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DMS tells you: how to choose hydraulic seals

DMS tells you: how to choose hydraulic seals


Hydraulic working pressure

The main problems in low-pressure systems are the tightness and friction characteristics of the seals. When the lip seal ring is under low pressure, the contact surfaces of the two seals are difficult to stick tightly, and the seal is not tight; once the rigid seal has a large deformation, the low pressure is not enough to eliminate the residual deformation, which has a bad effect on the seal; become a larger load, and the friction constantly changes while in motion, causing the system to crawl and jitter.

The main problem of the high-pressure system is the extrusion of the sealing ring. The extrusion is affected by the shape of the sealing ring, the hardness of the material, the extrusion gap and the working temperature, etc., which should be considered comprehensively. In order to prevent jamming and straining, the extrusion gap should not be too small.

When hydraulic components are subjected to high pressure and high frequency impact loads greater than 25MPa, buffer auxiliary seals should be installed in front of the seals to protect the seals and improve sealing and durability; when the hydraulic cylinder is under high pressure, attention should also be paid to preventing gas explosions. In order to avoid leakage caused by burning the sealing ring, the hydraulic cylinder should be exhausted of air as much as possible.


The service temperature of the seal mainly depends on the withstand temperature of the material, generally -50~150°C. When designing, it is necessary to understand the temperature performance of the material and select it according to the operating temperature. Excessively high temperature accelerates the aging of materials and causes the pressure resistance performance of seals to decrease. If the temperature is too low, the elasticity of the material will be reduced, the shrinkage will reduce the interference, and the contact pressure of the sealing surface will decrease, resulting in leakage.

Movement speed

The maximum speed of the reciprocating seal is limited by friction and wear. The movement speed of the rubber O-ring is not more than 0.3m/s, and the Y-type can reach 0.5m/s. The combined seal with PTFE as the friction surface can reach 6~7m/s. The reciprocating dynamic seal is prone to crawling at low speeds. Crawling is mainly affected by the friction characteristics of the seal, and the design is to fully consider the friction problem.

In general, lip seals perform better at low speeds than extruded seals.

work frequency

Working frequency refers to the length of continuous working time of hydraulic and pneumatic components. The frequency of work is high, pay attention to the influence of temperature rise on the material, and design a cooling device if necessary. When the working frequency is extremely low, the surface of the friction pair is prone to sticking, which increases the friction and aggravates the wear of the sealing ring.


If the reciprocating stroke is low, such as less than 5cm, it is prone to poor lubrication and heat generation, resulting in abnormal wear. The problems that need to be paid attention to in long-stroke seals are the bending of the piston rod and cylinder, and the eccentric and eccentric loads are likely to cause eccentric wear of the seals, and are affected by the surface roughness. There are relationships.

eccentric, vibration

Under the conditions of eccentricity and large vibration, the seal and the relative friction surface are in an unstable contact state. If the seal does not follow the relative friction surface insufficiently, it will cause leakage. The followability largely depends on the material flexibility.

Surface roughness of friction pair

Large surface roughness will accelerate the wear of the seal and reduce the life of the seal; small surface roughness will increase the processing cost, and it is not conducive to the establishment of the oil film, which will aggravate the wear.

Piston, piston rod seal

Common sealing rings for dynamic sealing: O-ring, Y-ring, V-ring, combined sealing ring

O-ring: easy to install, low price, working pressure greater than 7MPa, must be equipped with a retaining ring. The service life of the lip seal is shorter, and the processing accuracy is higher.

Y-ring: The service life is higher than that of O-ring, and the sealing performance and ultimate pressure after using the retaining ring are better than that of O-ring.

V-shaped ring: The movement friction resistance is larger than that of the Y-shaped ring, but the seal is reliable and the service life is long. When leakage occurs, only the pressure ring needs to be adjusted, and there is no need to replace the seal.

Dust ring


1) Simple structure, easy to assemble and disassemble;

2) The working speed is not greater than 1m/s;

3) Working temperature: -30~110℃;

Guide support ring

The guide support ring is beneficial to prevent the hydraulic cylinder from being strained, improve the stability of the movement, and increase the sealing working pressure of the hydraulic cylinder. The guide support ring of the piston part is generally made of synthetic resin with low friction coefficient, wear resistance and high hardness. Such as polytetrafluoroethylene.

retaining ring

The retaining ring is placed behind the sealing device to prevent the gap of the rubber sealing ring from being extruded. The retaining ring is composed of high hardness material and should also have a certain degree of elasticity.

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