Elastic distortions of a mixed (simple and re-entrant) piston-cylinder unit for pressure measurements up to 2.6 GPa

The main scientific reasons for this study arise from the need for primary standards for pressure measurements in liquids in the 1 GPa to 2.6 GPa range with a relative uncertainty of at least 10-3. An analysis of current primary standards for high-pressure measurements shows that few pressure balances are operative and routinely used for measurements and calibrations above 1.4 GPa. In this paper the preliminary studies and calculations for the construction of such a system, based on a mixed piston-cylinder unit to be used up to 2.6 GPa, are presented. The authors aim at optimization of dimension parameters with particular attention to both simple and re-entrant clearance dimensions, and give calculations of other important parameters such as piston fall rate versus pressure.