Abstract: A door assembly for securing an elongate filter cartridge in a dust collector. The door assembly utilizes a mounting plate engaged with the cover of an elongated filter cartridge so as to substantially seal the cartridge opening. The filter cartridge and mounting plate surround a support rod which extends through an aperture in an outer door that is engaged with the door wall of the dust collector so as to substantially seal the entrance of the dust collector. A spring assembly is positioned about the rod connects the door to the mounting plate. A compression spring within the spring assembly extends between the door and mounting plate, and a holder is tightenably and removably engaged with the end of the support rod thereby applying a closing force along the rod and sealing the cartridge in position in the dirty-air chamber.