The filter cartridge already contains both the suction pipe and extendible protective tubing (Img. 1). If the suction pipe is disconnected, the protective tubing can be extended somewhat, covering the point of disconnection (Img. 2). This means that the protective tubing can be joined or welded over the open air inlet so that the filter cartridge’s air inlet is still shielded from dust in the environment (Img. 3). The filter is removed by sealing the protective plastic film in advance to prevent contamination.