4230 Flow Meter
Section 3 Installation
3-10
3.5 The Bubble Line Anchor the bubble line in the flow stream at the appropriate
measuring point in the weir, flume, or other open channel flow
situation. Air slowly bubbles out of the line into the flow stream.
The pressure in the bubble line is proportional to the liquid level
in the flow stream, and the flow meter measures this pressure,
sensing the liquid level.
3.5.1 Standard Bubble Lines Two different bubble lines are available for use with the 4230:
•
1
/8" (0.32 cm) OD,
1
/16" (0.17 cm) ID, Teflon® line, 25 feet
long (7.6 m).
•
1
/4" (0.63 cm) OD,
1
/8" inch (0.32 cm) ID, vinyl line, 50
feet long (15.2 m).
You can specify either line at the time you order the unit. Isco
ships the bubble line in the flow meter's accessory package, and
Isco offers replacement lengths.
3.5.2 Comparing Vinyl and
Teflon Bubble L ines
The vinyl line has two significant advantages over the Teflon
line. First, the vinyl line has a longer usable length than the
Teflon line. This is due to the small inside diameter of the Teflon
tubing, which generates an undesirable friction head at lengths
greater than 25 feet. And second, experience has shown that the
larger ID vinyl line is less likely to clog than the Teflon line when
used in flow streams with suspended solids (for example,
domestic raw sewage or streams with a high grease content).
However, the smaller ID Teflon line also has advantages. First,
since it has a very small inside diameter, the air volume nec-
essary (and, as a result, battery power) is minimized, a definite
advantage for battery-powered installations. And second, almost
nothing attacks the Teflon line, while certain chemicals may
attack the vinyl.
In general, Isco recommends that, wherever practical, you use
the vinyl line. Practice has shown that this line usually results
in more trouble-free operation. Furthermore, if the distance
between the flow meter and the measuring point exceeds 25 feet,
you must use the vinyl bubble line. However, if power con-
sumption is critical, or there are known agents in the flow stream
that might attack the vinyl line, you should use the Teflon line.
3.5.3 Bubble Line Length No matter which line you use, Isco recommends you make it as
short as possible. This will minimize friction head effects in the
line and will also minimize the amount of line exposed to cuts,
kinks, etc. Shorten the line as necessary by cutting the tubing
with a sharp knife.
Long Bubble Lines – For certain applications (for example,
where it is necessary to exceed the 50-foot length of the bubble
line, or where the flow stream is extremely dirty and the end of
the line may clog), you may need to use a bubble line with an
inside diameter larger than either of the two standard lines.
Consult the factory for specific recommendations regarding size
of line, special connectors required, etc. In no case should the
inside diameter of the bubble line exceed
1
/4" (0.64 cm), and you
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