Application of Fusible Plugs
As thermally operated pressure relief component, fusible plugs find application in many industries due to their simple construction while reliable operation. Here are some examples.
Compressed Gas Cylinder / Air Bottle
The picture in the right shows a multi function valve with fusible plug installed for Clorine 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, automobile, 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.
The picture below demonstrates the structure of a receiver-drier with fusible plug installed.
- Transfertube
- Spring
- Capplatewithholes
- Body
- Cuppedshel
- Drier
- Connectingtube
- Filtercloth
- Rubbermat
- Strainerscreen
- Chargingvalve
- pressureswitch
- Outlet
- Sightglass
- Fusibleplug
- Inlet
- Holder
Oil and Gas Emergency Shutdown System
The ESD (Emergency Shut Down ) has a heat actuated fusiblie plug that is installed as a T assembly into the supply air line to a pneumatic spring return actuator. Depending on the selected temperature, the fusible plug will melt and divert the supply air and the actuator pressure to atmosphere. This will allow the actuator to drive the valve to the predetermined "Emergency Shutwodn" position. Temperature ratings for this application are usually 71°C or 100°C.
Steam Boiler
To give warning for low water 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 codes, 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, regarding dimensions, temperature ratings and/or pressure rating.
Fluid coupling
Hydraulic coupling is a safety component capable of protecting the motor and the machine from overtorque. Heating of 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.
Aircraft Wheel Tires
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 a 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.