Know the Design, Types, and Applications of U-cup Seals

Mar 26, 2021 Rubber Seals | LIP Seals

U cups are an integral part of a piston or cylinder sealing system. Although they may look round in shape, their unique U-shaped profile safeguards the pneumatic or hydraulic cylinder. There are two lips for sealing- inner and outer. The inner lip is movable or dynamic while the outer one is static. Within this, there are some sub-types of U-cups such as deep, standard, beveled, and so on. There are various types or patterns of U-cup seals, such as with or without an O-ring, and more. Usually made of polyurethane, these U-cups which resemble an O-ring are formed into U-shaped channels on either sides of the cylinder. This post discusses the types, design, and applications areas of U-cup seals.

Know the Design of U-cup Seals

The U-cup was basically designed to seal low pressure rod or piston cylinders in only one direction. It is a loader which means it puts pressure on the lip seal so that it squeezes and offers the required sealing force. However, it can efficiently handle high and low pressure applications, vacuum, and extreme temperatures. The design depends upon the seal type whether it is static or dynamic. The other factors that are an integral part of the design are surface finish, whether O-ring loaded, Z-seal, inner and outer diameters, machining dimensions, tensile strength of the material used, and so on.

Types of U-cups Discussed

U-cups are used for piston and rod sealing and can be interchangeable in terms of applications. There are, as mentioned above, various types and sub-types of U-cups.

Loaded U-cups: These are loaded with an O-ring which helps tight sealing at low pressures.
Unloaded U-cups: These are without O-rings and are suitable for heavy-duty sealing applications.
Spring Energized U-cups: These specially engineered U-cups comprise a metallic spring in place of the O-ring. These are useful in dynamic applications as the spring places the required load on the lips for proper sealing and compression of the mating surfaces.
Homogenous U-cups: These types of cups help avoid friction and ensure smooth sealing. These are suitable for specific friction-sensitive pneumatic applications.

Factors to Consider When Buying U-cups

There are some factors you may want to consider to be able to select the right type of U-cup for your application. Here are some of them:

Check if the material of the seal is compatible and can withstand the application temperature, pressure, and other physical parameters.
Ensure it does not react with the fluid inside and that it is resistant to abrasion, moisture, and chemical properties of the fluid.
Check with the manufacturer or supplier for documents related to part number/s, inner and outer diameters, surface finishes, tolerances, and so on.
Check the configuration and cross section size of the seal.
Opt for urethane U-cups if possible as they are durable, easy to install and remove, and generally do not have leakage issues. Also, they can withstand pressures as high as 5000 psi.
If the U-cup is being custom made or machined, talk to the manufacturer regarding non-standard diameters and tolerances such as the maximum possible extrusion gap you can allow.

Applications of U-cup Seals

U-cup seals find applications in various industries, primarily in hydraulic and pneumatic applications. Here are some of them:

Water treatment
Oil & gas
Petrochemical
Heavy engineering
Filling equipment
Automotive
Pipelines
Agriculture

If you are looking for U-cup seals, ensure you meet all the compatibility requirements and also source them from reliable and certified manufacturers and suppliers. SSP Manufacturing Inc. has a market presence of close to three decades and are experts in making various types of seals and gaskets including u-cup sealing solutions.