Fusible Plug from Sinomas
Fusible plug, occasionally also called safety plug or solder plug, is thermally operated non-reclosing pressure relief devices to function by the yielding or melting of the fusible alloys sintered in the plug body.
Sinomas has many years of experience for manufacturing of fusible plugs and offers the broadest range of fusible plugs in the world.
As a safety component manufacturer, Sinomas treats quality above anything else. This is not only what we are saying, but also what we are doing, in many aspects that you might not be aware of.
Plug Body Material
The material of the fusible plug body can be one of the following:
- Brass (Tin or Nickel plating is optional)
- Bronze
- Stainless Steel, mainly AISI316
Brass is the most popular material for the plug body due to its good machinability and physical performance. Bronze is used for steam boiler fusible plugs for better resistance to corrosion. Stainless steel fusible plugs are suitable for fire extinguishing applications on oil rigs and situations where higher service pressure is required.
For stainless steel plug body, it is necessary to treat the plug body with Nickel or Tin plating before soldering. This is to ensure the solderability of the alloy. In this case, the surface of the fusible plugs may not look as you expect to be unless you are willing to pay more on the cosmetic issue.
Standard Fusible Plug Series
We can make fusible plug according to customer specification regarding the size, the connection thread and the yield temperatures. Practically NPT fusible plugs of the following sizes and yield temperature are considered to be "standard". The drawing can be found in the page of fusible plug specifications.
| Temp. Rating | Size / Part Number | ||||||
| °F | °C | 1/8"NPT | 1/4"NPT | 3/8"NPT | 1/2"NPT | 3/4"NPT | 1"NPT |
| 140 | 60 | AQS18-60 | AQS14-60 | AQS38-60 | AQS12-60 | AQS34-60 | AQS01-60 |
| 160 | 71 | AQS18-71 | AQS14-71 | AQS38-71 | AQS12-71 | AQS34-71 | AQS01-71 |
| 195 | 90 | AQS18-90 | AQS14-90 | AQS38-90 | AQS12-90 | AQS34-90 | AQS01-90 |
| 212 | 100 | AQS18-100 | AQS14-100 | AQS38-100 | AQS12-100 | AQS34-100 | AQS01-100 |
| 250 | 121 | AQS18-121 | AQS14-121 | AQS38-121 | AQS12-121 | AQS34-121 | AQS01-121 |
| 280 | 138 | AQS18-138 | AQS14-138 | AQS38-138 | AQS12-138 | AQS34-138 | AQS01-138 |
| 360 | 182 | AQS18-182 | AQS14-182 | AQS38-182 | AQS12-182 | AQS34-182 | AQS01-182 |
| 445 | 229 | AQS18-229 | AQS14-229 | AQS38-229 | AQS12-229 | AQS34-229 | AQS01-229 |
Part Number Definition
Part number of Sinomas fusible plug is comprised of four parts:
AQS <thread size> - <nominal yield temperature>- (body material *)
- AQS is the part number prefix for Sinomas fusible plugs
- There are 6 standard NPT thread sizes: 18 for 1/8"NPT, 14 for 1/4"NPT, 38 for 3/8"NPT, etc. Attach "R"/"G" after the thread size number for BSPT/BSPP connection, e.g. 18R stands for R1/8" and 14G for G1/4"
- nominal yield temperature of fusible plug is expressed by temperatures in °C
- body materials: SS for stainless steel AISI316, BT for brass with Tin plating, BN for brass with Nickel plating. Brass without plating is employed by default.
BSPT (R) connections are popular for steam boiler fusible plugs, while M threads can be found in fusible plugs for auto condenser and fluid couplings.
Random part numbers will be given for those that can't be covered by above rules. For example, AQS/FC-125 refers to a type of fusible plug for fluid couplings.
Customized Fusible Plugs
In addition to standard product program, we also deliver customized fusible plugs based on customer requirement, or for replacement of those from other suppliers. We have the core competence to make eutectic alloys of different temperatures. The remaining issue is only to communicate on the dimensions. If with a sample or drawing, we can make fusible plug for replacement to you in no days, with the same or most probably better quality.
A good example is the fusible plug assembly (see left) we developed for portable oxygen bottles for a fortune 500 company in the US. The long term service pressure of the fusible plugs are 10MPa. We deliver hundreds of thousands of this product to the customer without any complaint.
Another example, the picture in the right shows a 145°C special fusible plug we made for Maersk. The threads are G1" at one side, G1¼" at the other side. We don't know exactly what the application is. But the feedback from the customer is very positive.
Fusible Plug Test
Globally there is no generally recognized product standard for all types of fusible plugs yet. We can only find a few discrete sentences from the standards of some applications where fusible plus are used, e.g. refrigeration (UL207-2004), compressed air cylinder (ISO3807-2) and steam boilers.
Sinomas has the necessary test equipments for all known requirements for fusible plugs, e.g. hydrostatic test (up to 15MPa), oil bath release test, ring gauges etc. We also have a test platform with a miniature steam boiler. This means the fusible plug can be tested in real operation mode.
Fusible Plug vs. Safety Valve
Fusible plugs and safety valves are both safety devices for pressure relief protections. They can be installed in parallel or separately. Fusible plugs are simple, cheap, reliable, fast acting but non-reclosing. They have to be replaced after operation. On the other hand, safety valves are more complicated and vulnerable to blockage which often leads to malfunction or leakage. The engineers have to make the decision based on the feature of their system.
