A surface treating head comprising a suction cavity having a suction cavity opening bounded by a front working edge and a rear working edge, at least one of the front and rear working edges being moveable between a first position in which the suction cavity opening is at a maximum and a second position in which the suction cavity opening is at a minimum, an actuating mechanism comprising a user-operable actuator for actuating at least one of the front and rear working edges between the first and second positions, and one or more air bleed vents, wherein actuation of the actuating mechanism causes the one or more air bleed vents to open and close.