CREAMERY MECHANICS 275 



not always be relied upon, hence the use of water cocks 

 placed next to the glass gauge. 



Water Gauge Cocks. Fig. yy shows the attachments 

 of these cocks. The water level should be kept as near 

 as possible to the middle cock. It should never go below 

 the lower cock, nor above the upper. These cocks should 

 be opened many times during the day and so long as 

 steam issues from the upper and water from the lower 

 cock, the water level is all right. 



Steatn Gauge. This shows the number of pounds of 

 steam pressure per square inch on the boiler by means 

 of a pointer moving around a dial. Below the dial is a 

 loop which contains water to prevent injury to the gauge 

 from the hot steam. The steam gauge is liable to get 

 out of order and will then fail to show the true pressure. 

 Such a condition is indicated by the safety valve. 



Safety Valve. This is placed on top of the steam 

 chamber and permits the escape of steam when the steam 

 pressure reaches the danger limit. It is an indispensable 

 boiler attachment as without it the boiler would be a 

 dangerous thing. There are two kinds of safety valves, 

 the "pop" and "ball and lever" types. The former is 

 considered the more desirable because it is not so easily 

 tampered with. Both can be set to blow off at different 

 pressures. 



Water Feed Apparatus. There are two ways of feed- 

 ing water into a boiler, namely, with injectors and with 

 pumps. 



Injector. This important boiler accessory, illustrated 

 in Fig. 78, is attached to the side of the boiler. It utilizes 

 the steam directly from the boiler for forcing water into 

 it against a pressure as great as that which sends it forth. 

 The principle which makes this possible may be stated 



