Hydvic Hydraulic Supply Concrete Mixer Sauer PV, SPV Hydraulic Piston Pump PV20 PV21 PV22 PV23 PV24 PV25 PV26 PV27 SPV20 SPV21 SPV22 SPV23 SPV24 SPV25 SPV26 SPV27 And Cement Mixer Eaton ACA Heavy Duty Variable Pump , as well as for the excavator, compactor, paver, etc.

Sauer PV series Axial piston variable displacement pumps, Series 20, are of swash plates construction with variable flow capability suitable for hydrostatic transmission in closed loop circuit. 

The Flow rate is proportional to the pump driven speed and displacement, which, in turn, is determined by the swash plate angle.  The latter infinitely adjustable between zero and maximum displacement.