be constructed to fit a housing of oval or other transverse section or one which tapers axially according to the wishes of the designer in use end 133 is connected to exhaust pipe 116 as by a clamp 157 and tube 152 is connected to scavenger tube 113 as by a clamp 158 the axis of the unit being vertical passage of exhaust gas through tube 130 in the direction of arrow creates a negative pressure at throat site 150 which draws through tube 113 air containing separated dust from cleaner 12 attention is now directed to fig9 11 which shows unit 125 to comprise a muffler into which an ejector is incorporated a casing 160 having an axis 159 is closed by end plates 161 and 162 and divided baffles 163 164 and 165 into chambers 166 167 168 and 169 an exhaust tube 171 having slots 172 at an end 173 extends in sealed relation through end plate 161 and baffles 163 and 164 to open at end 174 into chamber 168 fields of perforations in tube 171 are shown at 175 and 176 and communicate with chambers 166 and 167 respectively communication between chambers 168 and 169 is enabled by an aperture 177 in baffle 165 as shown in the drawing the axis 178 of tube 171 is parallel and close to axis 159 if desired the axes may coincide an ejector 180 is incorporated into unit 125 and comprises a housing 181 and an insert 182 housing 181 is cylindrical about an axis 183 and extends in sealed relation through end plate 162 and baffle 165 into chamber 168 inwardly housing 181 terminates at an end 184 axially spaced from end 174 of tube 172 insert 182 is configured and mounted.