A flow control valve comprising: a valve body having a distal valve body end, a proximal valve body end, a bore extending along a longitudinal axis, and a valve seat positioned at said distal valve body end; an inlet port and an outlet port each extending through said valve body to said bore, said outlet port having an inner surface; a valve member slidably disposed in said bore, said valve member including a drive head and a poppet, said poppet including a distal poppet end and a proximal poppet end, and said drive head having a threaded bore; a stepper motor having a shaft that is threadably engaged with said threaded bore in said drive head, said stepper motor operating to longitudinally displace said valve member in a longitudinal direction, parallel to said longitudinal axis, between a closed position and an open position; said valve member including a seat engagement surface that contacts said valve seat in said closed position and that is displaced away from said valve seat in said open position; a diaphragm extending between and connected to said valve body and said valve member such that said diaphragm deflects in response to movement of said valve member along said longitudinal axis; and a flow control needle mounted to said poppet that protrudes from said distal poppet end and is at least partially received in said outlet port when said valve member is in said closed position, said flow control needle cooperating with said inner surface of said outlet port to define an outlet flow orifice that varies in size when said valve member moves between said closed and open positions, wherein a poppet bore includes internal threads, and a barrel portion of the flow control needle includes barrel threads that thread and engage the internal threads in the poppet bore wherein rotation of the flow control needle in the poppet bore changes the longitudinal position of the flow control needle relative to the distal poppet end to fine tune fluid flow rate and accommodate variances due to manufacturing tolerances, characterized in that said seat engagement surface is positioned at said distal poppet end and is radially outward of said flow control needle. a valve body having a distal valve body end, a proximal valve body end, a bore extending along a longitudinal axis, and a valve seat positioned at said distal valve body end; an inlet port and an outlet port each extending through said valve body to said bore, said outlet port having an inner surface; a valve member slidably disposed in said bore, said valve member including a drive head and a poppet, said poppet including a distal poppet end and a proximal poppet end, and said drive head having a threaded bore; a stepper motor having a shaft that is threadably engaged with said threaded bore in said drive head, said stepper motor operating to longitudinally displace said valve member in a longitudinal direction, parallel to said longitudinal axis, between a closed position and an open position; said valve member including a seat engagement surface that contacts said valve seat in said closed position and that is displaced away from said valve seat in said open position; a diaphragm extending between and connected to said valve body and said valve member such that said diaphragm deflects in response to movement of said valve member along said longitudinal axis; and a flow control needle mounted to said poppet that protrudes from said distal poppet end and is at least partially received in said outlet port when said valve member is in said closed position, said flow control needle cooperating with said inner surface of said outlet port to define an outlet flow orifice that varies in size when said valve member moves between said closed and open positions, wherein a poppet bore includes internal threads, and a barrel portion of the flow control needle includes barrel threads that thread and engage the internal threads in the poppet bore wherein rotation of the flow control needle in the poppet bore changes the longitudinal position of the flow control needle relative to the distal poppet end to fine tune fluid flow rate and accommodate variances due to manufacturing tolerances, characterized in that said seat engagement surface is positioned at said distal poppet end and is radially outward of said flow control needle.