The present invention relates generally to an air pump, and more particularly to a bicycle air pump.
The conventional air pump is provided with a large cylinder and a small cylinder, which are shifted by a switching device in the midst of the inflation process. The operation of the switching device is done manually. The manual operation of the switching device causes a great deal of inconvenience to the user of the air pump.
The primary objective of the present invention is to provide an air pump which is free from the drawback of the conventional air pump described above.
The air pump of the present invention comprises at least two cylinders, a distribution guide tube, and a spring. The distribution guide tube is disposed at the lower end of an outer tube in which the large and the small cylinders are disposed. The distribution guide tube is provided therein with two air chambers, one of which is in communication with the large cylinder and is provided with a pressure leaking slide block in intimate contact with the inner wall of the air chamber. The pressure leaking slide block is provided with a channel which is opened or closed along with the movement of the slide block. The spring is disposed in the air chamber for providing the pressure leaking slide block with the recovery spring force. Another air chamber is in communication with the large and the small cylinders for inflating an inflatable object.