The Vickers Model 25V (T) vane pump has a displacement (cam ring fixed for maximum displacement) of 4.81 in3/rev. The specifications are:
Maximum speed 1800 rpm
Maximum pressure 2500 psi
As was done with the gerotor pump, performance at 1200 and 1800 rpm is compared.
Volumetric efficiency at 1200 rpm decreases from 97.3% at 500 psi to 84% at 2500 psi (Fig. 4.24a). For comparison, the gerotor pump at the same speed and pressure decreased from 91.5 to 78%. The vane pump volumetric efficiency is 5 to 6% higher than the gerotor pump. Leakage flow is less, thus the volumetric efficiency is higher.
Volumetric efficiency at 1800 rpm decreased from 97.8% at 500 psi to 88% at 2500 psi (Fig. 4.24b). As with the gerotor pump, the volumetric efficiency is higher at higher shaft speed across the whole pressure range.
The overall efficiency of the vane pump is quite low at low pressures. As shown in Figs. 4.25a and 4.25b, the overall efficiencies at both 1200 and 1800 rpm increase to a maximum at 1000 psi. The decrease in overall efficiency as pressure increases from 1000 psi to 2500 psi, is less for the vane pump than the gerotor pump. The vane pump efficiency curve is “flatter,” indicating that vane pump performance will change less as load pressure changes in the 1000 to 2500 psi range.
Overall efficiency is much lower than volumetric efficiency for the vane pump (Table 4.2). As previously stated, overall efficiency includes both the friction and the leakage power losses. For the gerotor pump, the friction power loss was small in comparison to the leakage power loss, so the two efficiencies are approximately equal. The vane pump, on the other hand, has a higher friction loss, so the overall efficiency is less than the volumetric efficiency.