Modeling a variable speed drive for positive displacement pump

Positive displacement pumps are critical to applications ranging from drug delivery to water jet cutters. The reciprocating motion of these pumps means that their output inevitably pulses at the rate proportional to the speed of the drive. However, if the constant speed drive, traditionally employed in PD pumps, is replaced by one that can dynamically vary speed and torque the possibility of controlling the form of the output pulses arises. To enable such a system this paper reports the modeling of a drive train connected to a Positive Displacement Pump. The drive train comprises a internal combustion engine to generate rotary power, a gearbox transmission to enable changes in the speed-torque ratio and a hydrodynamic coupling in between the two to accommodate flexible power flow. The behavior of the swept pumping volume is generated from a parametric model derived from a CFD analysis. The result demonstrates that there is a significant difference in the flow predicted by models that use average, rather than instantaneous speeds.