Abstract: The present invention provides a method and apparatus for controlling the flow of fluids being injected into an oil or gas well through a tubing string, including a generally cylindrical hollow body for connection to the tubing string for receiving and selectively conveying fluids received from the tubing string therethrough, the body having an open top end and an open bottom end, the body having a flow passage therein for conveying fluids from the top end of the hollow body to the bottom end of the hollow body, the top end being provided with a device for connecting the top end to the tubing string, the bottom end being provided with a device for connecting the bottom end to a tool for injecting the fluids into a well, a movable piston slidably received in the body, the movable piston being movable upward against a top seal to stop the flow of fluids through the flow passage and being movable downward against a stop to enable fluids to flow through the flow passage from the top end to the bottom end in respo