An hydraulic power generating pack 1 comprises a primary pump 23 of the multi-cylinder, reciprocating ram type with a reciprocable piston 27 located in each cylinder 28 and displaceable by a crank shaft 20 rotatable by a prime mover 2 to provide a primary hydraulic fluid output 32 at a predetermined constant pressure and constant volume, and a power take off 14 to drive a secondary pump 36 of the pressure compensated variable delivery type, the output 40 of which drives a pressure intensifier 42 serving to intensify, to the required secondary pressure and volume, hydraulic fluid supplied to the intensifier 42 at a first pressure and volume.