Dwyer TVF - Manual (Page 6)

SYMPTOM
FLOAT HANG-UP
FLOAT BOUNCE
APPARENT FALSE
READINGS, GAS
METERS
APPARENT FALSE
READINGS, LIQUID
METERS
USUAL CAUSE
Caused by particles, sludge, etc. (including failure to
remove the plastic tubing used to block meter float
during shipment) inside the core tube and/or sight
tube holding float. A bent snorkel tube/guide rod
(usually caused by careless disassembly or violent
surges) may also be causing float to stick. Violent
surges may also unseat the internals in extreme
cases.
Caused by pumping/compressor surges or other
pulsation sources, loose valve disks or similar
mechanical components, extreme violation of inlet
piping recommendations, or for gas applications,
harmonics commonly found in systems with low
pressure, low density gas.
Gas density not according to calibration data
(different pressure, temperature, gas, etc.), high
water vapor content, saturated gas going into vapor
or condensation phases, partially clogged core tube
slot or foreign matter interfering with float movement,
and/or violation of piping recommendations at high
flow velocities.
Liquid density not according to calibration data
(different temperature or new liquid or liquid mixture),
excessive dissolved or suspended solids or gases,
partial clogging of core tube slot or foreign matter
interfering with float movement, or viscosity levels
above the meter's immunity index (V.I.C.). Note: If the
meter is suspected of giving false readings, and none
of the causes mentioned is found, please advise as to
the method used in determining the suspected flow
“error.” Each flowmeter is individually calibrated by
traceable methods, and carefully inspected. There
may be some error in checking the meter against
another standard.
SUGGESTED REMEDY
Remedies include tapping the meter gently to
temporarily dislodge the float, but if problem reoccurs,
meter should be disassembled & cleaned, and/or
snorkel/guide rod straightened. If hang-up caused by
sludge or pipe scale, clean lines & install a filter or other
form of cleaner in supply line. If surges have caused the
internals to unseat, install a de-surger, accumulator, etc.
You may also wish to order a buffer kit — the buffer
serves as a resilient cushion for the float, and prevents
unseating.
Modification of piping, such as addition of a de-surger,
receiver, accumulator, vibration eliminators, loops,
hoses, etc. between the source and meter should
remedy the problem. Severe vibration may ultimately
damage the meter, and should be avoided. If "bounce"
seems to be from some other source, or shocks such as
"water hammer" (a potentially dangerous condition),
discontinue using the meter and contact factory.
Remedies include checking meter pressure &
temperature, determining actual gas mixture density &
correcting with appropriate formulae in this bulletin.
Modifying inlet piping, relocating meter to point of higher
temperature and/or lower pressure to eliminate vapor or
condensation phase effects, and/or cleaning the meter
(install filter or other form of cleaner if dirt repetitive
problem) may also be required. If accuracy still
questioned, return core tube/float assembly for
calibration check.
By determining the actual density (due to changes in
mixture, temperature, etc.), the correction formulae may
be applied. If dissolved gases are in the liquid, some
elimination means should be provided on the supply side
(also recheck all piping, as improper seals at connection
points are common sources of air in the liquid). If the
metered liquid is near the boiling point producing partial
"flash gas" at the meter, relocate the meter to point of
lower temperature and/or higher pressure, or cool lines
and/or increase system pressure. Note: It is potentially
dangerous to meter near the "flash point" of any fluid,
and this practice should be avoided. Consult the factory
for recommendations. The previous recommendations
regarding cleaning the meter and/or filtration will also
solve problems due to dirt. If metering liquids with high
viscosities, consult the factory (may require special
calibration). If none of these causes seem to be present,
return meter core tube/float assembly along with
application data.
TROUBLESHOOTING