About hydraulic cylinder seals?

Sat December 23, 2023

hydraulic seal

The hydraulic cylinder seal is installed on the shaft of the hydraulic pump and hydraulic motor to prevent the working medium from leaking out of the housing along the shaft and external dust from invading the inside of the body.As you can see, choosing a reputable hydraulic seals factory is very important.  

Category: piston seal, rod seal,static seal, rotary seal

Function: Prevent leakage of working medium

Composition: piston seal, rod seal, static seal, wear ring, bearing guidance, etc.

Properties: Excellent wear resistance, extrusion resistance, impact resistance.Quality properties rely on an excellent hydraulic seals factory.  

Seal is a mechanism that prevents leakage of working medium (internal and external leakage) and prevents external foreign matter (such as air, dust and water, etc.) from entering hydraulic components and hydraulic systems.Proper sealing requires cooperation with a high quality hydraulic seals factory.   

Although seals are auxiliary parts in hydraulic equipment, the quality of seals and sealing devices is one of the keys that directly affects whether the hydraulic system can work normally. To a certain extent, the quality of seals has restricted the improvement of performance and reliability of hydraulic components and hydraulic systems, the length of service life, and the key to the grade and level of hydraulic equipment and participation in international competition. This is also the key to domestic One of the main factors causing the quality difference of external hydraulic components. Often the loss caused by the failure of individual seals may be tens of millions of times the value of the seal itself.

Dust seal

Installed on the inside of the hydraulic cylinder end cover, the main sealing lip is exposed to the air, and the sealing medium is attached dust, lime sand, rainwater, frost and other dirt to prevent external dust and rainwater from entering the inside of the sealing mechanism and affecting the viscosity of the hydraulic oil. And the effect of scratching the sealing lip of the internal seal.

Dust seals are divided into various types and sizes, including polyester and outer metal frames. Therefore, the scope of use and targets are wider.

Advantages: excellent wear resistance, extrusion resistance, impact resistance, small compression deformation, wide adaptability, and easy installation.

Piston rod seal

Rod Seals

It is installed inside the dust-proof seal on the inside of the hydraulic cylinder end cover. Its function is to prevent hydraulic oil from leaking. It is one of the main pressure-bearing components. It bears one-way pressure, withstands large pressures and is in direct contact with the hydraulic oil. It requires good pressure-holding performance in a static state, high pressure-bearing performance during movement, good sealing performance, small friction factor, and strong extrusion resistance.

There are many cross-sectional forms and materials for piston rod seals, and different cross-sectional forms and materials are selected according to different working environments.

Piston seal

Installed on the piston, its main function is to seal the gap between the piston and the cylinder to prevent internal leakage of hydraulic oil. The piston seal is the main seal in the hydraulic cylinder. It bears pressure in both directions and is one of the most important seals that the hydraulic cylinder can withstand the pressure value. The main requirements for piston sealing are good sealing effect, good pressure maintaining effect in static state, strong pressure bearing capacity during movement, resistance to extrusion, small friction coefficient, long service life, etc.

There are various forms of piston seals, and the most appropriate form should be selected according to different usage environments.

Piston Seals

Wear ring

Wear ring

Installed on the inside of the hydraulic cylinder end cover, its main function is to support the piston rod; prevent the piston rod from being vertically stressed and causing uneven pressure bearing on the rod seal, resulting in poor sealing effect and short service life.

Bearing rings

Installed on the piston, its main function is to guide the piston to make linear motion and prevent the piston from deflecting due to uneven force, causing internal leakage and reducing the service life of the seal.

The service life of the Wear ring and bearing rings directly affects the use effect and life of the piston seal and piston rod seal, so the requirements for the Wear ring and bearing rings are also higher, such as small friction coefficient, high hardness, long service life, etc.

Wear rings and bearing rings come in many forms and are used in combination with the main seal.

Bearing rings

static seal


The static sealing ring of the end cover is installed at the contact position between the outer circle of the end cover and the inner wall of the hydraulic cylinder; the static sealing ring of the piston is installed between the piston and the piston rod.

They are all static sealing rings in the hydraulic cylinder. The end cover static seal prevents hydraulic oil from leaking from the gap between the end cover and the cylinder barrel. It is pressure-bearing on one side and requires strong anti-extrusion ability and good sealing effect. The piston static seal is The seal is a two-way pressure bearing to prevent hydraulic oil from leaking from between the piston and the piston rod. It requires strong anti-extrusion ability and good sealing effect.

Common static sealing rings are O-rings and back-up rings.

Rotary seal

Installed on the shaft of the hydraulic pump and hydraulic motor to prevent the working medium from leaking out of the housing along the shaft and external dust reaction from invading the inside of the body. General oil seals have a poor ability to withstand pressure, generally 0.2-0.3MPa, fluorine rubber pressure-resistant oil seals have a pressure-bearing capacity of 0.25-0.7MPa, and TYS Seals high-pressure oil seals have a maximum pressure-bearing capacity of 40MPa.

Rotary Seals

The reasons for leakage relate to installation issues, seal selection issues, and choice of hydraulic seals factory.
Main reason for leakage:

Installation issues

1 The wrong installation direction of the seal causes leakage.

2. Foreign matter, dust, etc. may be mixed in during installation or enter the sealing cavity in the pipeline, causing leakage.

3. Poor assembly causes damage to the seal and causes leakage.

4. There are scratches on the surface of the seal causing leakage.

5. The piston rod is not concentric and the eccentric load causes leakage.

Seal selection issues

1 The pressure is too high and the hardness of the seal is too small and it is squeezed out of the metal groove.

2 The sealing material and the medium are miscible, and the seal is softened or dissolved.

3. The seal is used in conditions where the temperature is too high, and the sealing material is carbonized.

4 Low temperature causes the sealing material to harden and shrink, causing leakage.

5. The use speed is too high, causing the seal to heat up, dry grind, carbonize and form leakage.

6. Poor lubrication under operating conditions causes seal wear and leakage.

7 The cavity used is vibrated and causes leakage.

8 Leakage due to wear of seals caused by dust.

9 The hardness of the seal is too high and cannot completely fill the metal groove, causing leakage.

10 The size of the seal does not match the metal groove, causing leakage.

11 Selecting seals that have been stored for too long and aged may cause leakage.

12It is also very important to choose a good quality hydraulic seals factory.

Relying on an unqualified seals factory risks poor sealing performance. Partnering with a proven hydraulic seals factory enhances quality and reliability.
By selecting the optimal hydraulic seals factory for your application, many leakage issues can be avoided through robust design and production control.

Sealing material

Sealing materials mainly use PTFE, rubber and synthetic resin. Due to the different performance characteristics of various materials, their uses are also different. When selecting, you need to make appropriate choices based on different usage requirements and different usage conditions.

A seal made of a certain material has good sealing performance for a certain working medium being sealed, but has extremely poor sealing performance for another medium. This is the compatibility of the sealing material and the hydraulic oil.

Sealing material compatibility with the hydraulic oil is also critical. The ideal hydraulic seals factory will have expertise across various materials like PTFE and rubber compounds to provide solutions tailored to your specific fluid and application environments.

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