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e er’s

Engin
bo o k
Note
Mechanical pressure gauges, which require no
external power, provide an affordable and are a reliable
source of accurate pressure measurement. When
selected using the criteria described below,
maximum gauge life can be expected. Step 2: Pressure Gauge Range

To properly select a pressure gauge, consider the ASME B40.1-1998 recommends that normal operating
gauge process, range, environment, accuracy, dial size, pressure be confined to 25%-75% of the scale. If
connection and mounting requirements. When selected pulsation is present in the process, maximum
using these 7 Steps, the gauge performance and operating gauge pressure should not exceed 50% of
reliability will greatly be enhanced. the full- scale range.
Pressure Gauge

Step 1: Gauge Process
Step 3: The Environment
The wetted parts of the pressure gauge, the bourdon
tube and socket must be compatible with the process Environmental considerations include ambient
media. If not compatible with the wetted parts of the temperature, air-borne particulate, condensation,
Selection

gauge, corrosion will occur. Corrosion of gauge wetted humidity, water and chemicals, all of which can affect
parts will eventually cause gauge failure and possibly gauge performance.
safety issues.
Ambient temperature may affect the accuracy and
Bourdon tubes are most often manufactured from integrity of the gauge. Gauges are available either
phosphor bronze, 316 stainless steel, or Monel. Less temperature compensated or non-temperature
frequently, they are produced from 304 stainless steel, compensated. Ambient conditions may require that the
Inconel, or steel. If the process medial is not gauge be isolated from temperature extremes. When
compatible with the wetted parts of the gauge, a required, the gauge should be isolated from
diaphragm seal/gauge isolator can be used to prevent temperature extremes with flexible capillary.
the process media from contacting the Bourdon tube.
The diaphragm seal when supplied with wetted parts When ambient conditions are corrosive, contain a large
compatible with the process not only protects the number of particulate or if the gauge will be exposed to
gauge from corrosion attack, but also serves to a wet or humid environment like humidity, wash-downs
prevent viscous or extremely dirty media from clogging or rain, specify a gauge that is
the Bourdon tube. When attached to a gauge, a weatherproof/hermetically sealed or liquid filled.
diaphragm seal will add an additional minimum error
of 0.5% to the gauge/seal Step 4: Accuracy
assembly.
For a mechanical pressure gauge, accuracy is defined
Both pulsation and vibration will as a percentage of the full- scale range.
decrease the life of the gauge if
not properly dampened. Gauges While requirements differ from one industry to another,
subject to pulsation and vibration the following are general guidelines:
should be liquid filled or
internally dampened. Ashcroft • Test Gauges and Standards: 0.25% through
gauges offer a unique patented 0.10% full scale
method of gauge dampening that provides the • Critical Processes: 0.5% full scale
performance of a liquid filled gauge without any of • General Industrial Processes: 1.0% Less Critical
the complications associated with liquid fills. Commercial Uses: 2.0%,

Available accessories that minimize stresses on the Refer to ASME B40.1-1998 or the DIN specifications
bourdon tube/movement and extend the life of the for more information on accuracy.
gauge include pulsation dampners, pressure snubbers,
gauge savers, and diaphragm seals.

CALL: 800-828-1470 FAX: 800-395-0543 WEB: www.transcat.com

diameters. • Panel surface mount back connect. gauge size and weight. • Panel hole front flange flush mount back connect CALL: 800-828-1470 FAX: 800-395-0543 WEB: www. required.10% generally have dial Indicate pressures above & below ambient pressure sizes of 41⁄2" or larger since more dial graduations are or positive & negative pressure. and past experience.transcat. Absolute Pressure - The pressure measured above a perfect vacuum. the gauge. BSP & SAE. Accuracy’s of 0. Process pressure gauges with 41⁄2" dial sizes or larger are most often This material was provided by Dresser Measurement – supplied with a 1⁄2" NPT connection to best support ASHCROFT GAUGES and INSTRUMENTS. DIN. Generally. Step 5: Dial Size Differential Pressure - The difference between to independent. readability requirements. Duplex Gauges - Selection Step 6: Gauge Connection Utilizes two independent sensing elements each connected to different but related pressure sources Gauges are available with a variety of connections including NPT.25% or 0. • Panel hole U-clamp flush mount back connect. but related Pressure Gauge Pressure gauge dial sizes range from 11⁄2" to 16" pressures. Engin Note eer’s book Glossary Of Terms Gauge Pressure - Indicates pressure from a single source and uses ambient pressure as zero. • Remote wall/surface mount lower connect. Step 7: Mounting Requirements Consider the following mounting options when selecting a pressure gauge: • Direct stem mount lower connect.com . JIS. Factors to consider when selecting a pressure gauge connection include process pressures. space limitations and required gauge accuracy determine dial Compound Pressure Gauges - size. leak integrity. space limitations. It’s the pressure indicated by an ordinary gauge added to the atmospheric pressure.