Hints On Maintenance Of Hydraulic Fluid In The System

Hydraulic Fluid Changes
Good maintenance procedures make it mandatory to keep the hydraulic fluid clean. A daily, weekly or monthly log should be kept on the hydraulic fluid condition.

No hard and fast rules can be established for changing the fluid because of the great variety of operating conditions. However, we do know that when filter elements are replaced frequently, service life of a system increases. Periodic testing of the fluid by the supplier is recommended to confirm suitability for continued use and to establish the correct fluid and filter element replacement interval.

Some of the considerations affecting hydraulic fluid are: operating temperature, type of service, contamination levels, filtration, and the chemical composition of the fluid.

Fluid Recommendations
The basic recommendations for fluid are stipulated in the Hydraulic Fluid and Temperature Recommendations for Industrial Machinery in this catalog. The fluids recommended give the assurance of adequate wear protection and excellent chemical stability under the most adverse operating conditions.

On mobile applications, the viscosity grade of the fluid should be changed in spring and autumn as is done with automotive engines. Hydrostatic transmissions and control mechanisms may require a different viscosity fluid. Fluid requirements are normally outlined in the original equipment manufacturers operation and maintenance manuals.

Draining The System
The system should be started and fluid heated before draining. This will lower the time it takes to drain the system and allow impurities suspended in the fluid to be removed. It is desirable to remove all fluid from the system. Bleeding of the fluid at the lowest point in the system will help in most cases.

Systems which have accumulated deposits that were not removed during draining must be flushed with a light viscosity fluid. The fluid should contain a rust inhibitor to protect metal surfaces against rust formation after draining.

When hydraulic fluid is added to replenish the system, it should be pumped through a 25 micron filter. If such a filter is not available, a funnel with a fine wire screen (200 mesh or finer) can be used. It is important that fluid be clean and free of all substances which will cause improper operation.

Fluid Contamination – Causes and Effects
Contamination
A contaminated system can be the result of several factors; system design inadequate, poor maintenance of the system, poor housekeeping of the system and adverse operating conditions.

System Design Inadequate
– Reservoirs which cannot be cleaned.
– Breathers that permit abrasives inherent in the atmosphere to enter the system.
– Poor cylinder packing design (no wiper to clean dirt from the piston rod).
– Improper piston rod design (piston rods with poor wear characteristic).
– Improper valving (anti–cavitation checks omitted from cylinder circuits with rapid drop characteristics).
– Failure to provide adequate filtration.

Poor Maintenance of the System
– Improper and unclean practices when adding fluid to the system.
– Failure to clean breathers.
– Failure to change pitted cylinder rods and worn cylinder packings.
– Failure to use good cleanliness practices when changing system components.
– Failure to change filter cartridges and/or filter at proper intervals.
– Failure to purge debris from the system after a pump failure.

Poor Housekeeping of the System
Surgical cleanliness is not required, however, ordinary clean practices during assembly will pay off in increased service life of the equipment.

Excessive and improper use of pipe thread sealer on lines and gaskets in the system can cause pump failures. This is especially true when a type of sealer is used that hardens.

Another source of contamination is fittings, hoses and lines which are received from a vendor uncapped. The use of brazed or welded fittings, and unpickled steel plating can also contribute to the contamination.

Preparation of pipes, tubes and fittings in this catalog should be referred to and followed. This will lower the possibility of premature failure due to contamination of the system.

Adverse Operating Conditions
From experience, we have found that machines used in a very dusty atmosphere and in windy areas require special components. For example, heavy duty breathers, chrome plated piston rods, plus frequent changes of the filter cartridges are also required.

Effects of Contamination
Contamination affects all types of hydraulic equipment adversely. Precision high tolerance parts are very susceptible to the effects of contamination. Dirty fluid causes wear which accelerates leakage and the development of heat in a system. Heat lowers the lubricity of a hydraulic fluid and causes additional wear.

If a hydraulic pump or motor should fail, the system becomes contaminated. Remove the unit for repair. The reservoir must be drained, flushed, and cleaned. All hoses, lines, cylinders and valves should be inspected for wear and particles of the unit that failed. Flush all components of the complete system to remove metallic particles.

Replace filter elements. Dispose of the fluid removed from the system and fill the reservoir with clean hydraulic fluid. Install a new or rebuilt unit and start-up the system. Allow the system to run for a period of time to verify normal operation. Filter elements should be changed after 40 or 50 hours of operation. This guarantees that the system is essentially clean and free of any residue of the failed unit.

A very good reference catalog on contamination is available titled Vickers Guide to Systemic Contamination Control. This catalog describes types and sources for contamination, effects of types and sizes of particles, specifying contamination levels, selecting a filter, locating a filter, design steps and worked examples of fluid sampling analysis. Order catalog 561 from your local Vickers representative.