What is the function of fusible plug in boiler?

Answer 1

The function of a fusible plug or soft plug is to relieve exceeded pressure inside the vessel allowing it to escape to the fire box extinguishing the fire and lowering internal pressure. The boilers I've owned have had ASME stamps on the plug and are required to be replaced every two years. The inside is not to be refilled if ruptured. The lead tin alloy is designed to melt between 440 and 450 degrees Fahrenheit. Cost on a 3/8 npt is around $80.00 Sellar industries manufactures them in lots so keep a spare ! There are two kinds a standard plug that is screwed into a flue (the water is exposed to the stamped side which its screwed into) or the fireside type (this one the stamped side is exposed to the fire box). I've used these on a flue-less boiler. It was a look out made in Tenn. that had inspection dates beginning 1858 1860 1906 1908, the dome stamp was 1 8 2 8 .in 9012 she was 184 years young and would have passed commercially @ 289 psi. Inspector gave it 125 psi for historical boiler use. This is a 100 psi vessel.

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