To provide a bidirectional constant pressure expansion valve and its manufacturing method capable of reducing costs in comparison with a conventional one.

According to this bidirectional constant pressure expansion valve 10, opposed members 13, 13 are received inside of a copper pipe 12, and bulging lock portions 12T formed by partially bulging the copper pipe 12 inward, are locked with locking grooves 13C formed on outer peripheral faces of the opposed members 13. Thus the pair of opposed members 13 are fixed to the copper pipe 12, the copper pipe 12 bites into angular portions of opening edges of the locking grooves 13C to provide metal seal, and the inside of the copper pipe 12 is partitioned into an one end-side area R1, an intermediate area R3 and the other end-side area R2. As fixing parts of the copper pipe 12 and each of the opposed members 13 are acted as the metal seal, the cost can be reduced in comparison with the conventional one comprising an O-ring 3.

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