ELASTIC DISTORTION CALCULATIONS ON A SPECIAL PISTON GAUGE (PG27) UP TO 28 MPA IN DIFFERENT OPERATIONAL MODES

The elastic distortions of a special hydraulic piston gauge (PG27) ope rating at up to 28 MPa in simple, reentrant and controlled-clearance c onfigurations were calculated by an iterative analytical technique. It was possible to determine die radial displacements of the piston and the cylinder at any pressure, and the pressure distribution in the cle arance with different fluids, and to compute the pressure distortion c oefficient of die piston-cylinder unit under conditions of use. Calcul ations show that the elastic distortion, the pressure distribution in the clearance and the pressure distortion coefficients are not fluid-d ependent, at least for two of the most commonly used fluids. In the si mple configuration, the radial distortion of the piston-cylinder unit at die maximum pressure is of the same magnitude as the undistorted ra dial clearance (0,527 mum). Agreement between the experimental and the calculated pressure distortion coefficients is about 1,4 % and corres ponds to less than 0,6 part per million difference in effective area a t 28 MPa. In the re-entrant configuration, the clearance between the p iston and cylinder decreases to a minimum value of 0,282 mum at 28 MPa . Agreement between the experimental and the calculated pressure disto rtion coefficients is within 14,3 % and corresponds to 8,0 ppm differe nce in effective area at 28 MPa. In the controlled-clearance configura tion, the distortions of the cylinder are, on average, equal to zero, as expected with controlled-clearance piston gauges, and die pressure distribution in die clearance is die most linear of the three operatin g modes. Agreement between the experimental and the calculated pressur e distortion coefficients corresponds to less than 11,0 ppm difference in effective area at 14 MPa and 28 MPa.