When selecting a
pressure gauge, it is important to consider the following factors
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 two thirds of the
gauge range.
Temperature Range: Maximum temperature limits for
AMETEK general equipment gauges that are soft-soldered
are -40ºF to 120ºF. Maximum temperature limits
for AMETEK
process gauges that are silver soldered or
welded are -40ºF to 190ºF and for AMETEK
liquid filled
gauges are 0ºF to 140ºF.
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,
although we offer several others from the factory.
Silicone can be used in applications with larger temperature
extremes. In applications where liquid filling is
not feasible, we offer a dampened movement option for
USG
Models 1981 and
1931 process gauges.
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 in this section to
aid you in the selection of the proper sensing element
material.
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 two thirds of the
gauge range.
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,
armored, capillary tubing can also be considered for use
with gauges that are subjected to very low or high ambient
temperatures.
Environmental Conditions: The normal ambient temperature
range for AMETEK general equipment gauges
(soft soldered) is -40ºF to 120ºF; for process gauges (silver
soldered/welded) -40ºF to 190ºF; and for liquid filled
gauges, 0ºF to 140ºF. The error caused by temperature
changes is approximately ±1% for every 50ºF change.
The reference temperature is 75ºF. 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.
Method of Mounting: Lower mount (LM) and center
back mount or lower back mount (CBM or LBM) connections
are available for most AMETEK gauges. AMETEK’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.
AMETEK 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.
Required Accuracy: AMETEK 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.
Case Venting: AMETEK
liquid filled gauges have an
elastomeric 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.