Filter cartridge arrangements, features thereof and assembly for use therewith, are provided. Selected filter cartridge features disclosed are particularly well adapted for use with a safety or secondary filter cartridge, usable with media thereof projecting into an open interior of a main filter cartridge, in use. An example filter cartridge is described, with a non-pleated end and a pleated end, although variations are also described. Advantageous main cartridges are also described. Methods of assembly and systems for use are described.

A filter element for filtering a fluid comprising a filter medium pack having an axial inlet side for receiving the unfiltered fluid and a circumferential side forming a radial boundary of the filter medium pack. The filter medium pack is configured for insertion into a housing of a filter system so as to enclose or partly enclose the circumferential side of the filter medium pack with an outer sidewall of the housing. The filter element comprises a bridge seal arrangement having a first collar-shaped portion comprising a first circumferential sealing surface sealingly coupled to the circumferential side of the filter medium pack or sealingly coupled to a border of the axial inlet side, and a second collar-shaped portion comprising a second circumferential sealing surface configured for encircling and sealingly cooperating with the outer sidewall of the housing.

A breathing tube which is designed for channelling inspiratory and/or expiratory breathing gas during at least partial artificial respiration of a patient, defines a virtual breathing-gas-flow path, which is imagined to pass centrally through the tube and along which the breathing tube channels the breathing gas. The breathing tube has a filter carrier in which is formed a filter-accommodating space, which has the breathing-gas-flow path passing through it and in which a breathing-gas filter, which can have breathing gas flowing through it, can be accommodated in an interchangeable manner. The filter carrier has a wall which encloses the filter-accommodating space at a radial distance from the virtual breathing-gas-flow path and has an introduction opening, which is arranged at a radial distance from the virtual breathing-gas-flow path and through which the breathing-gas filter can be introduced into the filter-accommodating space and can be moved into its operationally ready operating position.

A filter element for filtering a fluid comprising a filter medium pack having an axial inlet side for receiving the unfiltered fluid and a circumferential side forming a radial boundary of the filter medium pack. The filter medium pack is configured for insertion into a housing of a filter system so as to enclose or partly enclose the circumferential side of the filter medium pack with an outer sidewall of the housing. The filter element comprises a bridge seal arrangement having a first collar-shaped portion comprising a first circumferential sealing surface sealingly coupled to the circumferential side of the filter medium pack or sealingly coupled to a border of the axial inlet side, and a second collar-shaped portion comprising a second circumferential sealing surface configured for encircling and sealingly cooperating with the outer sidewall of the housing.