Anatomy of a hydraulic maintenance failure

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Would you part with $50 to save $70,000? This is a 'no-brainer' for most of us. Well, here's a story for you:

I recently conducted failure analysis and a reliability audit on a 300 kilowatt hydrostatic transmission. The hydraulic system was running a synthetic ester, biodegradable hydraulic fluid. This $45/gallon hydraulic fluid had been destroyed in under 12 months and a set of pumps shortly after. So with $20,000 of hydraulic fluid and $50,000 of pumps ruined in short order, my client was understandably wondering what went wrong.

The system was built and installed by a reputable distributor. From a hydraulic engineering perspective the circuit was adequately designed and the system well built. But from a maintenance and reliability perspective it left a lot to be desired. My client, the end user, didn't have a lot of experience with hydraulic equipment and was reliant on the company that built the system to guide them on its maintenance.

An oil analysis program had been set up, but it seems the only thing anyone was taking any notice of was particle contamination. If you've been reading this newsletter for a while, you'll know there's a lot more to hydraulic equipment reliability than just monitoring and controlling hard particle counts.

All the warning signs pointing to oxidative failure of the oil went unnoticed. The oil started polymerizing, coating internal components with sludge. These gum-like deposits block lubrication passages, reduce heat transfer and cause valve stiction. The oxidation process diminishes foaming resistance and air release properties of the oil, which in turn causes damage through aeration and gaseous cavitation.

By the time I got involved, the original set of pumps had already failed and the hydraulic fluid had a TAN of 10 and water content of 6,500 ppm. So I set about establishing the root cause of failure and instigating measures to ensure it didn't happen again.

It's not rocket science. But the problem for my client was the information they needed to prevent this maintenance disaster is not widely available. You won't find it in the machine manual and it's not taught in everyday, how-it-works, hydraulics classes.

As a consequence, most owners, operators, mechanics, technicians and engineers are clueless when it comes to proper maintenance of hydraulic equipment. It's not their fault - they just haven't been given the opportunity to learn.

The principles I applied and the procedures I put in place to prevent a reoccurrence of the failures described above, are the same ones I outline in Preventing Hydraulic Failures. Had my client had this information and applied it diligently at the outset, they could have saved more than $70,000 - and a lot of downtime and aggravation.

Related articles:

How to tell if your hydraulic equipment is 'sick'
If you have to change your hydraulic oil - then do this
Hydraulic cylinder failure caused by the 'diesel effect'

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