As thermally operated pressure relief component, fusible plugs find application in many industries due to their simple construction while reliable operation. Some examples are listed below:
Compressed Gas Cylinder / Air Bottle
The picture in the right shows a multi function valve with fusible plug installed for Chlorine cylinder. Typical gas cylinders that need to be fusible plug protected include:
- Chlorine
- Acetylene
- Oxygen
- CNG (compressed natural gas)
- LPG (liquefied petroleum gas)
We have fusible plugs available for high pressure gas cylinder. Please consult us for details.
A/C Condenser, Receiver Drier
When the condenser of refrigeration unit experiences bad cooling or overload, the temperature of refrigerant in the condenser or receiver-drier will rise to dangerous level. To avoid damage of compressor due to overheat of refrigerant, fusible plugs are required This application can be found in air conditioning, heat pump, automotive, truck container refrigeration, etc. When the pressure of the refrigerant reaches about 3MPa, the temperature will rise to the melting point of the fusible alloy. The refrigerant will be released from the central hole of the fusible plug. It will then save other components in the system from damage due to overheat and over-pressure.
Fluid Coupling
Fluid coupling (hydraulic coupling) is a safety component capable of protecting the motor and the machine from overtorque. Heat generated by the hydraulic coupling depends on the transmitted torque. In case of continuous application of an excessive torque, the coupling’s temperature may exceed what can be tolerated by the oil, the seals and the bearings.
To prevent this, fusible plug must be installed. All installed, operation-ready couplings should be fitted with at least one fusible plug according to many national regulations. There are normally 2 to 3 plugs installed on each coupling.
Fusible Loop System
Fusible loop system is used for fire / heat detection in oil and gas plant. Compared to flame detector and smoke detector, heat detector is slow in detecting fire because it only activates once a fire has produced sufficient heat of which heat detector could respond. However, heat detector could provide useful backup or as alternative to flame and smoke detectors.
The Fusible Loop System consists of the following: fusible plug, tubing network, fusible loop charge panel. If there is fire and the surrounding temperature rises 30°C higher than the maximum ambient temperature, the fusible plug (71°C or 100°C) will melt. The air in the loop relieves and subsequently the pressure inside the tubing reduces. Loss of pressure in the loop will be detected by pressure transmitter in the fusible loop charge panel and it will signal the control room. Next action in the control system could be activate fire alarm, trigger ESD, open deluge valve, etc.
To respond quickly in case of fire, the diameter of the fusible plug orifice should be similar to the diameter of tubings (about 8mm). Our 1/2″NPT fusible plugs meet this requirement perfectly.
Steam Boiler
To give warning for low water level or over pressure condition in steam boilers, fusible plugs are required. A fusible plug is threaded into a hole in the crown sheet of each combustion chamber, mostly from the fireside. When the boiler water level is close to level of the crown sheet, the fusible plug will be unprotected by water and the fusible alloy sintered will melt, leaving a hole through which steam will blow into the combustion chamber and furnace, giving warning to the fireman.
Due to the difference in local regulations, fusible plugs for steam boilers may looks very different in different countries. As long as the customer can supply the specification, we will be able to make the fusible plugs according to their requirements, e.g. dimensions, temperature ratings and/or pressure rating.
Aircraft Tire Wheels
To prevent explosion due to excessive brake heat, all aircraft tires are equipped with both fusible plugs and pressure relief valves for double security. For example, on Boeing 757 the fusible plug melts at around 200°C and the pressure relief valve will release the pressure at 375-450 psig. The wheel could be over 200°C and therefore the fusible plug will melt but the pressure will still be well under 375 psig.