Abstract: Methods and apparatus are disclosed for disposing a valve within a barrel of a conventional syringe to provide, first, a mixing syringe embodiment and, second, a sequential delivery syringe embodiment. Generally, the valve divides the syringe barrel into a proximal and a distal chamber. When used for mixing, the valve is self-displaceable by expansion of decompressing matter disposed within the valve against exterior matter permitting proximal displacement of the valve independent of character of matter in the distal chamber. For sequential delivery, switching of the valve occurs after switch opening causing pressure is relieved, thereby reducing inadvertent uncontrolled flow when the valve opens. In addition, a combination mixing and flush syringe is disclosed whereby a mixing and a flush capability is provided within a conventional syringe.