projection 220 corresponds approximately to the contour shape of the closure plate 219 or that of the inner side of the filter frame 213 receiving the closure plate 219 and plate 221 this means that the actuation arm 225 has approximately the same width as the plate 221 at its free end the actuation arm 225 carries an actuation nose 216 slightly displaced off centre which nose moves a closure member v of a mounting plate 201 for the dust filter bag 208 along with the nose in the manner described above the mounting of the actuation projection 220 on the plate 221 is explained in more detail with reference to fig2 to 26 the plate 221 has perpendicularly extending shanks 230 231 on which the the actuation projection 220 is mounted at its sides the shanks being connected at their free ends by means of a bar 232 at the opposite end from the axis 227 the actuation arm 225 of the actuation projection 220 is guided between the underside 235 of the plate 221 and the bar 232 a retaining nose 236 abuts against the bar 232 on extension of the springs 228 229 and prevents the arm from being withdrawn the springs.