Additional requirement on bursting strength of the filter:
If the machine is provided with a safety switch to protect the motor and the filter system, this switch must be rendered inoperative. All parts, with the exception of the main filter, can be dried in order to facilitate the flow of the clogging media. All bags and prefilters must be removed from the machine to ensure that the main filter is fully exposed to the clogging media and to the impelling force by covering the intake opening.
By using the method to measure Pi, as described in DIN EN 60335-2-69, Section 3.1.9, a clogging media (e.g. talcum powder) is vacuumed until 90 % of the maximum differential pressure has been reached. Afterwards, the intake opening of the machine is covered for 5 seconds and then opened for 1 second in order to obtain an impulse effect. The test with pulsating air flow must be repeated 30 times within 3 minutes.
The main filter may not exhibit any damages (e.g. breaking, loosening, crack formation).