Hydraulic and Pneumatic Seals

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Hydraulic Seals are relatively soft, non-metallic rings, placed in a groove or fixed in a combination of rings, forming a seal assembly. This assembly is used to block or separate fluid in reciprocating motion applications. Hydraulic seals use is critical in providing a way for fluid power to be converted to linear motion.  

Hydraulic seals can be made from a variety of materials such as polyurethane, rubber or PTFE (Teflon). The type of material is determined by the specific operating conditions or limits due to fluid type, pressure, fluid chemical compatibility or temperature.

A static seal is located in a groove and sees no movement, only sealing within its confined space.  A type dynamic hydraulic seal is called a rod seal and is exposed to movement on its inner diameter along the shaft or rod of a hydraulic cylinder.  Another type of dynamic hydraulic seal is called a piston seal and is exposed to movement on its outer diameter along the tube or bore of a hydraulic cylinder.

This class of seals is a U-seal or u-cup and come in loaded and unloaded styles. 

Loaded U-Seals come in the following styles, including:

  • RTUB standard loaded rod seals
  • Standard Loaded U-seals
  • Deep Loaded U-seals
  • B-Type Loaded U-seals
  • DRU-style Unloaded U-seals
  • BS (DRTU-style) Unloaded U-seals
  • DPU-style Unloaded U-seals
  • DSU-style Unloaded U-seals
  • HU-style Unloaded U-seals
  • 8400-style Unloaded Symmetrical U-seals (Pneumatics)

U-seals are available in standard and metric sizes.

Pneumatic seals, like hydraulic cylinders, something forces a piston to move in the desired direction.  Pneumatic cylinders use the power of compressed gas to produce a force in a reciprocating linear motion.  Pneumatic seals are symmetrical unloaded U-seals that work for both rod and piston applications. These are unloaded, meaning that there is a gap between the inner and outer lips allowing for greater flexibility. They can withstand pressure up to 1,250 psi, and temperatures from -65 to 300F. They have a symmetrical cross section, meaning the inside lip is the same as the outside lip.

Other items used with hydraulic seal applications include:
Pip Rings are complimentary to B-Type U-seals, transforming the B-Type U-seal from uni-directional to bi-directional seals.
Modular Back-up rings, made from urethane or nylon, are commonly used as spacers for U-seals.
Z-seals are symmetrical loaded U-seals that work for both rod and piston applications. The load is much larger, creating two complimentary methods of sealing, a nitrile lip, and a urethane base.

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