plug plug metal cylinder usually bronze brass tapered hole completely length hole sealed metal low melting point flows away pre determined high temperature reached initial use plug safety precaution low water levels steam engine boilers later applications extended use closed vessels air conditioning systems tanks transporting petroleum purpose plug operates safety valve dangerous temperatures dangerous pressures reached closed vessel steam engines plug crown sheet plate typically extending inch water space purpose act resort safety device event water level falling dangerously low plug water low melting point core away resulting noisy release steam serves warn operators danger runs completely dry result catastrophic failure boiler temperature gases steam engine reach temperature copper historically state longer sustain boiler pressure severe explosion result water boiler quickly fire removed extinguished hole plug small great effect reducing steam pressure small water passes expected great impact fire history device invented proponent high pressure opposed atmospheric steam engines consequence explosion new boilers detractors eager concept high pressure steam proved accident happened neglected boiler water publicised invention widely patent counter criticisms experiments experiments conducted boston 1830s initially cast doubt practice adding water soon escape steam device noted steam boiler fitted small observation window glass heated normal operating temperature water level water added found pressure rose suddenly observation glass shattered report concluded high temperature metal added water quickly explosion inevitable result assumption challenged institute specifically ruled theory investigation boiler explosion steam ship april year investigation wales came similar conclusion steam locomotive belonging railway inadvertently sent safety assembled pressure boiler built extent failed crown sheet uncovered weakened heat fire violently blew apart investigation led colonel dismissed theory succeeded starting sudden flood cold water caused generation steam boiler burst quoted results experiments national boiler certification insurance body proved weight copper present considered specific heat insufficient generate steam raise boiler pressure addition cold water caused pressure fall accepted correct action event operation plug add water original design simple solid plug filled low melting point narrow channel plug steam water immediately begins escape plug developed 1860s wide opening soon version solid brass bronze centre place layer low melting point plug release steam water sufficiently release centre plug plug fails dramatically opening entire bore immediately bore jet likely noticed noticed melted device found march crown sheet princess coronation pacific london midland failed hauling passenger train glasgow london established water journey earlier day melted gone unnoticed engine crew strong draught carrying escaping steam away maintenance composition investigation showed importance plug initially favoured offered lower melting points pure metals found aged poorly encourage development matrix water surface plug matrix having dangerously high melting point plug requirement pure tin replaced annually avoided lead contamination contamination regarded problem case changed brass copper free copper tin bronze avoid risk migrating housing plug plug 1920s investigations conjunction found use core increase melting point device prevent working needed melting points excess examples found typical current practice locomotives requires new inspected working days dependent water condition use locomotive months depending boiler operating pressure temperature applications principle plug applied transport petroleum gases small exposed patches containers lining membrane designed melt high temperature reached controlled release typical temperature explosive release higher temperature gas containers liquid fitted operating temperature common aircraft wheels typically larger high performance aircraft large thermal loads imposed abnormal landing braking conditions notably cause high pressure tyres rise point tyre burst relief mechanism gas directed cool braking surfaces fitted receivers air precaution oil present action heat air safe temperature core melt release pressure automobile air conditioning systems commonly fitted operating concerns environmental effects released gas function taken electrical switch patented patent published type safe uses plug contents water external temperature gets high
Fusible plug