Fusible Plug is one of several means to detect fire by sensing heat.
To make a complete heat detection system, fusible plug is installed along with pressurized tubing and a panel. Tubing will be pressurized by instrument air or nitrogen with constant pressure from the panel.
At the end of each tubing, fusible plug is located on the area where fire possibly present. It will melt at certain temperature during fire subsequently release the pressure within the tubing.
If the pressure falls below its set point, the panel will execute pre-determined action such as generate fire alarm, activating sprinkler system, etc.
Fusible Plug is one of the important topic which asked in interview.
Fusible plug is a type warning device .They are employed on compressed air system and steams,wellheads,and steam system ,to ti name a few applications.
They are considered as a last line of defense and often are used to avert a catastrophic failure occurring , for example ,an explosion.
How fusible plug work
The fusible allow within a fusible plug is designed to melt at a lower temperature than the surrounding plug body.
Fusible alloy melts before plug body.
If the plug is exposed to elevated temperatures, the fusible alloy will melt and a straight or tapered channel will be formed lengthwise through the plug body.
It is fitted on Main air compressor and Boiler.
Boilers
If we look at steam systems,fusible plugs are installed within boilers to reduce the risk of a boiler explosion as a result of low water firing. (Protect from low water firing )
A low water level scenario in a boiler would lead to overheating of the heat transfer surfaces and result in damage to the boiler would occur.
Low water firing of boilers has led to catastrophic failure in the past and continues to be a primary safety concern for boiler operators today.
Location of fusible plug in Main air compressor
Installed after air compressor
Compressed air storage vessels