PUMP 83 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 Kannequin 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 an- other 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 in- creased by the em- ployment of an air chamber, as shown in fig. 4, by which means a constant and equable flow is secured and the sud- den shock of reaction avoided. A dome- shaped vessel is placed in the course of the discharge pipe, a short distance beyond the up- per 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 lat- ter 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 direct- ly into it through a hole in the dome, and down to near the base. In either case the air cham- ber is replenished by allowing the wa- ter to" run off by a cock at its base. A double-acting force pump is shown in fig. 5. This pos- sesses the advan- tage of producing a more uninterrupted stream than the form shown in fig. 1, and if supplied with an air cham- ber the latter need FIG. 5. Double-Acting Force Pump. not be so large to effect the same equaliza- tion 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. FIG. 6. Plunger Pump. 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 be- ing forced in front of it through c, and up the pipe C D. When the pis- ton 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 fig- ure. When water is to be raised to a great height or against great resistance, as in the hydrostatic or hy- draulic press, a plunger in place of the ordinary pis- ton with packed head is used, which passes through a tightly packed box, as shown in fig. 6. Such plunger pumps were em- ployed in the water works at York buildings, London, in the last century, but they are described in Commandine's translation of Heron's Spirita- lia. 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 per- forming the func- tions of a piston head. Very large pumps are often used for drainage pur- poses, which are usually worked by steam engines sepa- rate from the pump itself. An enormous steam engine was em- ployed in the drain- age of Haarlem lake in Holland, which FIG. 7. Fire Engine. drove ten pumps having a united capacity of raising 112 tons of water at each stroke. (See DRAINAGE.) Large pumps are used for rais- ing water into reservoirs for supplying cities. (See WATER WORKS.) Most modern pumps
