Every machine or even every cylinder, provided its movements overlap with others, has a dedicated pump with a size based on the highest load speed v k required (Figure E 13). This means that high speeds require correspondingly high power:
Here the duration of the power output (speed) is often not relevant for the size of the motor. On the usage of constant pumps with Q k it is a disadvantage that the installed power P max is only required at one operating point (at p max , i.e. at corner power). If, on the other hand, variable pumps with power controllers are used, then the installed power can be exploited by increasing the flow rate Q v over a larger range.
In (Figure E 14) the cross-hatched area marks the flow rate gain compared to a constant pump of the same (corner) power.
Figure E 13: Single or separate drive for machines
Figure E 14: Q/p2 and P/p2 diagram for constant and variable pumps