BLAST PIPE FEED PUMPS. 



this being inadmissible tinder the conditions of the locomotive 

 engine, it is necessary to adopt some other expedient to produce 

 the necessary current of air through the tube. A blower, or 

 fanner, working in the funnel or in any other convenient position, 

 would answer the purpose ; but a much better expedient has been 

 adopted. 



The steam, after driving the piston, is allowed to escape, but in 

 order to turn it to profitable account, instead of being dismissed 

 into the atmosphere, where it would produce a cloud of vapour 

 around the engine, it is conducted through ;a pipe to the base of 

 the funnel, where it is allowed to escape in a jet directly up the 

 chimney. In this manner a puff of waste steam escaping from the 

 cylinders as the pistons arrive at the one end or the other, is 

 . injected into the chimney, and a constant succession of these puffs 

 take place, four being made for every revolution of the driving- 

 wheels. These continual puffs of vapour maintain in the chimney 

 a constant current upwards, by which the air and gases of com- 

 bustion are drawn from the fire-box through the tubes. 



The pipe by which these jets are directed up the chimney, 

 called the blast-pipe, serves the purpose of a most efficient 

 bellows. 



Those who are not familiar with steam machinery will not find 

 it difficult to comprehend that a bellows would produce the same 

 effect on the fire if it acted in the chimney, or even at the top of 

 the chimney, as if it were applied at the grate bars, provided only 

 that the mouth of the chimney near the fire be closed by a door, 

 as it always is in steam-engines. 



21. To keep the locomotive boiler supplied with water, and its 

 furnace with fuel, it is accompanied by a carriage called a tender, 

 which bears a supply of fuel, and a cistern of sufficient magnitude, 

 containing water. 



This cistern is connected with the interior of the boiler by pipes 

 and force-pumps. The force-pumps are worked by the engine. 

 The engineer is supplied with a lever, by which he can suspend 

 the action of the pumps at pleasure ; so that, if he finds the boiler 

 becoming too full, he can, to use a technical phrase, " cut off the 

 feed." Gauges are provided, by which he can at all times ascer- 

 tain the quantity of water in the boiler, or, which is the same, the 

 position of its surface. He is accompanied by a stoker or fireman, 

 who from time to time opens the door of the fire-box and feeds the 

 furnace. 



22. This general description of a locomotive and its accessories, 

 will be more clearly understood by the aid of diagrams, showing 

 the principal sections and plans of an engine and tender. 



A series of drawings, showing in section and elevation various 



123 



