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Hydraulic seals are a component of most hydraulic systems, in particular of their moving parts. Usually made of some type of soft, flexible elastomer that imparts them with exceptional water and air sealing capabilities, hydraulic seals are ring-shaped and designed to eliminate or limit the leakage of fluid being transferred within a hydraulic or pneumatic system. The elastomers with which hydraulic seals may be made include, among others, polymers, plastics, rubber, (PTFE) teflon, and polyurethane.

Industries they serve include aerospace manufacturing, agriculture, automotive manufacturing, chemical processing, defense contracting, food processing, marine products manufacturing, medical and pharmaceutical products development, nuclear power, pulp and paper, and waste disposal.

The applications of hydraulic seals are diverse and numerous. Hydraulic seals are found in brake devices, clean rooms, conveyors, mixers, presses, valves, and test equipment. Most often, though, they’re found in hydraulic cylinders. Hydraulic cylinders are those mechanical actuators that are used to give unidirectional force to agriculture and forestry vehicles, construction equipment and the like, using oil, water, or another pressurized fluid.

In this case, hydraulic seals are located on the cylinder head, on the rod shaft, or in the piston. There, they keep fluid from leaking past the interface between the rod and head, from leaking to the outside of the cylinder, and from flowing across the piston. Similarly, wear rings and rod wipers block contaminants from entering the cylinder. Read More…

Leading Manufacturers

Excelsior, Inc.

Rockford, IL | 815-987-2900

Performance Sealing, Inc.

Santa Ana, CA | 866-429-2536

Arizona Sealing Devices, Inc.

Chandler, AZ | 480-892-7325

MSP Seals

Greenfield, IN | 317-866-5000


Hydraulic seals are divided into two main groupings, static and dynamic.

Static seals are located in grooves and other confined spaces, where they act as gaskets; gaskets, in this context, are mechanical seals that fill the space between two or more mating surfaces that do not have any motion between them, held in place by pressure applied by the tightening of bolts. Static seals can be further broken down into groups of axial static seals and radial static seals. To achieve a secure seal, axial static seals must be squeezed between their upper and lower surfaces; radial static seals, on the other hand, accomplish the same thing when they are compressed between their inner and outer surfaces.

Dynamic seals, which are also known as shaft seals, instead function between two surfaces that do share motion. Types of motion they work in between include reciprocation, oscillation, and rotation.

Reciprocating dynamic seals are seated within glands that hold relative motion; here they move along an axis in between inner and outer surfaces. Most often, they’re used to power linear actuators, hydraulic cylinders, and pistons in internal combustion engines.

Oscillating seals operate with shafts that rotate using a limited number of turns around its axis. Because of the frequency with which these shafts rotate, oscillating seals are usually made of a relatively hard material and have self-lubricating capabilities.

Finally, rotary seals are placed where a hydraulic device experiences rotational motion from a housing and a shaft.

Other specific types of dynamic hydraulic seals include piston seals and rod seals, which are both cylinder seals that are designed with a flexible lip that rubs against the housing or shaft for improved sealing during linear movement. As such, they may also be categorized as lip seals. Lip seals are most often used to ensure the proper operation of revolving equipment and machinery.

Bonded seals are another type of hydraulic seal, characterized by the way they are stuck to metal washers.

For use with hydraulic oil, manufacturers may employ oil seals. Oil seals, which are called metric oil seals outside of the USA, are made with materials that allow them to resist breaking down or malfunctioning in the face of repeated oil exposure. In addition to preventing leaks, they retain oil and other lubricant for rotary applications. Materials that match this description include polyacrylate, silicone, Teflon, and a number of fluoroelastomers.

In addition to those already mentioned, other rubber materials used to fabricate seals include butadiene, nitrile, and butyl. Seals made with these and other elastomeric materials are usually fabricated through extrusion, although teflon seals are sintered in an oven from a powder form.

Seals may also be made from non-rubber materials, including felt and leather and, in the case of bonded seals, brass, bronze, aluminum, carbon steel, and stainless steel. All of the metal materials used to create seals may be plated or galvanized for added oxidation protection and strength. The adhesion between the rubber material and metal of a bonded seal is created via chemical bonding.

Those considering the purchase of a hydraulic seal must take into account a few things. First of all, they must note the space within which they are working. This will affect the diameters of both the inner and outer seals as well as the housing bore and the dimension of the outer shaft. Similarly, interested parties must determine the diameter the axial or radial cross section their application will require.

Furthermore, they must take note of vacuum rating, working temperatures, highest and lowest working speed, and minimum and maximum pressure. With these considerations, operators from all industries can expect reliable and efficient sealing.

Hydraulic Seal Informational Video