Principles of naval engineering - Historic Naval Ships Association

Chapter 11-BOILER FITTINGS AND CONTROLSCAP^«.HEAD CHAMBERSsuperheaterX ZsuperoutletAheaterSETTLING POTS INLETDRAIN VALVESCAP98.90Figure 11-29.— General arrangement of Yarwaysuperheater steam flow indicator.to maintain alignment with the internal armatureattached to the float shaft; thus the yoke pivotsas the armature moves up and down.The datum chamber is connected by pipingto the superheater inlet and outlet connectionsand thus provides the means for impressing differentialpressure on the instrument. As notedpreviously, the pressure difference betweensuperheater inlet and superheater outlet is usedas a measure of the rate of steam flow throughthe superheater.Remote Water Level IndicatorsRemote water level indicators are used onmost ships to provide a means whereby theboiler water level may be observed from thelower level of the fireroom. The two types ofremote water level indicators discussed hereare in common use on combatant ships; othertypes may be found on auxiliary ships.The Yarway remote water level indicatorconsists of three parts: (1) a constant-headchamber which is mounted on the steam drumat or near the vertical centerline of the drumhead;(2) a graduated indicator which is usuallymounted on an instrument panel; and (3) tworeference legs that connect the constant-headchamber to the indicator. The reference legsare marked A and B in figure 11-33, whichshows the general arrangement of a Yarwayremote water level indicator.A constant water level is maintained inleg A, since the water level in the constantheadchamber does not vary. The level in legB is free to fluctuate with changes in thesteam drum water level. The upper hemisphereof the constant-head chamber is connected tothe steam drum at a point above the highestwater level to be indicated; because of thisconnection, boiler pressure is exerted equallyupon the water in the two legs. The variableleg B is connected to the steam drum at a pointbelow the water level to be indicated; becauseof this connection, the water level in leg B isequalized with the water level in the steam drum.As may be seen in figure 11-33, each legis connected by piping to the indicator. In theindicator, the two columns of water terminateupon opposite sides of a diaphragm. The indicatingunit is almost identical with the indicatingunit of the Yarway superheater steamflow indicator, previously described.The general arrangement of a Jergusonremote water level indicator is shown in figure11-34, As may be seen, the operating principlesof this device are very similar to theoperating principles of the Jerguson steamflow indicator, previously discussed.Superheater Temperature AlarmsSuperheater temperature alarms are installedon most boilers to warn operating personnelof dangerously high temperatures in thesuperheater. One type of superheater temperaturealarm is shown in figure 11-35. The bulb.303