Construction machinery is inseparable from the oil cylinder, and the oil cylinder cannot be separated from the seal. A common seal is a sealing ring, also called an oil seal, which acts to isolate the oil and prevent the oil from overflowing or passing through.
Common sealing rings used in hydraulic cylinders are of the following types: dust ring, piston rod sealing ring, buffer sealing ring, guide support ring, end cover sealing ring and piston sealing ring.
 

Dust ring
The dust-proof ring is installed on the outside of the end cover of the hydraulic cylinder to prevent external contaminants from entering the cylinder. According to the installation method, it can be divided into a snap-in type and a press-in type.
 

 

Basic form of snap-in dust ring
The snap-in dust ring is more 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 variants of the structure. For example, the H and K cross-sections have a double-lip structure, but they are inseparable.
 

Press-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 of the polyurethane material and pressed into the end cover of the hydraulic cylinder. There are also many types of press-in dust rings, which are also divided into single lip and double lip.
 

Piston rod seal
The piston rod seal is also called a U-shaped cup, which is the main piston rod seal, installed on the inside of the hydraulic cylinder end cover, to prevent the hydraulic oil from leaking. The piston rod sealing ring is made of polyurethane or nitrile rubber. In some cases, it needs to be used with a support ring (also called a retaining ring). The support ring is used to prevent the sealing ring from being squeezed and deformed under pressure. There are also many variants of piston rod seals.
 

 

Common forms of piston rod seals
 

 

Some variants of piston rod seals

Buffer seal
The buffer seal is used as an auxiliary piston rod seal to protect the piston rod when the system pressure suddenly increases. There are three common types of buffer seals. Type A is a single-piece sealing ring made of polyurethane. Type B and Type C are two-piece, used to prevent seal extrusion and allow the seal to withstand higher pressure.
 

 

Several common forms of buffer seals

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. There are plastics, bronze coated with PTFE, etc. on the materials.
 

Guide support ring for hydraulic cylinder end cover and piston respectively
 

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 to prevent hydraulic oil from leaking from the gap between the end cover and the cylinder wall. Usually consists of a nitrile rubber O-ring and a support ring (retaining ring).

 

Piston seal
The piston seal 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 many variants, including the use of bronze coated with PTFE, and so on. On single-acting cylinders, there are also polyurethane U-shaped cups.
 

Several common forms of piston seals