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 .