Abstract: A rotary apparatus for use as a pump, motor, meter, or fluid brake is disclosed. A stationary base member has a circular fluid channel with a pair of spaced fluid inlet and outlet ports within the channel. A rotor having a hollow cylindrical body portion substantially surrounds the base member and encloses the channel and has one or more peg-like piston members extending inward from the inner periphery of the rotor. The pistons are received in the channel and separate the channel into one or more enclosed fluid chambers and sequentially pass over the inlet and outlet ports. A ring gear on the inner periphery of the rotor engages a smaller gear rotatably mounted on the base member which is connected to a disc-shaped divider for rotating the divider in timed relation with the rotor upon relative rotation. The divider rotates partially in the channel and is recessed on its side wall to receive and travel in coordinated movement with the pistons during travel in the channel.