Concentric has developed an variable flow oil pump (VFP) for diesel engines which the company claims uses less power than conventional fixed flow pumps, providing immediate fuel savings and offering the potential for a more energy-efficient oil system. The VFP oil pump has demonstrated savings for heavy-duty engines of between 3 and 4hp at rated speed and more than 1hp at cruise speed. Further benefits can be achieved if the oil system is optimised to allow the pump to provide only the pressure necessary at that point in the operating range. The VFP pump was originally designed to combine low cost and robustness with fuel savings of around 1%. However, even greater savings are available in a system where oil supply is matched to demand. The VFP pump is able to take advantage of the differing oil requirements for each point in the operating cycle. Although first developed for heavy-duty engines, VFP could also deliver significant savings in medium and light duty engines. Its principle is to align flow to demand, so limiting the power needed to drive the pump and hence fuel consumption. Two rotor sets control flow output. The driving rotor operates in the traditional, fixed arrangement while the offset position and resultant flow of the second, eccentrically mounted rotor can be controlled mechanically by a rack and pinion but is equally appropriate for electronic management. The design is compact, cost-effective and durable.