Whenever I present hydraulic maintenance training, a concept I
always enjoy explaining to my students is what I call the
perfect hydraulic fluid. And it’s very simple. The perfect
hydraulic fluid would have a viscosity index (the change in a
fluid’s viscosity relative to temperature) represented by a
horizontal line intercepting the Y axis at 25 cSt, Exhibit 1.
Exhibit 1. Temperature-viscosity diagram of the perfect
hydraulic fluid. Of course, no such fluid exists and I don’t
expect that such a fluid will be developed in my lifetime. But
if such a fluid was developed, its creator would have the key to
a gold mine. Exhibit 1. A perfect fluid’s viscosity index would
be represented by a horizontal line intercepting intercepting
the Y axis at 25 cSt. Fluid viscosity is one of the factors that
determines whether full-film lubrication is achieved and
maintained. If load and surface speed remain constant, but
elevated operating temperature causes viscosity to fall below
that required to maintain a hydrodynamic film,