According to the provided data, the most common failure types of hydraulic cylinders (HCs) include internal leakage, external leakage, seal wear, and the "crawling" phenomenon of hydraulic actuators.
The specific types of these failures and their causes are as follows:
Internal Leakage (IL)This is the most typical failure of hydraulic cylinders, referring to the unintended loss of fluid between the internal chambers of a cylinder.
Main causes:
Seal failure: This is the most common cause. Seals (such as piston seals, rod seals, etc.) may wear, harden, crack, or develop gaps due to prolonged use.
Component wear: Excessive clearance caused by wear between the piston and the cylinder barrel.
Physical damage: Scratches and seal failure are recognized as major causes of internal leakage.
Assembly and pressure issues: Poor assembly or horizontal lateral forces causing axis distortion; or operating pressure exceeding design limits, accelerating seal degradation.
Temperature effects: Extreme high temperatures may soften or decompose seals, while extremely low temperatures make them brittle.
External Leakage (EL)This refers to fluid escaping from the interior of the hydraulic cylinder to the external environment, which reduces system performance and poses safety risks.
Main causes:
Damaged seals: The most common cause is damage or wear to rod seals, piston seals, or wiper seals.
Environmental contamination: Dust, debris, and other contaminants entering the sealing mechanism impair sealing effectiveness.
Physical damage: Dents, scratches, or cracks on the exterior of the hydraulic cylinder compromise sealing integrity.
Corrosion: Moisture or contact with corrosive substances (e.g., chemicals, seawater) on the cylinder's outer surface leads to seal failure or surface abnormalities.
Seal FailureSeal failure is the primary cause of hydraulic cylinder leakage and manifests in various forms:
Seal wear: Accelerated by long-term use, insufficient lubrication, improper assembly, or particulate matter (e.g., dust) in the hydraulic fluid.
Seal hardening: Natural material aging over time, or prolonged exposure to UV radiation, chemicals, and extreme temperatures, resulting in loss of elasticity.
Scarring: Abrasive particles in the fluid or foreign matter entering the cylinder scratch the seals and their mating surfaces.
Hydraulic Actuator CrawlingCharacterized by slow, uneven movement of the piston or piston rod without external commands.
Main causes:
Air entrainment in fluid: This is the main cause of crawling. Air increases fluid compressibility, leading to vibration and unstable movement.
Worn valve components: Wear in valve parts increases clearances, causing high-pressure oil to leak to the low-pressure side.
Insufficient supply: Inadequate fluid supply or pressure resulting in degraded performance.
Abnormal viscosity: Excessively high viscosity due to cold hydraulic oil, or extreme temperatures impairing seal performance.
Wear and Corrosion of Other Components
Wear of other components: Metal parts such as the cylinder barrel and piston rod also experience wear due to friction, especially when external fine particles (e.g., sand and dust) enter the system, causing abrasive or fatigue wear.
Corrosion: Moisture entering the hydraulic cylinder due to external leakage or other causes oxidizes metal surfaces; the resulting corrosive particles further accelerate wear on seals and the cylinder barrel.
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