Gasman Flow sampling
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VI. Flow sampling
Attaching the flow cap
To perform manual sampling using Gasman, a flow cap must be fitted
onto the front of the unit, over the sensor. A flow cap is included with
your Gasman unit.
1. To fit the flow cap, firstly ensure the cap gasket is intact, slip the
flow cap over the sensor on the front of your Gasman unit, until
the cap is tightly fitted into place.
2. Attach the sampling tube or flow accessory onto a gas nozzle.
3. Attach the aspirator bulb onto the remaining gas nozzle.
4. To remove the flow cap, gently tease the cap from the sensor and
lift the cap away from the instrument.
When using the manual aspirator kit, adopt a consistent rhythm whilst
using the hand aspirator. Crowcon recommend squeezing once per
second to achieve a flow rate of approximately 0.5 - 1 litre/min. At least
10 pumps per sample are recommended.
The sampling tube supplied is normally a 2m (6ft) length. Longer lengths of sampling tube
can be provided, but will increase the time taken to get a sample from the point of sampling
to the Gasman instrument. When using an extended length of tubing a response time test is
recommended. Gas of known concentration should be sampled along the full length of tubing
to be used and the time taken for the sensor reading to reach the known gas levels should be
noted. This time should be used as the minimum for sampling before readings should be taken.
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