P U M P. 



209 



now been explained, has been described by Hachette, 

 in his 1'raitc Klemenlairf dt-s Machines,]). 158. 



Those who arc acquaintr.! with the Jim? manufacture 

 of water-proof cloth and canvass by Mr. Charles Mack- 

 into-.li ot (il;u^o\\ , will M-C that pumps of the above 

 description, with bag pistons, may be constructed more 

 i-lrgantly and durably by using those water-proof fa- 

 l>nr> made by a varnish obtained from the dissolution of 

 caoutchouc, in the nuj)tha procured from coal tar. 



9. Description of an Occasional Tump, nfa very simple 

 construction. 



cription This pump, which is represented in Fig. 13, was 

 suggested to Dr. Kobison while describing the con- 

 struction of a simple valve. In a square wooden trunk 

 A BCD, a piece of oak board EF is exactly fitted to the 

 trunk in an oblique position, and supported by an iron 

 pin, which goes through it at I, one-third of its length 

 from the lower extremity E. The two ends of the 

 board EF are bevilled so as to apply themselves accu- 

 rately to the sides of the trunk. If a stream of water 

 now rises upwards, it will press with more force on the 

 part IF of the board, than upon the part El, and con- 

 sequently it will force it up, and rush through, causing 

 the board to stand nearly parallel to the sides of the 

 trunk. In order to prevent it from rising into the 

 parallel position, its progress must be stopped by a pro- 

 jecting pin. If the stream of water now descends, its 

 pressure on the upper side of the board being again 

 greatest on the part IF, it will be forced back again 

 into its former position, and its two bevilled extremi- 

 ties resting on the opposite sides of the trunk, the 

 passage will be completely shut up. The board EF 

 will therefore perform the office of a very perfect 

 valve, both because it affords the freest passage for the 

 water, and allows very little to get back while it is 

 shutting; for the part IE brings up half as much wa- 

 ter as IF allows to go down. The tightness of this 

 valve may be greatly increased by fixing two thin fil- 

 lets Gand II to the sides of the trunk, and covering with 

 leather those parts of the board EF, which come in 

 contact with them. 



The valve being thus constructed, a square box, 

 abode, covered on the outside with soft leather, is 

 made to slide, without sticking, along the wooden trunk 

 ABCD, and a piston rod is fixed to a piece of wood e, 

 morticed into two of the sides of the box abode, 

 which project upwards like the gable ends of a house. 

 A valve similar to EF is placed in this box, and it be- 

 comes a pump of the usual form. Dr. llobison remarks, 

 that, if this pump is immersed so deep in the water 

 that the piston shall also be under water, its perform- 

 ance will be equal to any pump. 



Description 



of Dela- 



hire's 



double 



forcing 



pump. 



PLATE 



CCCCI.XX. 



Fig. 14. 



10. Description of Dela hire's Double Forcing Pump. 



This pump is represented in Fig. 14", and partakes 

 both of the nature of a forcing and a sucking pump. 

 It consists of the great barrel AB, to which is connect- 

 ed the rising pipe EF, with valves opposite to E and 

 F, and the main pipe CD, with valves opposite to 

 C and D. The piston b is of one piece, without any 

 valve, and the piston rod a b works in a collar of lea- 

 ther at A. When the piston is depressed to B, the 

 valve F will shut, and the air below the piston will be 

 driven through C up the pipe CD ; and, in consequence 

 of the rarefaction of the air above the piston, the valve 

 D will shut, and the water will rise up FE, through 



VOL. XVII. PART I. 



the valve D, into the barrel above the piston. When Pump, 

 the piston is raised towards A, it will force up the wa- ^""v* 1 - 

 ter above it, through the valve D, and up the pipe DC, 

 while water will rise through the pipe HF, and pass 

 through the valve at F, into the barrel below the 

 piston. 



11. Deicrifjtion of a Centrifugal Pump. 



In the centrifugal or rotatory pump, the centrifugal De*criptic 

 force produced by rotation is the immediate agent in ot ten- 

 raising the water, combined with the pressure of the lr ' fu s" l 

 atmosphere. This machine is represented in Fig. 15, 

 where AB is a vertical tube, moving round gudgeons ^ 

 at A and B, the lowermost of which is in the well from Fig. % W." 

 which the water is to be raised. To this vertical tube 

 is connected one or more horizontal arms CD, with an 

 aperture at one or both ends, by which the water is 

 discharged into a circular trough EF, from which it is 

 taken out by thr spout at F. The rotatory motion is 

 communicated to the vertical and horizontal pipe, bv a 

 handle, or by a band or string passing round the pul- 

 ley P. The machine is first filled with water, and 

 after it has acquired a sufficient velocity, the water is 

 thrown out by the centrifugal force, and its place sup- 

 plied by the pressure of the atmosphere necessary to 

 balance the effect of the centrifugal force. When the 

 purnp is filled, or is at rest, the valves shown at B shut, 

 and prevent the water from descending, but when the 

 machine is in motion, these valves are of course open. 



In 181(), an improvement was made upon the cen- 

 trifugal machine by M. Jorge. It consisted in making 

 the vertical tube AB immoveable, and in limiting the 

 rotatory motion to the horizontal pipe or pipes. The 

 advantages of this construction are, that the quantity 

 of matter put in motion is diminished, and that the 

 vertical tube may have any form, and any position 

 which local circumstances may require. See Recueil 

 des Machines de I' Academic, 1 732 ; and Hachette's 

 Traite Elementaire des Machines, p. 136. 



12. Description of Smeatons Pump for keeping up a 

 constant head of nater. 



This ingenious pump forms a part of the apparatus 

 by which Mr. Smeaton performed his experiments on 

 the effects of overshot and undershot water wheels; and 

 the object of it was to furnish the wheel with the same 

 quantity of water at each stroke. It is represented in 

 Fig. 16. where ABCD is the reservoir, in which the 

 water is to be kept at a constant height m n, so as to 

 flow out uniformly at an aperture in any of its sides. 

 The piston rod a b carries a cylinder a h, of such a 

 size that the surface m n is pressed as much up by the 

 descent of the portion af into the water, as it would 

 descend by following the piston b in its descent to- 

 wards EF. The diameter of the cylinder a f must be 

 a little less than that of the pipe CDEF, as a portion 

 of the latter is occupied by the forked rod h b, which 

 carries the piston. In consequence of the surface m n 

 remaining always at the same height, the efflux of the 

 water at any aperture in the sides of the reservoir 

 ABCD will be uniform. 



Description 

 of a pump 

 with a 

 double 

 piston. 

 PLATE 



CCCCI.XX. 



Fig. 17. 



Description 

 of Smea- 

 ton's pump. 

 for keeping 

 up a n n- 

 stant htad 

 of water. 

 PLATE 



CCCCI.XX. 



Fig. 16. 



13. Description of a Pump tvilha Double Pi 



Pumps with two pistons have been used principally 

 at sea and in fire-engines, as it is an object in both these 

 cases to apply the power of as many men as possible 

 2 D 



