Common examples for electrostatic discharges can be encountered in everyday life. When approaching a grounded surface after walking on insulating flooring material or while riding an escalator one might experience an electrostatic discharge first hand. These discharges generally do not pose a problem but when translated to various fields of engineering, such as in hydraulics, discharges can be the root cause for system failures. The pioneering fields of engineering for electrostatic charging in systems are petro-chemistry and electrical engineering. Researchers in both fields attempted to formulate models to calculate the electrostatic charging a priori. These models provide some indication regarding the magnitude of charge but are currently not suited for the application in hydraulic systems. This is due to the lack of necessary fluid and material parameters for the application of either one of the models. [1, 2]
Previous work in the pioneering fields focused on fluids and materials typical for their respective applications. This paper seeks to take the first step to remedy this situation by developing and commissioning a test bench for investigating a wide variety of hydraulic fluid-material combinations. The fluids pending investigation range from a typical hydraulic fluid based on a group I base oil to a pure polyalphaolefine of group IV. Common materials for hydraulic systems are investigated with a small scale test bench as well, such as steel and brass common to hydraulic applications as well as plastics and rubbers. In order to conduct these investigations a Searle viscometer is presented in this paper. In a Searle viscometer the cylinder is rotating while the cup or pipe remains stationary.
Initially this paper gives the necessity for a small scale test bench using experimental results of an existing large scale test rig. Subsequently, the design of a small scale test bench, the Searle viscometer, will be presented along with a method for measuring the charge density. The small scale test bench is based on the work of Washabaugh and is able to generate the necessary information required for using the chemical reaction-based model [3, 4]. The main feature of the chemical reaction based model is the consideration for different material and fluid influences, beyond the scope of viscosity and system geometry.