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fusible plug from SinomasFusible plug, occasionally also called safety plug, fuse plug, solder plug or melt fuse, 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:

  1. Brass (Tin or Nickel plating is optional)stainless steel fusible plug
  2. Bronze
  3. Stainless Steel, mainly AISI316
  4. Aluminum

Brass is the most popular material for 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.Aluminum plug body is rare but possible. They are required for fusible plugs for aircraft wheel tires due to their light weight.

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
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
230 110 AQS18-110 AQS14-110 AQS38-110 AQS12-110 AQS34-110 AQS01-110
257 125 AQS18-125 AQS14-125 AQS38-125 AQS12-125 AQS34-125 AQS01-125
280 138 AQS18-138 AQS14-138 AQS38-138 AQS12-138 AQS34-138 AQS01-138
355 180 AQS18-180 AQS14-180 AQS38-180 AQS12-180 AQS34-180 AQS01-180
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:customized fusible plugfusible plug with tin plating

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 our fusible plug is expressed by temperature 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 fusible plugs used in Japan, 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 replacing 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 a few days,with the same or most probably better quality.

customized fusible plug for oxygen bottle

A good example is the fusible plug assembly (see left) we developed for portable oxygen bottles for a fortune 500 company from USA. The long term service pressure of the fusible plugs are 10MPa. We have delivered hundreds of thousands of this product to the customer without any negative feedback.customized fusible plug for Maersk Another example, the picture in the right shows a 140°C special fusible plug we customized for Maersk. The threads are G1" at one side, G1¼" at the other side. The size is big while the demand is a little. Nevertheless we strive to make all customers happy.

RoHS and WEEE Compliant Fusible Plugs

If your products will be sold to countries in EU, you might be required to comply with RoHS and WEEE directives. Please inform us in the first place if that is true. The alloy formula and the costs will be different.

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.

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