Experimental Studies on Steady-state Oil Flows through Restrictors

Abstract

When orifices and nozlzes are used in oil hydraulic lines, some of their characteristics come out more distinctly, owing to a high oil viscosity, than for less viscous fluids like water and gas. Taking advantgae of this fact, this paper intends to contribute toward the study of steady-state constriction flows, by conducting a few elementary measurements of oil flows through restrictors. In the first place pressures are measured on a pipe wall before and after a circular orifice. The rseults force the classical picture of an orifice flow to be modified. That is, the pressure begins to decrease from several pipe-diameters upstream from the orifice, instead of sightly increasing toward the orifice as has conventionally been imagined. Furthermore, in the downstream region, the pressure recovery suddenly disappears for Reynolds numbers below a certain critical value. Secondly, the mouth area - pressure drop - flow rate relations are properly measured for a poppet-type restrictor. It turns out that a linear loss as well as a non-linear loss plays an important role in a constriction oil flow around a poppet. The results are further used to predict the static performances of the poppet valve when it works as a relief valve for an ordinary purpose.