Operations and Maintenance
Manual
Gauges and Gauges mounted on Diaphragm Seals
(consult ANSI B40.l or Branom for additional data)
VACUUM, COMPOUND AND
PRESSURE GAUGES
WARNING
Read before installing or using gauge.
Misuse of this product may cause explosion and personal injury.
Safety glasses are recommended when working with pressurized
equipment.
INSTALLATION:
Never hand-tighten a gauge by its body;
always use the wrench flats. Mount the gauge at or below eye
level to reduce parallax errors (visual angle errors). Be
sure the case is not distorted by mislocated or overtorqued
mounting. To avoid contaminating the pressure measuring system
in the gauge, leave a protective cap on the connection fitting
until just before the line connection is made.
If a thread sealant, such as teflon tape,
is used, be sure the sealant is compatible with the contact
fluids. For example, never use teflon tape in the presence
of silicon; use rector seal instead. Using the wrench flats,
make the fitting up to proper tightness to prevent leakage.
Do NOT, however, overtighten the fittings since they may then
be damaged beyond repair. Do NOT use the gauge case to screw
the gauge into place on the line fitting.
OPERATION: The most accurate reading
is made by closing one eye, come up to indication point slightly
from below to eye level, and then observing the position of
the needle with the increments of the dial. For greater accuracy,
mirror-dialed gauges help reduce the chances of parallax error.
A zero-corrector calibration adjustment is a desirable feature
for dry gauges (not available with liquid filled types). Mechanical
or fluid vibrations, pressure spikes, may cause the needle
to read off-zero. Calibration with portable pneumatic or hydraulic
pump and test gauge is an inexpensive method of maintaining
accuracy with a known accuracy and adjustable pressure settings.
At least 10 points on the gauge should be tested while increasing
from zero to full pressure and then while decreasing the pressure
from the full scale reading to zero. A leak may be indicated
by a continuously decreasing gauge reading, particularly if
the pressure has been "trapped" by a valve. If this is the
case, check all the components in the pressure system, including
the fittings and the valve, for leakage. Some gauges appear
to be out of calibration due to a static electrical charge.
Removing the static charge with "Armor All" or other suitable
cleaner should restore the gauge to proper calibration.
Pressure gauges must be correctly selected
and installed to avoid possible injury or damage caused by
misuse. Please note:
OXYGEN SERVICE: Gauges must be
specially cleaned for oxygen service by a qualified laboratory,
bagged and labeled for oxygen service. Branom offers this
service. Repairs and testing of oxygen gauges must be done
with clean air, nitrogen, or distilled water only. Never use
any gauge on oxygen service that has been used on any other
service, or tested with oil.
PRESSURE RANGE: Gauge dial range
should be twice the intended operating pressure range. Never
allow dynamic pressure to be applied beyond 90% of the scale.
Please take into consideration possible spikes of overpressure;
even those of short duration will cause impairment or failure.
Branom does offer PRESSURE LIMITING VALVES, which can be set
to guard against damage resulting from excess pressure. The
PLV shuts off the instrument line automatically, and seals
out pressure rises above the adjustable, pre-set value, and
automatically restores the instrument line when the pressure
falls below the setpoint. Gauges that shall see even occasional
fluctuations between positive and negative pressure (vacuum)
must be compound gauges, i.e. 30" Hg vacuum x 15 PSI or higher.
VIBRATION: Isolate gauge from
sources of vibration to avoid wear to movement, which results
in decreased accuracy. Mounting the gauge remotely from the
vibration via 1/4" copper or SS tubing is best; when this
is not possible, liquid filled gauges and the Vilter Stedigage
devices have been used with some success.
TEMPERATURE: Temperature of the
media entering the gauge should never exceed 1500F/650C
(there are some exceptions, such as the Noshok 400 series
@ 2600F). As in vibration, the best method to solve
high temperatures is to run a copper or other material coil
of 6' or longer, so that the temperature has been reduced
before entering the gauge. Some diaphragm seals with or without
remote capillary can sometimes also be used for this purpose;
due to the expense and possible additional errors in accuracy,
this is done usually only when solidification through temperature
variations can take place.
Corrosion: All wetted parts
of the gauge must be resistant to the process fluid utilized.
Again, a diaphragm seal (available in plastic, for example)
or an in-line isolator with the proper elastomer might be
used with corrosive fluids, when gauges made of exotic metals
or plastics are expensive or rare.
Pulsation: Excessive pulsations
may cause substantial premature wear or work-hardening of
the metallic parts and subsequent failure. Gauge readability
may also be reduced dramatically due to pointer flutter. Internal
spud restrictor screws, Liquid Filled Gauges, Porous disc
and piston type pressure snubbers, and needle valves are recommended
for this service. The needle valve is a particularly excellent
pulsation dampener, as it can be throttled down as needed
and also used as a shut-off valve. With porous disc snubbers,
the gauge should be filled with a compatible glycerin or glycol
or silicon, so that the disc can stay clean and porous as
long as possible.
Liquid Filling for Gauges and Seals:
Never use standard glycol or glycerin fills for applications
involving strong oxidizing agents, including (but not limited
to) oxygen, chlorine, nitric acid, and hydrogen peroxide.
These substances can combine explosively with a standard fill.
Typically, an inert liquid such as Fluorolube or Halocarbon
is used with strong oxidizers. These, however, are never to
be used with aluminum or magnesium.
AMMONIA Service: Wetted parts
of carbon steel or stainless grades of wetted parts can be
used with ammonia compounds. Gauges are available with corresponding
temperature scales as well as pressure. Never use viton elastomers
with ammonia.
Freon and Pressurized Nitrogen Service: Both
of these gases are inert, and therefore brass, steel, monel
or stainless grades of wetted parts can be used. High and
Low Side Gauges are available with corresponding temperature
scales as well as pressure for R12, R22, R502 and Rl34a.
STEAM SERVICE: Due to the high
temperatures involved with steam, a steam syphon or pigtail
filled with water should be attached to the gauge. A copper
tube spiral could serve the same purpose.
DIFFERENTIAL: Indicating the difference
between two pressures, the differential pressure gauge (DP
Gauge) must be chosen not only for its materials, but also
for the static pressure it will see. It is possible to have
a few inches of water column differential on a 500 psi line.
Some gauges can handle this high pressure, low differential
service, some cannot. Some gauges, such as a Magnehelic, are
designed only for air and gasses. Careful attention to detail
will insure proper selection.
WATER LEVEL: Feet of Water
Gauges are designed to be screwed into the side of a tank
near the bottom and to measure the hydrostatic pressure in
feet and inches. A Water Level Gauge, on the other
hand, is a gauge designed to be installed in a well with a
discharge column (tubing or pipe) and an airline of the same
length. This gauge has an adjustable outer ring on the dial,
calibrated counterclockwise, with two sets of figures. The
inner readings are from 0-190 feet; the outer include 200-390
feet. The adjustable dial ring is set at the total number
of feet of airline. Air pressure is then applied to the air
line, purging the air line of water and causing the pointer
to move away from the stop pin in a clockwise position. When
the air line has been completely purged of water, the gauge
hand will remain stationary, indicating the water level in
feet from the Surface on the inner scale of the adjustable
dial ring.
DIAPHRAGM SEALS &
ISOLATORS
Filled system gauges and isolators, with
or without trees (post for multiple instrument mountings),
must be calibrated in the orientation necessary for the installation.
It is recommended that testing under pressure be done 24-48
hours after filling and assembly, to insure that there are
no leaks (316SS fittings, in particular, tend to leak over
time, unless correctly torqued). Even minuscule leaks are
catastrophic in filled systems.
Extreme care must be taken during installation
to maintain the integrity of the seal between the gauge and
the isolation device. Any movement of the connections, however
slight, can cause a leak, and the device to "lose its fill".
Excessive vibration, stepping or even leaning on the device,
or personnel trying to turn the dial of the gauge for a better
viewing angle, all cause catastrophic failures by causing
leaks in the system.
Snubbers and needle valves should never
be placed between the gauge and the diaphragm seal. Shutoff
valves, either needle or ball valves (preferred), should be
screwed into the process outlet of the diaphragm seal, and
not be a part of the filled system. A snubber serves no purpose,
and indeed, brings needless problems and expense to the gauge/diaphragm
seal assembly. The use of a "gauge keeper" assembly, such
as the Conoflow 100 A series #580280SF is recommended to reduce
the possibility of gauge rotation and subsequent loss of fill.
The problems of standard in-line isolator
ring assemblies can be eliminated by the use of Onyx brand
patented system. The Onyx Isolator is filled at the factory
with high viscosity silicon fluid. After filling, the Isolator
Ring is permanently sealed a rubber "Module Seal", which enables
the user to remove or replace or move the dial of gauges and
other pressure instruments while the Isolator Ring is in the
process pipe, without having to vacuum fill the ring or pressure
instrument. No loss of fill, ever.
Pressure isolators frequently handle chemically
reactive and abrasive fluids; it is reasonable to expect the
elastomer sleeve to eventually wear out. Instrument oil must
be compatible with the process liquid. Mixing incompatible
fluids may cause a violent chemical reaction resulting in
equipment damage or personal injury.
Make sure the isolator elastomer is compatible
with the temperature, pressure and material being measured,
and that the mounted instruments are corresponding in nature.
The Onyx Isolator Ring Out-Performs
Conventional Isolator Rings And Standard Diaphragm Seals
Obtaining accurate pressure readings
on pipelines is difficult because slurries, abrasives
and solids clog gauges, switches and transmitters. Standard
diaphragm seals - which are drilled or welded at a point
on the pipeline - provide a temporary solution, but
they are vulnerable to plugging by debris or deposits
and stop working when slurry solidifies in the seal
chamber. Conventional isolator rings consist of a rubber
"inner tube" captured in a steel ring. The assembly
is installed between flanges in the process pipe, with
clear instrument fluid behind the rubber membrane transmitting
pressure to the gauge. The inside diameter of the ring
assembly matches the adjacent pipe, so the ring is continually
cleaned by the motion of the process fluid. A common
problem with this type of isolator ring is that any
air in the instrument will compress when pressurized.
This stretches the rubber membrane, causing accuracy
to degrade or the instrument to malfunction. (An air
bubble as small as a pea can make a sensor non-functional.)
To counter this obstacle, isolator ring manufacturers
use a vacuum pump to evacuate the air from the isolator,
before injecting the instrument fluid. To remove the
gauge for replacement or calibration, the entire ring
and gauge assembly must be removed from the process
pipe and the gauge and ring assembly again have to be
drained, evacuated and refilled. The customer for this
type of isolator ring will experience much downtime
and expense. Some manufacturers try to circumvent this
problem by adding a valve to the ring assembly. This
holds the fluid in the ring, but attempting to fill
the gauge by turning it upside down and pouring fluid
into it traps an air pocket at the tip of the Bourdon
tube. Also, attempting to remount the gauge by covering
the connection with your finger while turning it upright
and screwing it into the isolator is rarely successful.
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The Onyx Isolator Ring Offers The
Solid Solution Towards Solving Your Pressure Measurement
Problems
The Onyx Isolator Ring provides a
practical, cost-effective method for obtaining accurate
pressure measurements on slurries, abrasives and hard-to-handle
materials. The Onyx Isolator Ring is a new patented
design which solves the problems associated with many
of the isolator rings on the market today. The Onyx
Isolator Ring is vacuum-filled at the factory with a
high-viscosity silicone fluid; then, permanently-sealed
with Onyx's Revolutionary "Module-Seal". With the Onyx
Isolator Ring, there is no fill port anywhere on the
assembly: gauges, switches and transmitters are supplied
separately, are pre-filled, and have Onyx's special
fitting attached. You have the option of selecting any
combination of isolator ring and gauge and simply snapping
them together. With the Onyx Isolator Ring, you are
guaranteed hassle-free operation and added protection
for your sensitive indication instrumentation.
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