Abstract: A diaphragm pump having a diaphragm which is movable to and fro by an oscillating arm which is in turn driven by an electromagnet has its oscillating arm so mounted that it oscillates in a plane which is perpendicular to the principal lines of force of the magnetic field produced by the electromagnet and parallel to pole faces of the electromagnet. Preferably the electromagnet has a core which is substantially E-shaped with the ends of the arms of the E forming the pole faces and the oscillating arm oscillates in a plane perpendicular to the plane of the E. The oscillating arm is preferably mounted by means of a leaf spring to enable it to oscillate and the leaf spring is fixed to a bearing block projecting from a base plate which also carries the electromagnet.