Hydrostatics and pneumatics / [Dionysius Lardner].

  • Dionysius Lardner
Date:
1831
Catalogue details

Licence: Public Domain Mark

Credit: Hydrostatics and pneumatics / [Dionysius Lardner]. Source: Wellcome Collection.

    339/376 (page 323)
    V1 a short tube communicates with a strong close vessel of sufficient capacity ; through the top of this vessel the force pipe G H passes, and descends to a point near the bottom. By the action of the pump the water is forced into the vessel M N, and when its surface rises above the mouth H of the force pipe., the air in the vessel M N is confined above the water; and as the water is gra- dually forced in, this air is compressed, and acts with increased elastic force on the surface of the water : this pressure forces a column of water into the pipe H G, and maintains that column at an elevation proportional to the elastic force of the condensed air. When the air in the vessel M is reduced to half its original bulk, it will act on the surface of the water with double the atmospheric pressure; meanwhile, the water in the force pipe being subject only to once the atmospheric pressure, there is an unresisted upward force equal to the atmo- spheric pressure which sustains the column of water in the tube : a column will then be sustained about 34 feet in height. When the air is reduced to one third of its original bulk, the height of the column which it can sustain is 68 feet, and so on. If the force pipe termin- ate in a ball pierced with small holes, so as to form a jet d’eau, the elastic pressure of the air on the surface will cause the water to spout from the holes. It is of great importance in the forcing pump that the piston should be truly water-tight in the cylinder, and in practice this is not always very easily accom- plished. The arrangement represented in fig. 40. is better adapted to insure the perfect action of the pump than the form of piston already represented. In this case a polished cylindrical metal plunger P passes through a collar of leathers A B, which exactly fits it; and it is maintained perfectly air-tight and water-tight by being lubricated with oil or tallow. When the plunger is raised, the space it deserts is replaced by the water which rises through the valve V; and when it descends, the water which filled the space into which it y 2