are similarly constructed therefore only nipple 15 need be described referring to fig7 the nipple 15 is provided with an axial inlet 15a that includes a ball check valve 50 and an associated spring 51 for normally biasing the ball check valve 50 toward the closed portion between the inlet opening 15b and the ball check valve 50 there is provided a lateral passage 52 which connects to a bypass 53 extending parallel to the inlet passageway 15a an adjustable needle valve 54 is arranged to valve the lateral passage 52 to control the outlet flow of fluid medium therethrough the arrangement is such that the needle valve 54 is radially disposed so that the head end 54a projects slightly beyond the periphery of the nipple an adjusting collar 55 is threaded onto the periphery of the nipple so as to be rotatable relative thereto the leading end of the collar 55 is provided with an internal taper 55a arranged to engage the head end 54a of the needle valve thus by effecting rotation of the collar 55 relative to the nipple the needle valve 54 can be readily adjusted to control the flow of fluid medium exhausting through passage 52 and thereby control the speed of the rotary plate 12 accordingly as the fluid inlet nipples 15 16 are similarly constructed it will be apparent that the speed of the rotary plate in either direction can be independently controlled thus the rotational speed of the rotary plate 12 in one direction can vary relative to the rotational speed of the rotary plate 12 in the opposite direction and or the respective needle valve 54 can be adjusted so that the speed of.