Abstract: A family of sliding vane rotary power devices provides an internal combustion engine, a pump, a compressor, a fluid-driven motor, an expander device, a fluid-driven pump, and a compressor or a throttling device. All of these devices have an improved method of vane actuation comprising a freely sliding element partially enclosed by a medially extended outer vane portion and partly enclosed at its ends by a mirror-image encircling cam groove formed in a circumferentially-split external housing. As the rotor turns, the sliding elements engage the encircling extended vane portion and the mirror-image cam grooves cause the vanes to reciprocate radially in respective rotor slots while the outer vane tips follow the wall contour of the rotor with a minimal clearance so that the cavities rotate with the rotor and expand and contract as the rotor turns.