Hydraulic Cylinder Seals: Types, Materials, Functions

Hydraulic Cylinder Seals: Types, Materials, Functions


Hydraulic cylinder seals are an integral part of any hydraulic system because they control and maintain the pressure and movement of hydraulic fluid. Without them, hydraulic systems can't work correctly.

The correct  hydraulic cylinder seals, will maintain the integrity of the machine's system and extend its working life. Our hydraulic cylinder resealing services ensure such equipment runs at peak performance.

In this blog, we look at how hydraulic cylinder seals are designed to prevent leakage, the main types of seals, and the materials they are made of to withstand high pressure.

What Are Hydraulic Cylinder Seals?

Hydraulic cylinder seals form a barrier between different components in a hydraulic cylinder. They are made with specific materials that adjust to varying clearance gap sizes and must be strong enough to withstand the shear stress created by system pressure.

When selecting hydraulics cylinders seals, it is essential to consider the type of surfaces they will be used on. A static seal should be employed if there is no relative motion between mating surfaces. On the other hand, if there is motion between surfaces (either reciprocating or oscillating), then a dynamic seal should be used.

Main Functions of Hydraulic Cylinder Seals

hydraulic rod seals

A hydraulic cylinder seal protects the hydraulic fluid and prevents the hydraulic system's components from mixing with external fluids. They also help to improve a system's overall efficiency and reliability, among other things:

  • Pressure adaptability and contamination prevention: Hydraulic seals are designed to function with both low-pressure and high-pressure. Furthermore, they prevent contamination by acting as a barrier to keep dirt out.
  • Controlling leaks and preventing blowouts: Hydraulic cylinder seals are designed to create a pressure-tight seal around the piston rod, reducing friction and preventing leaks and blowouts. They are made from unique materials that resist wear from hydraulic fluid and feature a lip to create a positive seal around the piston rod.
  • Cost-effectiveness and easy maintenance: Hydraulic cylinder seals are designed to reduce the cost of parts and labor, be resistant to wear and tear, and require minimal maintenance. They are easy to install and replace and provide a high level of performance, making them a cost-effective and low-maintenance solution for hydraulic systems.
  • High durability and adaptability: Manufacturers around the globe make high-quality hydraulic cylinder seal kits that provide durability and a long lifespan. Constructed from top-notch materials, these advanced seals are engineered to withstand harsh conditions and keep the machinery running smoothly.
  • Safe and water resistance: Renowned for resisting water, chemicals, and wear and tear, hydraulic seals are a popular choice for mining businesses that want to speed up mineral extraction. They are also safe to use in various industries, such as those producing pharmaceuticals and chemicals.

Main Types of Hydraulic Seals

types of sealing

Different types of sealing are available for hydraulic cylinders, ranging from simple O-rings to complex rotary seals, hydraulic ram seals, and hydraulic oil seals. Depending on the application, the type of seal required will vary; but all seals serve the same purpose of creating a secure, fluid-tight seal.

Piston Seals

Piston seals, also known as piston rings, are mechanical seals that reduce leakage between components in a reciprocating motion. Therefore, the primary function of a hydraulic piston seal is to form a seal between the cylinder tube and piston, preventing the leakage of lubricants and gases.

They also help maintain the pressure within the cylinder, allowing the piston to move efficiently. Piston seals are used in various applications, such as air compressors, hydraulic pumps, and internal combustion engines. As critical components in any reciprocating system, they ensure the efficient movement of the parts while keeping the system sealed and maintaining the pressure within.

Wiper Seals

Wiper seals keep dirt, debris, and other contaminants from entering a system or machine. They are typically used for applications such as hydraulic cylinders, pumps, and valves and can be made from various materials, including rubber, polyurethane, and thermoplastic elastomers.

Designed with a lip that scrapes the system's surface when it moves, they eliminate any particles that may have accumulated. Additionally, wiper seals provide an extra barrier against entering liquids and gases. They are commonly used in conjunction with other seals such as O-rings, and rod seals to provide a comprehensive sealing solution.

Rod & Buffer Seals

Hydraulic rod seals consist of a metal rod inserted in a rubber or plastic sealing element. The sealing part conforms to the rod surface, creating a tight seal that prevents internal pressure from escaping and external contaminants from entering the cylinder.

In addition, the buffer seal cushions the rod from shock and vibration, increasing the life of the cylinder and its components. Rod and buffer seals are suitable for mobile and industrial applications, such as agricultural and construction equipment, where they are exposed to dirt, dust, and moisture.

The difference between a rod seal vs. piston seal: Rod seals are flexible and keep pressure in and contaminants out, while piston seals are rigid seals that keep pressure in and lubricate in.

Guide Rings & Lubrication

Guide rings are mounted on pistons and piston rods of hydraulic cylinders to absorb side loads and prevent metal-to-metal contact between sliding parts, such as rod and gland/piston and bore. They are typically placed inward of both the rod and buffer seal and should be lubricated on assembly with the same lubricant used in the hydraulic system.

These rings are available in metallic and nonmetallic options. Factors such as the diameter of the rod and piston, the stroke length, pressure, type of seal, and lubrication must be considered when selecting guide rings.

What Materials Are Used in Hydraulic Seals?

hydraulic cylinder seals

Choosing suitable seal material is crucial, as it determines the overall quality and durability of hydraulic seals. Your manufacturer can suggest appropriate materials - whether you need hydraulic seal rings, o-rings, or any other type of seal -  to meet specific application needs. Below are the most common materials used to create seals:

  • Rubber: A hydraulic rubber seal is suitable for applications requiring high flexibility and compressibility. Nitrile butadiene rubber (NBR), fluoroelastomer (FKM), and hydrogenated nitrile butadiene rubber (HNBR) are popular materials used to create these seals due to their resistance to grease, mineral oils, and other hydraulic fluids.
  • Polytetrafluoroethylene: PTFE has remarkable durability when exposed to extreme temperatures, pressures, and caustic chemicals. Its low coefficient of friction means it requires less lubrication than other seals, and it can perform effectively even when used dry.
  • Rigid plastics: Plastic hydraulic cylinder seals offer resistance to temperature, pressure, and chemical reactivity and come in various materials. The strength of seals can be improved by utilizing engineered plastics instead of commodity plastics. Plastic seals are much more rigid than rubber or PTFE seals, providing additional power to the cylinder.
  • Thermoplastic Elastomers: TPEs offer excellent strength and flexibility, making them ideal for hydraulic cylinder seals. They are highly resistant to abrasion and tearing and can keep constant pressure for extended periods. Their combination of plastic and rubber properties makes them an excellent choice for components that require durability and elasticity.

With a wide variety of hydraulic seals available, it is essential to select wisely to ensure cost-effective hydraulic cylinder repairs. Doing so will help to guarantee a long operating life and improved performance over the lifetime of the hydraulic cylinder. Incorrectly sealing equipment can lead to premature wear and eventual failure.


As a hydraulic cylinder repair company, our team has been resealing hydraulic cylinders for over 30 years. We can help you no matter what your hydraulic system needs, and we are always happy to offer seal recommendations and answer any questions.

Having done thousands of repairs, we have extensive knowledge and experience to expertly service your repairs and perform preventative maintenance. We also have a large inventory of seals and stock common steel shapes if your repair requires fabrication. If you’re looking for experienced and professional hydraulic repair service, contact Cylinders, Inc. today!

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