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Case Study

Press Fitting Seals for Gas Application

A Press Fitting Seal for Water Applications is Transformed into a Robust Gas Press Fitting Design


Design a rubber seal for gas press fittings that’ll last 50 years and comply with stringent global regulations.

A long-standing Minnesota Rubber & Plastics customer wanted to extend its current press fittings products with a new line for the gas market. We had previously designed a press fitting seal that provided a resistance force during assembly, which gives the plumber tactile feedback during the insertion process. This friction restricts the fitting from coming apart prior to pressing [Figure 1].

The customer now wanted these same features on a new line of natural gas and liquid petroleum gas fittings, which called for a new compound formulation. These new features make it easier to detect leaks and help techs properly check all system fittings. The unique design automatically rotates the seal for the plumber to prevent the sealing surface from coming into contact with the seal parting line.

The challenge was formulating a new compound in our advanced materials lab to resist chemical and physical degradation caused by a wide range of fuels and gases.


A custom HNBR formulation that withstands high pressures and temperatures.

To develop and select the perfect compound for this application, Minnesota Rubber & Plastic’s advanced materials lab researched the regulatory requirements and material performance targets. Based on these findings, we chose HNBR as the base compound.

During step two, we optimized the HNBR compound to withstand the client’s rigorous compression set resistance requirement, as well as heat and chemical resistance. Additionally, to meet the customer’s color requirement, we produced the
compound in yellow, which signals to plumbers and inspectors that the correct fittings were installed.

With rubber seals manufactured using the new compound, compression set was tested and exposed at temperatures of 100°C and 150°C, and produced lower compression set test results than competitors. These higher values resulted in:

• Longer sealing force retention
• Longer seal life
• Enhanced safety

What’s more, at low temperatures, the elastic modulus maintained its flexibility and sealing performance.


A “bullet-proof” seal helped make a press-to-connect fitting the best on the market.

Extensive customer and regulatory agency testing took place to certify the fittings and HNBR seals, which helped our customer go to market with a more cost-effective and competitive offering.

Passed regulatory tests included CSA LC4, (1000°C sealing) and DIN EN 549. Based on client feedback, our customer’s new product’s ultimate success is due to close collaboration between both companies, an innovative fitting design, and a robust seal that will last a half-century.

Copper Press Fitting being crimped.
Physical propertiesMRP’s C2536YHHNBR Competitor
Micro-Hardness Type M, IRHD64.470.1
Compression Set Resistance, 22 hours @ 100°C, %11.221.4
Compression Set Resistance, 22 hours @ 150°C, %18.460.6
Elastic Modulus at 0°C (MPa)*13.418.3
Elastic Modulus at -20°C (MPa)*24.860.8
Elastic Modulus at -30°C (MPa)*100.4264.5
Tg per DMA (°C)*-40.4-34.9
*DMA Settings: 1.0°C/minute heating rate from -100°C to +100°C at 10Hz with 0.7% dynamic strain with a static/dynamic ratio of 1.5

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Since 1945, Minnesota Rubber and Plastics has built a worldwide reputation as a leader in advanced technologies.

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It is a global solutions provider in the development and launch of complex products, from high-tolerance medical components and assemblies to final sterile packaged devices for the most demanding applications using medical-grade elastomers, and thermoplastics.

The company’s reputation is founded on its unique science-based approach that has made it a preferred manufacturing partner for industry leaders in North America, Europe, and Asia. It is well known for its ability to provide cost-effective solutions to technically demanding applications.

Minnesota Rubber and Plastics’ experience in advanced material formulation enables it to be compliant with FDA, EC 1935/2004, NSF 61, and NSF 51, plus ISO 10993 and ISO 13485, to meet your unique product requirements. Its 70-year-plus history in the design and manufacture of complex devices makes it the preferred partner for industry leaders throughout the world.@media screen and
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