A regulator (10, 110, 210) for flow modulation during blood collection, said regulator comprising a housing (12, 112, 212) having a housing inlet (14, 114, 214), a housing outlet (16, 116, 216), and a wall defining a housing interior (20, 120, 220), at least a portion of said wall comprising a flexible member (22, 122, 222), further characterized by: a valve (24, 124, 224) having a first end (26, 126, 226) associated with said flexible member (22, 122, 222), the valve (24, 124, 224) extending into the housing interior (20, 120, 220) and having a second end (28, 128, 228) positioned to cooperate with an orifice (30, 130, 230) of the housing inlet (14, 114, 214) or the housing outlet (16, 116, 216), wherein upon application of a differential pressure within the housing interior (20, 120, 220), the flexible member (22, 122, 222) and the valve (24, 124, 224) are automatically movable with respect to either the housing inlet (14, 114, 214) or housing outlet (16, 116, 216) to vary the geometry of the orifice (30, 130, 230) of the housing inlet (14, 114, 214) or the housing outlet (16, 116, 216) to modulate a flow of blood moving through the housing (12, 112, 212), wherein the housing inlet (14, 114, 214) is associated with a blood source and the housing outlet (16, 116, 216) is associated with a vacuum source, and wherein the differential pressure is initiated by the application of a vacuum from the vacuum source to the housing outlet (16, 116, 216), wherein the application of the vacuum to the housing outlet (16, 116, 216) forces the second end (28, 128, 228) of the valve (24, 124, 224) into the orifice (30, 130, 230) of the housing inlet (14, 114, 214) or the housing outlet (16, 116, 216) to decrease a rate of the flow of blood passing through the housing (12, 112, 212), and wherein the second end (28, 128, 228) of the valve (24, 124, 224) is configured to at least partially withdraw from the orifice (30, 130, 230) of the housing inlet (14, 114, 214) or the housing outlet (16, 116, 216) to increase the rate of the flow of blood passing through the housing (12, 112, 212) when a pressure within the housing (12, 112, 212) by the vacuum is equalized with an atmospheric pressure, characterized in that the valve (24, 124, 224) comprises a concentric annulus having an inner stem connected to the flexible member (22, 122, 222), wherein the application of a vacuum pressure within the housing (12, 112, 212) causes the flexible member (22, 122, 222) to be drawn into the housing interior (20, 120, 220) to lengthen the concentric annulus. a valve (24, 124, 224) having a first end (26, 126, 226) associated with said flexible member (22, 122, 222), the valve (24, 124, 224) extending into the housing interior (20, 120, 220) and having a second end (28, 128, 228) positioned to cooperate with an orifice (30, 130, 230) of the housing inlet (14, 114, 214) or the housing outlet (16, 116, 216), wherein upon application of a differential pressure within the housing interior (20, 120, 220), the flexible member (22, 122, 222) and the valve (24, 124, 224) are automatically movable with respect to either the housing inlet (14, 114, 214) or housing outlet (16, 116, 216) to vary the geometry of the orifice (30, 130, 230) of the housing inlet (14, 114, 214) or the housing outlet (16, 116, 216) to modulate a flow of blood moving through the housing (12, 112, 212), wherein the housing inlet (14, 114, 214) is associated with a blood source and the housing outlet (16, 116, 216) is associated with a vacuum source, and wherein the differential pressure is initiated by the application of a vacuum from the vacuum source to the housing outlet (16, 116, 216), wherein the application of the vacuum to the housing outlet (16, 116, 216) forces the second end (28, 128, 228) of the valve (24, 124, 224) into the orifice (30, 130, 230) of the housing inlet (14, 114, 214) or the housing outlet (16, 116, 216) to decrease a rate of the flow of blood passing through the housing (12, 112, 212), and wherein the second end (28, 128, 228) of the valve (24, 124, 224) is configured to at least partially withdraw from the orifice (30, 130, 230) of the housing inlet (14, 114, 214) or the housing outlet (16, 116, 216) to increase the rate of the flow of blood passing through the housing (12, 112, 212) when a pressure within the housing (12, 112, 212) by the vacuum is equalized with an atmospheric pressure, characterized in that the valve (24, 124, 224) comprises a concentric annulus having an inner stem connected to the flexible member (22, 122, 222), wherein the application of a vacuum pressure within the housing (12, 112, 212) causes the flexible member (22, 122, 222) to be drawn into the housing interior (20, 120, 220) to lengthen the concentric annulus.