rod seals

Overview of Orientations & Types of Hydraulic Seals

Overview of orientations and types of hydraulic seals. 

Hydraulic seals are available in a wide variety of orientations and different types. The basic types of hydraulic seals that are used in industrial products are rod seals, flange packing, and U-cups.

When purchasing hydraulic seals, it is necessary to consider the following:

  • Diameter of the outer shaft
  • Diameter of the inner seal
  • Diameter of the housing bore
  • Thickness and radial cross section
  • Operating speed and pressure
  • Temperature
  • Vacuum rating

Orientations of Hydraulic Seals

For the various industrial products, the sealing directions are different, which we are discussing below:

  • Rod seal: A rod seal is a type of radial seal. It is fitted into the housing bore. The sealing lip is found in contact with the shaft.
  • Piston seal: This is also a type of radial seal and is a variation of the rod seal. Here the sealing lip is in contact with the housing bore and not with the shaft. It is in the shaft where the seal is pressed.
  • Symmetric and axial seals: A symmetric seal works symmetrical or equal to the piston and rod seals. The axial seal goes in contact or in axis with the housing component.

Hydraulic Seals Types

Basically they are of two types.

  • Dynamic Seals: A dynamic seal is used to separate a fluid from possible contaminants and usually puts a gap between moving and non-moving surfaces. Finds its applications in piston ring. When selecting dynamic seals, it is necessary to focus into a variety of dimensions like inside diameters, outside diameters, radial cross section, axial cross section, and housing bore.
  • Exclusion Seals: They are used to separate contaminants and debris from machine bearings and moving shafts. These hydraulic seals are further sub divided into scrapers, V-ring, and wipers. V-rings are rubber made while wipers have lip seals that are flexible. Scrapers use scraping edges in removing contaminants from the bearings. 



Craig Cook

Simple Explanation of Seals

There are numerous sealing products, technologies, and techniques to keep oil in and contaminants out of the hydraulic system, each providing unique benefits. Further, in some harsh applications, the features of individual seals do not fulfill the demanding requirements for the equipment and a sealing system is required.

Here are the basics of seal designs:


  • Provide aggressive wiping force to prevent mud, water, dirt and other contamination
  • Allow lubricating oil film to return to system on inward stroke
  • Protect main sealing elements, thus increasing life of seals
  • Are often made from Polyurethane, which offers high abrasion resistance
  • Are often used as a linkage pin grease seal

Rod seals:

  • Contain system fluid from escaping to atmosphere
  • Must provide sealing function at low and high pressure
  • Require excellent extrusion and wear resistance
  • Should provide good pump-back capability for lubricating oil film
  • Often must withstand up to 6000 psi

Buffer seals:

  • Must withstand high pressure exposure
  • Protect the rod seal against pressure spikes
  • Pressure relieving capability prevents pressure build-up between seals
  • Increase rod seal life
  • Allow for wider extrusion gaps
  • Require high wear resistance

Wear bands:

  • Prevent contact between metal parts in the cylinder
  • Center rod and piston from housing elements
  • Increase seal life




Craig Cook

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