Developed Measuring Methods for Hydraulic Fluid Dynamics and Viscosity at Extreme Pressures and Temperatures

Hydraulic fluid is one of the most important components in every fluid power system. Therefore, fluid properties have to be known with a good accuracy in an increasing number of applications, for example in system’s design, modelling and control. The fluid of interest may be a power transmission fluid as well as a fuel. In defining the needed fluid characteristics, the large variety of different fluid types sets many demands for a single measuring system. Moreover, known fluid properties, of fuels in particular, are needed at constantly higher pressures and temperatures, raising the bar for practical measuring concepts — user-friendliness, safety and equipment cost are also essential criteria. In this paper, two accurate, but rather simple and affordable measuring concepts are presented. The speed of sound in a fluid, hydraulic fluid density and adiabatic tangent fluid bulk modulus are all defined with a direct measurement of the pressure wave propagation. The dynamic and kinematic fluid viscosities are defined with a remotely operated, modified falling ball viscometer. Both the presented methods have been developed further from the previously published concepts of the same authors. With these improved systems, all the mentioned fluid parameters can reliably be measured at up to at least 2,500 bar and at up to at least +150°C. Moreover, the same equipment can be applied to any type of hydraulic fluid, a fuel or a power transmission fluid, regardless of the base fluid, additives or viscosity grade. In addition to presenting the measuring concepts and the equipment used in detail, a selected sample of experimental results will also be presented to demonstrate the performance characteristics of the methods.