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About Pressure Gauges
Pressure gauges are instruments that are designed to
measure the pressure of a gas or liquid. Pressure gauges monitor and
indicate the internal pressure and/or the vacuum of vessels or systems,
especially those having dynamic working characteristics that require
constant monitoring. Standard pressure gauges typically utilize a Bourdon
tube, a sensing element for measuring pressures 15 psi or more. Bourdon
tubes are spirally wound or C-shaped and are usually made of stainless
steel or copper alloy. When a pressure change occurs, the pressure gauges
flex and produce a rotational movement, causing the gauge indicator to
move. A diaphragm seal or gauge isolator can be used to prevent the Bourdon
tube from coming into contact with the process material, if the tube
and material are not compatible.
Pressure gauges vary in style, size and wetted parts material, depending
on the application. Display types include graphical and video displays,
digital readouts or analog meters and needles. The scale of an analog
pressure gauge can display one or two units on the same face (e.g. psi,
kPa, Bar, inches Hg, cm Hg). Some pressure gauges have pointers that
can be adjusted to zero by turning a screw or a knob. Adjustable or stationary
set hands are separate pointers that indicate a preset pressure. Some
pressure gauges do not display a measure of pressure. Instead, they monitor
pressure and send an electronic output signal for any required changes
in the system. Throttling devices, which are used to decrease the effects
of pressure pulsation and/or vibration on pointer movement, include throttling
screws, pulsation dampeners, elastomeric bladders, pressure snubbers
and needle valves. Pressure gauges can also be equipped with electric
contacts to turn on signal lights, sound alarms or operate a pump or
valve.
There pressure gauges have a wide variety of industrial applications
in which the pressure gauges are utilized. Specialty tanks, such as fire
extinguishers and medical gas cylinders use pressure gauges. Liquid filled
gauges are utilized in nitrous systems on nitrous bottles or solenoids.
Gauges made of stainless steel can be used in applications that have
strict sanitary requirements and are capable of withstanding high pressure
cleaning. Some pressure gauges are specifically designed for use in high
purity semiconductor gas and liquid applications with a range from vacuum
to 6,000 psig. Pressure gauges are essential for applications in which
the accurate functioning of a vessel or system directly depends on the
accuracy of the gauge reading, such as in pesticide sprayers.
The accurate selection of pressure gauges requires the consideration
of some key factors, including the gauge process, range, environment,
accuracy, dial size, connection and mounting needs. Compatibility of
the wetted parts of pressure gauges, including the Bourdon tube and socket,
with the process material is essential, as corrosion might otherwise
occur. Liquid filled pressure gauges or gauges that are internally dampened
are better choices for applications in which the gauges would be subject
to pulsation and vibration. It is recommended that the normal operating
pressure be confined to 25-75% of the scale, no higher than 50%, if pulsation
is present. Dial size is typically determined by readability requirements,
space limitations and required gauge accuracy. Pressure gauges connections
should be selected with the following in mind: process pressures, gauge
size and weight, space limitations and leak integrity. Gauge performance
can be affected by ambient temperature, air-borne particulate, condensation,
humidity, water and chemicals.
Featured
Articles
http://sst.pennnet.com/Articles/Article_Display.cfm?Section=ARTCL&ARTICLE_ID=206475&VERSION_NUM=1&p=5
http://www.mme.tcd.ie/~clyons/PresMes.pdf
Types of Pressure Gauges
- measure any pressure above
vacuum (zero pressure).
- measure the air pressure of pneumatic equipment.
- , also called “sea level gauges,” are
the most commonly used gauge. Ambient gauges are preset to read zero
pressure
at standard atmospheric pressure (14.7 psi).
- measure both pressure and vacuum.
- , also referred to as “general purpose gauges” or “equipment
gauges,” are low-cost measuring instruments designed for applications
that do not have severe conditions. Commercial gauges may be ruggedly
constructed but are not typically economical to repair.
- provide the relative pressure between
two measurement points. An indication of differential pressure only
occurs when one pressure is higher or lower than the other.
- are industrial standard gauges, typically battery-powered,
which use a digital display rather than an analog dial display. Digital
readouts are typically easier to read and provide a greater accuracy
than dials.
- are instruments that indicate the pressure of
the fuel supply to the intake manifold in a combustion engine.
- have heavy-duty sensing elements and case designs
and higher accuracy requirements than general purpose gauges, are built
for extended life and are designed for harsh, corrosive environments.
- can be filled with various fluids, such as silicone
oil, mineral oil and glycerin. The liquid fill provides protection
to internal components of the gauge in severe environments in which
the gauge may encounter excessive vibration and pulsation.
- are designed to accurately measure pressures less
than 15 psig using a capsule sensing element.
- are instruments that measure and display the pressure
of the oil circulating in any lubricating system.
- are extremely sensitive and highly accurate
instruments that are used in applications which demand precision and
consistent results, such as instrument shops, gauge repair and calibration
shops and testing laboratories.
- are made from corrosion resistant material to meet the
demanding heavy-duty operating and construction requirements of the
chemical and petroleum industries. Process gauges are also designed
to fulfill the exacting accuracy and service life needs of a variety
of process applications.
- have a scale that is compressed at either one or both
of its ends.
- indicate negative atmospheric pressure or the degree
of rarefaction below atmospheric pressure.
- are designed to determine and monitor the pressure
of any system that uses water.
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