STICTION FORCES AND THEIR INFLUENCE ON VALVE PERFORMANCE OF RECIPROCATING PUMPS

摘要

Self-actuated valves of reciprocating pumps come in variousshapes (disk, ball, cone) and are spring loaded lightly only inmost cases. The kinematics and the pressure drop are importantdesign criteria. The smooth operation, reliability and volumetriceficiency of a pump are largely influenced by the valves.Over pressure spikes at the beginning of the discharge strokeare frequently observed in high pressure pumps. These spikesare caused by effects of acceleration and stiction and oftenresult in high amplitude pressure pulsations, high noise levels,valve wear and fatigue of the valve springs.Since these phenomena reduce the service life and the performanceof the pump, various valve configurations were testedacross a wide operational spectrum (pressure, stroke frequency,viscosity). The investigations centered mainly on the dischargevalve (pressure side).In a test pump the pressure in the working chamber and onthe discharge side, the stroke of the valves and the local structureborn noise emission were determined. A strong dependencyof the pressure spikes on the geometric configuration of thevalve seats was clearly demonstrated. Experiences collected inthe field were generally confirmed.As expected, wide contact-areas (in parallel and spherical sealingsurfaces) experienced higher pressure spikes than valves havingline-contact only. Significant differences exist betweenplanar, conical, spherical-conical and spherical areas of contact.A special experimental setup permitted detailed and preciseexamination of the opening phase of a valve for various springloads, viscosities of the fluid and velocities of separation of thevalve from the seat. The over pressure spikes during the openingphase to be attributable to a fluid dynamical effect in thevalve gap represents the most important result of these investigations.This effect results from the pressure drop caused by thefluid flowing into the valve gap during the opening travel of thevalve. Mathematical simulation of the pressure profiles in thegap is feasible. Based on the 'pseudo-adhesion' and the wellknown modelling approach of the kinematics of a valve accordingto [1], a computer program was developed allowing mathematicalprediction of the over pressure peaks during the openingphase of a valve. The good correlation of the values obtainedvia computation and the experimental data will be shown.