56 



THE APPLICATIONS OF PHYSICAL FORCES. [BOOK i. 



In the pumps used in large hydraulic works, the different parts 

 must necessarily be constructed with great solidity, on account of the 

 considerable pressure and resistance to which they are subjected. 

 The piston is then generally a massive metal cylinder, as represented 

 in Fig. 38. It is then called a plunger. It will be seen that on 

 each side of the pump-barrel is a valve, opening upwards. One 

 of these, to the left of engraving, admits water into the barrel 

 while the plunger is making its upward stroke, while the other 



opens as soon as the plunger 

 begins to descend, and allows 

 the water to escape into the 

 delivery pipe. 



The mechanism which draws 

 up the water in suction pumps 

 is not always a piston moved 

 alternately upwards and down- 

 wards in a cylindrical body, 

 and making the vacuum from 

 the side of the pipe which 

 brings the liquid. In certain 

 pumps called oscillating pumps, 

 there is a fixed blade, oscillat- 

 ing on an axis > which acts as 

 piston, and both sucks up the 

 water by causing a vacuum by 

 one of its arms, whilst it 

 presses the water already 

 brought by the movement of 

 the other part. Fig. 39 repie- 

 sents a Bramah's oscillating 



pump, and clearly shows the action of the movable piece and 

 valves. 



In rotatory pumps (Fig. 39 gives a cut of Stoltz pump) the suction 

 pipes c and forcing pipes c' are connected by two openings a and a, 

 with a circular drum A, in the interior of which a ring, concentric with 

 the drum B, is in motion. Four blades p, p, p, p, rest both on the 

 interior surface of the drum and on the surface of an eccentric ; 

 closing hermetically the circular space, and consequently producing the 



FIG. 38. Plunger pump. 



