All About U-Seals

If you've ever looked for new U-Seals, you've definitely come across a few terms: U-cups, Polypaks, Un-Loaded & Loaded, Single Lip, Double Lip, and so on. If you are in need of this part and are unfamiliar with these sorts of seals, it might be very perplexing. But don't worry; in this post, we'll go over the most frequent forms and terminologies for U-Seals. Hopefully, after reading this, replacing and dealing with them will be lot easier, and you'll have a better grasp of what to look for.

Let us begin by looking at what an actual U-Seal is used for, followed by a breakdown of the most frequent forms. U-Seals are a form of rod or piston cylinder seal (hydraulic/pneumatic) with a distinctive "U" profile. The outer is a static lip seal that protects against mating surfaces with no relative motion between them. On the other hand, the interior of the U-Seal is a dynamic lip seal that is employed when surfaces are in motion. Finally, before we proceed, let's look at loaded and unloaded.

Loaded or unloaded?

Loaded U-seals, also known as U-Cups or Polypaks, are loaded with an o-ring or spring between the two mouths of some seals to boost sealing force at low pressures while blocking or separating fluid in reciprocating motion applications. The loaded U-Cup is formed by adding a "loader or energizer" to a lip seal, converting it into a squeezing seal. This gives a high sealing force at low pressures. As the system pressure rises, so does the lip loading, which automatically compensates for the increased pressure while maintaining a positive seal. Unloaded seals simply do not have these components.

Types of U-Seals
 

The conventional U-seal profile has a square cross section and is suitable for both rod and piston applications.The term "standard" denotes that the height and cross-section are the same, and the lips are not beveled. Essentially, this indicates that the outside and inside of the lip are identical. This design is typically utilized to replace old hydraulic packing and o-rings without modifying the gland design. Remember, this is not to be confused with "standard sealing," which refers to how it seals inside the application rather than the seal itself.

Deep- The deep o-ring loaded U-seal design is a modified variant of the normal square form. The deep U-Cup has a height larger than the cross section, which improves the stability of higher applications. The rectangular shape provides higher "down stream" stability, while the increased lip interference allows for better low pressure sealing.Typically, when replacing o-rings, you would need to modify the gland for this seal, but this design is great for packing replacement.

Type B- "B-Type" merely denotes that the lips are beveled. However, like our last example, they are also profound. Again, this simply indicates that the height is bigger than the cross-section.This improves film breaking and increases unit loading at the sealing surface. By adding the rear bevel to the lips, the seal contact is aligned near the centerline of the o-ring energizer, providing greater sealing force that improves both low and high pressure sealing capabilities. This sort of seal is typically seen in rod cylinders.

Square B- The square B has more sealing ability owing to the rear bevel lip design, yet it still allows you to change o-rings without affecting the groove. They are also intended to provide improved low-pressure performance and a longer seal life due to their unique film breaking characteristics.

Summary

When changing U-Seals on cylinders, it is critical to know what to check for. Keep in mind that many of the parts inside the different housings that you must pass through in order to access the seals may also need to be replaced. While your components are already disassembled, spend some extra time analyzing which parts will be the next to exhibit indications of wear and strain. It is usually ideal to replace whatever you can at once in order to save time and money in the long run.
 

Remember that we are here to help with any questions you may have. Although we are not trained hydraulic engineers, we will try our best to answer any queries you may have. Please contact us via our contact page, social media, phone, or email at us, and be sure to check out our U-seals.