Common Types Of Hydraulic Cylinder Seal Rings
The seal rings commonly used in hydraulic cylinders include the following types: dust seals, piston rod seals, buffer seals, guide support rings, end cover seals piston seals, etc.
1. Dust ring
The dust ring is installed on the outside of the hydraulic cylinder end cover to prevent external contaminants from entering the cylinder. According to the installation method, it can be divided into snap-in type and press-in type.
■Basic form of snap-in dust ring
The snap-in dust ring is the most common. As the name suggests, the dust ring is stuck in the groove on the inner wall of the end cover and is used in less harsh environmental conditions. The material of the snap-in dust ring is usually polyurethane, and there are many variations in structural forms, such as H and K-shaped cross-sections with double-lip structures, but they remain the same.
■ Some variations of snap-in dust rings
Press-in dust wipers are used under harsh, heavy-load conditions. They do not get stuck in the groove. Instead, the polyurethane material is wrapped with a layer of metal to increase strength and is pressed into the hydraulic cylinder end cover. Press-in dust rings also come in many forms, including single-lip and double-lip.
2. Piston rod sealing ring
The piston rod seal, also called a U-cup, is the main piston rod seal and is installed inside the hydraulic cylinder end cover to prevent hydraulic oil from leaking. The piston rod sealing ring is made of polyurethane or Buna-N rubber. In some cases, it needs to be used together with a support ring (also called a retaining ring). The support ring is used to prevent the sealing ring from extrusion deformation under pressure. Rod seals also come in many variations.
3. Buffer sealing ring
Buffer seals serve as auxiliary piston rod seals to protect the piston rod when system pressure suddenly increases. There are three common types of buffer seals. Type A is a one-piece seal made of polyurethane. Types B and C are two-piece and are used to prevent seal extrusion and allow the seal to withstand higher pressures.
4. Guide support ring
The guide support ring is installed on the end cover and piston of the hydraulic cylinder to support the piston rod and piston, guide the piston to move linearly and prevent metal-to-metal contact. Materials include plastic, Teflon-coated bronze, etc.
5. End cover sealing ring
The end cover sealing ring is used to seal the cylinder end cover and the cylinder wall. It is a static seal used to prevent hydraulic oil from leaking from the gap between the end cover and the cylinder wall. Usually made of nitrile rubber. It is composed of a shaped ring and a support ring (back-up ring).
6. Piston sealing ring
The piston sealing ring is used to isolate the two chambers of the hydraulic cylinder and is the main seal in the hydraulic cylinder. Usually two-piece, the outer ring is made of PTFE or nylon, and the inner ring is made of nitrile rubber. There are also variations, including Teflon-coated bronze, among others. On single-acting cylinders, polyurethane U-shaped cups are also used.
In Conclusion
The reason why hydraulic cylinders need to be sealed is because of internal and external leakage. When internal or external leakage occurs in a hydraulic cylinder, the cavity volume of the hydraulic cylinder will become smaller and the efficiency will become lower, thereby reducing the performance of the hydraulic cylinder during operation. When the situation is severe, the system pressure will not rise and it will be unable to continue working.
At the same time, from the perspective of environmental protection, leakage should be avoided as much as possible, and it is very important to take necessary sealing measures. Therefore, the hydraulic cylinder seal rings can prevent liquid or gas leakage and prevent external impurities from entering the sealing area, thereby ensuring the normal operation and reliability of the system.
