Abstract: An air pump particularly suitable for use with bicycles includes a first elongated tube forming a pump chambe and housing, a second elongated tube coupled with a piston through a connecting rod to reciprocate the piston within the pump chamber, and a flexible hose pneumatically coupled at one end with an air passage extending through the piston and having at its opposing end an air valve coupling. The first and second elongated tubes have outer diameters of a size permitting them to be received in and clamped by a seat tube collar of a bicycle frame and the seat post collar of a seat of the bicycle. The piston includes an annular sliding valve member used with a tapered annular valve seat which permits air compression to pressures of about 200 psi while preventing blowby. A second valve along the air passage prevents back flow. The elongated tubes are fixedly secured together in a releasable fashion to prevent relative axial motion or rotation, permitting the use of the pump as a bicycle seat post.