Page 61 - ebook fluid mechanics_finalize

FLUID MECHANICS

Bourdon tubes measure gage pressure, relative to ambient atmospheric pressure,

as opposed to absolute pressure; vacuum is sensed as a reverse motion. When the

measured pressure is rapidly pulsing, such as when the gauge is near a reciprocating

pump, an orifice restriction in the connecting pipe is frequently used to avoid unnecessary
wear on the gears and provide an average reading; when the whole gauge is subject to

mechanical vibration, the entire case including the pointer and indicator card can be filled

with an oil or glycerin. Typical high-quality modern gauges provide an accuracy of ±2% of
span, and a special high-precision gauge can be as accurate as 0.1% of full scale.

3.4 Buoyancy

3.4.1 Archimedes Principle

Archimedes' principle indicates that the upward buoyant force that is exerted on a body
immersed in a fluid, whether fully or partially submerged, is equal to the weight of the

fluid that the body displaces. Archimedes' principle is a law of physics fundamental to fluid

mechanics. Archimedes of Syracuse formulated this principle, which bears his name.

Figure 3.18 : Archimedes Principle

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