10 Farm Mechanics. 



very important in the construction and management of a 

 boiler to so arrange conditions as to have as little difference 

 of temperature in all parts of the boiler as possible; be- 

 cause unequal temperature tends to develop strains in the 

 metal and to tear or loosen rivets and cause leaks. 



637. Gage Cocks. Boilers are commonly provided with 

 three gage cocks, represented at 13,13 in Fig. 244 and at 

 13 in Fig. 249. These are for the purpose of showing 

 where the upper surface of the water is in the boiler at 

 any time. The lower gage cock is placed about two inches 

 above the upper surface of the upper flues in the horizontal 

 boiler. 



When the engine is running the water is held in the 

 boiler near the level of the middle gage cock and is fed 

 into the boiler so as to reach the upper gage cock only 

 when the engine is to be shut down to stand for some time 

 without allowing the fire to go out. 



638. Gage Glass. The ohject of the gage glass is to 

 show at a glance just what the water level in the boiler 

 is at any moment and its position is represented in Figs. 

 244 and 249 at 3. 



It should always be kept in mind that it is not safe to 

 rely entirely upon the indications of the gage glass be- 

 cause it is peculiarly liable to become clogged with sedi- 

 ment from the boiler ; on this account the lower cock should 

 be frequently opened to blow it off and clear out any 

 sediment, and the water level in the boiler should fre- 

 quently be tested by means of the gage cocks. 



When the engine is to be stopped to stand with the fire 

 on for any length of time the gage glass should be closed, 

 shutting off the water first and then the steam ; this is to 

 lessen evaporation and to prevent escape of water from the 

 boiler in case the gage glass should break. When opening 

 the gage again the steam should be turned on first, the 

 water last, and the pet cock opened to blow off any sedi- 

 ment and show that the gage is in proper working order 



