User Manual

1.0 SELECTION & APPLICATION
Users should become familiar with ASME B40.100 (Gauges
– Pressure Indicating Dial Type – Elastic Element) before
specifying pressure measuring gauges. That document –
containing valuable information regarding gauge construction,
accuracy, safety, selection and testing – may be ordered from:
ASME International
Three Park Avenue
New York, N.Y. 10016-5990
800-843-2763 (US/Canada)
001-800-843-2763 (Mexico)
973-882-1170 outside North America
email: [e-mail]
www.asme.org
WARNING: To prevent misapplication, pressure gauges
should be selected considering media and ambient operating
conditions. Improper application can be detrimental to the
gauge, causing failure and possible personal injury, property
damage or death. The information contained in this manual is
offered as a guide in making the proper selection of a pressure
gauge. Additional information is available from Ashcroft Inc.
The following is a highlight of some of the more important con-
siderations:
1.1 Range – The range of the instrument should be approxi-
mately twice the maximum operating pressure. Too low a
range may result in (a) low fatigue life of the elastic element
due to high operating stress and (b) susceptibility to over-
pressure set due to pressure transients that exceed the nor-
mal operating pressure. Too high a range may yield insuffi-
cient resolution for the application.
1.2 Temperature – Refer to Section 2 of this manual for
important information concerning temperature related limita-
tions of pressure gauges, both dry and liquid filled.
1.3 Media – The material of the process sensing element must
be compatible with the process media. Use of a diaphragm seal
with the gauge is recommended for process media that (a) is
corrosive to the process sensing element; (b) contain heavy
particulates (slurries) or (c) are very viscous including those
that harden at room temperature.
1.4 Oxidizing media – Gauges for direct use on oxidizing
media should be specially cleaned. Gauges for oxygen ser-
vice should be ordered to variation X6B and will carry the
ASME required dial marking “USE NO OIL” in red letters.
Gauges for direct use on other oxidizing media may be
ordered to variation X6W. They will be cleaned but carry no
dial marking. PLUS!
™
Performance gauges or Halocarbon
filled gauge or diaphragm fill is required for use with oxidiz-
ing media; order variation XCF.
1.5 Pulsation/Vibration – Pressure pulsation can be damp-
ened by several mechanisms; the patented PLUS! Perfor-
mance gauge will handle the vast majority of applications.
One exception to this is high frequency pulsation which is
difficult to detect. The only indication may be an upscale zero
shift due to movement wear. These applications should be
addressed with a liquid filled gauge, or in extreme cases, a
remotely mounted liquid filled gauge connected with a length
of capillary line. The small diameter of the capillary provides
excellent dampening, but can be plugged. The Ashcroft 1106
pulsation dampener and 1112 snubber are auxiliary devices
which dampen pulsation with less tendency to plug.
1.6 Gauge fills. – Once it has been determined that a liquid
filled gauge is in order, the next step is selecting the type of fill.
Glycerin satisfies most applications. While being the least
expensive fill, its usable temperature range is 20/180°F.
Silicone filled gauges have a broader service range:
–40/250°F. Oxidizing media require the use of Halocarbon,
with a service range of –40/250°F. Pointer motion will be
slowed at the low end of the low end of these temperature
ranges.
1.7 Mounting – Users should predetermine how the gauge
will be mounted in service: stem (pipe), wall (surface) or panel
(flush). Ashcroft wall or panel mounting kits should be ordered
with
the gauge. See Section 3.
2.0 TEMPERATURE
2.1 Ambient Temperature – To ensure long life and accura-
c
y, pressure gauges should preferably be used at an ambi-
ent temperature between –20 and +150°F (–30 to +65°C).
At very low temperatures, standard gauges may exhibit slow
pointer response. Above 150°F, the accuracy will be affected
by approximately 1.5% per 100°F. Other than discoloration of
the dial and hardening of the gasketing and degradation of
accuracy, non-liquid filled Type 1279 (phenolic case) and
1379 (aluminum case) Duragauge
®
gauge, with standard
glass windows, can withstand continuous operating tempera-
tures up to 250°F. Unigauge models 2
1
⁄2˝ and 3
1
⁄2˝ 1009 and
1008S liquid filled gauges can withstand 200°F but glycerin
fill and the acrylic window of Duragauge
®
gauges will tend to
yellow. Silicone fill will have much less tendency to yellow.
Low pressure, liquid filled Types 1008 and 1009 gauges may
have some downscale errors caused by liquid fill expansion.
This can be alleviated by venting the gauge at the top plug
(pullout the blue plug insert). To do this the gauge must be
installed in the vertical position.
Although the gauge may be destroyed and calibration lost,
gauges can withstand short times at the following tempera-
tures: gauges with all welded pressure boundary joints, 750°F
(400°C); gauges with silver brazed joints, 450°F (232°C) and
gauges with soft soldered joints, 250°F (121°C). For expected
long term service below –20°F (–30°C) Duragauge
®
and 4
1
⁄ 2˝
1009 gauges should be hermetically sealed and specially
lubricated; add “H” to the product code for hermetic sealing.
Add variation XVY for special lubricant. Standard Duralife
®
gauges may be used to –50°F (–45°C) without modification.
2.2 Accuracy – Heat and cold affect accuracy of indication.
A general rule of thumb for dry gauges is 0.5% of full scale
change for every 40°F change from 75°F. Double that al -
lowance for gauges with hermetically sealed or liquid filled
cases, except for Duragauge
®
gauges where no extra
allowance is required due to the elastomeric, compensating
back. Above 250°F there may exist very significant errors in
indication.
2.3 Steam service – In order to prevent live steam from
entering the Bourdon tube, a siphon filled with water should
be installed between the gauge and the process line.
Siphons can be supplied with ratings up to 4,000 psi. If
freezing of the condensate in the loop of the siphon is a pos-
sibility, a diaphragm seal should be used to isolate the gauge
from the process steam. Siphons should also be used when-
ever condensing, hot vapors (not just steam) are present.
Super heated steam should have enough piping or capillary
line ahead of the siphon to maintain liquid water in the
siphon loop.
2.4 Hot or very cold media – A five foot capillary line assem-
bly will bring most hot or cold process media within the recom-
mended gauge ambient temperature range. For media above
4