lfMJ HYDRAULICS. 



could suppose, in the same time, from such a 

 simple contrivance. 



The chain-pump consists of two square or cylin- 

 drical barrels, through which a chain passes, having 

 a great number of flat pistons, or valves, fixed 

 upon it at proper distances. This chain passes 

 round a kind of wheel-work, fixed at one end of 

 the machine. The teeth of this are so contrived 

 as to receive one-half of the flat pistons, which go 

 free of the sides of the barrel by near a quarter of 

 an inch, and let them fold in, and they take hold 

 of the links as they rise. A whole row of the 

 pistons, which go free of the sides of the barrel by 

 near a quarter of an inch, are always lifting when 

 the pump is at work, and as this machine is gene- 

 rally worked with briskness, they bring up a full 

 bore of water in the pump. It is wrought either 

 by one or two handles, according to the labour 

 required. 



The many fatal accidents which happen to ships 

 from the choaking of their pumps makes it an im- 

 portant object, in naval affairs, to find some ma- 

 chine for freeing ships from water, not liable to so 

 dangerous a defect. The chain-pump being found 

 least exceptionable in this respect, was adopted in 

 the British navy; but the chain-pump itself is not 

 free from imperfections. If the valves are not well 

 fitted to the cylinder, through which they move, 

 much water will fall back; if they are well fitted, 

 the friction of many valves must be considerable, 

 besides the friction of the chain round the sprocket- 

 wheels, and that of the wheels themselves. To 

 which may be added, the great wear of leathers, 

 and the disadvantage which attends the surging 

 and breaking of the chain. The preference, there- 

 lore, which has been given to chain-pumps over 



