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PULSATION

 

Air Sampling pumps used for Occupational Hygiene applications are predominantly compact, battery powered, and bodily worn devices designed to maintain a ‘constant’ volumetric flow rate by the use of electronic control circuitry. ‘Constant’ inlet flow is not truly ‘constant’ but in fact represents mean flow value with a superimposed rapidly changing component. These rapid variations in flow are known as Flow Pulsation and are associated to the rotation and fundamental principle of the internal pump mechanism.

Some sampling pumps lack effective pulsation damping. Whilst this may be irrelevant to some sampling strategies, in a size selective sampling application this can lead to undesirable sampling errors.

The Casella Flow Detective can automatically and reliably warn of pulsation levels exceeding 10% (according to ISO13137). For pulsation levels below 10% the Flow Detective maintains its accuracy of +/- 2%. When the pulsation warning is shown above 10% the measurement accuracy will begin to reduce and it is recommended that efforts are made to reduce the pulsation levels.

Being aware of a high pulsation level makes it is possible to take precautions such as adding an additional flow dampener to the sample line, operating the pump with longer and more flexible tubing, operating with a higher inlet pressure loading to reduce pulsation level, or use a different sampler.