ABSTRACT
Piston vacuum gauges are mechanical devices that measure pressure directly. The pressure is determined by the measurement of a force effect exerted by a gas on a freely floating piston. The piston vacuum gauges may substitute the standard gauges operating with liquid media. The exchange of energy between molecules and surfaces is a complex process, which is associated with the gas type and the state of solid surfaces. Vacuum gauges can also operate on the principle of the interaction of a mechanical element and a gas system where either the mechanical element or the gas system is in motion. The motion of a sensing element or a gas can mutually be oriented either in a normal or in tangential direction with respect to the object area. The chapter discusses tangential force effect, friction force, between the mechanical element and gas is discussed in the category of viscosity gauges, while the normal force effect on a mechanical element.
