thereby pushing diluent column 15 a and plunger 9 a into the space defined by grooves 12 pistons 9 a and 9 b are under radial compression since plunger 9 a is under compression when assembled it expands when it enters the space surrounding grooves 12 thereby providing resistance to further movement this is depicted in fig2 the hydraulic coupling between the two pistons 9 a and 9 b is removed once the piston 9 a is positioned with the grooves around it allowing the fluid to transfer to chamber 1 as housing 3 is further rotated diluent 15 a flows by piston 9 a through grooves 12 and into space 13 b containing lyophilized drug 14 until all the diluent is pushed into housing 1 at which time housing 3 reaches the end of its travel e g approximately u00be turn the amount of rotation can vary e g on the thread pitch selected this is depicted in fig3 the air displaced by diluent 15 a escapes through the hydrophobic vent in cap 13 a in this position piston 9 a and 9 b have made contact and jointly form a seal over the fluid transfer slots the syringe assembly is rocked in a back and forth motion until the drug is totally dissolved and thoroughly mixed with diluent 15 a to inject the drug into the body cap 13 a is removed and while holding the syringe assembly in the vertical position orifice 13 is pressed against the skin the thumb is then used to press injection button 7 this action locks the button in position at detents 16 actuator 4 seats against the chamfered end.