48 POWER AND THE PLOW 



turned on when sufficient steam pressure to operate it has 

 been secured by ordinary draft. When the engine is running, 

 the exhaust steam is usually turned into the stack through an 

 exhaust nozzle. The intensity of the draft created by this 

 means can, of course, be controlled. 



The water space in a boiler extends around the fire box and 

 to some distance above the highest flues. Above this is the 

 steam space, including a bell-shaped projection known as a 

 steam dome, into which the driest steam rises. From the 

 top of the steam dome extends the pipe for taking steam to 

 the cylinder, this usually being protected by a wire gauze 

 strainer in order to mimimize the percentage of water carried 

 over into the cylinder with the steam. 



The Water Supply 



For supplying water to the engine the plowing outfit nec- 

 essarily includes one or more portable tanks, which are usually 

 made of steel with riveted seams. They have a capacity of 

 from ten to sixteen barrels and are provided with a hand pump 

 for filling and emptying. A box on top affords space for 

 carrying a considerable quantity of coal or odds and ends. 

 On the engine, in addition to the water contained in the boiler, 

 there must be tank capacity sufficient for at least an hour's 

 run. Engines therefore carry from one to three tanks with a 

 capacity of from fifteen to twenty barrels. These are usually 

 placed to secure the most advantageous distribution of weight 

 upon the drivers. It is now possible, by the aid of a hose- 

 crane and steam jet, to economize labor and time by filling 

 the engine supply tanks from the wagon tank without stopping 

 the outfit. 



The traction engine boiler is supplied with water from the 

 supply tanks either by a pump or an injector, and sometimes 

 both. The pump may be attached to the cross-head of the 

 engine, in which case it can operate only when the engine is 

 running. A more convenient type is an independent steam 



