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Buy your travel insurance here

Geoff At Home
I have spent a lot of my career in the hydraulics (fluid power) industry: enough to realise that no matter how complex or shiny the pump, system or machine may be, the most complex component is the fluid. Normally in hydraulics, the fluid is only noticed when it forms a puddle on the ground under the machine due to some misfortune. This is a shame because the fluid represents the greatest single cumulative R&D investment and the greatest economy of scale of any system component, and it performs the most critical functions in the most mysterious and intriguing ways. It is also, potentially, the most sensitive part of the system to harm, and any damage or contamination of the fluid will have rapid consequences for all the other system components.



Hydrostatic systems transfer power by the compression of a fluid to a high pressure by a pump and the release of this pressure by friction or transfer out of the system by motors and other components. Tribologically, the fluid lubricates and cools a diverse array of sliding and rolling interfaces that are all completely hidden from view.



Most hydraulic machines go for long periods of operation or rest with no thought given to the fluid level or condition: it tends to be a topic that most end users are simply happy to react to when an extreme condition is reached. In a research and development context, however, consistent and correct fluid condition is critical to ensuring stability and repeatability of tests. Small changes in the friction or wear of an interface can be sufficient to determine a "pass" or "fail" result, yet such results can easily be produced not only by the adjustments to loading, geometry, surface finish or other parameters deliberately under test, but also by the loss of a few centistokes due to non-reversible shear-thinning, the increase in water contamination above some critical level or the depletion of the fluid "additives" which are the main embodiment of the oil companies' R&D investment in this product.



In hydraulics research and development, therefore, the routine monitoring of fluid condition is essential. In my opinion, it should simply be regarded as a form of travel insurance. It can be a chore to set up, it carries a small cost, and most of the time it is not needed as this month's results turn out to be identical to last month's. However, every so often, it will prove itself as an investment that pays back. Perhaps this would be by the identification of a negative trend on a certain key parameter, or maybe it would simply enable the inclusion of a simple statement of "fluid properties within specification" in a test report to a key customer - in my experience the customers that are most worth having appreciate seeing such a statement before they have to ask for it.



So before I embark on the voyage of discovery that will be my next R&D test of a hydraulic component or system, my travel insurance checklist looks like this:


  • Kinematic viscosity at 40°C and 100°C (cSt)


  • Acidity (TAN)


  • Water (ppm)


  • Additive elements: Ba, Ca, Mg, P, Zn (ppm)


  • Contamination and wear metals (ppm)


  • Contamination count (per ISO 4406: 1999)


  • Visible debris, appearance, colour etc. (descriptive)

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