Closure apparatus with removable plug

Claim 1

A CLOSURE APPARATUS FOR CONTROLLING FLUID FLOW THROUGH A KELLY INTO A DRILL STRING AND INCLUDING AN ARRANGEMENT WHEREBY TOOLS MAY BE LOWERED THROUGH THE CLOSURE APPARATUS, COMPRISING: (A) A MEMBER HAVING A PASSAGE THERETHROUGH, (B) MEANS FOR CONNECTING THE MEMBER IN FLUID COMMUNICATION WITH THE DRILL STRING AND KELLY, (C) AN ANNULAR SHOULDER LOCATED IN SAID PASSAGE, (D) A BODY HAVING A CONFORMING SURFACE ADAPTED TO CONTACT SAID SHOULDER TO SHUT OFF FLUID FLOW THROUGH SAID PASSAGE, (E) GUIDE MEANS IN SAID PASSAGE FOR ALIGNING SAID BODY WITH SAID SHOULDER, (F) RESILIENT MEANS FOR URGING SAID BODY INTO CONTACT WITH SAID SHOULDER TO MAINTAIN A STANDING COLUMN OF FLUID IN THE KELLY, (G) SAID RESILIENT MEANS YIELDING ON PREDETERMINED FLUID PRESSURE ACTING THROUGH THE KELLY WHEREBY FLUID MAY FLOW THROUGH SAID PASSAGE, (H) A PLUG THREADEDLY ENGAGED IN THE UPPER END OF SAID BODY, AND (I) A PROJECTION EXTENDING UPWARDLY FROM SAID PLUG SO THAT SAID PLUG MAY BE THREADEDLY DISENGAGED AND LIFTED UPWARDLY OUT OF SAID BODY WHEREBY TOOLS MAY BE LOWERED THROUGH SAID BODY AND INTO THE DRILL STRING.