SKC Limited Universal Pump Step By Step Guide - Manual (Page 17)

www.skcltd.com 224-G3 Issue C Page 15
Bag Sampling using the Universal Pump
Where there is a need for the sample not to come into
contact with the pump or where the atmosphere may be
aggressive (as found with stack sampling) a method of
collection using an intermediate vessel is recommended.
The intermediate vessel can be any container of adequate
size that is air tight. For example, the SKC Vac-U-
Chamber. Some people use large Tupperware containers
if the bags are small, but any air tight vessel, metal, plastic
or otherwise can be used.
You will need :-
• Universal sample pump (fully charged)
• Sample bag of required size
• Vac-U-Chamber or container of adequate size
• Two air tight fittings for lid of container
• Calibration device that is capable of measuring the
desired flow rate
• Toolkit to adjust the flow rate
Please note: The container must be of a large size in
comparison with the sample bag otherwise too much
back pressure is imposed on the pump.
The set up is as shown in the figure below.
A container is prepared by placing two air tight fittings
in the lid, one is for the suction from the pump, the
other is to supply the sample bag with the sampled
air. By turning the pump on, air inside the container
is drawn out producing a negative pressure inside the
container. In order to maintain pressure equilibrium
inside the container, air is now drawn into the sample
bag via the tube to atmosphere.
1. Before placing the bag into the container open
its valve. Pinch closed the tube from the bag to
atmosphere (or sample point) at a point outside the
container.
2. Place the bag into the container and close the lid.
3. When ready to take the sample remove the clamp
from the tube running from the bag to atmosphere.
4. Switch on the pump.
5. When the sample has been taken switch off the
pump and re-clamp the tube running from the bag
to atmosphere.
6. Remove the bag from the container and close the
valve. The tube from the bag can now be removed
without loss of sampled air.
There is no way in which the volume taken into the
bag by this method can be accurately determined,
unless some kind of calibration device is fitted in-line
from the bag to atmosphere. An estimated volume can
be obtained from the flow rate of the pump multiplied
by the run time. This should not, however, be used
to produce accurate results of concentration of
contaminants.