Abstract: An safety valve includes a housing for defining a fluid flow passageway having a spring loaded seat body and spring mounted therein. The seat body is held in an open position by the spring and is composed of an elastomer material. According to the novel method of using the safety valve, when fluid flows against the seat body a resulting drag force causes the spring to compress. When the fluid flow reaches a predetermined excess flow rate level, the seat body sealingly engages the flow passage to substantially inhibit the flow of fluid except for a small by-pass flow passing downstream via a small channel disposed within the seat body.