Quick exhaust valves are installed at the rod or blind end of a pneumatic cylinder to provide a quick extension and retraction of the equipment. Quick exhaust valves operate by increasing the speed of the pneumatic cylinder's rod in order to expel the exhaust air at the port of the cylinder directly.The function of a quick-release valve (Fig. 23) is to rapidly exhaust air from the controlled device. It is normally located adjacent to the controlled device, rather than requiring exhaust air to return and exhaust through the control valve. This decreases release time.On a semi-automatic tyre changer, the head and locking plate is bolted and handle mounted at the front/side of the column by the swing arm; whereas on a fully automatic tyre machine the whole rear column operates through pneumatics, using compressed air to manoeuvre the mounting head and locking it in place.