206 



PUMP. 



Pump. O f the air in the suction pipe CDEF lifts the valve v, 

 ^ *Y W "* / and expands into the barrel. The whole air in the 

 suction pipe being thus more rare than that of the at- 

 mosphere, the pressure of the latter upon the surface 

 of the water will force it up a short way in the suction 

 pipe, till the equilibrium is restored. By a second 

 stroke of the pump the same effect is produced, and the 

 water rises a little higher in the suction pipe, till it 

 gets into the barrel, when it will be forced up the main 

 or rising pipe DHG by the descent of the piston c d. 



In examining the operation of this pump, it must be 

 obvious that it begins its action as a sucking pump, and 

 finishes by being a lifting pump. On this account the 

 piston is made with a double cone, as the air and wa- 

 ter would pass by the sides of the lower cone when 

 the piston is drawing up; but this is prevented by the 

 leather of the upper cone applying itself to the surface 

 of the barrel. 



Forcing & 8 the forcing pump works by starts, it must obvi- 



," P W ! th ously furnish an intermitting stream of water. There 



PLATE ' are manv cases > particularly in fire engines and water- 



CCCCLXX. m g engines, where it is desirable to have a constant 



Figs. 6, 7. current ; and this effect may be obtained very simply, 



by the application of an air vessel MN, Fig. 6. and 7. 



which is fitted upon the main or rising pipe of the 



forcing pump. In both these figures, the parts of the 



forcing pump to the left of, and below the valve ef, are 



exactly the same as that in Fig. 5. 



In Fig. 6. the air vessel MN is joined laterally to the 

 rising main pipe ; and in Fig. 7. it surrounds an inter- 

 ruption of the main GH. In order to explain the ac- 

 tion of these air vessels, let us suppose that the pump 

 has received water above the valve ef, a part of that 

 water will get into the vessel MN, and compress the 

 air within it with a force proportional to the height of 

 the column in the main GH. The next stroke of the 

 piston draws up more water, and raising it higher in 

 the main, the air in the air vessel is more powerfully 

 compressed. When the water is at last raised to the 

 place where it is to be delivered, or to the end of the 

 main from which it is to issue, the air in the air vessel 

 is so much compressed, that it balances the whole 

 height of the column above it. Now, if the aperture 

 at the top of the main, from which the water flows, 

 were large enough to allow the water to issue with the 

 same velocity as that of the piston, it would flow peace- 

 ably over, rising no higher by each successive stroke, 

 and occasioning no additional compression of the air in 

 the air vessel. But if the aperture of the main is di- 

 minished to half its size, the water forced up by the 

 piston has not time to issue during the stroke, and con- 

 sequently a part of it must go into the air vessel, and 

 increase the compression of the included air. If the 

 piston has now ended its stroke, and raises no more 

 water, the compression of the air in the air vessel ex- 

 ceeding the pressure of the water in the main, the air 

 will press upon the surface rv rv of the water in the 

 vessel, and force it out at the aperture of the main in 

 an uniform current, while the piston is returning to 

 make another stroke. 



4. Description of an Improved Lifting Pump. 



Description This pump, shown in Plate CCCCLXX. Fig. 8. is a 

 of an im- sucking pump, converted by a slight addition into a 

 l - lifting pump, and fitted for propelling water with any 

 pfJrE P velocit y and to any required distance. Near the top 

 cocctxx. ? f . the work ing barrel ABCD of a sucking pump, is 

 Fig. 8. joined the pipe ~Fef, terminating in a rising main ef GH. 



The top of the barrel AB is terminated with a strong Pump, 

 plate AB m n, and a stuffing box AB, through which \^^^^ 

 the polished piston rod ab works air-tight like the 

 piston rod of a steam-engine, so as to prevent either 

 the escape of air or water. The piston cd, which 

 is hollow, has a valve y opening upwards; and there 

 is a similar valve v at the lower end CD of the bar- 

 rel, and there may be advantageously placed a valve 

 x at the bottom ef of the main, though it is not ne- 

 cessary. 



Let the piston cd be now supposed to be down near 

 v. When it is drawn up it pushes up the air above it, 

 (which will keep down the valve y) driving it through 

 the valve x in the main where it escapes. The air be- 

 tween cd and v will now expand into the upper part of 

 the barrel below the piston, and it will be rarefied to 

 such a degree, that the predominating pressure of the 

 atmosphere upon the water below will raise it in the 

 suction pipe. When the piston again descends, the air 

 displaced into the barrel from the suction pipe by the 

 ascending water, will get through the valve y, and, 

 upon again drawing up the piston, this air will be dri- 

 ven off and escape through the rising pipe as before. 

 The water is at last brought into the working barrel 

 by repeated strokes. It gets through the valve?/ when 

 the piston is down, and when the piston is drawn up, 

 the wate,r is drawn up along with it, and forced up the 

 rising pipe through the valve x. 



The advantages of this pump are, 1. That the rare- 

 faction can be made very complete by bringing the 

 piston near the bottom of the working barrel ; 2. That 

 the piston-rod being pulled in place of pushed, is less 

 liable to be bent ; 3. That the parts of the pump are 

 more accessible for repairs ; and, 4. That while by put- 

 ting a cock at x, water may be obtained for common 

 purposes ; the pump, by merely shutting this cock, 

 may be used also for extinguishing fire, or for convey- 

 ing the water to distant places. 



5. Description of the Forcing Pump with a Solid 

 Plunger. 



This pump, shown in Fig. 9. differs from the com- Description 

 mon forcing pump only in the substitution of a solid of the tore- 

 plunger ab in place of a piston of the usual form. This in pump 

 plunger is turned truly cylindrical, and polished, and with a 8ol1d 

 its diameter is a little less than that of the inside of the p "^ r " 

 barrel. It slides through a collar of leathers AB, CCCCMX. 

 which Dr. Robison has described in the following Fig. 9. 

 manner : " The top of the barrel terminates in a flanch 

 AB, pierced with four holes for receiving screw bolts. 

 There are two rings of metal of the same diameter, 

 and having holes corresponding to those in the flanch. 

 Four rings of soft leather of the same size, and similar- 

 ly pierced with holes, are well soaked in a mixture of 

 oil, tallow, and a little rosin. Two of these leather rings 

 are laid on the pump flanch, and one of the metal rings 

 above them. The plunger is then thrust down through 

 them, by which it turns the inner edges downwards. 

 The other two rings are then slipped on at the top of the 

 plunger, and the second metal ring is put over them, 

 and then the whole are slid down to the metal ring. 

 By this the inner edges of the last metal rings are 

 turned upwards. The three metal rings are now forced 

 together by the screwed bolts, and then the leathern 

 rings are strongly compressed between them, and 

 made to grasp the plunger so closely that no pressure 

 can force the water through them. The upper metal 

 ring just allows the plunger to pass through it, but 



