When a second member of a power plant is in a first position with respect to a first member, a first communication port communicates with a fluid pressure supply source and second and third communication ports communicate with first and second pressure chambers of a fluid pressure motor. The second and third communication ports are shut off from a fourth communication port connected to a reservoir. Different positions of the second member result different communication and shut off relationships among the first to fourth ports. The first to fourth communication ports are provided in a plurality of communication port groups each formed by the first to fourth communication ports.

A power split transmission has a drive shaft with a first mechanical branch comprising a planetary gear arrangement with at least two sun gears, a first ring gear and a planetary web, on which double planetary gears are arranged, which mesh with the sun gears and with the first ring gear, at least one of the sun gears being coupled to the drive shaft, with a continuously adjustable second branch, which can be connected at least partially to the first, mechanical branch via the planetary gear arrangement and comprises at least two adjustable hydraulic units which can be energetically coupled to one another and can be operated in each case in both directions as a motor or pump, and with an output shaft which can be coupled to the drive shaft via the first, mechanical branch and the second branch, the planetary gear arrangement being assigned a planetary reversing gear by means of which the direction of rotation of the first, mechanical branch can be reversed.