Several factors affecting sealing performance
 

1. Speed

At very low speeds (<0.03m/s), consider the smoothness of the equipment's operation and whether any "creeping" occurs. At very high speeds (>0.8m/s), the lubricating oil film may be damaged, causing friction and heat generation due to poor lubrication of the oil seal, significantly shortening its lifespan.

Polyurethane or rubber-plastic oil seals are recommended for operation within the 0.03m/s to 0.8m/s speed range.

2. Temperature

Low temperatures can reduce the elasticity of polyurethane or rubber-plastic oil seals, causing leakage and even making the seal hard and brittle. High temperatures can cause the seal to expand and soften, rapidly increasing friction and reducing its pressure resistance during operation. The recommended continuous operating temperature range for polyurethane or rubber-plastic oil seals is -10°C to +80°C.

3. Operating Pressure

Oil seals have a minimum service pressure requirement. For low-pressure operation, low-friction, low-starting resistance oil seals are essential. Polyurethane oil seals are not suitable for pressures below 2.5 MPa. For high pressures, pressure deformation of the oil seal must be considered, requiring the use of anti-extrusion retaining rings and special groove processing requirements.

Furthermore, different oil seal materials have different optimal operating pressure ranges. The optimal operating pressure range for polyurethane oil seals is 2.5 to 31.5 MPa.

The effects of temperature and pressure on sealing performance are interrelated, so comprehensive consideration is necessary. See the table:
 

4. Working Fluid

In addition to strictly following the manufacturer's recommendations for selecting the working fluid, maintaining the fluid's cleanliness is crucial. Aging or contamination of the fluid not only causes component failure and accelerates the aging and wear of oil seals, but also can cause dirt to scratch or become embedded in the seals, rendering them ineffective. Therefore, it's crucial to regularly check the fluid's quality and cleanliness, and replace the oil filter or fluid according to equipment maintenance specifications. Air trapped in the fluid in the cylinder, when compressed under high pressure, can generate high temperatures and burn the oil seals, even carbonizing them. To prevent this, bleed the hydraulic system during initial operation. The hydraulic cylinder should also be operated at low pressure and slow speed for several minutes to ensure that all remaining air has been expelled before normal operation.

5. Lateral Loads

A support ring is generally required on the piston to ensure the cylinder can withstand heavy loads. Seals and support rings play completely different roles, and seals cannot replace the load-bearing characteristics of support rings. Hydraulic cylinders subject to lateral forces must be equipped with support rings with strong load-bearing capacity (metal rings can be used for heavy loads) to prevent leakage and abnormal wear of the oil seal under eccentric operation.

6. Hydraulic Shock

Hydraulic shock can be caused by many factors, such as an excavator bucket suddenly striking a rock or a crane lifting or lowering a heavy object. Besides external factors, high-pressure, high-flow hydraulic systems can also easily cause hydraulic shock when the actuator (hydraulic cylinder or hydraulic motor, etc.) switches direction, if the reversing valve is not performing properly. The transient high pressure generated by hydraulic shock can be several times the system operating pressure. Such high pressure can tear the oil seal or partially force it into the gap in a very short time, causing serious damage. Cylinders subject to hydraulic shock should generally have a buffer ring and retaining ring installed on the piston rod. The buffer ring is installed in front of the oil seal to absorb most of the impact pressure, and the retaining ring prevents the oil seal from squeezing into the gap under high pressure and causing the root to be damaged.