of valve body 24 interior surface 78 has a tapered portion 79 that cooperates with outer surface 72 of tapered second end portion 62 of piston 28 to meter fluid through expansion valve assembly 16 preferably interior surface 79 is tapered at a second predetermined angle so as to provide a sufficiently long orifice tube length when piston 28 is moved in its full open position downstream with stop surface 74 abutting stop members 80 formed on the interior surface of distal end 52 in accordance with another aspect of the invention to insure that fluid flows though flow passageway 64 expansion device 16 is provided with piston sealing member 30 in a preferred embodiment sealing member 30 is an o ring and is positioned around first cylindrical end portion 56 end portion 38 of screen assembly 26 cooperates with an annular surface 48 to retain sealing member 30 on piston 28 and to insure that refrigerant is forced to flow though passageway 64 without requiring machining of an annular ring on an outer surface 81 of first cylindrical end portion 56 during system operation piston 28 is positioned in an open position with piston 28 being displaced fully leftward such that stop surface 74 of piston 28 is spaced.