[163] Exercise: Horizontal grinding machine (pump delivery)

The slide on a horizontal grinding machine is hydraulically actuated. A machine operator determines that the reciprocating movement of the machine is no longer reaching the desired speed. A possible cause of this is reduced pump delivery. To investigate this, it is necessary to plot a characteristic curve for the pump and compare this with the values achieved during initial commissioning. As an additional exercise, the circuit diagram and parts list for the necessary test assembly should be prepared.

In order to draw the characteristic curve for the pump, the volumetric flow of hydraulic fluid delivered by the pump (Q) is plotted against the operating pressure achieved (p). The manufacturer's characteristic curve exhibits a slight downward gradient, since the new pump manifests increasing internal leakage losses as necessary to provide internal lubrication. The newly-plotted curve shows a clear deviation; the leakage oil losses have become greater at higher operating pressures, the volumetric efficiency has become worse. The main reason for this is pump wear. Regarding the circuit diagram for the test assembly: The adjustable flow control valve 1V3 is adjusted in such a way that the pressure gauge 1Z1 shows the desired system pressure. The pressure relief valve 1V2 is used to limit the system pressure, while valve 1V1 acts as a safety valve for the pump.

The measured values taken as the basis for this exercise do not allow for the characteristic curve of the electric motor. The motor characteristic thus forms part of the calculated error.