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Isco 4700 Refrigerated Sampler
Section 2 Installation
2.6.1 Alternative to Strainers
2.6.2 Maximum
Unanchored Depth
2.7 Routing the Suction
Line and Strainer
2.8 Connecting the
Sampler to External
Devices
2-14
When sampling from high velocity streams with heavy sus-
pended solids, some field investigations suggest that more repre-
sentative samples are obtained without the strainer. Consider
attaching a short piece of thin walled aluminum tubing to the
end of the suction line; anchor the tubing so that the inlet opens
upstream. The aluminum tubing's thin wall will not disturb the
flow stream, and most sample analyses disregard aluminum
ions. Under most conditions, the pre-sample line rinse removes
any debris over the tubing entrance.
Table 2-2 lists maximum unanchored depths for each type of
suction line. During a pre- or post-sample line rinse, the suction
line is filled with air which might cause the suction line and
strainer to float. If the depth of the strainer exceeds the listed
value, securely anchor the strainer.
Note
Even if the maximum depth is not exceeded, it is a good idea
to anchor the suction line and strainer when sampling from
high velocity or turbulent flow streams.
Route the suction line so that it has a continuous slope from the
liquid source to the sampler. This helps to drain the line during
pre- and post-sample line rinses. If a suction line exposed to
freezing climates does not fully drain, there is a risk of liquid in
the suction line becoming frozen. Frozen liquid will cause the
sample collection to fail. A warm sampling source can usually
prevent this, provided there are no loops in the suction line.
Some extreme situations may require more protective measures,
such as insulating the suction line, or applying heat tape.
For representative samples, place the strainer in the main
current of the flow stream, not in an eddy or at the edge of flow.
Placing a strainer at the bottom may produce samples with
excess heavy solids and no floating materials, while placing it at
the top may produce the opposite conditions.
You can connect the sampler to an external instrument (Figure
2-11) for a variety of reasons. Typical reasons include:
• Receiving flow pulses from a flow meter device for
variable time or variable volume sample collection.
• Receiving an enable pin signal to enable sampler
operation once site conditions warrant sample collection.
• Sending a three-second event mark at the beginning of
every sample collection event.
• Receiving a linear 4-20 mA analog representation of the
flow rate for variable time or variable volume sample
collection.
• Sending alarm signals when user-specified sampler
events occur.
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