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Wika Bourdon Tube Pressure Gauges
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Mechanical
Pressure Gauges
Indicating pressure gauges with an elastic measuring element are used
extensively to measure pressures in technical applications because they
are both robust and easy to handle. These Wika pressure gauges
incorporate measuring elements which deform elastically under the
influence of pressure. Wika Mechanical pressure gauges are produced with
bourdon tube, diaphragm, and bellow and spring elements and are
accordingly different. Wika measuring elements are made of copper
alloys, alloyed steels or produced with special materials for specific
measuring applications. Pressures are only measurable in conjunction
with a reference pressure. The atmospheric pressure alone serves as
reference pressure and the pressure gauge shows how much higher or lower
the measured pressure is in relation to the given atmospheric pressure
(i.e. an overpressure measuring instrument). The measured pressure is
shown in standard measuring ranges on over 270 degrees on the dial.
Liquid filled pressure gauges offer optimal protection against
destruction by high dynamic pressure loads or vibrations as a result of
their cushioning. Switching operations can be carried out when combined
with alarm contacts. Electrical output signals (for example, 4...20mA)
can be used for industrial process automation in combination with
transmitters.
1. Wika Bourdon Tube Pressure Gauges
Bourdon tubes are circular-shaped tubes with an oval cross-section. The
pressure of the media acts on the inside of this tube which results in
the oval cross section becoming almost round. Because of the curvature
of the tube ring, the bourdon tube bends when tension occurs. The end of
the tube, which is not fixed, moves, thus being a measurement for the
pressure. This movement is indicated by a pointer. Bourdon tubes bent at
an angle of approx. 250° are used for pressures up to approx. 60 bar.
For higher pressure, bourdon tubes are used which have a number of
superimposed coils of the same diameter (i.e. helical coils) or
helical-shaped coils (i.e. helical springs) at one level. Bourdon tubes
can only be protected against overload to a limited extent. For
particularly difficult measuring operations, the Wika pressure gauge can
be provided with a chemical seal as a separation or protection system.
The pressure ranges are between 0...0.6 and 0...4000 bar with a reading
accuracy (or accuracy class) from 0.1 to 4.0%.
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2. Wika Diaphragm Element Pressure Gauges
Diaphragm elements are circular-shaped, convoluted membranes. They are
either clamped around the rim between two flanges or welded and subject
to the pressure of the media acting on one side. The deflection caused
in this way is used as a measurement for the pressure and is indicated
by a pointer. Compared with bourdon tubes, these diaphragm elements have
a relatively high activating force and because of the circular clamping
of the element they are insensitive to vibration. The diaphragm element
can be subjected to higher overload through load take-up points (by
bringing the diaphragm element against the upper flange).
Moreover, the Wika pressure gauge can also be protected against
extremely corrosive media by coating with special material or covering
with foil.
Wide connection ports, open connection flanges and purging plugs can be
integrated for measuring highly viscous, impure or crystallizing media.
Pressure ranges are between 0...16 mbar and 0...40 bar in accuracy class
0.6 to 2.5.
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3. Wika Capsule Element Pressure Gauges
The Wika capsule element consists of two circular-shaped, convoluted
membranes sealed tight around their circumference. The pressure acts on
the inside of this capsule and the generated stroke movement is shown by
a pointer as measurement of pressure. Pressure gauges with capsule
elements are more suitable for gaseous media and relatively low
pressures. Overload protection is possible within certain limits. The
activating force is increased if a number of capsule elements are
connected mechanically in series (a so-called capsule element
"package"). Pressure ranges are between 0...2.5 mbar and 0...0.6 bar in
the accuracy class 0.1 to 2.5.
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4. Wika Absolute Pressure Gauges
These instruments are used where pressures are to be measured
independently of the natural fluctuations in atmospheric pressure. As a
general rule all the known types of element and measuring principles can
be applied.
The pressure of the media to be measured is compared against a reference
pressure which, at the same time, is absolute zero. For this purpose an
absolute vacuum is given as reference pressure in a reference chamber on
the side of the measuring element not subject to pressure. This function
is achieved by sealing off the appropriate measuring chamber or
surrounding case. Measuring element movement transmission and pressure
indication follow in the same way as with the already described
overpressure gauges.
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5. Wika Differential Pressure Gauges
The difference between two pressures is determined directly and shown on
the differential pressure gauge. Again, all of the measuring elements
known from overpressure gauges and the measuring principles can be
applied.
Two sealed medium chambers are separated by the measuring element or
measurement elements, respectively. If both operating pressures are the
same, the measuring element cannot make any movement and no pressure
will be indicated.
A differential pressure reading is only given when one of the pressures
is either higher or lower. Low differential pressures can be measured
directly in the case of high static pressures.
Very high overload capability is achieved with diaphragm elements. The
permissible static pressure and the overload capability on the + and -
side must be observed. Transmission of the measuring element movement
and pressure indication is the same as with the already described
overpressure gauges in the majority of cases. Pressure ranges are
between 0...16 mbar and 0...25 bar in the accuracy class 0.6 to 2.5.
Areas of Application*
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Filter
technology (monitoring filter pollution)
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Filling
level measurement (in enclosed containers)
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Flow
measurement (pressure drop)
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