A Guide to Selecting Seal Materials for Leak Test Connectors & Fittings

The #1 cause of avoidable failed parts is leaking seals and fittings. That’s because the seal fittings and tubing are part of the tested volume and directly impact the leak test results. It’s one of the reasons why we’ve created our CTS Connect products and full line of seals—to ensure parts are securely sealed and eliminate any uncertainty. Our goal is to help you get the most accurate leak test possible.

There are many parameters that go into determining the choice and design of a fitting but one that we get a lot of questions about is choosing the right seal material.

Definitions of Types of Seal Materials

CTS offers a variety of materials for our seals. The standard connects are available in standard or medical grade urethane, but we also provide a range of custom options. If you are new to seals, or if your current sealing method is not working, here are some of the most popular types we sell.

• Standard Urethane: The most common seal material. CTS has developed a proprietary version proven to resist wear and is resistant to all types of fluids and chemicals. Our urethane has more rebound, but less abrasion resistance.
• Fiber Filled Urethane: The addition of fiber makes our seals more tear-resistant, which can be beneficial for a gasket shaped seal like the example pictured below. This material is used in many of our seals that test engine blocks, for example. It works better than standard urethane because it can handle multiple cycles and will retain its shape to higher pressures.

The picture below shows a 40a durometer fiber filled gasket.  

• Premium Urethane: Developed for CTS custom leak test machines, we decided to add it to our material offerings. It’s designed to be more abrasion resistant than standard urethane, though the rebound is a little less resistant. If you are using standard urethane in an environment with a lot of automation and are experiencing a lot of wear and having to change seals often, premium urethane may be an option to try.
• Medical Urethane: FDA approved and comparable to premium urethane, although with slightly less abrasion resistance. The compression set for medical urethane is different than standard urethane and requires more force at the same durometer. Key advantages to medical urethane are ROHS compliance, low moisture sensitivities, ease of use, and a wide range of hardnesses.
• Rubberized Urethane: Falls between plastic and rubber. It is stronger than rubber which gives it the ability to handle higher pressures without losing shape. CTS offers this material in 55 durometer. This material is used with many of our CTS Connects, specifically on our CI (connect internal) pneumatic seals.
• Silicone: An ultra-clean, platinum-catalyzed, heat cured material. It has strong physical properties and lower shrinkage than urethane. CTS offers durometers between 20s and 60s. Our proprietary silicone is used most in our CTS Connect applications. Our standard Connects use a 40a durometer silicone seal.
  

CTS offers other specialized materials based upon our customers’ needs. Reach out to us with questions about additional material options.

Considerations in Specifying Seal Materials

Durometer is the measure of hardness of the material. The durometer hardness for our urethane ranges from 20a to 90a and has a range of +/- 5 so if you need a 15 durometer seal, our 20 durometer will work well. When choosing which hardness you need you will want to know what you are sealing and how you want it sealed. If you need the seal to expand to seal your surface once pressure is applied, a lower durometer is a better choice rather than the harder durometers. Harder durometers will retain their shape and resist deformation and abrasion. If you are unsure, we usually suggest starting with the 50A durometer as a good starting point.

The temperature of the part being tested is another consideration when deciding on material. Silicone is the best option for higher temperatures with a max rating of 500 degrees Fahrenheit. If in doubt, talk to one of our specialists.

Shelf Life of Seal Materials

Like the food you buy at the grocery store, urethane also has a shelf life. Urethane is best used within one year, while silicone’s shelf life is less than one year. Proper storage will help keep the material in optimal condition. Protection from extremes in temperature and exposure to bright light will maximize the life of the seal. Protection from harsh chemicals will also help.

Signs of Premature Seal Wear

Troubleshooting premature seal wear is important and will save you time and money. Is there anything about the testing that has changed, e.g., a change in test pressure? Have production levels increased? Is the seal being seated correctly in the holder? All of these can affect the life of the seal. You can leverage our experience in developing and designing sealing fixtures to identify and address any of these issues.

The choice of seals has an impact on the reliability of your leak test. We are here to help find the right one for your specific requirements.

Need a leak-tight fitting for your application? Check out our CTS Connects, a line of standard and custom options featuring our proprietary longer lasting designs.