through the piston wall 88 is a locking piston rod 90 a fluid channel 92 along the length of the rod 90 openly communicates the inner face of a floating piston 94 with the open well bore conduit 70 the floating piston 94 is axially confined within the inner bore of the inner traveling locking sleeve 86 by a retaining ring a mixing ball 99 is placed within the sample formation fluid receiving chamber 95 that is geometrically defined as that variable volume within the interior bore 80 of pressure housing 60 between the valve sub assembly and the end area of the traveling trap sub assembly 82 a body lock ring 100 having internal and external barb rings selectively connects the rod 90 to the inner traveling locking sleeve 86 the selective connection of the barbed lock ring 100 permits the sleeve 86 to move coaxially along the rod 90 from the piston 84 but prohibits any reversal of that movement another construction detail of the inner traveling locking sleeve 86 is the sealed partition 122 between the opposite ends of the sleeve 86 the chamber 124 created between the partition 122 and the piston head 106 of the rod 90 is sealed with the atmospheric pressure present in the chamber at the time of assembly the body lock ring 100 between the locking piston rod 90 and the inner bore wall of the inner traveling locking sleeve 86 above the partition 122 does not provide a fluid pressure barrier consequently the chamber 126 between the partition 122 and the body lock ring 100 functions at the same fluid pressure.