A method and apparatus for controlling the flow of fluid in an injection well includes a main valve assembly having a valve and a retrievable nozzle selective lock assembly (RNSLA). The RNSLA is operable when positioned within the valve body to open the valve when fluid is pumped into the well and closes the valve when fluid flow is terminated. The RNSLA includes a replaceable orifice nozzle so that orifices of different dimensions may be used in conjunction with the valve assembly. In an alternate embodiment, the RNSLA includes a variable output nozzle assembly to maintain the valve in a protected open position without chattering over a wide range of flow rates.