Hydraulic Seals

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Mechanical Power has been supplying high performance seals to many different industries. Applications that require high performance seals to protect their equipment and operations utilize our seals on a daily basis.

Seals are critical components in system performance regardless of industry. Ex: High-pressure hydraulic seals are designed to prevent leakage of fluids from cylinders, but power transmission seals are designed to prevent internal contamination.

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Manufacturing of Hydraulic Seals

Elastomers, natural and manmade polymers with weak molecular attraction and high elastic characteristics, are commonly used in hydraulic seals. Rubber and plastics are the two most common materials used in hydraulic seals (including PTFE, such as Teflon, and polyurethane). Butadiene, nitrile, butyl, and silicone are some of the other elastomer compounds utilized to make seals. Extrusion is used to make seals out of these and other elastomeric materials, though Teflon seals are sintered in an oven from a powder form.

Non-elastic materials like felt and leather can also be used to make seals. Metallic materials are used in some types of hydraulic seals (for example, bonded seals) (including brass, bronze, aluminum, carbon steel, and stainless steel). For enhanced oxidation protection and strength, all metal materials used to make seals can be plated or galvanized. Chemical bonding is used to generate adhesion between the rubber and metal of a bonded seal.

Hydraulic seals types

Hydraulic seals are commonly found in hydraulic cylinders, which are mechanical actuators that transform hydraulic pressure (from oil, water, or another pressurized fluid) into unidirectional force for agricultural and forestry vehicles, construction equipment, and other processes.

Hydraulic seals are typically situated on the cylinder head, rod shaft, or piston. Seals prevent fluid from seeping through the interface between the rod and the head, leaking to the outside of the cylinder, and flowing across the piston in these areas.

Static and dynamic hydraulic seals are the two primary categories.

Static seals are gaskets that are frequently found in grooves and other tight places. The term “gasket” refers to a mechanical seal that fills the area between two or more mating surfaces that do not move and is maintained in place by bolt tightening pressure. Although the quantity and exact location of static seals varies based on the cylinder construction, they always perform the same objective of filling gaps between immovable surfaces. Static seals are divided into two categories: axial static seals and radial static seals.

Axial static seals must be squeezed between their top and bottom surfaces to establish a secure seal. When radial static seals are compressed between their inner and outer surfaces, they accomplish the same function.

Dynamic seals, also known as shaft seals, are used to close gaps between two surfaces that move in the same direction. Reciprocal, oscillatory, and rotational motions are among the motions they deal with.

Within glands that hold relative motion, reciprocating dynamic seals are situated. They travel between the inner and outer surfaces along an axis. In internal combustion engines, they’re most commonly employed to power linear actuators, hydraulic cylinders, and pistons.

Oscillating seals have shafts that revolve a finite number of times around their axis. Oscillating seals are normally formed of a moderately hard material and have self-lubricating capabilities due to the frequency with which these shafts revolve.

Where a hydraulic equipment receives rotating motion from a housing and a shaft, rotary seals are used.

Hydraulic Seals Types

A hydraulic seal’s specific actions varies slightly depending on where it is in relation to the hydraulic cylinder. Piston seals and rod seals, both cylinder seals with a flexible lip that rubs against the housing or shaft for enhanced sealing during linear movement, are the most common hydraulic seals. As a result, piston seals and rod seals are classified as lip seals. These seals are commonly employed to ensure the proper operation of rotating machinery and equipment.

Piston seals, in particular, prevent leakage or fluid passage across the piston. Many piston seals are single-acting, which means they only focus pressure on one side of the piston. The piston may travel the bore of a cylinder and the cylinder can move with maximal mechanical effort thanks to this concentrated pressure increase. As a result, (dynamic) piston seals are critical for maintaining a hydraulic system’s efficiency.

Double-acting piston seals can concentrate pressure on both sides of a piston, effectively pushing the ram to which the piston is usually linked. Static piston seals, in contrast to the dynamic varieties of piston seals just explained, seal the gap between the piston and the piston rod (rather than the piston and the cylinder bore).

Rod seals act by preventing fluid leakage from the cylinder from the outside. They are normally single-acting, and a supplementary rod seal is frequently added. Static rod seals fill gaps between the cylinder head and the cylinder bore, whereas dynamic rod seals work in the space between the piston rod and the cylinder head. Rod seals help manage lubricating fluid for the rod, the wiper seal, and the rod seal itself, in addition to containing hydraulic fluid within the cylinder.

Other types of hydraulic seals commonly encountered in hydraulic cylinders include the following. Rod wipers, commonly referred to as scrapers or wiper seals, keep impurities out of the cylinder. Dirt and moisture are two pollutants that can make a hydraulic cylinder inoperable (among other foreign particles). When wiper seals retract into the cylinder, they remove these impurities.

Buffer seals improve the rod seal’s performance by acting as a “buffer” against high internal fluid pressure. They also protect the rod seal from any pollutants that might make their way into the cylinder (such as metal chips).

Because they center the piston and piston rod while guiding them through the cylinder and preventing metal-on-metal contact, guide rings are also known as wear rings. Within a hydraulic cylinder, wear rings can be observed on both the rod and piston.

O-rings are unusual in this list because their shape, rather than their location or purpose, is used to identify them. O-rings are donut-shaped and exist in a variety of materials (rubber, silicone, fluorocarbon) and diameters, as their name suggests (e.g. less than an inch to several meters wide).

These types of seals provide very effective sealing barriers when mechanically deformed by pressure. O-rings are the most prevalent type of hydraulic seal on the market today due to its low cost and relative simplicity.

Oil seals, sometimes known as metric oil seals outside of the United States, are built of materials that allow them to withstand repeated oil exposure without breaking down or failing. Polyacrylate, silicone, Teflon, and a variety of fluoroelastomers are examples of such materials. Oil seals keep oil and other lubricants in rotary applications in addition to preventing leakage.

The way metallic bonded seals adhere to metal washers distinguishes them.

In essence, X rings (also known as quad or square rings) are improved versions of O-rings. Their four-lobed design allows them to seal up to twice as well as standard O-rings while requiring less mechanical distortion. X rings can function as both static and dynamic sealing.


Hydraulic seals are used in a variety of industries because they are so important to the operation of hydraulic systems. Aerospace manufacturing, agriculture, automotive manufacturing, chemical processing, snow removal, food processing, marine products manufacturing, medical and pharmaceutical product development, nuclear power, pulp and paper, and heavy machinery are among the industries that hydraulic seals serve.

Hydraulic seal applications are as varied and numerous as the industries in which they are used. Construction equipment, agricultural machinery, brake devices, clean rooms, conveyors, mixers, presses, valves, and test equipment all use hydraulic seals.

Hydraulic seals for custom applications

Custom seals, such as silicone sealant strips, are used in the aerospace industry to seal various hydraulic components within aircraft systems. EMI shielding gaskets, for example, are used in the electronics sector to avoid undesired electromagnetic interference in various equipment.

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