The most common causes of hydraulic system failures are:
• Clogged and dirty oil filters
• An inadequate supply of oil in the reservoir
• Leaking seals
• Loose inlet lines, which cause pump cavitations and eventual pump damage
• Incorrect type of oil
• Excessive oil temperature
• Excessive oil pressure.
A majority of these problems can be overcome through a planned preventive maintenance regime. The overall design of the system is another crucial aspect. Each component in the system must be properly sized, compatible with, and form an integral part of the system. It is also imperative that easy access be provided to components requiring periodic inspection and maintenance such as strainers, filters, sight gages, fill and drain plugs and the various temperature and pressure gages. All hydraulic lines must be free of restrictive bends, as this tends to result in pressure loss in the line itself.
The three maintenance procedures that have the greatest effect on system life, performance and efficiency are:
1. Maintaining an adequate quantity of clean and proper hydraulic fluid with the correct viscosity
2. Periodic cleaning and changing of all filters and strainers
3. Keeping air out of the system by ensuring tight connections.
A vast majority of the problems encountered in hydraulic systems have been traced to the hydraulic fluid, which makes frequent sampling and testing of the fluid, a vital necessity. Properties such as viscosity, specific gravity, acidity, water content, contaminant level and bulk modulus require to be tested periodically. Another area of vital importance is the training imparted to maintenance personnel to recognize early symptoms of failure. Records should also be maintained of past failures and the maintenance action initiated along with data containing details such as oil tests, oil changes, filter replacements, etc.
Oxidation and corrosion are phenomena which seriously hamper the functioning of the hydraulic fluid. Oxidation which is caused by a chemical reaction between the oxygen present in the air and the particles present in the fluid, can end up reducing the life of the fluid quite substantially. A majority of the products of oxidation are acidic in nature and also soluble in the fluid, thereby causing the various components to corrode.
Although rust and corrosion are two distinct phenomena, they both contribute a great deal to contamination and wear. Rust, which is a chemical reaction between iron and oxygen, occurs on account of the presence of moisture-carrying oxygen. Corrosion on the other hand is a chemical reaction between a metal and acid. Corrosion and rust have a tendency to eat away the hydraulic component material, causing malfunctioning and excessive leakage.