Introduction

Construction machinery is inseparable from Oil Cylinders, and oil cylinders are inseparable from seals. A common seal is a sealing ring, also called an oil seal, which isolates oil and prevents it from overflowing or passing through.

Common types of seals used in Hydraulic Cylinders include dust wipers, piston rod seals, buffer seals, guide support rings, end cover seals and piston seals.

alt. Guide Support Ring

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.

(1) 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.

(2) The press-in dust ring is used under harsh and heavy-load conditions. It does 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.

Piston Rod Seal

The piston rod seal, also known as the 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 nitrile 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 being extruded and deformed under pressure. Rod seals also come in many variations.

alt.Piston Rod Sealing Ring

Buffer Seal

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.

Guide 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.

End Cover Seal

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 composed of nitrile rubber O-ring and support ring (back-up ring).

Piston Seal

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 Teflon 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.

Summary

The sealing system of the hydraulic cylinder is a precise and complex system. The six sealing elements each perform their own duties and cooperate with each other to ensure the reliable operation of the hydraulic system. From the first line of defense of the wiper to the inner core seal of the piston seal, every step is critical. With the advancement of material science and the continuous innovation of sealing technology, modern hydraulic seals are developing towards higher performance, longer life and stronger environmental adaptability. An in-depth understanding of the characteristics and applications of these seals will not only help in the correct selection and installation of seals, but also provide an important basis for the maintenance and fault diagnosis of hydraulic equipment, ultimately ensuring the efficient and stable operation of the entire hydraulic system.