The effective area of a pressure balance at low pressures

Abstract

A theory is given for calculating the effective area of a gas-operated pressure balance from the piston and cylinder dimensions when the gas in the piston-cylinder gap in the transition and molecular flow ranges. Calculations using the theory show that the effective area decreases with increasing ratio of molecular mean free path length to gap width as the nature of the gas flow changes from viscous to molecular. This calculated area tends to a limiting value (for wholly molecular flow) which depends strongly on the ratio of gap width to piston radius.