Free piston device with electrically driven linear actuator

The device has a linearly moveable piston device (12) and a runner (36) connected to the piston. It also has a stator (50). The piston is driven by the effect of a medium which expands in an expansion chamber. The device has a first displacement chamber (20) in which the piston on which the medium acts is moveable. It also has a second displacement chamber (46) in which the associated runner is movable. The first and second displacement chambers are separate chambers.