Raising gear for submerged air diffusers of the type which are supplied with compressed air from above the surface via a rigid vertical suspension pipe. The top end of the rigid pipe is fixed into a mounting pivoted on a horizontal spindle which is set in a bracket fixed to a wall of the tank. The rigid pipe is coupled via a flexible pipe to an air supply, so that the mounting can be swung through 180 degrees. In this position, the rigid pipe extends vertically upwards from the wall bracket so that the diffuser is raised above the tank. The mounting is mechanically linked to a lifting handle accessible in the side of the tank. When the handle is pulled the mounting pivots and the diffuser is raised. The lower end of the link from the lifting handle is pref. hinged on a common pivot with two other links, of these, the first is a radius arm having angular movement about a horizontal axis in the fixed bracket while the other transmit a turning moment to the pivoted mounting.