Chapter 11-BOILER FITTINGS AND CONTROLS 



38,57 

 Figure 11-23.— Arrangement of soot blowers 

 on a 1200 psi single-furnace boiler. 



Some soot blowers on some boilers are of 

 the retractable type— that is, the element does 

 not remain in the furnace all the time but in- 

 stead can be retracted into a housing or shroud 

 between the inner and outer casings. 



The scavenging air connection shown in 

 figure 11-24 supplies air to the soot blower 

 element and thus keeps combustion gases from 

 backing up into the soot blower head and piping. 

 A hole in the outer casing allows air to enter 

 the other end of the scavenging air line; thus, 

 scavenging air is blown through the soot blower 

 whenever the forced draft blowers are in op- 

 eration. A check valve is installed in the 

 scavenging air piping, very near the soot blower 

 head; this valve closes whenever steam is ad- 

 mitted to the soot blower element. 



Blow Valves 



Some solid matter is always present in 

 boiler water. Most of the solid matter is 

 heavier than water and therefore settles in 

 the water drums and headers. Solid matter 

 that is lighter than water rises and forms a 

 scum on the surface of the water in the 

 steam drum. Since most of the solid matter 

 is not carried over with the steam, the con- 

 centration of solids remaining in the boiler 

 water gradually increases as the boiler steams. 



For the sake of efficiency and for the pro- 

 tection of the boiler pressure parts, it is 

 necessary to remove some of this solid matter 

 from time to time. Blow valves and blow lines 

 are used for this purpose. 



Light solids and scum are removed from 

 the surface of the water in the steam drum by 

 means of the surface blow line— which, as we 

 have already seen, is an internal boiler fitting. 

 Heavy solids and sludge are removed by using 

 the bottom blow valves which are fitted to each 

 water drum and header. Both surface blow 

 valves and bottom blow valves on modern naval 

 boilers are globe-type stop valves. 



Both the surface blow and the bottom blow 

 valves discharge to a system of piping called 

 the boiler blow piping . The boiler blow piping 

 system is common to all boilers in any one 

 fireroom. Guarding valves are installed in the 

 line as a protection against leakage from a 

 steaming boiler into the blow piping and 

 against leakage from the blow piping back 

 into a dead boiler. A guarding valve installed 

 at the outboard bulkhead of the fireroom gives 

 protection against salt water leakage into the 

 blow piping. After passing through this guard- 

 ing valve, the water is discharged through an 

 overboard discharge valve (sometimes called a 

 skin valve) which leads overboard below the 

 ship's waterline. Figure 11-25 shows thegeneral 

 arrangement of boiler blow piping for one of 

 the newer single-furnace boilers. 



Water Gage Glasses 



Every boiler must be equipped with at least 

 two independent devices for showing the water 

 level in the steam drum, and at least one of 

 these devices must be a water gage glass. 

 Some boilers have more than two devices for 

 indicating water level. Various combinations of 

 water level indicating devices are used on 

 naval boilers. Perhaps the most common ar- 

 rangement on older boilers is two water gage 

 glasses, one 10 inches long and one 18 inches 

 long. Newer boilers may have two water gage 

 glasses and one remote water level indicator 

 or they may have one water gage glass and 

 two remote water level indicators. 



Several types of water gage glasses are 

 used on naval boilers. The older water gage 

 glasses differ in some ways from the ones 

 installed on the newer 1200-psi boilers, and 

 gages made by different manufacturers may 



297 



