Steam Enyt 



511 



In ca^e a gage glass should be broken \vlicn ihe pressure 

 is on the waier should be shut off first ami then the 

 steam-, after which a new glass may be put in. 



639. Pressure Gage. The pressure gage is intended to 

 show the number of pounds per square inch of steam 

 pressure there is on the boiler at any moment and to serve 

 as an indicator to the fire- 

 man of the condition of 



his fire. It is represented 

 at 4 in Fig. 244 and the 

 interior construction of 

 this gage is shown in Fig. 

 246. 



As the steam enters the 

 hollow spring shown in 

 the figure its pressure 

 tends to straighten it be- 

 cause the pressure on the 

 longer circumference is 

 greater than that on the 

 shorter one. The motion 



thus produced is communicated, through a segment lever 

 and pinion, to the index which is made to revolve over a 

 dial upon which the pressure may be read. 



It should be remembered that a steam gage may get 

 out of order and fail "to show the true pressure. In such 

 cases the operator must be guided by the safety valve. 

 (640). Some pressure gages are provided with a siphon 

 placed between the boiler and the gage, which prevents 

 the dry steam entering the spring at too high a tempera- 

 ture and also automatically drains out the water, thus 

 preventing injury from freezing. 



640. Safety Valve. The safety valve is connected with 

 the steam chamber of the boiler where, A .'hen the pressure 

 reaches a point as hi^h as the boiler is intended to carry, 

 it may be opened by the pressure and the steam be allowed 



FIG. 246. Construction of steam gage. 



