How to reduce non-linearity in effective area caused bythe O-ring seal in a high-pressure balance

Abstract

The oil-operated pressure balance is standard equipment in the field of pressure metrology. A pressurebalance is simply configured to measure a force acting on an area. This area is determined as the effective area of a piston-cylinder assembly, and the weight force as the product of masses acting on the piston and the acceleration due to gravity. The accuracy of the pressure balance depends largely on the effective area of the piston-cylinder assembly. Accurate determination of this value is required for accurate pressure measurement. Most commonly used pressure balances are in a simple piston-cylinder configuration where the piston and cylinder can deform freely under high pressure. The simple piston-cylinder assembly has an O-ring chamber on the cylinder bottom to seal it. The oil pressure acting on the bottom of the cylinder surrounded by the O-ring may thus deform the cylinder, causing non-linearity of the effective area, i.e. a change in the pressure distortion coefficient. Using a numerical analysis based on the finite element method (FEM), we predict that this non-linear effect could be significantly reduced by an appropriate change in cylinder configuration.