Determination of Discharge Coefficient in an Orifice Created by Spool and Three Different Poppet Types in the Hydraulic Control Valves

In mathematical modeling and design of hydraulic systems, it is very important to determine the flow rate through control valves on the basis of discharge coefficient and also the orifice cross section created in the valves. Although the discharge coefficient depends on the oil flow type through the orifice, it is usually assumed as constant in hydraulic valves. Thus, in this paper, the discharge coefficient of orifice created by spool and three conventional poppet types in hydraulic valves were examined experimentally. Then, based on the experimental data, the curve fitting of discharge coefficient versus square root of Reynolds number was extracted for four types of orifice created by the moving members including spool, cone, spherical and cylindrical. Curve assessment showed that the discharge coefficient in turbulent flow for all four types of moving members was constant, but in the laminar flow conditions, the discharge coefficient linearly varied by square root of Reynolds number for them. The discharge coefficient in turbulent flow conditions for the orifice created by spool was lower than the other moving members. While, the slope of the linear part of the discharge coefficient curve for this orifice was more than others.