Needle Valves as Pressure Regulators

The potential of needle valves issuing into sudden expansions as the primary components of large closed conduit pressure regulating structures is analyzed. Results are presented of research projects conducted to evaluate the hydraulic characteristics of needle valves. The flow characteristics of the needle valve are described by presenting a submerged jet issuing from a circular orifice into an expansion chamber. The basic principles and equations of fluid mechanics are applied to qualitatively predict the cavitation, pressure fluctuation, and energy dissipation capabilities of submerged jets. A brief literature review of related studies is presented, followed by a description of the facilities used for testing and the results. These results indicate that needle valves are ideally suited for pressure regulation in closed conduit systems. Specifically they have the capability of dissipating large amounts of energy with little cavitation or pressure fluctuations. However, special attention should be given to the design to maximize the streamlining of the valve and to eliminate the possibility of local cavitation zones.