33 and through a channel selector tube 4 that connects the channel selector passage 35 to the channel selector 65 the channel selector 65 distributes pressurized air or nitrogen and vacuum pressure to a selected one of the outer pressure ring 52 the middle pressure ring 53 the inner pressure ring 54 the inside pressure rings 56 the central membrane 58 and the inner tube 47 by receiving the air nitrogen or vacuum pressure through a pressure ring passage 37 extending through the hub 33 and the frame 40 respectively the pressurized air or nitrogen or the vacuum pressure is distributed to the pressure rings 52 54 inside pressure ring 56 central membrane 58 or inner tube 47 through a corresponding one of the multiple proxmial tubes 3 and distal tubes 1 as shown in fig3 the channel selector 65 typically includes a casing 66 which defines a casing interior 67 the channel selector tube 4 is disposed in fluid communication with the casing interior 67 through a casing opening 66 a a disc shaped active ratchet wheel 68 having multiple ratchet fingers 69 extending upwardly therefrom in a circular pattern is slidably disposed in the bottom portion of the casing interior 67 the upper extending end of each ratchet.