PUMP. 



211 



Pump, 



every quarter of an hour they could relieve themselves 

 by changing hands, which was done by chan^iii(r 

 places. They were intended to make no mon; than 

 twenty-five strokes per minute, moving tin- pump 

 rod 17* inches up and down at each stroke, tin- 

 barrel being a nine-inch bore. This was much better 

 tii.in making shorter strokes, and quicker as they usu- 

 ally do. Their hands moved up and down about (our 

 feet six inches, and by working with tin* stroke at a 

 moderate rate, so as to hold it an hour, four men would 

 in that time deliver 20 tons, at a height of 2-: 

 This was upon a supposition of raising the water to 

 the usual height ; but when, by the application of the 

 maxims before described, this perpendicular was short- 

 ened to 16 or 17 feet, then nearly the same delivery 

 could be made by three men, or proportionably more 

 by four men ; that is, as 17: 22:: 20: 26 tons, at 17 

 feet. The foot of the pump was let through the ship's 

 inner planking or ceiling, betwixt two of the floor 

 timbers, and did not touch the bottom or outside plank- 

 ing within 2j| inches, the lower end being rounded 

 within side like a trumpet mouth, it being a bud plan 

 to have the pump standing upon its lower extremity, 

 with holes bored to let in the water, as it is thus very 

 liable to be choaked by dirt. A plank of the ceiling 

 was made to lift up near the pump's foot, that a man 

 could occasionally get in his arm, to clear away any 

 chips, sand, or dirt, or other matter that should hap- 

 pen to be drawn thither." 



16. Account of Mr. Willy's Improvement on Pumps. 



IVmj . 



17- On Chain Pumps. 



Account of Th e disadvantage of raising the water to a higher 

 ,. level than is actually required, seems to have given rise 



provcrnent to ^ r< Ditty's improvement on the pump. Smeaton 

 on pumps, had already remedied this evil, as we have just seen, 

 in ships' pumps. In distilleries, &c. as well as in ships 

 it is used to force the water to the top of the barrel, 

 and allow it to run off to a lower level. Hence if the 

 water descends from the top of the pump to a place of 

 delivery much below the top of the barrel, the fall of 

 the water through this height is a mechanical force 

 which is entirely wasted, and which might be advan- 

 tageously employed in raising the water through part 

 of the pump barrel. Mr. Witty avails himself of this 

 power in the following manner : " Instead," says he, 

 " of letting the water or liquid escape from a common 

 pump at the usual place of delivery, I caused it to 

 descend again in a syphon pipe to the lowest level at 

 which it can conveniently be delivered ; and as this 

 descent is considerable in ships, brew-houses, &c. a 

 considerable saving of labour is effected in working 

 pumps by a descending column of water or liquor 

 counterbalancing as much in length of the rising co- 

 lumn in the pump as the height which it descends in 

 the syphon pipe to the place where it can be delivered." 

 If we consider the water which in ordinary pumps 

 falls from the top of the barrel to the place of its recep- 

 tion as a mechanical force which is lost, we may avail 

 ourselves of it, by various contrivances for assisting in 

 the work to be performed. In Mr. Witty's contrivance, 

 the men at the pump raise the water to the bottom of 

 the short leg of the syphon, and it is then drawn through 

 the syphon by the water of the larger branch. There 

 are many cases, however, where we may allow the work- 

 men to raise the water to the top of the barrel, and 

 employ the direct force of the descending fluid to work 

 another pump, or perform any other piece of work that 

 may be required. 



In our article HYDRODYNAMICS, Vol. XI. p. r,(')6, we On chin 

 have already given a drawing and description of the 

 chain pump, both as constructed with plugs and with 

 buckets, (see Plate CCCXX. Fi>. 6. and Plate 

 CCCXXIV. Fig. 4. and 5.) but as these pumps have 

 been found by long experience to be the most useful 

 at sea, and the least liable to be* deranged by accidental 

 causes, we propose to give some farther account of 

 'them in this place. 



Kvery English ship of war has four chain pumpt, 

 and three hand pumps, which are all fixed in the same 

 well. The old chain pumps were very defective ma* 

 chines previous to the improvements made upon them 

 by Mr. Cole. The sprocket wheels n>, tv, Fig. 5. Plate 

 CCCXXIV. had no contrivance to prevent the chain 

 from sliding or jerking back on the surface of the 

 wheel. The links were not only too short, but were 

 ill united, and hence they created much friction in 

 passing round the sprocket wheels, and often broke in 

 situations of a critical kind. In Mr. Cole's improve- 

 ment, the links are formed of two long plates of iron, 

 with a hole at each end, and fixed together by two 

 bolts, which act as pins for the joints. The buckets 

 or saucers a, b, c, Fig. 4. Plate CCCXXIV. are circular 

 plates of brass with a piece of leather between them; and 

 the sprocket wheels W, VV, are formed like the trundles 

 used in mills. They consist of two iron wheels fixed 

 at eight inches distance on the axle, and united by 

 several round iron bolts. The links of the chain have 

 hooks which rest on these bolt?, and the chain is thus 

 kept upon the wheel, and prevented from starting back 

 when loaded with a column of water. Mr. Cole has 

 constructed his chain pump so that the chain may be 

 taken up and repaired, or any ballast removed with 

 which it may be choaked. In a comparison of Mr. 

 Cole's pump with one of the old construction, it was 

 found to raise one ton of water in 434 seconds, with 

 the power of four men, whereas the old pump required 

 seven men to raise one Ion of water in 76 seconds. Mr. 

 Cole's pump was introduced into the navy more than 

 thirty years ago, and the principal alteration it has ex- 

 perienced since that time is the substitution of a curved 

 metal tube in place of the lower sprocket wheel, as 

 the chain passes over it more easily than over a wheel. 

 The cranks are now made to take off, and they arc 

 large enough to permit thirty men to work at once. 



M. Hachette has given in his Traite des Machines, 

 Plate ix. a detailed drawing of all the parts of an im- 

 proved chain pump, to which the reader is referred. 



Various experiments have been made on the effect 

 of chain pumps, both vertical and inclined. With a 

 vertical one employed in the construction of the Pont 

 tie la Concorde at Paris, Jour men raised 2000 cubic 

 feet, (68.55 cubic metres,) of water to the height of 

 16^ feet, (5.3 metres,) in one hour, or S6S.S15 cubic 

 metres of water to the height of one metre, or 90.83 

 for each man. M. Hachette considers this as too great 

 a mean of the force of four men. 



M. Perronet, in building the bridge of Orleans, ob- 

 served that a vertical chain pump, wrought by twelve 

 men, divided into three relays, raised in 24 hours, 

 to the height of 15 feet, (4.87 metres,) 500 cubic feet, 

 (17.14 cubic metres,) of water. M. Perronet, however, 

 thought that the exertion was in this case extraordinary, 

 and he proposed to reduce the result one-sixth, to make 

 it applicable in ordinary cases. With this reduction 



6 



