PRESSURE GAUGE
INSTALLATION,
OPERATION AND
MAINTENANCE
I&M008-10098-5/02 (250-1353H) 1M AMR 5P1/08
2
1.0 Selection and Application
1.1 Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
1.2 Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
1.3 Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
1.4 Oxidizing media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
1.5 Pulsation/Vibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
1.6 Gauge fills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
1.7 Mounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
2.0 Temperature
2.1 Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
2.2 Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
2.3 Steam service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
2.4 Hot or very cold media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
2.5 Diaphragm seals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
2.6 Autoclaving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
3.0 Installation
3.1 Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
3.2 Gauge reuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
3.3 Tightening of gauge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
3.4 Process isolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
3.5 Surface mounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
3.6 Flush mounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
CONTENTS
P
age
4.0 Operation
4.1 Frequency of inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
4.2 In-service inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
4.3 When to check accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
4.4 When to recalibrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
4.5 Other considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
4.6 Spare parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
5.0 Gauge Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
6.0 Accuracy: Procedures/Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-10
6.1 Calibration - Rotary movement gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
6.2 Calibration - 1009 Duralife
®
Pressure Gauge . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
6.3 Positive Pressure Ranges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-15
3
CONTENTS
7.0 Diaphragm Seals
7.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
7.2 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
7.3 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
7.4 Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
7.5 Failures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
8.0 Dampening Devices
8.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
8.2 Throttle Screws & Plugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
8.3 Ashcroft Gauge Saver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
8.4 Ashcroft Pulsation Dampener . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
8.5 Ashcroft Pressure Snubber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
8.6 Campbell Micro-Bean
8.7 Ashcroft Needle Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
8.8 Chemiquip
®
9.0 Resources
9.1 Training Videos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
9.2 Pressure Instrument Testing Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
9.3 Tools & Tool Kits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
Page
®
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
Pressure Limiting Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
Cover photo courtesy of Johnson/Yokogawa Co.
Campbell Micro-Bean®is a registered trademark of J.A. Campbell Co.
Chemiquip®is a registered trademark of Chemiquip Products Co. Inc.
4
1.0 SELECTION & APPLICATION
Users should become familiar with ASME
B40.1 (Gauges – Pressure Indicating Dial
Type – Elastic Element) before specifying
pressure measuring instruments. 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)
95-800-843-2763 (Mexico)
973-882-1167 outside North America
Email: infocentral@asme.org
WARNING:
sure 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 considerations:
1.1 Range – The range of the instrument
should be approximately 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 overpressure set due to pressure
transients that exceed the normal operating
pressure. Too high a range may yield insufficient resolution for the application.
1.2 Temperature – Refer to page 6 of this
manual for important information concerning
temperature related limitations 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 dia-phragm seal with the gauge
is recommended for process media that (a) are
corrosive to the process sensing element; (b)
To prevent misapplication, pres-
ontain heavy particulates (slurries) or (c) are
c
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 service 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!
®
gauges or Halocarbon filled
gauge or diaphragm fill is required for use
with oxidizing media; order variation XCF.
1.5 Pulsation/Vibration – Pressure pulsation
can be dampened by several mechanisms; the
patented PLUS! Performance gauge will han-
dle 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 112
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
20/250°F. Silicone filled gauges have a
broader service range: –40/250°F. Oxidizing
media require the use of Halocarbon, with a
service range of –50/250°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 paragraph 3
Installation.
5
2.0 TEMPERATURE
2.1 Ambient Temperature – To ensure long
life and accuracy, pressure gauges should
preferably be used at an ambient temperature between –20 and +150F (–30 to +65C). At
very low temperatures, standard gauges may
exhibit slow pointer response. Above 150F, the
accuracy will be affected by approximately
1.5% per 100F. Other than discoloration of the
dial and hardening of the gasketing, non-liquid filled type 1279 (phenolic case) and 1379
(aluminum case) Duragauge
glass windows, and Duralife
1008 and 1009, can withstand continuous
operating temperatures up to 250F. Liquid
filled gauges can withstand 200F 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
“burping” the gauge by gently pushing the top
fill plug to one side to admit air to the case.
Although the gauge may be destroyed and calibration lost, gauges can withstand short
times at the following temperatures: gauges
with all welded pressure boundary joints,
750F (400C); gauges with silver brazed joints,
450F (232C) and gauges with soft soldered
joints, 250F (121C). For expected long term
service below –20F (–30C) Duragauge
1
⁄
2˝ 1009 gauges should be hermetically
4
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 –50F (–45C)
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 allowance
for gauges with hermetically sealed or liquid
filled cases, except for Duragauge
where no extra allowance is required due to
the elastomeric, compensating back. Above
250°F there may exist very significant errors
in indication.
®
, with standard
®
gauges types
®
and
®
gauges
.3 Steam service – In order to prevent live
2
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 possibility, a diaphragm
seal should be used to isolate the gauge from
the process steam. Siphons should also be
used whenever 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 assembly will bring most hot or cold
®
process media within the recommended gauge
ambient temperature range. For media above
750F (400C) the customer should use his own
small diameter piping to avoid possible corrosion of the stainless steel.The five foot capillary
will protect the gauges used on the common
cryogenic (less than –300F (200C) gases, liquid
argon, nitrogen, and oxygen. The capillary and
gauge must be cleaned for oxygen service. The
media must not be corrosive to stainless steel,
and must not plug the small bore ofthe capillary.
2.5 Diaphragm seals – As mentioned above, a
diaphragm seal should be used to protect
gauges from corrosive media, or media that
will plug the instrument. Diaphragm seals
are offered in a wide variety of designs and
corrosion resistant materials to accommodate
almost any application and most connections.
Request bulletin OH-1 for details.
2.6 Autoclaving – Sanitary gauges with
clamp type connections are frequently steam
sterilized in an autoclave. Gauges equipped
with polysulfone windows will withstand
more autoclave cycles than those equipped
with polycarbonate windows. Gauges
equipped with plain glass or laminated safety
glass should not be autoclaved. Gauge
cases should be vented to atmosphere (removing the rubber fill/safety plug if necessary)
before autoclaving to prevent the plastic
window from cracking or excessively distorting. If the gauge is liquid filled, the fill should
6
lso be drained from the case and the front ring
a
loosened before autoclaving.
3.0 INSTALLATION
3.1 Location – Whenever possible, gauges
should be located to minimize the effects of
vibration, extreme ambient temperatures and
moisture. Dry locations away from very high
thermal sources (ovens, boilers etc.) are preferred. If the mechanical vibration level is
extreme, the gauge should be remotely located (usually on a wall) and connected to the
pressure source via flexible tubing.
3.2 Gauge reuse – ASME B40.1 recommends
that gauges not be moved indiscriminately
from one application to another. The cumulative number of pressure cycles on an in-service
or previously used gauge is generally
unknown, so it is generally safer to install a
new gauge whenever and wherever possible.
This will also minimize the possibility of a
reaction with previous media
3.3 Tightening of gauge – Torque should
never be applied to the gauge case. Instead,
an open end or adjustable wrench should
always be used on the wrench flats of the
gauge socket to tighten the gauge into the fitting or pipe. NPT threads require the use of a
suitable thread sealant, such as pipe dope or
teflon tape, and must be tightened very
securely to ensure a leak tight seal.
CAUTION: Torque applied to a diaphragm
seal or its attached gauge, that tends to loosen
one relative to the other, can cause loss of fill
and subsequent inaccurate readings. Always
apply torque only to the wrench flats on the
lower seal housing when installing filled,
diaphragm seal assemblies or removing same
from process lines.
3.4 Process isolation – A shut-off valve
should be installed between the gauge and
the process in order to be able to isolate the
gauge for inspection or replacement without
shutting down the process.
3.5 Surface mounting – Also known as wall
.
ounting. Gauges should be kept free of piping
m
strains.The gauge case mounting feet,if applicable, will ensure clearance between the pressure relieving back and the mounting surface.
3.6 Flush mounting – Also known as panel
mounting. The applicable panel mounting
cutout dimensions can be found at
www.ashcroft.com
4.0 OPERATION
4.1 Frequency of inspection – This is quite
subjective and depends upon the severity of
the service and how critical the accuracy of
the indicated pressure is. For example, a
monthly inspection frequency may be in order
for critical, severe service applications.
Annual inspections, or even less frequent
schedules, are often employed in non-critical
applications.
4.2 In-service inspection – If the accuracy of
the gauge cannot be checked in place, the user
can at least look for (a) erratic or random
pointer motion; (b) readings that are suspect
– especially indications of pressure when the
user believes the true pressure is 0 psig. Any
gauge which is obviously not working or indicating erroneously, should be immediately
valved-off or removed from service to avoid a
possible pressure boundary failure.
4.3 When to check accuracy – Obviously any
suspicious behavior of the gauge pointer warrants a full accuracy check be performed.
Even if the gauge is not showing any symptoms of abnormal performance, the user may
want to establish a frequency of bench type
inspection.
4.4 When to recalibrate – This depends on the
criticality of the application. If the accuracy of
a 3-2-3% commercial type gauge is only 0.5%
beyond specification, the user must decide
whether it’s worth the time and expense to
bring the gauge back into specification.
Conversely if the accuracy of a 0.25% test
gauge is found to be 0.1% out of specification
then obviously the gauge should be recalibrated.
7
.5 Other considerations – These include (a)
4
bent or unattached pointers due to extreme
pressure pulsation; (b) broken windows which
should be replaced to keep dirt out of the
internals; (c) leakage of gauge fill; (d) case
damage – dents and/or cracks; (e) any signs of
service media leakage through the gauge
including its connection; (f) discoloration of
gauge fill that impedes readability.
4.6 Spare parts – As a general rule it is recommended that the user maintain in his
parts inventory one complete Ashcroft
instrument for every ten (or fraction thereof)
of that instrument type in service.
5.0 GAUGE REPLACEMENT
. Gauges showing significant friction error
f
and/or wear of the movement and linkage.
g. Gauges having damaged sockets, especially
damaged threads.
h. Liquid filled gauges showing loss of case
fill.
NOTE: ASME B40.1 does not recommend
moving gauges from one application to another. This policy is prudent in that it encourages
the user to procure a new gauge, properly tai-
®
lored by specification, to each application that
arises.
6.0 ACCURACY:
PROCEDURES/DEFINITIONS
It is recommended that the user stock one
complete Ashcroft
(or fraction thereof) of that instrument type in
service. With regard to gauges having a service history, consideration should be given to
discarding rather than repairing them.
Gauges in this category include the following:
a. Gauges that exhibit a span shift greater
than 10%. It is possible the Bourdon tube
has suffered thinning of its walls by corrosion.
b. Gauges that exhibit a zero shift greater
than 25%. It is likely the Bourdon tube
has seen significant overpressure leaving
residual stresses that may be detrimental
to the application.
c. Gauges which have accumulated over
1,000,000 pressure cycles with significant
pointer excursion.
d. Gauges showing any signs of corrosion
and/or leakage of the pressure system.
e. Gauges which have been exposed to high
temperature or simply exhibit signs of
having been exposed to high temperature
– specifically 250°F or greater for soft soldered systems; 450°F or greater for brazed
systems; and 750°F or greater for welded
systems.
®
instrument for every ten
Accuracy inspection – Readings at approximately five points equally spaced over the
dial should be taken, both upscale and downscale, before and after lightly rapping the
gauge to remove friction. A pressure standard
with accuracy at least 4 times greater than
the accuracy of the gauge being tested is recommended.
Equipment – A finely regulated pressure supply will be required. It is critical that the piping system associated with the test setup be
leaktight. The gauge under test should be
positioned as it will be in service to eliminate
positional errors due to gravity.
Method – ASME B40.1 recommends that
known pressure (based on the reading from
the pressure standard used) be applied to the
gauge under test. Readings including any
error from the nominal input pressure, are
then taken from the gauge under test. The
practice of aligning the pointer of the gauge
under test with a dial graduation and then
reading the error from the master gauge
(“reverse reading”) can result in inconsistent
and misleading data and should NOT be used.
8
alibration chart – After recording all of the
C
readings it is necessary to calculate the errors
associated with each test point using the following formula: ERROR in percent = 100
times (TRUE VALUE minus READING) ÷
RANGE. Plotting the individual errors
(Figure 1 on page 10) makes it possible to
visualize the total gauge characteristic. The
plot should contain all four curves: upscale –
before rap; upscale – after rap; downscale –
before rap; downscale – after rap. Rap means
lightly tapping the gauge before reading to
remove friction as described in ASME B40.1.
Referring to Figure 1 on page 10, several
classes of error may be seen:
Zero – An error which is approximately equal
over the entire scale. This error can be manifested when either the gauge is dropped or
overpressured and the bourdon tube takes a
permanent set. This error may often be corrected by simply repositioning the pointer.
Except for test gauges, it is recommended
that the pointer be set at midscale pressure to
“split” the errors.
Span – A span error exists when the error at
full scale pressure is different from the error
at zero pressure. This error is often proportional to the applied pressure. Most Ashcroft
gauges are equipped with an internal, adjusting mechanism with which the user can correct any span errors which have developed in
service.
ntermediate points if the response of the
i
gauge as seen in Figure 1 on page 10 is not
®
linear. The Ashcroft Duragauge
pressure
gauge is equipped with a rotary movement
feature which permits the user to minimize
this class of error. Other Ashcroft gauge
®
designs (e.g., 1009 Duralife
) require that the
dial be moved left or right prior to tightening
the dial screws.
Hysteresis – Some Bourdon tubes have a
material property known as hysteresis. This
material characteristic results in differences
between the upscale and downscale curves.
This class of error can not be eliminated
by adjusting the gauge movement or dial
position.
Friction – This error is defined as the difference in readings before and after lightly tapping the gauge case at a check point. Possible
causes of friction are burrs or foreign material in the movement gearing, “bound” linkages
between the movement and the bourdon tube,
or an improperly tensioned hairspring. If correcting these potential causes of friction does
not eliminate excessive friction error, the
movement should be replaced.
(Continued on page 10)
Linearity – A gauge that has been properly
spanned can still be out of specification at
9
TYPICAL CALIBRATION CHART
INDICATED VALUE (PSI)
True Value – Increasing – Increasing – Decreasing – Decreasing –
PSI Without RAP With RAP Without RAP With RAP
0 –.4 0 –.4 0
40 +.8 +1.0 +1.4 +1.1
80 +.4 +.5 +1.2 +1.0
120 –.4 –1.0 +.8 +.6
160 –.8 –.5 +.6 +.4
200 +.4 +.8 +.4 +.4
ERROR (% OF FULL SCALE)
True Value – Increasing – Increasing – Decreasing – Decreasing –
% of Range Without RAP With RAP Without RAP With RAP
0 –.20 0 –.20 0
20 +.40 +.50 +.70 +.55
40 +.20 +.25 +.60 +.50
60 –.20 –.05 +.40 +.30
80 –.40 –.25 +.30 +.20
100 +.20 +.40 +.20 +.20
1.0
Fig. 1
◆
0.5
●
0.0
▲
Error (% of Full Scale)
–0.5
▲ ▲ upscale – without rap
● ● upscale – with rap
◆ ◆ downscale – without rap
■ ■ downscale – with rap
■
●
▲
◆
■
◆
●
▲
■
●
▲
◆
■
●
▲
●
▲
–1.0
0 20 40 60 80 100
% of Range
10
6.1 Calibration – Rotary Movement Gauges
– Inspect gauge for accuracy. Many times
gauges are simply “off zero” and a simple
pointer adjustment using the micrometer
pointer is adequate. If inspection shows the
gauge warrants recalibration to correct span
and/or linearity errors, proceed as follows:
ovement should be rotated counter clock-
m
wise. Rotating the movement one degree
will change this error by approximately
0.25%. Rotating the movement often
affects span and it should be subsequently
rechecked and readjusted if necessary
according to step 6.1e and 6.1f.
a. Remove ring, window and, if solid front
case, the rear closure assembly.
b. Pressurize the gauge once to full scale and
back to zero.
c. Refer to Figure 2 on page 8 for a view of a
typical Ashcroft system assembly with
component parts identified.
d. For solid front gauges, adjust the microme-
ter pointer so that it rests at the true zero
position. For open front gauges the pointer
and dial must also be disassembled and
the pointer should then be lightly pressed
onto the pinion at the 9:00 o’clock position.
e. Apply full scale pressure and note the
magnitude of the span error. With open
front gauges, ideal span (270 degrees) will
exist when at full scale pressure the pointer rests exactly at the 6:00 o’clock position.
f. If the span has shifted significantly (span
error greater than 10%), the gauge should
be replaced because there may be some
partial corrosion inside the bourdon tube
which could lead to ultimate failure. If the
span error exceeds 0.25%, loosen the lower
link screw and move the lower end of the
link toward the movement to increase
span or away to decrease span. An adjustment of 0.004 inch will change the span by
approximately 1%. This is a repetitive procedure which often requires more than one
adjustment of the link position and the
subsequent rechecking of the errors at zero
and full scale pressure.
g. Apply midscale pressure and note error in
reading. Even though the gauge is accurate at zero and full scale, it may be inaccurate at the midpoint. This is called linearity error and is minimized by rotating
the movement. If the error is positive, the
h. While recalibrating the gauge, the friction
error – difference in readings taken with
and without rap – should be noted. This
error should not exceed the basic accuracy
of the gauge. If the friction error is excessive, the movement should be replaced.
One possible cause of excessive friction is
improper adjustment of the hairspring.
The hairspring torque,or tension, must be
adequate without being excessive. The
hairspring should also be level, unwind
evenly (no turns rubbing) and it should
never tangle.
NOTES:
1 For operation of test gauge external zero
reset, refer to Figure 3 on page 12.
2 For test gauge calibration procedure,
refer to Figure 4 on page 13.
6.2 Calibration – 1009 Duralife
®
Gauge –
Inspect gauge for accuracy. Many times
gauges are simply “off zero” and a simple
pointer adjustment using the adjustable
pointer is adequate. If the inspection shows
that the gauge warrants recalibration to correct span and/or linearity errors, proceed as
follows:
Remove ring, window, gasket and pointer
using Ashcroft tool kits 1205T and 1206T.
6.3 Positive Pressure Ranges –
a. Remove dial and lightly press pointer onto
pinion at 9:00 o’clock position.
b. Apply full scale pressure and rotate span
block as shown in Figure 5a on page 15
until pointer rests at 6:00 o’clock position.
c. Fully exhaust pressure and check that
pointer still is at 9:00 o’clock position. If
not repeat steps 1 and 2 until span is
correct.
(Continued on page 10)
11
BOURDON TUBE
SEGMENT
TIP
LINK
BACKPLATE
SOCKET
ROTARY MOVEMENT
PINION
HAIRSPRING
Fig. 2
ASHCROFT SYSTEM ASSEMBLY
Fig. 3
INSTRUCTIONS FOR USE:
LOOSEN RING LOCKING SCREW “A’’
OBTAIN REQUIRED ADJUSTMENT BY ROTATING
KNOB “B’’ CLOCKWISE OR COUNTER-CLOCKWISE.
TIGHTEN SCREW “A’’ DOWN ON KNOB “B.’’
Applicable only for test gauge with hinged ring design.
*
TYPE 1082 EXTERNAL ZERO ADJUST FEATURE*
B
A
12
RING
F
ig. 4
TYPE 1082 TEST GAUGE CALIBRATION PROCEDURE
13
. Remove pointer and reassemble dial and
d
dial screws (finger tight).
. Repeat steps 4 through 8 until span is
h
correct.
e. Lightly press pointer onto pinion.
f. Check accuracy at full scale. If error exceeds
1% return to step 1, otherwise proceed.
g. Check accuracy at midscale. If error exceeds
1% slide dial left or right to compensate.
h. Continue at
Vacuum range –
a. Using a pencil, refer to dial and mark the
0 and 25 inch of Hg positions on the case
flange.
b. Remove the dial.
c. Apply 25 inches of Hg vacuum.
d. Lightly press pointer onto pinion carefully
aligning it with the 25 inch of Hg vacuum
mark on case flange.
e. Release vacuum fully.
f. Note agreement of pointer to zero mark on
case flange.
below.
*
i. Remove the pointer.
j. With 25 inches of Hg vacuum applied,
reassemble dial, dial screws (finger tight)
and pointer.
k. Apply 15 inches of Hg vacuum and note
accuracy of indication. If required, slide dial
left or right to reduce error to 1% maximum.
l. Continue at
Now complete calibration of the gauge as
*
follows:
a. Firmly tighten dial screws.
b. Firmly tap pointer onto pinion, using brass
back-up tool from Ashcroft kit 1205T if
gauge has rear blow-out plug. If gauge has
top fill hole no back-up is required.
c. Recheck accuracy at zero, midscale and full
scale points (Figures 5a & 5b on page 15).
d. Reassemble window, gasket and ring.
below.
*
g. If span is high or low, turn span block as
shown in Figure 5b on page 15.
14
25
V
s
1009 DURALIFE®PRESSURE GAUGE CALIBRATION
15
7.0 DIAPHRAGM SEALS
7.1 General – A diaphragm seal (isolator) is a
device which is attached to the inlet connection of a pressure instrument to isolate its
measuring element from the process media.
The space between the diaphragm and the
instrument’s pressure sensing element is
solidly filled with a suitable liquid.
Displacement of the liquid fill in the pressure
element, through movement of the
diaphragm, transmits process pressure
changes directly to a gauge, switch or any
other pressure instrument. When diaphragm
seals are used with pressure gauges, an additional 0.5% tolerance must be added to the
gauge accuracy because of the diaphragm
spring rate.
Used in a variety of process applications
where corrosives, slurries or viscous fluids
may be encountered, the diaphragm seal
affords protection to the instrument where:
illed prior to being placed in service. Ashcroft
f
diaphragm seal assemblies should only be
filled by a seal assembler certified by Ashcroft
Inc. Refer to section 3.3 for a cautionary note
about not applying torque on either the
instrument or seal relative to the other.
7.3 Operation – All Ashcroft
seals, with the exception of Type 310 miniseals, are continuous duty. Should the pressure instrument fail, or be removed accidentally or deliberately, the diaphragm will seat
against a matching surface preventing damage to the diaphragm or leakage of the
process fluid.
7.4 Maintenance – Clamp type diaphragm
seals – Types 100, 200 and 300 – allow for
replacement of the diaphragm or diaphragm
capsule, if that ever becomes necessary. The
Type 200 top housing must also be replaced
with the diaphragm. With all three types the
clamping arrangement allows field disassembly to permit cleaning of the seal interior.
®
diaphragm
• The process fluid being measured would
normally clog the pressure element.
• Pressure element materials capable of
withstanding corrosive effects of certain
fluids are not available.
• The process fluid might freeze due to
changes in ambient temperature and damage the element.
7.2 Installation – Refer to sales bulletin OH-1
for information regarding (a) seal configurations; (b) filling fluids; (c) temperature range
of filling fluids; (d) diaphragm material pressure and temperature limits; (e) bottom housing material pressure and temperature limits; (f) pressure rating of seal assembly; (g)
accuracy/temperature errors of seal assembly;
(h) diaphragm seal displacement. The volumetric displacement of the diaphragm must
at least equal the volumetric displacement of
the measuring element in the pressure
instrument to which the seal is to be attached.
It is imperative that the pressure instrument/diaphragm seal assembly be properly
7.5 Failures – Diaphragm failures are generally caused by either corrosion, high temperatures or fill leakage. Process media build-up
on the process side of the diaphragm can also
require seal cleaning or replacement. Consult
Customer Service, Stratford CT for advice on
seal failures and/or replacement.
WARNING: All seal components should be
selected considering process and ambient
operating conditions to prevent misapplication. Improper application could result in failure, possible personal injury, property
damage or death.
8.0 DAMPENING DEVICES
8.1 General – Some type of dampening device
should be used whenever the pressure gauge
may be exposed to repetitive pressure fluctuations that are fairly rapid, high in magnitude and especially when transitory pressure
spikes exceeding the gauge range are present
(as with starting and stopping action of valves
and pumps). A restricted orifice of some kind
is employed through which pressure fluctua-
16
ions must pass before they reach the bourdon
t
tube.The dampener reduces the magnitude of
the pressure pulse thus extending the life of
the Bourdon tube and movement. This reduction of the pressure pulsation as “seen” by the
pressure gauge is generally evidenced by a
reduction in the pointer travel. If the orifice is
very small the pointer may indicate the average service pressure, with little or no indication of the time varying component of the
process pressure.
Commonly encountered media (e.g. – water
and hydraulic oil) often carry impurities
which can plug the orifice over time thus rendering the gauge inoperative until the dampener is cleaned or replaced.
Highly viscous media and media that tend to
periodically harden (e.g., asphalt) require a
diaphragm seal be fitted to the gauge. The
seal contains an internal orifice which dampens the pressure fluctuation within the fill
fluid.
.4 Ashcroft Pulsation Dampener – Type
8
1106 Ashcroft pulsation dampener is a moving pin type in which the restricted orifice is
the clearance between the pin and any one of
five preselected hole diameters. Unlike a simple throttle screw/plug, this device has a selfcleaning action in that the pin moves up and
down under the influence of pressure fluctuations.
8.5 Ashcroft Pressure Snubber – The heart
of the Type 1112 pressure snubber is a thick
porous metal filter disc. The disc is available
in four standard porosity grades.
8.6 Campbell Micro-Bean
®
– Type 1110
Micro-Bean is a precision, stainless steel, needle valve instantly adjustable to changing
conditions of flow and viscosity. A very slight
taper on the valve stem fits into tapered hole
in the body. The degree of dampening is easily adjusted by turning the valve handle. A filter is built into the Micro-Bean to help prevent plugging.
8.2 Throttle Screws & Plugs – These accessories provide dampening for the least cost.
They have the advantage of fitting completely
within the gauge socket and come in three
types: (a) a screwed-in type which permits
easy removal for cleaning or replacement; (b)
a pressed in, non-threaded design and (c) a
pressed in, threaded design which provides a
highly restrictive, helical flow path. Not all
styles are available on all gauge types.
8.3 Ashcroft Gauge Saver – Type 1073
Ashcroft gauge saver features an elastomeric
bulb that fully isolates the process media
from the bourdon tube. In addition to providing dampening of pressure pulses, the bourdon tube is protected from plugging and corrosion. The space between the bulb and bourdon tube is completely filled with glycerin.
Felt plugs located between the bulb and bourdon tube are first compressed some amount to
restrict the flow of glycerin through an orifice
and thus provide a degree of dampening. The
greater the compression of the felts the
greater the degree of dampening.
8.7 Ashcroft Needle Valves – Type 7001 thru
7004 steel needle valves provide varying
degrees of dampening similar to the Campbell
Micro-Bean but with a less precise and less
costly adjustability. Like the Micro-Bean
these devices, in the event of plugging, can
easily be opened to allow the pressure fluid to
clear away the obstruction.
®
8.8 Chemiquip
Pressure Limiting Valves –
Model PLV-255, PLV-2550, PLV-5460, PLV5500 and PLV-6430, available with and without built-in snubbers, automatically “shut off”
at adjustable preset values of pressure to protect the gauge from damage to overpressure.
They are especially useful on hydraulic systems wherein hydraulic transients (spikes)
are common.
17
9.0 RESOURCES
9.1 Training Videos
9.1.1 Test gauge calibration
®
9.1.2 1009 Duralife
9.1.3 Duragauge
9.1.4 Diaphragm seal filling
9.2 Pressure Instrument Testing Equipment
9.2.1 Type 1305D Deadweight Tester
9.2.2 Type 1327D Pressure Gauge Comparator
9.2.3 Type 1327CM “Precision” Gauge Comparator
9.3 Tools & Tool Kits
9.3.1 Type 2505 universal carrying case for 1082 test gauge
9.3.2 Type 266A132-01 span wrench for 1082 test gauge
9.3.3 Type 1280 conversion kit for 4
9.3.4 Type 1283 conversion kit for 4
9.3.5 Type 1284 conversion kit for 6˝ lower & back connect
9.3.6 Type 1281 socket O-Ring kit for 1279/1379 lower connect
9.3.7 Type 1285 4
9.3.8 Type 1286 6˝ ring wrench for 1379 lower & back connect
9.3.9 Type 1287 cone tool for installing diaphragm & spring on 1279/1379 back connect
9.3.10 Type 1105T calibration tool kit (all gauges except 1009 Duralife
9.3.11 Type 3220 pointer puller (all gauges except 1009 Duralife
9.3.12 Type. 3530 pinion back-up tool for 1009 Duralife
9.3.13 Type 1230 throttle plug insertion (1⁄4 NPT) for 1009 Duralife
9.3.14 Type 1231 throttle plug insertion (1⁄2 NPT) for 1009 Duralife®(body only)
9.3.15 Type 1205T calibration hand tools for 1009 Duralife
9.3.16 Type 1206T ring removal & assembly tools for 1009 Duralife
gauge calibration
®
gauge calibration
1
⁄2˝ lower connect 1279/1379
1
⁄2˝ back connect 1279/1379
1
⁄2˝ ring wrench for 1279/1379 lower & back connect
®
)
®
®
®
)
®
18
19
Ashcroft Inc.,
250 East Main Street
Stratford, CT 06614-5145
U.S.A.
Tel: 203-378-8281
Fax: 203-385-0408 (Domestic)
Fax: 203-385-0357 (International)
email: info@ashcroft.com
www.ashcroft.com
Visit our web site www.ashcroft.com
All sales subject to standard terms and conditions of sale. I&M008-10098-5/02 (250-1353H) 1M AMR 5P1/08
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