Principles of naval engineering - Historic Naval Ships Association

,SLOTSPRINCIPLES OF NAVAL ENGINEERINGCOMPRESSION SCREWRELEASE NUTLOCKING NUTLEVER PINTOP LEVERCOMPRESSIONSCREWLOCKING NUTLEVER PINTOP SPRINGWASHERDROP LEVERSPRINGBOTTOM SPRING WASHERFEATHER GUIDERETAINING RINGLOCKING SCREWSPINDLEFEATHER GUIDEFEATHERHUDDLING CHAMBERACTUAL LOCATIONOF RING PIN IS 90°TO THE RIGHTWHEN FACING THEOUTLETRING PINADJUSTINGISEAT BUSHINGy, N.P.T. FOR DRAINBASEFORWRENCHESFigure 11-18.— Steam drum safety valve (huddling chamber type).98.80type of valve is made byraising or loweringthe adjusting ring and by raising or loweringthe nozzle ring.Safety valves are always installed at thesuperheater outlet as well as on the steam drum.Superheater safety valves are set to lift justbelow, at, or just above the pressure which liftsthe steam drum safety valves, in order to ensurean adequate flow of steam through thesuperheater when the steam drum safety valvesare lifted.Most double-furnace boilers are fitted witha pressure-pilot operated superheater outletsafety valve assembly of the type shown infigure 11-20. This assembly consists of threeconnected valves: a small spring-loaded safetyvalve installed on the steam drum; an actuatingvalve installed on the steam drum; and an actuated(or unloading) valve installed on the superheater.The stem of the drum valve is connectedmechanically, by means of a lever, to the stemof the actuating valve. The actuating valve is292