MIL-HDBK-1005/16
11.6.2.2 Sample Gathering Subsystem. Three basic sample
gathering methods are available in commercial samplers:
mechanical, forced flow, and suction lift. Figures 25 and 26
illustrate forced flow and suction lift sample gathering
subsystems, respectively. Figure 27 illustrates an open channel
mechanical sample gathering subsystem that can be used for both
weir and flume installations. These subsystems are compared in
Table 20.
11.6.2.3 Sample Transport System. A majority of commercially
available composite samplers have fairly small diameter tubing in
the sample train. This tubing is vulnerable to plugging because
of the buildup of fats, other solids, and insoluble components.
Adequate flow rates must be maintained throughout the sampling
train to effectively transport suspended solids.
To optimize sampler performance and reliability, the
following features are desirable:
a)
Use a sample transport line with at least a
1/4-inch (6-mm) internal diameter.
b)
For most applications, replaceable sample lines
are preferable.
c)
For most applications, select samplers that
minimize contact of the water/wastewater with metal surfaces
during sample transport.
d)
For peristaltic pumps, use a sample line that is
transparent and flexible, and made of an inert material such as
Tygon.
For collection of organics, use sample lines constructed
of silicone rubber. Do not use silicone rubber transport lines
for trace metal sampling since zinc may be a contaminant.
e)
Conduct tests on sample transport lines and
containers to ensure that the sample is not contaminated.
f)
Prevent clogging of sample lines by avoiding sharp
bends, twists, or kinks.
g)
Flush the sample line prior to and immediately
after each sample collection. A clean water flush is effective
but not feasible in most instances. A complete air purge is
sufficient for non-permanent or winter operation.
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