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Selecting a Pressure Gauge |
Selecting a Pressure Gauge
Selecting the appropriate Pressure Gauge for the correct application can
sometimes be a challenge depending on the application. Following the guidelines
below can help ensure the gauge chosen is suitable for the application.
Bourdon Tube Pressure Gauge Operating Principal
Ningfeng utilizes bourdon tubes that are ¡°C¡± or spiral shaped pressure tubes that
are utilized throughout all industries. The bourdon tube is very thin and formed
into a semicircle (C-shaped) or spiral. As pressure is applied through the
socket, the bourdon tube straightens itself causing the precision movement to
shift upward or downward for vacuum measurements. The movement then transforms
the motion of the bourdon tube pointer which indicates the inputted pressure.
The bourdon system is analog based and does not require any additional power
sources. Ningfeng¡¯ pressure gauges measure full vacuum (Hg), compound and
pressure ranges up to 20,000+ psi and suitable for all clean and non-clogging
liquids and gaseous media.
Environment & Application
As the bourdon tube is in direct contact with the medium being measured, the
medium characteristics must be considered. If the application is corrosive, the
medium may solidify at various temperatures or it may contain solids that will
leave deposits inside the bourdon tube. For gases or liquids that will not
solidify under normal conditions or leave deposits, a bourdon gauge is
acceptable, otherwise, a diaphragm seal should be used. Choosing the material of
the pressure gauge is important at this stage, again if the environment is
corrosive, stainless steel internals and casing should be chosen over brass.
Brass is more suitable for general applications. Moisture and weather conditions
must also be considered as their effect may be harmful to a gauges¡¯ performance.
Temperature
Normal temperature ranges are -40¡ãC to 70¡ãC (-40¡ãF to 158¡ãF) for dry gauges and
-25¡ãC to 65¡ãC (-13¡ãF to 149¡ãF) for glycerine filled.
Gauge Options
Restrictor screws, snubbers and liquid filling are excellent options for
reducing the effects of vibration and pulsation and increasing the service life
of pressure gauges. In situations where temperature is extreme, utilizing a
syphon or remote monitoring the pressure gauge with a capillary and diaphragm
seal are some alternatives.
Pressure Range
Select a pressure range with full scale pressure range of approximately twice
the normal operating pressure. The maximum operating pressure should not exceed
75% of the full scale range. Failure to select a gauge with in these criteria
may ultimately result in fatigue of the bourdon tube.
Connections
Bottom and back (centre and lower) connections are available for various
Ningfeng
gauges. The standard thread is NPT, however, other options are available such as
BSP, SAE and many other special fittings.
Accuracy
The degree of accuracy required for the specification should be determined to
ensure the proper gauge is used. Ningfeng offers pressure gauges with accuracy ¡À
0.10% to ¡À 3/2/3%.
* Continuous product improvements may result in specifications being changed
without notice.
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Selection of a Pressure Gauge
When selecting a pressure gauge, it is important to consider the
following factors:
1. Pressure Range (specify units of measure)
2. Temperature Range
3. Conditions affecting wear of the system
4. Pressure Fluid Composition
5. Pressure Fluid Temperature
6. Environmental Conditions
7. Method of mounting
8. Required Accuracy
9. Case Venting
1. Pressure Range: A gauge range of twice the working pressure is
generally
recommended for maximum accuracy, safety and for extended gauge life.
The
operating pressure should always be limited to 75% of the gauge range.
When
pressure pulsations are encountered, the operating pressure should be
limited to
2/3 of the gauge range.
2. Temperature Range: Ambient temperature for Ningfeng General Equipment
gauges that are soft-soldered is ¡§C40 F to 120 F. Ambient temperature
for
Ningfeng Process gauges that are silver soldered or welded is ¡§C40 F to
190F and
for Ningfeng Liquid Filled gauges it is 0 F to 140 F.
3. Conditions Affecting Wear of the System: In applications involving
severe
pressure fluctuations, vibrations and/or pulsation the use of
restrictors or pressure
snubbers is recommended. Also, liquid filled gauges should be
considered. The
fill fluid will lubricate the movement and reduce friction and wear.
Liquid filling
can also prevent moisture or corrosive atmospheres from affecting the
gauge
internals. The most common fill fluid is glycerin. Silicone can be used
in
applications with larger temperature extremes.
4. Pressure Fluid Composition: Since the sensing element of a pressure
gauge
may be exposed directly to the measured medium, consider the
characteristics of
this medium. It may be corrosive, it may be gas or liquid, it may
solidify at
various temperatures, or it may contain solids that will leave deposits
inside the
sensing element. For pressure fluids that will not solidify under normal
conditions
or leave deposits, a Bourdon tube pressure gauge is acceptable.
Diaphragm
chemical seals should be considered when the pressure gauge wetted parts
are not
compatible with the measured media. Please refer to the ¡®Chemical
Compatibility
Chart¡¯ to aid you in the selection of the proper sensing element
material.
5. Pressure Fluid Temperature: Steam and other hot media may raise the
temperature of the gauge components above safe working limits of the
sealed
joints. In these cases, it is recommended that a siphon or a chemical
diaphragm
seal be used in conjunction with the pressure gauge. Chemical diaphragm
seals
and remote capillary can also be considered for use with gauges that are
subjected
to very low or high ambient temperatures.
6. Environmental Conditions: The normal ambient temperature range for
Ningfeng General Equipment gauges (soft soldered) is ¡§C40 F to 120 F,
for
Process gauges (silver soldered / welded) ¡§C40 F to 190 F, and for
Liquid Filled
gauges 0 F ¡§C 140 F. The error caused by temperature changes is
approximating + /
- 1% for every 50 deg. F change. The reference temperature is 75 F.
Remote
mounting of the pressure gauge using a chemical diaphragm seal and
capillary
line is one alternative for applications involving extreme ambient
temperature.
Moisture and weather effects must also be considered. Liquid filled
gauges can
prevent condensation build up. For outdoor use, stainless steel, brass,
or plastic
cased gauges are recommended. Mechanical shock, vibration, dust and
humidity
are some other considerations in selecting a pressure gauge.
7. Method of Mounting: Bottom (LM) and back (CBM or LBM) connections are
available for most Ningfeng gauges. Ningfeng¡¯s cataloged products have
standard NPT threaded connections. Other types such as metric threads,
straight
threads, hose barbs, and other special fittings are available as special
order.
Ningfeng pressure gauges are calibrated in the vertical, upright
position and
should be mounted as such. For applications where the gauge is mounted
sideways, horizontally, or upside down, the gauge should be recalibrated
in the
position in which it will ultimately be used.
8. Required Accuracy: Ningfeng manufactures pressure gauges with
accuracies
from + / - 3/2/3% (ASME Grade B) to + / - .25% (ASME Grade 3A) of full
scale.
Generally, the more accurate gauges have a larger dial diameter and are
more
costly.
9. Case Venting: Ningfeng Liquid Filled gauges have an elastometric vent
/ fill
plug tip which can be easily cut (after installation) to permit case
venting. This is
recommended for all liquid filled gauges, especially those with maximum
pressure ratings of 100 psi and under. This will compensate for
atmospheric
changes that could effect the calibration of the filled gauge.
Automotive Florida Natural Growers Rhone Poulen
Firestone Bacardi Rum GATX
Toyota Plant as Hershey¡¯s Chocolate Chevron
Honda Plant Seagram Elf Atochem
Ford Plant (Powerhouse) Molson Brewery National Refinery Ltd.
General Motors (Paint Plant) Labatts Brewery Qatar Petroleum
Hyundai Plant Thomas Lipton Petro Peru
BF Goodrich Kraft Canada White Rose
Chevrolet Motor Welsh Foods Power Generation
Aerospace &
Transport Coca Cola General Electric
Kraft Food New Zealand Thermal Power Plant
Singapore Mass Rapid Transit Genesee Brewery Olkaria III Thermal Power
Plant
Toronto Transit Commission Anheuser Busch Burnt Lake Thermal Pilot Plant
Air New Zealand Miller Brewery Lungmen Nuclear Power Plant
Air Canada Mckee Foods Ontario Hydro Nuclear Power Plant
U.S. Air Force Stouffer Foods Ontario Hydro Coal Power Plant
Singapore Aerospace Nestle Ontario Hydro Power Plant
Canadian National Railway Dutch Mills Korean Electric Company
Pearson International Airport CP Meiji Central Hudson Gas & Electric
Calgary International Airport TIPCO Duke - Fluor
ST Areospace Vietnam Mills New York Power Authority
N.Y.C. Transit Authority Vietnam Hue Brewery Southern Illinois Power
Niagara Frontier Transit Authority Tropicana Hudson Power Generating
Civil (HVAC) Hi-Tech Montana Dakota Utilities
Nortel Networks Tuas Power Plant
First Canadian Place Intel USA Sembcorp Utilities
Pearson International Airport Intel USA Poltti Project
Red Deer Hospital Xerox Canada Pharmaceutical
Calgary International Airport Xerox USA Merk Sharpe & Dohme
Kansas City Airport Linear Technologies McNeill
BCE Place Motorola Zenith Goldline
Ford Motor Head Office Lucent Technologies Upjohn
Sick Children Hospital Hitachi Astra Pharm
Mount Sinai Hospital Government Bristol Myers-Squibb
St. Joseph Hospital NATO Novapharm
Toronto Western Hospital US Coastguards Searle Ltd.
SJB Concrete & Testing Services Canadian Department of Defense Mova
Buffalo International Airport US NAVY Connaught Laboratory
Industrial US Department of Defense Pfizer
Atmospheric Environment (Canada) Nuovo Pigne
Strathcona Mine Petro-Chemical Eli Lily
Atlantic Packaging Plant Recope Glaxco Welcome
Formosa Plastics Shell Oil Water Treatment
Dow Corning Offshore Oil Rigs Casitas Municipal Water
Dupont Coastal Chem District Pressure Filtration Plant
General Electric Lion Oil Petronas Dugun Water Supply
3M PARCO Oil Refinery Bertam Water Treatment Plant
Proctor & Gamble Aden Refinery PKNS Bangi Pumping Station
Celulosa Gwill Chemical Plant Anchorage Water & Wastewater Utility
Arauco Infineum Tampa Water Treatment
Codelco Mobil US Filter
Food & Beverage Khalda Petroleum Florida Municipal WWTP
Alpha Laval Texaco Chesapeake Utilities
McCain Foods Great Lakes City of Lakeland
Heinz Cross Oil
Aults Dairy Vista Chemicals
Winters Instruments has provided instrumentation solutions for some of
the largest engineering firms in the world including:
Fluor Daniel
SNC-Lavalin
Giffels
Foster Wheeler USA
Ormat
Kvaerner
Bechtel
Stone Webster
Black & Veatch
Rust Engineering |
Selecting a pressure Gauge
Adequate safety results from intelligent planning, careful selection and
installation of gauges into a pressure system. The user should inform
the supplier of all conditions pertinent to the application and
environment so the supplier can recommend the most suitable gauge.
The pressure sensing element in most gauges is subjected to high
internal stress, and applications exist where the possibility of
catastrophic failure is present. Pressure regulators, chemical seals,
pulsation dampeners or snubbers, siphons, manifolds and other similar
items are available for usage in these potentially hazardous systems.
The potential hazard increases at higher operating pressure.
When selecting a pressure gauge, it is important to consider the
following factors
to insure safety and accuracy.
Pressure Gauge Operating Principle
Gauge Types
Gauge Size
Gauge Mounting & Connection
Pressure Range
Pressure Fluid Composition
Gauge Case & Housing
Front Ring & Window
Dial/Pointer
Temperature/Ambient Conditions
Accuracy
Liquid Filled Option
Shock, Vibration, Pulsation
Chemical Diaphragm Seals/Gauge Protection
Chemical Compatibility Table
Pressure Conversion Chart
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Copyright © 2003-2005,
Cixi Ningfeng Pressure Gauge Factory,
TBP
All rights reserved.
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