A universal housing body for a refrigeration expansion device including a movable orifice piston. The body is adapted for interchangeable use with a piston of a first variety having a radial boss portion extending along a first axial distance, L.sub.1, from a forward boss end having an annular sealing surface of a first maximum sealing diameter, d.sub.max1, to a rearward boss end, and a piston of a second variety having a radial boss portion and an annular seal member having a forward surface defining with a rearward end of the boss portion a second axial distance, L.sub.2, therebetween greater than the first axial distance L.sub.1, and having a second minimum sealing diameter, d.sub.min2, greater than d.sub.min1 and less than d.sub.max1. The housing body has an internal fluid passageway extending from a forward end to a rearward end which couplable with a flange end of an associated adapter. An annular valve seat, having an inner diametric extent, d.sub.i, intermediate d.sub.min2 and d.sub.max1, is defined within the passageway such that a stop surface of the adapter is positionable within the passageway a spaced-apart distance from the valve seat to define a third axial distance, L.sub.3, greater than L.sub.2. The passageway is configured to receive the piston for movement between a forward and a rearward piston position, whereby in the forward position the sealing surface of the first variety piston and the forward surface of the second variety piston is disposed in an abutting, fluid-tight sealing engagement with the valve seal.