What is the definition of bo rdon gauge?
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Figure 9-4.-The Bourdon gauge. Bourdon Gauge The Bourdon gauge
is shown in figure 9-4. It works on the same principle as that of
the snakelike, paper party whistle you get at a New Year party,
which straightens when you blow into it. Within the Bourdon gauge
is a thin-walled metal tube, somewhat flattened and bent into the
form of a C. Attached to its free end is a lever system that
magnifies any motion of the free end of the tube. On the fixed end
of the gauge is a fitting you thread into a boiler system. As
pressure increases within the boiler, it travels through the tube.
Like the snakelike paper whistle, the metal tube begins to
straighten as the pressure increases inside of it. As the tube
straightens, the pointer moves around a dial that indicates the
pressure in psi. The Bourdon gauge is a highly accurate but rather
delicate instrument. You can easily damage it. In addition, it
malfunctions if pressure varies rapidly. This problem was overcome
by the development of another type of gauge, the Schrader. The
Schrader gauge (fig. 9-5) is not as accurate as the Bourdon, but it
is sturdy and suitable for ordinary hydraulic pressure
measurements. It is especially suitable for fluctuating loads. In
the Schrader gauge, liquid pressure actuates a piston. The pressure
moves up a cylinder against the resistance of a spring, carrying a
bar or indicator with it over a calibrated scale. The operation of
this gauge eliminates the need for cams, gears, levers, and
bearings. Diaphragm Gauge The diaphragm gauge gives sensitive and
reliable indications of small pressure differences. We use the
diaphragm gauge to measure the air pressure in the space between
inner and outer boiler casings. In this type of gauge, a diaphragm
connects to a pointer through a metal spring and a simple linkage
system (fig. 9-6). One side of the diaphragm is exposed to the
pressure being measured, while the other side is exposed to the
pressure of the atmosphere. Any increase in the pressure line moves
the diaphragm upward against the spring, moving the pointer to a
higher reading. When the pressure decreases, the spring moves the
diaphragm downward, rotating the pointer to a lower reading. Thus,
the position of the pointer is balanced between the pressure
pushing the diaphragm upward and the spring action pushing down.
When the gauge reads 0, the pressure in the line is equal to the
outside air pressure. MEASURING AIR PRESSURE To the average person,
the chief importance of weather is reference to it as an
introduction to general conversation. At sea and in the air,
advance knowledge of what the weather will do is a matter of great
concern 9-4