1. Manring,N. D and Kasaragadda, S.B. The theoretical Flow Ripple of an External GearPump, Jounal of Dynamic Systems, Measurement and Control, Transactions of ASME, vol. 125, 2003, 396-404.
2. Pump and Pumping Systems (by energy efficiency)API Standard 647, 1995, Positive Displacement Pump-Reciprocating, Second edition, American Petroleum Institute Washington,D. C.
3. Best Practices in selecting and applying Positive Displacement Pumps by John E. Peterson.
4. A comparison of Positive Displacement and Centrifugal Pump applications by John E. Purcell.
5. Mechanical Engineers Hand book by James Carvill.