The common seal is the seal ring, also known as the oil seal, which can isolate the oil and prevent the oil from overflowing or passing through.
Here, we have sorted out the types and forms of some common oil cylinder sealing rings.
Fig. 1 Sealing rings.
The common sealing rings used in hydraulic cylinder are as follows: dust ring, cylinder rod sealing ring, buffer seal ring, guide support ring, end cover seal ring and piston seal ring.
Fig. 2 The position of different seal rings.
The dust ring is installed on the outside of the end cover of the hydraulic cylinder to prevent external pollutants from entering the cylinder.
According to the installation method, it can be divided into snap-in type and press-in type.
Fig. 3 Basic form of snap-in dust ring.
Snap-in type dust ring is the most commonly used type.
As the name suggests, the dust ring is stuck in the groove of the inner wall of the end cover, which is used in less harsh environmental conditions.
The material of the snap-in dustproof ring is usually polyurethane, and there are many variations in its structure.
For example, the type H and K-sections are double-lip structure, but they remain essentially the same despite all apparent changes.
Fig. 4 Some variants of snap-in dust ring.
The press-in dust ring is used under severe and heavy load conditions.
It is not stuck in the groove, but is wrapped with a layer of metal to increase the strength and pressed into the end cover of the hydraulic cylinder.
There are many types of the press in dust rings, including single lip and double lip.
Fig. 5 Press in dust ring and some variants.
2. Cylinder rod sealing ring
Cylinder rod sealing ring, also known as u-cup, is the main piston rod seals, which is installed inside the end cover of hydraulic cylinder to prevent hydraulic oil leakage.
The cylinder rod seal ring is made of polyurethane or nitrile rubber.
In some cases, it needs to be used together with the support ring (retaining ring).
The support ring is used to prevent the seal ring from extrusion deformation under pressure.
There are also many variants of cylinder rod sealing rings.
Fig. 6 Common types of cylinder rod seal ring.
Fig. 7 Some variants of cylinder rod sealing rings.
3. Buffer seal ring
As an auxiliary piston rod seal ring, the buffer seal ring is used to protect the piston rod when the system pressure suddenly increases.
There are three common types of buffer seals.
Type A is a single-sealing ring made of polyurethane.
Type B and type C are two-piece type, which are used to prevent seal extrusion and allow the seal to bear higher pressure.
Fig. 8 Common types of the buffer seal ring.
4. Guide support ring
The guide support ring is installed on the end cover and piston of the hydraulic cylinder, which is used to support the piston rod and piston, guide the piston to do linear motion, and prevent metal to metal contact.
The materials are plastic, bronze coated with polytetrafluoroethylene, etc.
Fig. 9 Guide support ring used on the end cover of the hydraulic cylinder and the piston.
5. End cover sealing ring
The end cover seal ring is used to seal the cylinder end cover and the cylinder wall.
It is a static seal to prevent the leakage of hydraulic oil from the gap between the end cover and the cylinder wall.
It is usually composed of NBR O-ring and support ring (retaining ring).
Fig. 10 End cover sealing ring.
6. Piston sealing ring
The piston seal ring is used to isolate the two chambers of the hydraulic cylinder and is the main seal in the hydraulic cylinder.
It is usually two-piece, the outer ring is made of PTFE or nylon, and the inner ring is made of NBR.
There are also a variety of variants, including the use of bronze coated with polytetrafluoroethylene, and so on.
Polyurethane u-cup is also used in single-acting oil cylinder.
Fig. 11 Common types of the piston seal ring.