The profiles can be categorized into wide, narrow, and Y-type, among others, depending on the height-to-width ratio. The Y-shaped seal's cross-section is Y-shaped, which is a typical lip seal. Y-shaped seals can be further divided into those with unevenly high lips for shaft use, unevenly high lips for bore use, and equally high lips for universal shaft and bore sealing. The manufacturing materials of Y-shaped seals also vary, allowing for classifications such as acrylonitrile butadiene rubber (NBR) Y-seals, fluororubber Y-seals, and polyurethane rubber Y-seals.
Product Application Range
Y-seal rings are widely used in reciprocating motion sealing devices, with a longer service life than O-rings. The applicable working pressure for Y-seal rings does not exceed 40MPa, and the working temperature ranges from -30 to 80℃.
Operating speed range: 0.01～0.6m/s when made of nitrile rubber; 0.05～0.3m/s when made of fluororubber; and 0.01～1m/s when made of polyurethane rubber. The sealing performance, service life, and working pressure limit at different retaining rings are best with polyurethane rubber material for Y-seal rings.
Product Performance
Y-seal gaskets are commonly used as sealing components in reciprocating motion sealing devices in hydraulic and pneumatic systems, with longer service life and superior sealing performance compared to O-seals. The lip of the Y-seal is wider than a single V-seal, resulting in better sealing performance. Only one is needed, thus reducing friction compared to the V-seal. Y-seals can be adjusted to meet pressure and sealing performance requirements by altering their cross-sectional structure and dimensions. They are suitable for working pressures not exceeding 40MPa; operating temperatures from -30 to 80℃; and operating velocity ranges; for nitrile rubber, it is 0.01 to 0.6 m/s, while for polyurethane rubber, it is 0.05 to 0.1 m/s.
Sealing Principle of the Y-shaped ring
1. Bi-directional seals for piston-type applications require a pair of Y-shaped sealing rings, which increases the axial size. The cross-sectional dimensions of a standard Y-shaped seal are larger than those of an O-ring, necessitating a wider groove size for installation. To facilitate installation, split grooves may sometimes be employed. Many countries have now developed Y-shaped seals with smaller cross-sectional dimensions, and the size and installation issues are gradually being improved.
2. The function of the Y-type seal is mainly reflected in the piston rod or piston sealing of hydraulic cylinders. The sealing of the Y-type seal can be divided into two pressure conditions: without medium pressure, it relies solely on the pre-compression amount of the lip to fit the seal; with medium pressure, the medium fills into the groove between the inner and outer lips, exerting a pressure push on both lips, causing them to expand more and then adhere to the sliding parts. Therefore, when installing the Y-type seal, the cavity should face the medium. Outepei Seals would like to remind you that the maximum working pressure the Y-type seal can withstand is around 20 MPa. When the pressure exceeds this value, an auxiliary support ring can be used to fix and increase the bearing pressure. The Y-type seal also has a certain self-compensation ability to deal with gradual wear during use.
3. The Y-shaped seal is suitable for sealing reciprocating motion at medium and low pressures, such as between pistons and cylinders, and piston rods and piston caps. It primarily relies on the lip pressing against the sealed surface for its sealing function. Consequently, the sealing lip is prone to wear and deformation due to heat. Therefore, the lip size is a critical factor in design, including the outer and inner diameters of the lip. The pre-compressed Y-shaped seal adheres to the mating surface with its open lip. Without internal pressure, there is only a minimal contact pressure caused by the deformation of the lip tip. Under sealed conditions, every point in contact with the sealing medium experiences a normal force equal to the medium's pressure, causing the bottom of the lip to be axially compressed, the lip to be circumferentially compressed, the contact area to broaden, and the contact stress to increase. As internal pressure rises further, the distribution and magnitude of the contact pressure change, making the lip and sealing surface fit more closely, enhancing the seal's effectiveness—this is the "self-sealing" action of the Y-shaped seal. Due to this self-sealing action, a single Y-shaped seal can effectively seal pressures up to 32MPa. The effective sealing pressure of a pressure-actuated seal is the sum of the pre-pressure and fluid pressure. The Y-shaped seal applies the fluid pressure effectively to the seal through the lip action, allowing the pre-pressure to be reduced to a minimal value. Moreover, as the fluid pressure increases, the effect of the pre-pressure diminishes, making the pre-pressure's role negligible in high-pressure scenarios. Reducing the sealing friction is beneficial at this point, as the sealing friction is proportional to the sealing contact pressure. Therefore, the Y-shaped seal, while ensuring sealing, has less friction than a squeeze-type seal. The Y-shaped seal is primarily used for reciprocating seals. As its working principle indicates, the lip should face the side with higher pressure during installation to function properly. Hence, the Y-shaped seal can only act in one direction.
4. When the mating parts move at working speed, a sealing oil film forms between the sealing lip and the sliding surface. The presence of the oil film improves the friction conditions of the sealing ring, reducing wear; the oil film also serves as a seal in pneumatic sealing. During the reciprocating motion of hydraulic components, the thickness of the oil film varies when the moving parts extend and retract, and this difference in oil film thickness can lead to leakage. Therefore, even when the Y-shaped ring is operating normally, there is a small amount of leakage, which increases with higher reciprocating speeds. This is because at higher reciprocating speeds, the frequency of reciprocation becomes very frequent, and the fluid dynamic effect of the oil film increases its thickness, leading to rapid accumulation. As the viscosity of the working oil increases, the oil film thickness also increases, and the amount of leakage caused by the reciprocating speed increases. However, since the viscosity of hydraulic oil decreases with temperature, when hydraulic equipment starts up at low temperatures, there is a significant amount of leakage at the beginning of the movement. As the temperature rises during operation due to various losses, the leakage gradually decreases. The leakage conditions of the piston during reciprocating travel are different. When the internal pressure is low, the leakage during the withdrawal stroke increases with the increase in internal pressure; during the insertion stroke, it decreases with the increase in internal pressure. When the internal pressure is sufficiently high (about greater than 7.5 MPa), the leakage no longer changes with the internal pressure.
5. When the internal pressure p1 within the Y-shaped seal is low, the friction force increases as the internal pressure rises. Once the internal pressure is sufficiently high, the friction force no longer experiences significant changes. If lubrication is good, there may even be a downward trend. Overseas testing results for the startup friction of Y-shaped seals indicate that startup friction is not significantly related to stopping time, which distinguishes it from O-rings.
6. This is highly beneficial for machinery with intermittent motion. Additionally, when the internal pressure is low, the starting friction increases with the rise of internal pressure. However, once the internal pressure exceeds 5 MPa, the starting friction becomes independent of the internal pressure. Therefore, for high-pressure intermittent machinery, there is no issue of excessive starting friction. After the sealing lip wears, due to the action of the medium pressure, the lip has a certain degree of automatic compensation capability.
Common Material Medium
Y-shaped seals are commonly made of polyurethane rubber, which offers excellent sealing performance, a long service life, and high working pressure limits when used with different retaining rings.
For example, with common Y-shaped ring materials such as nitrile rubber, fluoro rubber, and polyurethane rubber.
Nitrile rubber's oil resistance improves with increased Acrylonitrile content. Generally, it exhibits excellent resistance to fuel oils and aromatic solvents, but is not resistant to ketones, esters, and halogenated hydrocarbons.
Fluorinated rubber is generally superior to nitrile rubber, boasting outstanding heat and oil resistance properties.
Polyurethane rubber boasts excellent wear resistance and good airtightness, with moderate temperature resistance and only medium oil, oxygen, and ozone aging resistance. It is not resistant to acids, bases, water, steam, and ketones.
In summary, it depends on the material you choose for the Y-shaped ring.
Recommend fluoro rubber, with nitrile rubber as a secondary option; of course, the former has better performance but is also slightly more expensive!
Appendix: Comparison of performance parameters between the two
