earth 39 s surface or another location in the well in the system 10 the line 20 is a hydraulic control line but in other embodiments the line could be an electrical line a fiber optic line or any other type of line furthermore it is not necessary for a safety valve to be operated using any type of line at all in keeping with the principles of the invention at this point it should be noted that the invention is not limited to the specific details of the system 10 described herein many other types of systems and methods can be used without departing from the principles of the invention referring additionally now to fig2 the safety valve 18 is representatively illustrated in an enlarged scale cross sectional view in this view it may be seen that the safety valve 18 includes unique features which make it particularly suitable for use in situations where it is desired to flow cement through the flow passage 16 of the tubular string 12 in completion operations the flow passage 16 extends longitudinally through the safety valve 18 a closure mechanism 22 is used to selectively permit and prevent flow through the passage 16 the closure mechanism 22 includes a flapper 24 seat 26 spring 28 and pivot 30 as depicted in fig2 the closure mechanism 22 is in an open position in which flow through the passage 16 is permitted in a closed position of the closure mechanism 22 the spring 28 biases the flapper 24 to pivot upwardly about the pivot 30 and thereby sealingly engage the seat 26 and prevent flow through the passage 16 a tubular opening prong 32 holds the flapper 24 pivoted downward as shown in fig2 while the tubular string 12 is installed in the.