drain as the testing string 10 is removed from the well bore such that fluid in the interior of the test string may drain from the test string conduit 10 as the test string is removed from the well bore the preferred tester valve 25 is one such as disclosed in the aforementioned u s pat no 3 856 085 issued dec 24 1974 to holden et al and owned by the assignee of the present invention this preferred tester valve may include a pressure operated isolation valve for supplementing spring pressure in the tester valve with well annulus pressure as the tester valve is lowered into the well bore 3 at the end of testing string 10 such a pressure operated isolation valve is disclosed in the aforementioned u s pat no 3 976 136 issued aug 24 1976 to farley et al or that disclosed in the aforementioned u s pat no 3 964 544 issued june 22 1976 to farley et al both of which are owned by the assignee of the present invention the preferred tester valve 25 is illustrated in part in fig2 a and 2b the preferred tester valve 25 includes a tubular outer housing assembly having an open bore 40 therethrough the outer housing assembly includes an upper housing adapter 41 an upper ball retaining sleeve 42 a ball section housing 43 an upper intermediate housing 44 a spring section housing 45 having power port 46 a lower intermediate housing 47 and a gas chamber housing including an outer housing portion 48a and an inner housing portion 48b from this point downward the preferred tester valve 25 may.