Abstract: A ferris wheel type parts washer has its ferris wheel driven by a rotary fluid pressure motor under the control of a variable rate fluid flow control mechanism with means provided for sensing approaching registry of a parts supporting station on the ferris wheel with the parts transfer conveyor for slowing the rotation of the ferris wheel and with means sensing substantial registry of the parts supporting station and the parts transfer conveyor for stopping the fluid pressure motor and locking the ferris wheel in parts transfer registry with the conveyor, such locking means capable of camming the ferris wheel into parts transfer registry should it be slightly out of transfer registry when its movement is arrested. The disclosure shows mechanism for unlocking the ferris wheel and quickly accelerating it to maximum speed.