further on the lower surface of the circular plate member 18 is provided a circular groove 14 for housing a vane guide ring 80 described later the radius of the groove 14 is larger than that of the outlet 13 and it extends from the center p of the eccentric shaft 19 the vane guide ring 80 is slidingly fitted in the groove 14 enabling vanes 31 33 to rotate while radially inner ends thereof are situated closely proximate the outer periphery of the roller with a film of oil interposed therebetween any spaces formed between the roller and the vanes are occupied by an oil film as shown in fig3 a pair of diametrically opposite guiding slots 81 83 are formed in the ring 80 through the slots 81 83 are movably fitted respective protrusions 71 73 protruding from rear ends of respective ones of the vanes 31 33 at the skirt of the cylinder 20 is provided a circular plate bearing 120 for rotatably supporting the cylinder 20 a hole 121 disposed at a center of the bearing 120 rotatingly receives the rotation shaft 21 fig4 is a longitudinal sectional view showing the arrangement of components illustrated above the.