receives nose 50 extending from the stop face 30 it will be noted that the outer end of the valve member 40 is recessed from the stop face 30 and o ring 52 seals around the fill port 36 process tube 54 is connected through a vacuum control valve not shown to a vacuum source not shown and is connected through a fill fluid control valve not shown to a source of heat pipe filling fluid not shown process tube 54 communicates with passage 56 which in turn communicates with passage 58 which opens through nose 50 to the fill port 36 when the valve member 40 is off of its seat 38 process tube 54 is connected to the interior chamber 32 of heat pipe 16 when the valves on the process tube 54 are controlled the chamber is first evacuated and then a preselected amount of the desired heat pipe fluid is introduced into the chamber 32 piston 60 is mounted in cylindrical chamber 62 and is sealed therein by means of o rings 64 and 66 it is rotatable in its chamber 62 by means of hex shank 68 which extends leftward exteriorly of block 22 the piston 60 is maintained in its chamber 62 by means of cover plate 70 screwed on the left end of block 22 hex driver 72 engages a hexagonal recess in the right end.