Nilfisk Power P40 and P20 Allergyvac series H13 HEPA filter, it goes behind the grill at the rear of the machine,
This is a very highly, efficient H13 HEPA filter working after the motor, hence collects the carbon from the carbon brushes in the motor.
Usually, I should imagine this filter needs to be replaced after 12 months, or sooner in dusty conditions or if the dustbags bursts or is fitted incorrectly.
Ensure genuine Nilfisk dustbags are used as these are complete with a replacement pre-filter.
There is also a lesser efficiency filter the H12 with a part number 147-0432-500 that can be used if you choose.
They may also be used in the Nilfisk GU355 Dual commercial upright vacuum cleaner and the Nilfisk GU455 Dual upright commercial vacuum cleaner
According to EN 60335-2-69 The Terms "TYPE H" FILTRATION and HEPA FILTRATION are NOT INTERCHANGEABLE
The HEPA classification only considers the "efficiency of filtration" eg H10 H11 H12 H13 H14 U15 U17 NOT the SUITABILITY FOR USE with HAZARDOUS or COMBUSTIBLE dusts.
As it's light, maximise the saving on postage and buy some of the related parts below, such as dustbags and the filters or a new floor tool.
At the moment standard postage within Australia, is capped at a maximum of $20!