Modeling and Experimental Validation of Disc and Reed Style Check Valves for Hydraulic Applications

Abstract

The goal of this thesis is to develop a computationally inexpensive, accurate, and practical mathematical model of a hydraulic reed style check valve. While the modeling of disc style check valves is well represented in literature, reed valve modeling research has focused on applications in air compressors and internal combustion engines, where the working fluid has low density, viscosity, and bulk modulus. However, in a hydraulic system, the fluid – namely oil – is dense, viscous, and stiff, contributing additional physical effects that must be considered. Furthermore, the operating pressure in hydraulic systems is higher than in pneumatic systems, creating additional challenges from a structural perspective. In this thesis, a one degree of freedom hydraulic disc and reed style check valve model were developed using a hybrid analytical, computational, and experimental approach. The disc valve equation of motion was derived from Newton’s second law applied to the disc considering forces including pressure, spring reaction, and drag. Euler- Bernoulli beam theory was used to derive the reed valve equation of motion. In each case, the valve flow rate was modeled as quasi-steady orifice flow using an empirical discharge coefficient. A non-contact method of experimentally measuring check valve position during operation using a laser triangulation sensor (LTS) was developed. An acrylic viewing window was installed in the check valve manifold to allow optical access. To precisely measure position through air, acrylic, and oil, refraction of the laser light was accounted for using Snell’s law. Finally, the disc and reed valve models were validated in the context of a single cylinder hydraulic piston pump across a range of operating conditions. Pump delivery, which is a measure of volumetric efficiency, and check valve position were chosen as the validation metrics. Experimental results showed that both the disc and reed check valve model accurately predicted the timing of valve opening and closing. The disc valve model predicted pump delivery within 5% of measured values for all cases while the reed valve model predicted pump delivery within 3% of measured values for all cases.