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Helpful Technical Tips From the President of Applied Motion Technologies


TECHNICAL TIPS FOR WINTER 2009-2010

The only maintenance item in a hydraulic system —

Make the biggest single improvement in hydraulic system reliability and life by maintaining hydraulic fluid cleanliness and condition. About half of the hydraulic equipment users maintain proper fluid cleanliness and about half don't. Those that do not maintain proper cleanliness and condition routinely experience valve and pump failures.

It would not be unusual for standard spool type directional control valves to last for 15 years or more if fluid cleanliness and condition is properly maintained. Piston pumps can remain serviceable for 4 to 5 years or longer. Standard proportional valves can maintain good operational characteristics for 10 to 15 years, too.


What are the basic hydraulic fluid maintenance concepts and procedures we need to understand for modern industrial hydraulic systems?

1. Start with a goal of achieving ISO class 17/15/12 fluid cleanliness through the use of high efficiency 5 micron pressure filters and return line filters. This overall cleanliness level will work very well for most hydraulic systems.

2. Use high efficiency, 5 - 10 micron air filters for tank venting and get rid of the old screen breathers.

3. Develop methods to add hydraulic fluid to the tank/reservoir where the hydraulic fluid is filtered as it is being pumped into the tank - no more pouring fluid into the tank through breather holes.

4. Make sure that there are no (unfiltered) holes in the tank that are open to atmosphere.

5. Maintain maximum water content in the hydraulic fluid (mineral oil fluid) of less than .5% (1/2 of 1 percent) - the lower the water content the better. Water in mineral oil fluid promotes biological growth and produces low Ph (acidic conditions).

6. Prevent air cavitation - air that enters the suction port of the pump. Air promotes oxidation and break down of the fluid. Air can enter the pump through vortex action within the tank. Vortices can be produced by low tank levels or poor tank design. This results in the breakdown of the fluid through the formation of carbon soot/char.

7. Preheat the reservoir if necessary to prevent 'cold' startups. Depending upon the fluid type and its viscosity index minimum tank temperatures of approximately 60 degrees F. (or higher) should be provided at startup.

8. Cool the reservoir if necessary so that hydraulic fluid temperatures do not exceed 100 - 125 degrees F. depending upon the type of hydraulic fluid that is being used.

9. Sample the hydraulic fluid at regular intervals and have the fluid sample analyzed. The fluid report should contain both quantitative and qualitative information. That is, the report should show the overall cleanliness according to ISO 4406 (a 3 number cleanliness code as shown in #1 above). The report should make statements regarding the 'quality' of the fluid or how close the fluid sample is chemically to that brand and type of new fluid. Use this report to adjust your fluid maintenance routine as necessary.

10. Change fluid filters based on 'dirty' filter indicators and not by a schedule. Use high quality filter elements that are designed for the location in which they are used.


Don't have a fluid maintenance program? - Call us. We can help you with this work and we can design a specific fluid maintenance program that will improve hydraulic system reliability and longevity.