4230 Flow Meter
Section 3 Installation
3-15
The best way to overcome this problem is to completely isolate
the bubble line from the flow stream velocity by placing it in a
stilling well, as described below. If this is not possible, you can
perhaps create a cavity in the bottom of the channel, and locate
the outlet of the bubble line in the depression, again isolating it
from the flow stream velocity.
In flow streams carrying large amounts of solids, however, this
may cause problems because of silt collecting in the depression,
restricting the bubble line. A third alternative is to put a 90
degree bend in the end of the bubble line, forming a horizontal
leg approximately two inches (5 cm) long, and orienting this hori-
zontal leg downstream, parallel with the flow. Tests have shown
that this orientation of the bubble line minimizes the effect of
flow stream velocity.
3.5.9 Stilling Wells If the installation includes a stilling well in the primary mea-
suring device, you should probably install the bubble line in the
stilling well. Attach the line securely to the stilling well, using
stainless steel and/or plastic mounting hardware.
For details on the construction and use of stilling wells, refer to
Section VI, Section 93, of the Water Measurement Manual, pub-
lished by the United States Department of the Interior, Bureau
of Reclamation (1967). Not all stilling wells are suitable for
bubble line installation. If the well is subject to silting or buildup
of foreign material, you should probably avoid it and mount the
bubble line in the flow stream proper.
3.5.10 Flume Bubble Line
Fittings
The large variety of primary measuring devices and installations
makes comprehensive bubble line installation instructions
impractical. However, valid general observations on bubble line
installation can be made. Flumes can be specified to include a
bubbler fitting. In new construction, this is highly recommended.
It may even be possible to modify an existing installation to
include a permanent bubbler fitting.
3.5.11 Bubble Line
Extensions
For some applications, metallic bubble line extensions may be
helpful. Isco offers both stainless steel and copper bubble line
extensions. The stainless steel tube may be easier to install in
the flow stream than the plastic bubble line because of its rel-
ative rigidity. Two different extensions are available to match the
two standard bubble lines.
The extension for the Teflon bubble line includes a silicone
rubber tubing connector, and the tubing installation is as
described above. The vinyl bubble line attaches by simply
slipping the vinyl tube over the end of the extension. Some people
have found that the use of a copper extension to the bubble line is
advantageous in applications where algae tends to grow in the
bubble line.
To Next Page
Loading...
