How many types of sealing rings are there?

Buffer Sealing ring
The buffer Sealing ring serves as an auxiliary piston rod sealing ring to protect the piston rod in the event of a sudden increase in system pressure. There are three common types of buffer sealing rings. Type A is a single piece sealing ring made of polyurethane. The B and C types are two-piece, used to prevent Seal compression and allow the seal to withstand higher pressure.
Several common forms of buffer sealing rings
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 in a straight line, and prevent metal to metal contact. The materials include plastic, bronze coated with polytetrafluoroethylene, etc.
Guide support rings for hydraulic cylinder end caps and pistons, respectively
End cover sealing ring

The end cap sealing ring is used to seal the end cap and cylinder wall of the oil cylinder. It is a static seal used to prevent hydraulic oil from leaking out from the gap between the end cap and cylinder wall. Usually composed of nitrile rubber O-rings and support rings (retaining rings).

Piston Sealing ring
The piston sealing ring is used to isolate the two chambers of the hydraulic cylinder and is the main seal inside the hydraulic cylinder. Usually two piece, the outer ring is made of polytetrafluoroethylene or nylon, and the inner ring is made of nitrile rubber. There are also various variants, including the use of bronze coated with polytetrafluoroethylene, and so on. On single acting cylinders, polyurethane U-shaped cups are also used.
Dust ring
The dust ring is installed on the outer side of the hydraulic cylinder end cover 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.
Basic form of snap in dust ring
The most common type of dust ring is the snap in type. 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 various variations in its structural form, such as the double lip structure of the H and K sections, but it never changes.
Press-in dust ring
The pressure type dust ring is used under harsh and heavy load conditions, not stuck in the groove, but wrapped with a layer of metal outside the Polyurethane Material to increase strength, and pressed into the hydraulic cylinder end cover. There are also various forms of pressed in Dust Seals, including single lip and double lip.
Piston rod sealing ring
The Piston Rod Seal ring, also known as a U-shaped cup, is the main piston rod seal installed on the inside of the hydraulic cylinder end cover to prevent hydraulic oil leakage. The piston rod sealing ring is made of polyurethane or nitrile rubber, and in some cases, it needs to be used together with a support ring (also known as a retaining ring), which is used to prevent the sealing ring from being squeezed and deformed under pressure. There are also various variants of piston rod sealing rings.
Engineering machinery cannot do without oil cylinders, and oil cylinders cannot do without seals. A common sealing element is a sealing ring, also known as an Oil Seal, which serves to isolate oil and prevent it from overflowing or passing through.
The common types of sealing rings used for hydraulic cylinders include dust rings, piston rod sealing rings, buffer sealing rings, guide support rings, end cover sealing rings, and piston sealing rings.