Used when a generator with a PTO (power take off) is available fixed
displacement pumps give a singe (fixed) flow at a given engine RPM.
These are the traditional type of hydraulic pump installation and are favoured
when long runtimes or intensive usage is needed.
Highly robust these systems are relatively expensive & require a proper
engineering feasibility study before each installation.
Used in conjunction with a DC “Power Valve” power pack in an integrated
hydraulic system, a variable displacement pump offers variable flow capacities
and a multitude of pressure settings.
A variable displacement pump can also be used when a fixed flow is needed but
the engine RPM is likely to vary. This would typically be a main engine or
gearbox mounted pump.
In both cases the motor used to run the pump
needs to have a least 30% more power available at the RPM used, than the power
rating of the thruster it is supposed to run.
Variable displacement pumps are also more costly than both fixed flow and DC