FIRE-ENGINE CHAIN PUMP. 



closed ; if it go up E is closed and F open. A stream, therefore, 

 continually flows through one valve or the other into the pump- 

 barrel. In like manner, whether the piston ascend or descend, 

 one of the valves, c or D, must be open. 



19. The simple pumps used for watering gardens are shown in 

 fig. 19, at the head of this tract, a single or double-action force- 

 pump projecting a jet of water over the ground to be irrigated. 



20. The fire-engine is a double forcing-pump, each barrel of 

 which acts upon the principle explained above. 



A section of such an engine, in its most usual form, is represented 

 in fig. 20. 



The solid pistons a a are alternately forced down upon the water 

 which has been drawn into the barrels upon the principles already 

 explained, and the water is thus forced into the air vessel e. The- 

 reaction of the compressed air drives the water with a proportion- 

 ate force through the force-pipe d into a long, flexible, leathern 

 hose, upon the end of which a large jet-pipe is screwed. The 

 firemen carry this jet-pipe near to or into the building on fire, 

 and with it throw up to great heights a constant stream of water, 

 which, falling on the burning bodies, extinguishes the fire. 



Fig. 20. 



21. A form of lifting-pump, called the chain-pump, is commonly 

 used to discharge the water from the hold of ships of war and 

 other vessels of the large class. This pump consists of an endless 

 chain which passes over two rollers, one of which is established on 

 the deck, above the level at which the water is to be discharged, 

 and the other at the bottom of the hold. Attached to the chain, 

 and placed at right angles with it, are a series of saucers, or'a sort 



191 



