U-Cups are commonly used in linear applications to seal the rod or piston. There is a variety of U-Cup configurations available to properly seal a wide range of demanding applications. KC Seals offers a multitude of U-Cup designs and produces them from a broad range of materials. Below is a list of our most common types of u-cup designs; should you have an alternative design, please contact us at info@kcseals.ca or click the book a meeting button to discuss your project.


Most common types of U-Cups

Loaded U-Cups

Loaded U-cups are O-Ring energized, bevelled lipped rod or piston seals that are commonly referred to as a Polypak®. Typically used in slow start applications, the O-Ring energizer helps to increase the sealing force preventing any bypass. As the pressure increases, the sealing force increases and the O-Ring ensures complete lip actuation under most conditions. The bevelled sealing lips improve sealing function from an unloaded U-Cup. Additionally, loaded U-Cups can be utilized in a variety of different applications, as they come in an assortment of materials.

Unloaded U-Cups

Unloaded U-Cups are asymmetric and symmetric rod or pistons seals typically used for general purpose applications. The trimmed sealing lip offers high static and dynamic tightness, with excellent adaptability to deflection on long-stroke applications. An unloaded U-Cups sealing geometry can be modified to help increase seal-ability and decrease friction depending on the application requirements.

Spring-loaded U-Cups

Spring-loaded U-cups encompass a variety of products that can be customized to operate in a broader range of applications than any other seal product available. This is possible due to the availability of seal jacket materials and configurations in combination with spring loads, spring materials and spring sizes. Commonly, spring energized seals are called upon to retrofit applications where traditional seal products such as O-rings, U-cups and rubber lip seals fail due to issues of chemical compatibility, pressure, temperature, friction or high-speed dynamics.

Quality You Can Rely On


All parts are measured on our Zeiss O-Machine and or Keyence CMM, which utilize optical and contact measurement technology in a comprehensive analysis. The O-Machine includes multi-sensor coordinate measuring, white light sensors for non-contact assessments and extremely accurate 3D scanners.

We follow AQL 2.5 levels 1 and 2 sample size quantities, and all molded parts are manufactured to RMA A2 tolerances. 

What comes with your orders:

  • Every order is sent with either a paper or digital QC document that includes ID, OD, C/S, Height, angles, and any other dimensions your organization feels critical. 


Our rubber and plastic materials supply is diversified amongst the top compounders in North America. Each polymer has been qualified to meet typical exploration and production well conditions, including mechanical, tribological, thermal, and specific immersive properties.

What comes with your orders:

  • Every order comes with an MTR that includes a batch number, cure dates, and a set of mechanical properties.

Available Materials

With such a wide range of available materials please contact us to discuss your project.

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