A regulator for flow modulation during blood collection, said regulator comprising a housing having a housing inlet , a housing outlet , and a wall defining a housing interior , at least a portion of said wall comprising a flexible member , further characterized by : a valve having a first end associated with said flexible member , the valve extending into the housing interior and having a second end positioned to cooperate with an orifice of the housing inlet or the housing outlet , wherein upon application of a differential pressure within the housing interior , the flexible member and the valve are automatically movable with respect to either the housing inlet or housing outlet to vary the geometry of the orifice of the housing inlet or the housing outlet to modulate a flow of blood moving through the housing , wherein the housing inlet is associated with a blood source and the housing outlet 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 , wherein the application of the vacuum to the housing outlet forces the second end of the valve into the orifice of the housing inlet or the housing outlet to decrease a rate of the flow of blood passing through the housing , and wherein the second end of the valve is configured to at least partially withdraw from the orifice of the housing inlet or the housing outlet to increase the rate of the flow of blood passing through the housing when a pressure within the housing by the vacuum is equalized with an atmospheric pressure, characterized in that the valve comprises a concentric annulus having an inner stem connected to the flexible member , wherein the application of a vacuum pressure within the housing causes the flexible member to be drawn into the housing interior to lengthen the concentric annulus. a valve having a first end associated with said flexible member , the valve extending into the housing interior and having a second end positioned to cooperate with an orifice of the housing inlet or the housing outlet , wherein upon application of a differential pressure within the housing interior , the flexible member and the valve are automatically movable with respect to either the housing inlet or housing outlet to vary the geometry of the orifice of the housing inlet or the housing outlet to modulate a flow of blood moving through the housing , wherein the housing inlet is associated with a blood source and the housing outlet 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 , wherein the application of the vacuum to the housing outlet forces the second end of the valve into the orifice of the housing inlet or the housing outlet to decrease a rate of the flow of blood passing through the housing , and wherein the second end of the valve is configured to at least partially withdraw from the orifice of the housing inlet or the housing outlet to increase the rate of the flow of blood passing through the housing when a pressure within the housing by the vacuum is equalized with an atmospheric pressure, characterized in that the valve comprises a concentric annulus having an inner stem connected to the flexible member , wherein the application of a vacuum pressure within the housing causes the flexible member to be drawn into the housing interior to lengthen the concentric annulus. <EOS>