Purpose
A fusible plug operates as a safety valve when dangerous temperatures, rather than dangerous pressures, are reached in a closed vessel. In steam engines the fusible plug is screwed into the crown sheet (the top plate) of the firebox, typically extending about an inch (25mm) into the water space above. Its purpose is to act as a last-resort safety device in the event of the water level falling dangerously low: when the top of the plug is out of the water it overheats, the low-melting-point core melts away and the resulting noisy release of steam into the firebox serves to warn the operators of the danger before the top of the firebox itself runs completely dry, which could result in catastrophic failure of the boiler. The temperature of the flue gases in a steam engine firebox can reach 1000 °F (550 °C), at which temperature copper, from which historically most fireboxes were made, softens to a state which can no longer sustain the boiler pressure and a severe explosion will result if water is not put into the boiler quickly and the fire removed or extinguished. The hole through the plug is too small to have any great effect in reducing the steam pressure and the small amount of water, if any, that passes through it is not expected to have any great impact in quenching the fire.
Read more about this topic: Fusible Plug
Famous quotes containing the word purpose:
“Our policy is directed not against any country or doctrine, but against hunger, poverty, desperation and chaos. Its purpose should be the revival of a working economy in the world so as to permit the emergence of political and social conditions in which free institutions can exist.”
—George Marshall (1880–1959)
“In using the strong hand, as now compelled to do, the government has a difficult duty to perform. At the very best, it will by turns do both too little and too much. It can properly have no motive of revenge, no purpose to punish merely for punishment’s sake. While we must, by all available means, prevent the overthrow of the government, we should avoid planting and cultivating too many thorns in the bosom of society.”
—Abraham Lincoln (1809–1865)
“A major misunderstanding of child rearing has been the idea that meeting a child’s needs is an end in itself, for the purpose of the child’s mental health. Mothers have not understood that this is but one step in social development, the goal of which is to help a child begin to consider others. As a result, they often have not considered their children but have instead allowed their children’s reality to take precedence, out of a fear of damaging them emotionally.”
—Elaine Heffner (20th century)