F04B 9/1378

Piston machines or pumps characterised by the driving or driven means to or from their working members the means being fluid the fluid being elastic, e.g. steam or air having plural pumping chambers the pumping members not being mechanically connected to each other {the movement of each piston in one direction being obtained by a single-acting piston fluid motor the movement in the other direction being obtained by an hydraulic connection between the fluid motor cylinders}