Rotating liquid pumping system

A mechanism such as a rotor of an open rotor gas turbine engine comprises a rotor assembly 100 rotatable about a rotational axis A. The rotor assembly 100 has a fluid pathway 110 including a pump 114 carried by the first rotor assembly 100 for driving fluid along the fluid pathway 110. The fluid may be oil for lubricating components of the mechanism. The fluid is collected by an annular channel-shaped collector 111 and pumped through surface coolers 116 to an outlet pipe 119. From the pipe 119 the fluid migrates along a path 500 under centrifugal force, returning to the collector 111.