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Applications

As thermally operated pressure relief components, fusible plugs are used across many industries due to their simple construction and reliable operation. Some examples are listed below:

Compressed Gas Cylinders / Air Bottles
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fusible plug for valves on gas bottles

The picture above shows a multi function valve with fusible plug installed for Chlorine cylinder. Typical gas cylinders that require fusible plug protection 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
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fusible plug for condenser receiver-drier

When the condenser of refrigeration unit experiences bad cooling or overload, the temperature of refrigerant in the condenser or receiver-drier may rise to dangerous levels. To prevent compressor damage caused by overheating of the refrigerant, fusible plugs are required. This application is common in air conditioning systems, heat pumps, automotive A/C, and truck container refrigeration. When the pressure of the refrigerant reaches about 3 MPa, 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, thereby protecting other components in the system from damage due to overheat and over-pressure.

Fluid Coupling
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fusible plug for fluid coupling

A fluid (hydraulic) coupling protects motors and machinery from excessive torque. Heat generated by the hydraulic coupling depends on the transmitted torque. In the case of prolonged overload, the temperature can exceed the limits that can be tolerated by the oil, the seals and the bearings.

To prevent this, fusible plugs must be installed. Many national regulations require that all operation-ready couplings be equipped with at least one fusible plug. There are normally 2 to 3 plugs installed on each coupling.

Fusible Loop Systems
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fusible loop system

Fusible loop system is used for fire / heat detection in oil and gas plant. Compared with flame or smoke detectors, 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, they can serve as a useful backup or an alternative.

A Fusible Loop System consists of the following: fusible plug, tubing network, fusible loop charge panel. When a fire occurs and the ambient temperature rises by about 30°C above normal, the fusible plug (71°C or 100°C) will melt. The air in the loop relieves and subsequently the pressure inside the tubing reduces. This pressure drop is detected by a pressure transmitter in the control panel, which then signals the control room. The system can subsequently activate alarms, trigger an ESD, or open a deluge valve.

For rapid response, the orifice diameter of the fusible plug should match the tubing diameter (about 8 mm). Our 1/2″NPT fusible plugs meet this requirement perfectly.

Steam Boilers
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fusible plugs for steam boilers

Fusible plugs are installed in steam boilers to warn of low water levels or overpressure. A fusible plug is threaded into a hole in the crown sheet of each combustion chamber, usually from the fireside. When the water level drops to the level of the crown sheet, the plug becomes exposed to heat and the fusible alloy melts, 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 look very different in different countries. As long as customers can provide the required specifications — including dimensions, temperature ratings, and/or pressure ratings — we can manufacture according to their requirements.

Heat Melt Plugs for Blowers
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heat melt plug for blowers

Sinomas heat melt plugs are used to protect blowers from overheating. They activate thermally when the blower’s discharge temperature exceeds its safe limit. Our plugs are totally customizable regarding the temperature of activation, plug materials, thread type and size etc. The advantages are:

  • Unique thread pattern and left-hand thread prevent overriding with conventional pipe plugs.
  • No expulsion of melt metal when activated
  • Audible alert when activated
  • Typical activation temperature: 390°F / 199°C

Upon request we can supply replacements compatible with existing market models, for example Tuthill 92278 BLOWERS- SHUR-MELT PLUG, T5CDL Series blower heat plugs, etc.

Aircraft Tire Wheels
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To prevent explosions caused by 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. This means that even if the wheel temperature exceeds 200°C, the fusible plug will melt before pressure reaches a dangerous level.