pressure or by centrifugal force. It is usual to denominate them rotary force pumps and centrifugal pumps. The cylinder and piston pump will be described first.-The Force Pump. It is probable, as has been intimated, that the earliest valve pump was a force pump, and was similar in construction and action to that shown in fig. 1 when the lower valve is immersed in the reservoir, so that exhaustion, suction, or atmospheric pressure has no essential connection with its working. When the piston P is raised, water will rush into the chamber through v, and when the piston is close, while the valve

FIG. 1.-Force Pump. depressed this valve will w will be raised by the water, which is forced up into the pipe d. Upon raising the piston again, the pressure being removed from beneath the valve w, the weight of water above will cause it to close and thus prevent any return. But water from external pressure will again rush through the valve v, and the descending piston will again force it up through the valve w into the discharge pipe. The operation may be continued until there is enough water in the pipe d to exert a pressure per square inch equal to that exerted by the propelling power upon each square inch of the piston head.The Common Suction Pump. The functions of this pump depend upon the relative pressure of a column of water within the pipe and that of the atmospheric pressure upon the water outside of it. At the level of the sea the pressure of the atmosphere, when water boils at 212° F., is equal to sustaining a column of mercury of 29.922 in. when at a temperature of 60°. (See BOILING POINT.) The atmospheric pressure is therefore capable of sustaining, under the same conditions, a column of water 33.8 ft. high, or a little more than 13 times as high as the column of mercury, the specific gravity of the fluid metal being 13.557 at 62.6° F. (See MERCURY.) Consequently, if the lower end of a vertical tube of sufficient length is immersed

FIG. 2.-Common Suction Pump.

ՀԱՐ

in water and the tube completely exhausted of air, the water will rise to a height of 33.8 ft. above its level in the reservoir. The action of the common suction pump, fig. 2, will be easily understood from a consideration of this fact. The piston P, fitting the cylinder air-tight, on being raised will expand the air beneath it, and therefore diminish its pressure upon the water in the pipe beneath, according to the law of Boyle or Mariotte. (See PNEUMATICS.) When the piston is depressed the lower valve will shut in consequence of the pressure being greater above than below, and the valve in the piston, opening upward, will open when the density of the air in the cylinder becomes greater than that of the external air, and its contents will thus be expelled. Succeeding motions of the piston will thus continue to exhaust the air within the pipe until the pressure of the air on the water in the reservoir is sufficient to force the water in the pump up to the lower or suction valve. If the exhaustion is complete the water will rise to a height of 33.8 ft. This effect can be secured by filling the pump with water at the top before commencing. Now, as a column of water 33.8 ft. high ordinarily measures the extent of the pressure of the atmosphere at the level of the sea, it follows that if the suction valve is placed at a greater distance above the water in the reservoir the pump will not work. At an elevation, as upon the side or top of a mountain, the atmospheric pressure being less, the valve must be placed lower. At a height of 15,700 ft., where water boils at about 186° and the barometer stands at about 17.5 inches, the lower valve requires to be within 19.7 ft. above the level of the water in the reservoir, this being the height of a column of water which will balance the atmospheric column.-The Lift Pump. By a slight change in the form of the suction pump, and the addition of a valve at x, fig. 3, the modern form of the lift pump is produced, and the water may be raised to a height corresponding to the amount of power applied. The form shown in this figure is that of a lift and suction pump combined. Removing the lower valve o, and immersing the pump till the valve w in the piston is below the surface of the external water, the machine becomes simply a lift pump. The suction pump is also often called a lift pump. A form which is often figured in books employs an exterior frame supporting a piston rod which enters the pump at the lower end, pushing the piston

FIG. 3.-Lift Pump.

FIG. 4.-Force Pump with Air Chamber.

up instead of raising it through a packed box at the top of the cylinder. Such were the old pumps used by Rannequin in the water works at Marli, and by Lintlaer in the engines erected during the reign of Henry IV. at the Pont Neuf, to supply the Louvre from the Seine. The lift pump is in fact another kind of force pump, and in its simplest form may have been one of the first employed. The efficiency of the force pump, as well as of the lift pump, may be greatly increased by the employment of an air chamber, as shown in fig. 4, by which means a constant and equable flow is secured and the sudden shock of reaction avoided. A domeshaped vessel is placed in the course of the discharge pipe, a short distance beyond the upper valve. When the water in the discharge pipe is raised to a height of 33.8 ft. above the level of the water in the air chamber, the latter will of course be half filled with water, the air being compressed to one half its original volume by the double pressure of water and atmospheric air upon it. It may be remarked that, as in the case of the hydraulic ram, the air in the chamber becomes gradually absorbed by the water as it passes through the pump, and must from time to time be replaced. The discharge pipe, instead of branching off from the base of the air chamber, may pass directly into it through a hole in the dome, and down to near the base. In either case the air chamber is replenished by allowing the water to run off by a cock at its base. A double-acting force pump is shown in fig. 5. This possesses the advantage of producing a more uninterrupted stream than the form shown in fig. 1, and if supplied FIG. 5.-Double-Acting Force Pump. with an air chamber the latter need not be so large to effect the same equalization of current. Double-acting force pumps, either with or without the air chamber, are often employed at large town water works for raising water to the distributing reservoirs.

83

Such a pump acts as follows. When the solid piston head P descends, the valves a and e are forced shut, while d and c are opened, water entering behind the piston through d and being forced in front of it through c, and up the pipe CD. When the piston is raised the position of the valves is reversed, the water entering through a and being forced out through e. This is the position shown in the figure. When water is to be raised to a great height or against great resistance, as in the hydrostatic or hydraulic press, a plunger in place of the ordinary piston with packed head is used, which passes through a tightly packed box, as shown in fig. 6. Such plunger pumps were employed in the water works FIG. 6.-Plunger Pump. at York buildings, London, in the last century, but they are described in Commandine's translation of Heron's Spiritalia. It is evident that the introduction of the plunger into the cylinder must expel an equal volume of water through the upper valve, and on being withdrawn allow the entrance of the same quantity through the lower valve. The fire engine is a combination of two force pumps, as shown in fig. 7, the water being forced from each into the common air chamber A, and so on through the discharge pipe E, to which may be attached the hose. The power applied as a motor may be various, as that of man, of animals, of water, or of steam. The earliest application of a steam engine to a pump was by Newcomen in 1713. The contrivance of Savary can hardly be called an application of a steam engine to a pump, because the steam cylinder was a part of the pump itself, the steam performing the functions of a piston head. Very large pumps are often used for drainage purposes, which are usually worked by steam engines separate from the pump itself. An enormous steam engine was employed in the drainage of Haarlem lake in Holland, which drove ten pumps having a united capacity of raising 112 tons of water at each stroke. (See DRAINAGE.) Large pumps are used for raising water into reservoirs for supplying cities. (See WATER WORKS.) Most modern pumps

E

FIG. 7.-Fire Engine.

other old form of rotary pump of the 16th century is shown in fig. 11. A wheel of a diameter and thickness proportional to the capacity of the pump has its periphery formed into three cams, which give space for the passage of water between them and the inner surface of the cylindrical box in which it moves, and also raise and drop a broad sliding vertical bar, B (seen edgewise), which acts as a shut-off to the passage of the water within the box, directing it into the pipe A. The cams act the part of pistons, the water entering at the bottom of the cylinder and being forced in the direction of the arrows. To prevent its return on stopping the pump, a lift valve is placed in the discharge pipe, which shuts when the pressure above exceeds that below it. There are many other and recent forms of rotary force pumps, acting much upon the same principles, with the addition of devices which se

85

space outside of B is the water space. This cylinder is enclosed by the disk D, which is attached to the shaft. An eccentric ring, E, is attached to the disk D so that in revolving its outer surface touches the inside of the case A, while the interior surface upon the opposite side of the ring touches the outside of the ring B. The eccentric ring E acts as the piston of the pump. The suction and discharge are respectively shown in both sections at I and J, the direction of the water being indicated in fig. 12 by the arrows. The parts are separated by the sliding valve HH, which is moved back and forth on its seat by means of two tumblers shown in fig. 13 between H and H. These tumblers are moved by the eccentric ring E, which passes between them. The centre ring B is made enough deeper than the casing A, as shown in fig. 12, to equalize the quantity of water within and without the eccentric piston ring E. F is the cover or outside case, and contains a closed bearing for the end of the shaft. The inner part of the disk D forms a collar G to the shaft, and by means of a screw at the end this collar can be forced tightly against its seat K, thus avoiding the use of packing. In the centre of the seat there is a circular groove, shown in section at K K, which connects by a drilled channel with the suction part. Any tendency to escape of water at the seat by pressure is thus overcome by vacuum force.-The chain pump consists of an endless chain carrying cups or disks around two drums, one beneath the surface of the water in the well or stream, and the other at a convenient elevation. The ascending part of the chain passes through a pipe just large enough to allow the cups or disks, which act as pistons, to move with little friction. It will thus be seen that the chain pump is little

else

Bagley and Sewall's Rotary Pump. cure greater efficiency. One of the latest of these is Bagley and Sewall's, patented by L. D. Green, of which fig. 12 is a vertical longitudinal, and fig. 13 a transverse section. A is the main case, made in one piece, and having attached the ring B, seen in both sections. The

FIG. 14.-Old French Chain Pump.

than a modified form of rotary pump. When the water is to be raised to a moderate height, it often becomes a convenient and useful machine. Fig. 14 shows the form of an old French chain pump used in the ship yards at Marseilles, described by Belidor. It was worked

FIG. 15.-Massachusetts Pump.

by two galley slaves, who were relieved every | hour. It is uncertain where the chain pump originated, but it was probably first used in China in the form of an inclined trough with drums at either end, giving motion to a chain or rope with scoops or blocks attached. The centrifugal pump is a machine which acts upon an entirely different principle from that of any pump so far described. The force which elevates the water is the centrifugal force developed by the revolution of a fan wheel. An early efficient form of centrifugal pumps was constructed in Massachusetts in 1818, and called the Massachusetts pump. It resembles an ordinary fan blower, as will be seen by the cut, fig. 15. It consists of a horizontal shaft to which are attached four eccentric blades, narrowed toward their extremities and located within a cylindrical-shaped box, from which a discharge pipe F passes upward. The water is received at the centre, around the shaft, which is so placed that the blades just graze the inner surface of the box at the junction of the discharge pipe, into which the water is necessarily forced. The apparatus is placed below the level of the water, as the vacuum power is small. A more recent form of centrifugal pump is Appold's, shown in figs. 16 and 17, which was first exhibited at the world's fair in London in 1851. The efficiency of a centrifugal pump depends upon the form of its blades, and Mr. Appold made a great improvement, nearly doubling the efficiency of the Massachusetts pump, by giving them the form shown in section by the dotted lines in fig. 17. The revolving fan wheel, shown in fig. 16 at c, is fixed

the whole being rotated in the contrary direction. The lower part of the discharge pipe is enlarged into a drum somewhat similar to that of the Massachusetts and of the Gwynne pump, and the water issues from all parts of the periphery of the fan wheel and is forced upward into the discharge pipe A. Calculations have been made as to the height to which water may be carried with one of these pumps, but they do not possess much practical value, as the power of each machine varies with its construction; and 20 ft. is the practical limit, although by means of a very high velocity, not practicable for ordinary use, a height of 50 ft. has been reached. Gwynne and co.'s centrifugal pump is a modification of Appold's, and was shown at the same exhibition. A sectional view is given in fig. 18. Six equidistant arms, extending first in the direction of radii, but toward their outer ends curved and pointing backward as regards the direction of rotation, are fixed within a drum, which again moves within an outer drum. The water enters at the centre, and taking the course of the arrows ascends the discharge pipe. Three of the arms commence at the axis, but the other three, alternating, commence at the circle of admission. The two drums are only in contact at a small ring surrounding the central opening. The arms diminish in breadth toward their outer extremities to render the flow of water smooth, as the increase of centrifugal force at the periphery causes an increase in the velocity of the water, and therefore it requires a less space through which to move.-There are numerous practical points about the different kinds of pumps, to mention which would require a too extended detail. It may be remarked that a pump is one of the most difficult machines to keep in order. It is exposed, if not constantly in use, to great changes of moisture and dryness, and its metallic parts, particularly if of iron, soon become rusty. It is often convenient to have valves partly made of leather, but these cannot be expected to last long; if constantly in use they soon wear out, and if they are allowed to become dry they shrink and cease to perform their offices well.-A kind of steam pump without a piston, called a "pulsometer," is the invention of Mr. C. H. Hall of New York. It consists of two long-necked chambers joined together at the top, where a ball valve by falling one way or the other opens one of the chambers to the admission of steam. The water is admitted at the bottom of the chambers, and passes into

FIG. 18.-Gwynne's Centrifugal Pump.