Abstract: A steam trap in accordance with the preferred embodiment of the invention disclosed herein includes a valve body member formed with inlet and discharge passages and having a valve seat intermediate the passages that cooperates with a valve member to control the flow of fluid. The valve member is movable in a control chamber and is spaced from the control chamber to form an orifice through which fluid can flow from the inlet side of the valve member into the control chamber for controlling the operation of the valve. In accordance with one aspect of the invention, the valve member is made of a material having a different coefficient of thermal expansion than the material forming the control chamber so that the orifice size and the pressure drop thereacross vary non-linearily with temperature whereby the opening and closing of the trap can approximate the saturation curve of the fluid.