Abstract: The expansion valve 103 of the refrigerating machine is controlled by the difference between the pressure in a bulb 104 containing a fixed amount of fluid and the pressure in the evaporator 2. The bulb is mounted in the discharge pipe 1 of the evaporator and is heated by a resistor. In the absence of droplets of liquid refrigerant in the flow through the discharge pipe, i.e when the refrigerant flow rate tends to become too low with respect to the cold demand, the resistor heats up the fluid in the bulb, the pressure in the bulb increases and moves the expansion valve to a more opened position. As soon as droplets hit the bulb in the discharge pipe, said droplets cool down the bulb despite the heating effect of the resistor and the expansion valve is moved to a more closed position. Thus, the flow rate control uses variations in heat transfer coefficients in the discharge pipe rather than superheat temperature in the discharge pipe.

Abstract: A machine for the compression or expansion of a fluid comprising a multi-thread screw having opposite low and high pressure ends, the screw being mountable for rotation about an axis to cooperate in substantially fluid-tight manner in a cylindrical bore of a stationary casing, at least one pinion having teeth disposed for meshing engagement with the screw threads and rotatable about an axis transverse with respect to the axis of screw rotation. The screw is carried by a shaft supported by two sets of bearings respectively disposed on each end of the screw. The casing bore is open at both ends and the high pressure end of the casing includes a hoop having an internal bore diameter substantially smaller than the diameter of the bore. The low pressure end of the casing bore is of a diameter at least equal to the diameter of the screw for introduction of the screw into the casing bore during assembly of the screw and casing.