ABSTRACT
Pressure is a universal processing condition. The mass of air has weight, and this weight pressing downward causes atmospheric pressure. Perhaps the area that has caused the most concern in the change to System International d’ Unites (SI) units is pressure measurement. The new unit of pressure, the pascal, is unfamiliar even to those who have worked in the older centimetre, gram, second metric system. Dead weight testers are primary pressure standards. They generate pressure by applying weight to a piston that is supported by a fluid, generally oil or air. This instrument measures the pressure difference in the compartment on each side of a bell-shaped chamber. If the pressure to be measured is gauge pressure, the lower compartment is vented to atmosphere. The slack or limp-diaphragm instrument is used when very small pressures are to be sensed. The most common application of this gauge is measurement of furnace draft.
