1、 Definition of Lip Seal
A lip seal is a sealing element, usually made of elastic material. It has the shape of a lip and fits tightly with the interface of mechanical equipment to prevent media leakage. The name of the lip seal comes from its shape, similar to human lips.
Lip Seal Overview
A lip seal is a self-sealing function; it relies on the lip to be close to the sealing surface, blocking the leakage channel and obtaining a sealing effect. The working pressure of the lip seal is the sum of the pre-compression force and the fluid pressure. When the pressure of the medium to be sealed increases, the lip is propped up and fits more closely to the sealing surface; thus, the sealing is further enhanced: in addition, the lip edge has the function of scraping the oil, which enhances the sealing performance of the lip seal. The representative lip sealing ring can be divided into Y-ring, V-ring, U-ring, L-ring, J-ring, and X-ring according to the shape of the cross-section.
Y-ring: Simple and compact structure, strong resistance to root wear, more stable working position. A support ring is required only when the pressure fluctuates wildly. A blocking ring should be added when high pressure is applied.
V-ring: Multiple overlapping uses, high-pressure resistance, long service life, but friction resistance, large size; installation and adjustment are more complicated. They are widely used in high-pressure systems, especially for high-pressure, large diameters, long strokes, and other harsh conditions.
U-ring: Simple structure, low coefficient of friction. They are used for low-speed reciprocating motion seals.
L-ring: For small diameter, low pressure piston seals.
J-shaped ring: Piston rod seals for low pressure.
X-ring: The X-sealing ring is a four-lip seal; the shape is similar to X, also known as X-ring. It is based on the performance of the 0-shaped ring and made improvements and enhancements; its standard size is ultimately the same as the American AS 568 standard-shaped ring. It can replace most of the 0-ring occasions. Compared with the 0-shaped ring, due to the star sealing ring in the sealing lip between the formation of lubrication cavity, with minor friction resistance, start resistance; because of its fringe position in the section of the concave, the sealing effect is good; non-circular cross-section, to avoid rolling in the reciprocating movement.
X-ring seal has a wide range of applications. The appropriate material is selected according to temperature, pressure, and medium. The mutual constraints between all operating parameters should be considered to adapt the star seal as a sealing element to a given application. When determining the application specification, the peak temperature, the continuous operating temperature, and the operating cycle must be considered. The temperature rise due to frictional heat must also be considered in rotating applications. X-ring mechanism: The star seal is a self-tightening, double-acting sealing element. The radial and axial force depends on the pressure of the system; with the compression, the deformation of the star seal ring will increase, and the total sealing force will increase to form a reliable sealing against the rising pressure.
2， The characteristics of the lip seal ring
1. Good elasticity: Lip seals are usually made of rubber and other elastic materials, can be well adapted to the shape of the interface of mechanical equipment, and play a good sealing effect.
2. Wear-resistant and corrosion-resistant: lip sealing ring material usually has a specific wear-resistant and corrosion-resistant performance, can be used in various harsh operating environments, and maintains long-term stability.
3. Easy to install: Lip Seal is straightforward to install; insert it into the interface of the mechanical equipment without using tools.
Lip seals are mainly used in reciprocating seals. Compared with extruded seals like 0-shaped seals, reciprocating seals using lip seals have better overall performance and longer service lives.
The sealing compression force of the lip seal is changed with the change of medium pressure, and it should permanently be altered according to the shift in medium pressure in the work; that is to say, it can guarantee enough sealing compression force and not produce too big a friction force. Extruding type seal mainly relies on pre-pressure to produce sealing force; the contact pressure of the sealing ring is given in advance, and it cannot be changed according to the change of medium pressure in the work if it is required to seal a tremendous pressure. The pre-pressure must be very large, and a large pre-pressure will increase the sealing ring, the sealing surface contact stress, and the contact area. Generate a considerable friction resistance. Excessive friction can cause seal breakage, causing starting difficulties at low pressures or creeping phenomena. Lip seals can compensate for the small amount of wear and tear by lip bracing and deformation to ensure the sealing effect and sealing life, while the 0 ring with the reduction of friction margin directly affects its sealing.
In addition, a 0-shaped ring in reciprocating motion sealing is prone to tumbling, torsion, and other phenomena; lip seal tumbling and torsion phenomena are less noticeable.
The main disadvantage of lip seals compared to 0-shaped seals is that they can only be used as one-way seals, and if they are to be used as bi-directional seals, two seals have to be used, which increases the length of the seal: the groove is difficult to design, and oil trapping between the two seals can cause damage from back-pressurization: whereas pre-pressurized seals have a symmetrical cross-section shape, can be used as bi-directional seals, and have a smaller volume and an easy groove design.
Based on the above comparison, in the case of allowing a small amount of leakage, extruded seals can reduce the size of the groove. In the case of high sealing performance requirements, it is necessary to use a lip seal with better overall performance.
Characteristics Of Lip Seals Ror Reciprocating Seals
| O-ring (extruded seal) | Y-Seal (Lip Seal) | |
| Avantages | A small sealing ring cross-section size mounting groove can be designed as an integral groove, allowing for easy groove processing and sealing ring mounting.Bi-directional sealing (for double pressure) | Good sealing, low-pressure friction, minor wear and tear can be automatically compensated, and long service life. |
| Disadvantages | Poor sealing is prone to tumbling and torsion, resulting in breakage of low-pressure friction. When the friction is significant, the friction margin decreases, directly affecting the sealing properties. | Unidirectional function: sealing bidirectional fluid needs to use a pair of seals, and the sealing structure is complex and extensive. Trapped oil between the two seals may result in backpressure breakage. The seal ring section size is large, and groove processing is complicated to open the split installation groove. |
| Main use | Small size slide valve allows small leakage of piston and rod seals | Suitable for sealing pistons and piston rods with high requirements for comprehensive sealing performance. |
3、The application of lip seal ring
Lip seals can be widely used in various mechanical equipment, such as automobiles and industrial equipment. It is usually used to play a sealing role to prevent media leakage, but it also can play a role in absorbing vibration, reducing noise, and so on.
4， The lip seal maintenance method
Lip seals in ordinary use need to pay attention to maintenance to avoid wear and aging in use. Its maintenance methods include often checking the state of the lip seal and timely replacement of the aging seal to prevent damage to use.
In short, the lip seal is widely used in various mechanical equipment in the sealing element. It can play a good sealing role in preventing media leakage with good elasticity, wear and corrosion resistance, easy installation, and other characteristics. When in use, it is necessary to pay attention to maintenance and timely replacement of aging seals to ensure the regular operation of mechanical equipment.
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