with punch in place above it, secured by its gland; 3 the punch head cistern, the screwed cover having a hole in its center to guide the end 2 of pump plunger 9, having cup leather packing 10, at its lower end; 5 represents the lower socket which carries the arm 4 to operate the piston 6. The suction valve 11 is supported by the spring underneath; 12 is the safety vent; 13 the release or lowering valve operated by the stem 7 which is pushed downward by the projection of the piston 6 whenever the lever is turned and pressed downwards as described in lowering the lifting jacks. The relief valve is kept seated by the spring 14. 8 represents the body of the pump 16 its packing and 15 the ram packing ring. No. 16 does not move, but the ram 17 does, having a cup leather reversed at its upper end applied in the same way and manner as 16, with screwed packing ring. The discharge valve is located behind the pump plunger 9 and is, therefore, invisible.

A hydraulic punch mounted upon three legs or supports is shown in Fig. 143, and it also has a shackle at its back to suspend the punch in mid air as occasion requires.

Fig. 143.

The details of this punch are like Fig. 142. It has two guards, one each side of the punch to pull the material operated upon off the punch as it is raised by the lower lever. Another very convenient style of hydraulic punch is shown in Fig. 144 where A represents the body of punch, B the operating lever with the lowering or adjusting lever shown broken off. The punch proper is shown at C. The center of gravity of this punch has been so nicely located that by suspending from the handle the ram hangs plumb.

Fig. 144.

Fig. 145.

THE HYDRAULIC PRESS.

The hydraulic press consists of
1. A Lever,
2. A Pump,
3. and a Ram working in a
4. Cylinder.

Bramah in the year 1796 brought out a very interesting apparatus which illustrates the law of the equality of pressure which has been widely adopted in the practical use of the hydraulic press. The principle upon which this press works is due to Pascal but it remained for Bramah to put it to practical use. Enormous pressures are developed by operating the hand lever shown at M in Fig. 145, which is connected with pump plunger P. The pump barrel A is very thick and receives its supply from the cistern H through the suction pipe a.

Fig. 146.

Water is delivered from the pump A through a heavy lead pipe into the cylinder B of the hydraulic press. The ram P is made tight by the leather packing n and has a table or platform attached to its upper end as shown. The stationary part Q consists of a heavy cast-iron plate supported by four wrought-iron or machinery steel columns. By operating the handle M of the pump any substances placed between the table on the ram P and the plate Q may be compressed to any reasonable extent.

The pressure which can be obtained by this press depends on the relation of the ram P to that of the plunger P. If the former has a transverse section fifty or a hundred times as large as the latter, the upward pressure on the ram will be fifty or a hundred times that exerted upon the pump plunger. By means of the lever M an additional advantage is obtained.

If the distance from the fulcrum to the point where the power is applied is five times the distance from the fulcrum to the plunger P the pressure on it will be five times the power. Thus, if a man acts on M with a force of sixty pounds, the force transmitted by the plunger P will be 300 pounds, and the force which tends to raise the ram will be 3,000, supposing the section of ram is a hundred times that of the pump plunger.

Over-pressure, is prevented by safety-valve shown in front of the pump A. Fig. 146 shows an enlarged section of the pump used in connection with this press. When the plunger P rises a partial vacuum is formed below it and the suction valve O rises allowing the pump barrel to fill with water through the strainer and suction pipe in the cistern.

When the plunger descends the valve O closes and the water passes through the discharge valve h into the pipe K, thence into the cylinder B of the press where it acts upon the ram. When the press has done its work the ram may be lowered by opening the relief valve r. The safety valve is shown at i. By removing the plug h the discharge valve can be reached to grind it in when necessary.

Note.—Hydraulic Pressure Transmission. Water under high pressure—500 to 3000 lbs. per square inch and upwards—affords a very satisfactory method of transmitting power to a distance, especially for the movement of heavy loads at small velocities, as by cranes and elevators. The system consists usually of one or more pumps capable of developing the required pressure; 2, accumulators, described on the next page; 3, the distributing pipes, and 4, the presses, cranes, or other machinery to be operated. This property of fluids invests us with a power of increasing the intensity of a pressure exerted by a comparatively small force, without any other limit than that of the strength of the materials of which the engine itself is constructed. It also enables us with great facility to transmit the motion and force of one machine to another, in cases where local circumstances preclude the possibility of instituting any ordinary mechanical connection between the two machines. Thus, merely by means of water-pipes, the force of a machine may be transmitted to any distance, and over inequalities of ground, or through any other obstructions.

THE HYDRAULIC ACCUMULATOR.

This useful and indispensable apparatus was designed by Sir William Armstrong. Its use was to secure a uniform pressure of water in a reservoir by weight so that however much or little of this water was used the pressure would remain constant.

In the first accumulator which is still in use the ram was attached to the foundation while the cylinder rose and fell as the pressure was utilized. The weights were annular in shape and were hung upon the outside of cylinder. In the modern types of accumulators the cylinder is stationary and the ram supporting the weights is made to rise and fall.

By means of a hydraulic accumulator a uniform pressure can be established and maintained on all parts of a hydraulic main or system.

The volume of water which is used intermittently for the purpose of operating presses—draw-benches for brass and copper tubing and the like is replaced by a pump or pumps which are started and stopped automatically by a connection between the accumulator and the throttle or belt shifter of the pump. The accumulator is used for a double purpose of maintaining a constant pressure and to store up any surplus force of the pumps. The friction loss in the transmission of power by water through mains is very small, as for example: It has been found that water under a pressure of 700 lbs. per square inch may be transmitted through well proportioned mains, one mile with a loss of only two per cent.

The useful work stored in an accumulator may be calculated by the following rule: Multiply the area of ram in square inches by the length of the stroke in inches by the pressure m pounds per square inch divided by 33,000 lbs. the equivalent of one H. P.

This represents the work done by one full stroke of the accumulator ram in descending from its highest position to its lowest.

Example. Required the work done by one stroke of a ram twelve inches in diameter, and a stroke of twenty-two feet, under a pressure of 750 lbs. to the square inch. Area of 12 ram = 113·097 square inches. No. of ins. in 22 ft. = 264. Then
113·097 × 264 × 750
————————– = 678·582 H.P.
33,000

Mr. Tweddel designed the accumulator shown in Figs. 147 and 148 to furnish the varying demand for water where only one appliance of this kind is used in connection with a hydraulic system of shop tools more especially where these tools are numerous.

The ram or spindle A is fixed top and bottom and acts as a guide for the cylinder B which slides up and down upon it.

This cylinder is loaded with weights marked to indicate the pressure which the accumulator will balance with those weights in use. The water is pumped into the bottom through the pipe C, and fills the annular space around the spindle. The entire weight of cylinder is raised by the pressure of water acting only on the area of the end of brass sleeve DD, which is only ¹/₂ inch thick all around the center spindle, and extends down through the bottom packing in cylinder, as shown in sectional view. Fig. 149.

A compact arrangement is thus gained and any reasonable, required cubical capacity may be reached by lengthening the stroke.

The accumulator is supplied by two pumps having plungers 1³/₈ diam. by 3¹/₂ stroke, speed 100 to 120 rev. per minute.

When the loaded cylinder B reaches the top of its stroke, by means of a small chain it closes the suction cock E, which shuts off the water supply of the pumps.

To put in a new bottom packing, the cylinder is let down to rest on the wooden blocks G, and the spindle is lifted out of its tapered seat at the bottom by a tackle hooked into the eye-bolt at the top. To renew the top leather the bracket holding the top end of spindle A, has to be removed.

This accumulator (having only a small area) falls quickly when the water is withdrawn, thus producing a combined blow and squeeze, which is of great advantage in hydraulic riveting.

The Hydraulic Intensifier is a cylinder having two diameters, in principle very like the tandem compound engine. It is used for increasing the pressure of water in hydraulic mains, pipes, or machines, using only the energy of the pressure water to effect the change. But for this distinction a steam pump would be an intensifier. An intensifier worked the reverse way is a “diminisher” as a hydraulic pump usually is, giving a reduced pressure.

The intensifier is in some respects analogous to the electric transformer.

The intensifier as used in connection with hydraulic apparatus was patented in the year 1869 by Mr. Aschroft, but the principle upon which it works is very much older. Intensifiers are made both single and double acting.

PERCENTAGE OF THE TOTAL AMOUNT OF WATER TAKEN FROM THE RESERVOIR.

For explanation of these tables see page 177.

HYDRAULIC RAM.

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.

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 32⁸²/₁₀₀ gallons would be delivered.

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.

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.

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.

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.

PUMPS AS HYDRAULIC APPARATUS.

In Figs. 153 and 154 are shown representations of certain apparatus, long used in schools, to explain the rather obscure operation, of even the simplest of pumps; these models are made of glass so that all the movements of the valves, etc., may be clearly noted. Credit is due to Monsieur Ganot, author of Elements of Physics, for the following.

Fig. 153 represents a model of a suction-pump such as is used in lectures, but which has essentially the same arrangement as the pumps in common use. It consists, 1st, of a glass cylinder, B, at the bottom of which is a valve, S, opening upwards; 2nd, of a suction-tube, A, which dips into the reservoir from which water is to be raised; 3rd, of a piston, which is moved up and down by a rod worked by a handle, P. The piston has a hole in its center; this upper aperture is closed by a valve, O opening upwards.

When the piston rises from the bottom of the cylinder B, a vacuum is produced below, and the valve O is kept closed by the atmospheric pressure, while the air in the pipe A, in consequence of its elasticity, raises the valve S, and part of it passes into the cylinder. The air being thus rarefied, water rises in the pipe until the pressure of the liquid column, together with the pressure of the rarefied air which remains in the tube, counterbalances the pressure of the atmosphere on the water in the reservoir.

When the piston descends, the valve S closes by its own weight, and prevents the return of the air from the cylinder into the tube A. The air compressed by the piston opens the valve O, and escapes into the atmosphere by the pipe C. With a second stroke, the same series of phenomena is produced, until after a few strokes the water reaches the cylinder. The effect is now somewhat modified; during the descent of the piston the valve S closes, and the water raises the valve O, and passes above the piston by which it is lifted into the upper reservoir D. There is now no more air in the pump, and the water forced by the atmospheric pressure rises with the piston, provided that when it is at the summit of its course it is not more than 34 feet above the level of the water into which the tube A dips.

In practice the height of the tube A does not exceed 26 to 28 feet; for although the atmospheric pressure can support a higher column, the vacuum produced in the barrel is not perfect, owing to the fact that the piston does not fit exactly on the bottom of the barrel. But when the water has passed the piston, it is the ascending force of the latter which raises it, and the height to which it can be brought depends on the power which works the piston.

The action of this pump, a model of which is represented in Fig. 154, depends both on exhaustion and on pressure. At the base of the barrel, where it is connected with the tube A, there is a valve, S, which opens upwards. Another valve, O, opening in the same direction, closes the aperture of a conduit, which discharges from a hole, o, near the valve S, into a vessel, M, which is called the air-chamber. From this chamber there is another tube, D, up which the water is forced.

At each ascent of the piston B, which is solid, the water rises through the tube A into the barrel. When the piston sinks the valve S closes, the water is forced through the valve O into the reservoir M, and thence into the tube D. The height to which it can be elevated in this tube depends solely on the motive power which works the pump.

If the tube D were a prolongation of the tube Jao, the flow would be intermittent; it would take place when the piston descended, and would cease as soon as it ascended. But between these motions there is an interval, which, by means of the air in the reservoir M, ensures a continuous flow. The water forced into the reservoir M separates into two parts, one of which, rising in D, presses on the water in the reservoir by its weight; while the other, by virtue of this pressure, rises in the reservoir above the lower orifice of the tube D, compressing the air above. Consequently, when the piston ascends, it no longer forces the water into M, the air of the reservoir, by the pressure it has received, reacts on the liquid, and raises it in the tube D, until the piston again descends, so that the jet is continuous.

Hydraulic Machine Tools. Probably in no department of engineering has the use of hydraulic power met with more success than in its application to certain machine tools. This success is owing to the peculiar suitability of pressure—water as the motive agent for the performance of a certain class of operations requiring the exertion of a great force with comparative slow motion, as in punching, riveting, forging and the like.

The wide spread and successful use of hydraulic machines—of which a few only have been described and illustrated upon the pages of this book—is due to the necessity for such tools and the inventive ability of our tool designers.

A large fixed hydraulic riveter is shown in Fig. below; it is capable of exerting on the rivet a pressure of 40 tons or more; the machine has a working pressure of 1,500 pounds per square inch. Working pressures of 5,000 to 10,000 pounds per square inch are used in hydraulic forging presses, but in the riveter much less pressure is required.

CLASSIFICATION
OF PUMPS