Principles of naval engineering - Historic Naval Ships Association

PRINCIPLES OF NAVAL ENGINEERINGI 1SEE ENLARGED VIEWFOR BELLEVILLESPRING ASSEMBLYCOVERSTUD BOLTSGLASSASBESTOS GASKETASBESTOS GASKETMICA GASKETJ^-*^*STAMPBRASS GASKETCENTERPLATEENLARGED VIEW OFBELLEVILLE SPRING ASSEMBLY(IN SETS OF SIX SPRINGS)COVER"PLACE THIS SIDENEXT TO WATERFigure 11-28.— Recent type of water gage glass.38.239A permanent horseshoe magnet is rigidlymounted on that side of the deflection platewhich is free to move. The poles of the magnetstraddle a tubular well in which a spiral-shapedstrip armature is mounted on jeweled bearings.A counterbalanced pointer is attached to the endof the armature mounting shaft.When the deflection plate moves in responseto variations in pressure, the magnet is madeto move along the axisof the well. As the magnetmoves the spiral-shaped armature rolls in orderto keep in alignment with the magnetic field betweenthe poles of the magnet. Thus a rotarymotion is imparted to the armature mountingshaft; and the rotation of the shaft causes thepointer to move. The pointer moves over abrightly illuminated vertical dial which is dividedinto green and red zones to represent safe andunsafe operating conditions.The Jerguson superheater steam flow indicator,shown schematically in figure 11-32,consists of three main parts: (1) a datumchamber assembly, (2) a valve manifold, and(3) an indicating unit.The Jerguson indicator is essentially amercury-filled manometer with a stainless steelfloat in one leg. As the pressure differentialbetween the superheater inlet and the superheateroutlet varies, the mercury level in theinstrument changes and thereby actuates theindicating pointer. The movement of the floatin the manometer is transmitted to the pointeron the scale by means of a magnetic couplingdrive. The coupling consists of an internalmagnetic armature on the end of the float shaftand an externalyoke with magnetically energizedarms. The yoke, forming a part of the pointersystem, pivots on precision bearings in order302