A double acting pump mechanism is described for mounting on a wheel for inflating a pneumatic tire. The double acting pump mechanism includes a housing having a first pump chamber and a second pump chamber; wherein a diaphragm separates the first pump chamber from the second pump chamber; the housing further including an inlet port in fluid communication with the first pump chamber, and an outlet port in fluid communication with the second pump chamber, and wherein the outlet of the first pump chamber is in fluid communication with the inlet of the second pump chamber; a striker plate is positioned for reciprocation in the housing; the striker plate being connected to a diaphragm holder, wherein the diaphragm holder engages the diaphragm and actuates the diaphragm in the first and second pump chamber. Preferably the striker plate is actuated by a permanent or electro magnet mounted on a stationary part, or the striker plate is actuated by an electrically driven magnet.