Abstract
Pressure-responsive elements commonly used in indicating and recording instruments are manometers, free-piston gages, Bourdon tubes, diaphragms, and bellows. The mathematics of the primary elements, manometers, and free-piston gages is simple and direct. Analyses of Bourdon tubes and diaphragms show that predictions of their performance curves are not amenable to precise calculation even under the simplest conditions, which conditions do not generally obtain in instruments. Generally, the instrument maker must rely upon empirical knowledge, coupled with approximate calculations, for design data. Linkage adjustments must be provided to correct for variations in dimensions and materials normally encountered in manufacture.
Emphasis is placed on the usefulness of bellows as pressure elements, and approximate formulas for calculating their behavior are given. The results of considerable experimental work on the characteristics of bellows of various sizes and materials show that in many cases they are ideal elements for pressure-responsive instruments. An example of such use in a special-duty pressure gage is given.