PRINCIPLES OF NAVAL ENGINEERING 



REGULAT0R,,^^I^^_t)li3 

 CONN. 



38.59 

 Figure 11-26.— Older type of water gage glass. 



equal pressure on each side of the ball, the 

 ball remains on its holder. But if the water gage 

 breaks, the sudden rush of water through the 

 bottom connection forces the ball upward onto 

 its seat and thus prevents further escape of 

 hot water. No check valve is installed in the 

 top cutout connection. 



Most boilers are designed to carry the nor- 

 mal water level at the middle of the steam 

 drum, and most water gages are mounted in 

 such a way that the normal water level shows 

 at the midpoint of the water gages or, in the 

 case of staggered gages, at the midpoint be- 

 tween the bottom of the lower gage and the 

 top of the higher gage. However, this general 

 rule does not apply to some boilers. If the 

 designed normal water level is NOT intended 

 to be shown at the midpoint of the water gages, 

 the location of the normal water level should 

 be marked on the gages. 



The water level is considered to be within 

 allowable limits as long as it can be seen in 



one or more water gage glasses. However, the 

 water level must always be maintained as 

 close to the normal level as possible. As 

 long as the water level is visible in one gage, 

 you can bring the water level back to normal 

 by increasing or decreasing the amount of 

 water fed to the boiler. If the water level 

 cannot be seen at all, the situation must be 

 treated as an emergency requiring the imme- 

 diate securing of the boiler. 



Water gages must be blown down before 

 the boiler is cut in on the line, at the end of 

 each watch, and at any time when there is the 

 slightest doubt about the water level in the 

 boiler. Frequent blowing down is necessary 

 because the gage connections are easily clogged 

 with dirt, scale, or other solid matter. Failure 

 to blow through the water gages could lead to 

 false indications of water level. 



Superheater Steam Flow Indicators 



Many boilers— particularly double-furnace 

 boilers— are equipped with superheater steam 

 flow indicators. Where installed, these indica- 

 tors must be kept in good operating condition 

 at all times. The superheater outlet thermom- 

 eters indicate temperature at the superheater 

 outlet, not inside the superheater; and, on a 

 double-furnace boiler, it is possible to have no 

 flow through the superheater while the ther- 

 mometers are giving perfectly normal readings 

 at the outlet. In other words, there is no way to 

 be sure a superheater is not being overheated 

 unless both the superheater outlet thermometers 

 and the superheater steam flow indicator are in 

 good working condition. 



Superheater steam flow indicators measure 

 the steam pressure differential between the 

 superheater inlet and the superheater outlet. 

 Since the pressure drop across the superheater 

 is proportional to the rate of steam flow 

 through the superheater, the pressure drop can 

 be used as an indication of the rate of steam 

 flow. Superheater steam flow indicators are 

 usually calibrated in inches of water, since 

 they measure a relatively small pressure dif- 

 ferential. 



Two types of superheater steam flow indi- 

 cators are in common naval use. Although 

 both respond to the pressure differential be- 

 tween the superheater inlet and the super- 

 heater outlet, they differ in the mechanism by 

 which this pressure difference is measured 



300 



