Modeling and Analysis of Spool Valves With Eccentric Clearance

Equations of motion of spool valves have been set up under ideal conditions without considering some important factors that may have a significant influence on dynamical behavior and performances of spool valves especially when valve sizes are small. In this paper, these factors are brought into considerations. One of them is the eccentric clearance existing between the spool and the sleeve of a valve due to fabrication errors. Another is the viscosity of a Newtonian fluid assumed to flow through the valve orifices, which generally results in shear forces acting on the valve spool. This paper discusses how equations of motion of spool valves are derived and solved with considerations of these factors. Concepts of Poiseuille flow and Couette flow are utilized to obtain axial forces acting on the valve spool. The resulting equations of motion of spool valves have the simple form of a second order linear ordinary differential equation under the imposed idealizations. The influences of these factors on the motion behavior of spool valves are in turn discussed.