FIRING WITH VARIOUS FUELS. 33 



The draft should be strong enough to make the fire burn 

 freely and at a white heat. It may be necessary to reduce 

 the exhaust nozzle to get the proper draft, but it should 

 never be reduced more than is necessary, as back pressure 

 reduces the power of the engine. If unburnt straw be seen 

 coming out of the smoke-stack, it shows the exhaust nozzle 

 is too small. Do not expect the engine to steam well when 

 the front end of the boiler is low. The engine should be level 

 or a little high in front. If the engine has been steamed up 

 for some time without running, the screen in the smoke- 

 stack may be so filled up as to seriously interfere with the 

 draft. 



Exhaust Nozzles. Case engines are equipped with ex- 

 haust nozzles as follows : The Nine-^Horse power engines 

 have exhaust elbows with one and one-half inch opening, 

 and brass nozzles for reducing this to one and one-quarter, 

 or one and one-eighth inches. The Twelve-Horse power 

 engines have exhaust elbows with one and one-half inch 

 opening, and nozzles for reducing this to one and three- 

 eighths, or one and one-quarter inches. The Fifteen and 

 Twenty-Horse power engines have exhaust elbows with 

 one and three-quarter inch openings, and brass nozzles for 

 reducing this to one and one-half or one and one-quarter 

 inches. The Twenty-five Horse power engines have exhaust 

 elbows with two and one-quarter inch opening, and brass 

 nozzles for reducing this to one and three-quarter or one 

 and one-half inches. 



