HYDRAULICS. 197 



those which work by the pressure of the atmo- 

 sphere, must have arisen from one circumstance, 

 that they have been found less liable to choak. 



In point of friction, of coolness, and of cheap- 

 ness, the sucking-pump has so evidently the ad- 

 vantage over the chain-pump, that it will not fail 

 to gain the preference, whenever it shall be no 

 longer liable to be choaked with gravel and with 

 chips. 



Buchanan's pump, which, like the common 

 pump, acts by the pressure of the atmosphere, is 

 not liable to the defects incident to other pumps 

 upon that principle, being essentially different from 

 any now in use. 



The principal object of its invention was to 

 remove the imperfection of choaking, and in 

 attaining this important end, a variety of collateral 

 advantages have also been produced, which en- 

 hance its utility. 



The points in which it differs essentially from 

 the common pump, and by which it excels, are, 

 that it discharges the water below the piston, and 

 has its valves lying near each other. 



The advantages of this arrangement are, that 

 the sand or other matter, which may be in the 

 water, is discharged without injuring the barrel or 

 the piston-leathers; so that besides avoiding unne- 

 cessary tear and wear, the power of the pump is 

 preserved, and not apt to be diminished or de- 

 stroyed in moments of danger, as is often the case 

 with the common and chain-pumps — that the valves 

 are not confined to any particular dimensions, but 

 may be made capable of discharging every thing 

 that can rise in the suction-piece, without danger 

 of being choked — that if there should happen 

 upon any occasion to be an obstruction in the 



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