Installation
10 - EN
VA Master FAM540
CI/FAM540-X1
3.3
Operating conditions
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A variable area flowmeter is specified for a defined set of operating
conditions. For liquids and gases, these are pressure and
temperature-related properties (density and viscosity) under
operating conditions. For gases, in particular, this means operating at
a specific pressure and temperature. The specified accuracy of the
instrument is always based on these operating conditions.
Pressure drop
The available operating pressure at the flowmeter must be higher
than the pressure drop listed for the flowmeter in these specifications.
It is important to also consider the pressure drop downstream from
the flowmeter due to losses in the pipeline and other fittings.
Damping and compression oscillations when metering gases
If a specific critical volume is exceeded between the closest throttling
locations up and downstream of the flowmeter, compression
oscillations (float bounce) may occur when the operating pressure is
low. If the minimum required upstream pressure listed in this
specification is not maintained, then the flowmeter must include a gas
damping option (see Fig. 3).
Indicator
housing
Magnet
follower
system
Float guide
G00402
Gas damping
Conical meter
pipe
Float
Fig. 3:
Flowmeter with gas damping
To prevent self-generated compression oscillations, the following
information should taken into consideration:
•
Select a flowmeter with the lowest possible pressure drop.
•
Minimize the pipeline length between the flowmeter and the
closest up or downstream throttling location.
•
Increase the operating pressure, and consider its effect on the
flowrate values due to the change in the gas density at the new
operating conditions.
Pressure shocks
Especially when metering gases, it is possible that pressure shock
waves can occur when fast opening solenoid valves are employed
and the pipeline volume is not throttled, or if there are gas bubbles in
a liquid. As a result of the sudden expansion of the gas in the
pipeline, the float is forcibly driven against the upper float stop. Under
certain conditions, this can lead to destruction of the instrument. The
installation of gas dampers will not compensate for such pressure
shocks.
Solids in the fluid
Variable area flowmeters can only be used under certain conditions
for metering fluids containing solids. As a function of the concen-
tration, particle size and type of solid, increased mechanical abrasion
may occur especially at the critical metering edge of the float. In
addition, solidified deposits on the float can change its weight and
shape. These effects can, as a function of the float type, lead to
erroneous measurement results. In general, the use of appropriate
filters is recommended in such applications.
When metering fluids containing magnetic particles, we recommend
the installation of a magnetic separator upstream of the flowmeter.
Temperature diagram
G00404
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
-100 -50
0
50 100 150 200 250 300 350 400 450
T [°C]
M
T
[°C]
amb
1
2
3
3
1
2
Fig. 4:
Max. medium temperature (T
M
) and ambient
temperature
(T
amb
)
1
Alarm output
-20 ... 70 °C (-4 ... 158 °F)
2
Current output -40 ... 70 °C (-40 ... 158 °F)
3
With insulation
For Ex design, see chapter Explosion-protection relevant.
Insulation
G00441
Fig. 5:
Maximum insulation = Flange diameter
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