Analysis of a proportional control valve flow coefficient with the usage of a CFD method

The main objective of this article is to analyse flow coefficient of a proportional directional valve with integrated spool position controller. The valve geometry has been modified by creating additional undercuts on the spool, which provide improtied flow characteristics, especially at low flow rates. The analysis consisted of two phases, including computer simulations and test bench experiments. At first, flow through the valve was simulated by the means of CFD method in ANSYS/Fluent software, assuming the fixed spool positions. Based on the results, flow coefficient values were determined. The results showed, that in the examined gap width range, the coefficient value is mainly related to the spool position, and to a lesser extent to the volumetric flow rate. Hence, a proposal to formulate the flow coefficient value as a function of spool position or spool position and flow rate was made. Three approximating functions were determined in Matlab system on the basis of the obtained CFD results: a linear curve is mu = f (x(g)), as well as a linear polynomial surface and a quadratic polynomial surface mu = f (x(g), Q). Next, the results were verified by experiments conducted at a test bench. The best fit flow coefficient function was then used in the subsequent simulations on a multi-actuator system comprising three parallel-connected valves supplied by a single pump. In this case, each valve was set a different fixed spool position, which resulted in a different throttle gap width. Analysis of the system was carried out using an own-developed computer software for solving the analytical equations. Finally, the results were compared to those obtained by means of a CFD method, and a satisfactory compliance was achieved.