Constant differential pressure valve

A constant differential pressure valve provided in a flow passage of refrigerant circulating through a refrigeration cycle, for controlling a flow rate of the refrigerant such that a differential pressure of the refrigerant across the constant differential pressure valve is held at a constant level set by a value of an electric current supplied to a solenoid coil thereof, the constant differential pressure valve comprising:

• a pipe forming a part of the refrigerant flow passage;
• a fixed core in the form of a hollow cylinder fixed in said pipe;
• a movable core in the form of a hollow cylinder disposed in said pipe in a manner opposed to said fixed core in an axial direction such that said movable core is movable in the axial direction;
• the solenoid coil circumferentially disposed outside said pipe in a manner surrounding said pipe, for generating a magnetic circuit including said movable core and said fixed core by an electric current which is externally supplied, to generate an electromagnetic force a magnitude of which corresponds to a value of the supplied electric current to thereby move said movable core to a predetermined reference position with respect to said fixed core;
• and
• a differential pressure control mechanism provided in said pipe, for performing valve-opening or valve-closing operation while moving said movable core to and from the predetermined reference position to adjust an internal passage cross-section, to thereby control the flow rate of the refrigerant such that the differential pressure of the refrigerant across the valve is held at the constant level.