Flowserve Gaseous Noise Control - PRO-QUIP

ConceptionDevelopmentManufactureOutlet velocities below 0.33 Mach are desirable. Highervelocities may be acceptable, but require an engineeringreview for each application. Velocities must be assessedfor the most difficult flowing conditions at the followingcritical points (as shown in Figure 1.5: Critical VelocityZones on page 6):• The inlet passageway to the valve• The internal flow area of the seat retainer at all plugpositions• The gallery flow area formed between the outsidediameter of the seat retainer and the inside diameter ofthe valve body• Outlet passage flow areaP 1 /P 2 , the Pressure RatioThe driving force behind velocity and noise is containedin the P 1 /P 2 ratio, which represents the energy availableto generate noise. When this ratio is low, the energy containedin the fluid stream will be low and the noise generatedwill typically be low as well. Each noise solution willhave a range of pressure ratios where the design is mosteffective. Noise control trim is most effective when pressureratio of the service is below the trim design limits.Reducing Pressure while Controlling VelocityThe most common method to reduce noise is to separatea large pressure drop into smaller pressure steps whichwill produce far lower velocities at each step. A numberof mechanisms are available to reduce the pressure withoutcreating excessive velocity. Designs which make efficientuse of these mechanisms will create the lowestnoise possible.Sudden Expansion and ContractionA fluid that experiences a sudden expansion or contractioncreates turbulent zones in the fluid flow. These turbulentzones takes energy out of the fluid in the form ofpressure. This is the primary effect used by orifice platesto create a pressure drop.Figure 1.1: Pressure Drop Through a Control ValveFigure 1.2: Velocity Through a Control Valve