INTRODUCTION OBJECTIVES - Plant Services

Chapter 4 — Hydraulic Pumps 119Variable-Displacement, Pressure-Compensated Vane Pumps. A variabledisplacement,pressure-compensated vanepump is a pump that automatically adjuststhe amount of volume it displaces perrotation by centering the rotor when thepressure in the system starts to build. SeeFigure 4-17. A variable-displacement,pressure-compensated vane pump operatesby adjusting a cam ring to allow thevolume per revolution to change accordingto system pressure. This type of pumpprotects itself against excessive pressure byreducing power consumption as the flowrate decreases. When pressure reaches acertain value, the compensator spring forceequals the hydraulic piston force. As pressurecontinues to increase, the compensatorspring is compressed until concentricity onthe compensator ring is achieved. Maximumpressure is then achieved. At this point, thepump is protected because it produces nomore flow, resulting in no power loss and nofluid heating. A thrust block is used to ensuresmooth movement and correct placement ofthe cam ring.Variable-displacement, pressurecompensatedvane pumps are the mostcommonly used vane pumps and haveease of maintenance over the life of thepump. Setting the maximum fluid flowof a variable-displacement, pressurecompensatedvane pump is performedusing the following procedure:1. Connect the outlet side of the pumpdirectly to a pressure gauge.2. Turn the pump ON and record the pressurewhen the pump rotor becomes centered.3. Use the pressure adjustment screw toset the desired fluid flow.TERMSA variable-displacement,pressure-compensatedvane pump is a pumpthat automatically adjuststhe amount of volume itdisplaces per rotation bycentering the rotor when thepressure in the system startsto build.Figure 4-17. A variable-displacement, pressure-compensated vane pump is a pump that automaticallyadjusts the amount of volume it displaces per rotation by centering the rotor whenthe pressure in the system starts to build.