Elastic distortions in piston-cylinder units, used in primary standard piston gauges, are responsible for large uncertainties in pressure measurement values typically higher than 50 MPa. The present study considers the results obtained in the calculation of the pressure distortion coefficients of two 100 MPa piston-cylinder units and one 500 MPa unit. The calculation of distortions in the above piston-cylinder units follows the application of an analytical technique taking account iteratively of mechanical distortions and pressure distribution in the piston-cylinder clearance. The distortion values experimentally determined on the outer surface of the cylinders are compared with the calculated results. Pressure distributions in the piston-cylinder clearances, and piston and cylinder radial displacements, are calculated for various conditions of use and the results allow the pressure distortion coefficient of each unit to be obtained. Different effects on piston-cylinder units are evaluated to acquire useful information on piston gauges and to improve their accuracy.

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