The lifeblood of a mobile hydraulic rig, its hydraulic fluid, keeps the system functioning like a great mechanical workhorse. Thanks to the forces stored in that oily fluid, the heavy equipment reliably moves bulky loads. The parts mesh with the oil to responsively direct that payload, and the operator loses himself in the work until the foreman calls time. Trouble is impending, though, for the oil’s viscosity is fluctuating.
What is Hydraulic Fluid Viscosity?
Here’s a critical fluid property that affects all valves and cylinders. If the oil thins, then the fluid becomes compressible, which leads to an equipment performance reduction. If the hydraulic oil is characterized by a higher than advised viscosity index, the pumps and valves won’t function properly. Even if the index is just slightly above the specified viscosity margins, the shear factor stored in this thick liquid will cause serious problems. Heat and premature component failures take over when a high VI Index strikes.
The Triple Consistency Factor
Ideally, the “thickness” or cohesiveness of the hydraulic oil should hit a sweet spot. Temperature changes and system fatigue incidents won’t impact this mythical oil. In reality, there are three indexed viscosity points appended to any high-end hydraulic fluid. There’s the minimum viscosity point, the optimum viscosity, and the maximum viscosity index. Like a unique fingerprint, these three factors alter as they’re charted on a graph, with the system temperature providing the greatest performance debilitating influence. As detailed earlier in this post, a viscosity rating that drops below the minimum viscosity margin will result in a thinner oil. Shorn of volumetric efficiency, the equipment powered by that watery oil becomes less responsive.
Penetrating the Maximum Index Ceiling
In this undesirable case study, the hydraulic system is choked with a glutinous oil. The mobile equipment is sluggish, so mechanical failures spread like wildfire. The pumps will work hard to inject energy into that overly thick oil, but energy consumption figures will likely skyrocket until the very act of running the gear becomes impossible. Even a once trouble-free startup operation sends waves of friction and shock through a machine frame when an unacceptably high hydraulic fluid viscosity index impacts the system.
The sweet spot is referred to as optimum viscosity. It’s a fluid thickness value that stabilizes the hydraulic system, maximizes control responsiveness, and keeps frictional issues under control. High VI products are, of course, available from sales outlets, while low viscosity issues usually arise due to a fluid breakdown event. The system temperature is a primary offender here, for the three critical viscosity values alter as equipment temperatures vary.
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