A pump comprising a motor 2, gearbox 3, rotational to reciprocal action transmission 4, and diaphragm pump 5, in which the motor and gearbox output shafts, reciprocal movement axis, and diaphragm pump shaft are aligned coaxially on a main axis. The transmission may comprise a sleeve 23 connected to the rotor with a plurality of arms engaging an annular track formed by axially extending formations. There may be a bearing between the sleeve the arms may be axially spaced apart in pairs. The pump casing may be comprised of two parts 45, 46 with a screw thread connection axially coincident with the transmission. The casing may comprise a chamber for the gearbox, a mount for the motor, and the lower part may comprise a pump chamber with a fluid inlet aperture 42 and a fluid outlet aperture 43 with umbrella valves. The casing may comprise air vents for cooling, and have a bayonet fitting 71 on the second part. The gearbox may comprise a two-stage planetary gear set with a 30:1 ratio, and the transmission turning 100rpm output form the gearbox into 400 reciprocations per minute.
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