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Among the many components commonly found in machines that rely on hydraulic power, hydraulic seals are likely overlooked by most. However, these seals are both widespread and vital in many applications. A basic familiarity with hydraulic seals, what they do and which ones to use for replacements can go a long way in keeping up with maintenance and repair.

Design and Function

Hydraulic seals are polymer components fitted within hydraulic systems to prevent either escape of hydraulic fluids or foreign materials entering. Most commonly, they’re found in hydraulic cylinders that provide driving force to the system. Hydraulic seals come in numerous forms depending on their intended purpose and can be made of polyurethane, rubber, nylon, PTFE, silicone and more. Broadly, they’re classified as static or dynamic seals, depending on whether the adjacent components are stationary or in motion relative to each other.

Factors of Choosing Seals

There is no singular material nor profile that fits every single application. A hydraulic seal must be designed to work within the conditions it’s to be installed in. These considerations vary, but often include:

  • Intended function, duty cycles and environment for the cylinder
  • Dimensions and specifications for surrounding hardware
  • Pressure range of surrounding fluids, as well as frequency of oscillations
  • Temperature range of surrounding components at rest and when operating
  • Type of fluid and its physical and chemical properties

Generally, good materials for hydraulic surfaces respond well under compression and relaxation, retain elasticity across temperatures, are sufficiently hard and flexible to maintain integrity and do not react chemically with the expected hydraulic fluids. This means rubbers, thermoplastics and forms of PTFE are most commonly used; the specific choice, as well as additional treatments, vary depending on the exact application.

For installation, manufacturing and repairs, choosing the right hydraulic seals are crucial to a functional hydraulic system. In turn, understanding how seals are used—and how they can fail—lets you make an informed decision on maintenance.