Adjustment equipment for hydraulic pumps which, for a drive with constant rotation speed (e.g. electric motor), restricts the power P as a product of the flow rate Q and pressure p to a maximum value, so the power drawn cannot exceed the drive power installed. Power limiting may be subordinate to some form of pressure reduction (pressure controller for a variable pump), something referred to as pressure limitation. As the pressure p 11 increases, the displacement volume V 11 and therefore the flow rate Q 11 are reduced in accordance with the power hyperbola. This occurs on an approximate basis by means of springs connected one behind the other in the adjustment equipment (Figure L 14).
If the drive involves combustion engines, i.e. with variable rotation speed, the torque M 1 will be kept constant the same way by V 1 adjusting itself to the changing pressure.
If more than one pump is being used at a combustion engine, pure power limiting is often dispensed with in favour of limit load control. Power limiting makes it easier to adjust the installed power to the maximum pressure or flow rate requirements associated with a load cycle (Figure L 15).
In practice, power limiting is still predominantly referred to as "power control", even though the process takes place in the open loop control system (with force adjustment) and not in the control circuit(with power as the reference variable).
Figure L 14: Power limiting using a spring assembly
Figure L 15: Q /p and P /p diagram with constant and variable pump