Pipe joint made of synthetic resin

1. A pipe joint made of synthetic resin, the pipe joint comprising:

an inner ring having a protrusion formed on an outer circumference at one end portion in an axial direction, the protrusion being pressed into a leading end portion of a tube made of synthetic resin;

a joint body made of synthetic resin, the joint body having, on an inner circumferential side, an annular sealing groove into which the other end portion, of the inner ring, in the axial direction is pressed in a state where the protrusion is pressed into the leading end portion of the tube, the joint body having a male screw portion formed on an outer circumference thereof; and

a union nut made of synthetic resin, the union nut having, on an inner circumference thereof, a female screw portion to be tightened onto the male screw portion of the joint body in a state where the other end portion, of the inner ring, in the axial direction is pressed into the sealing groove,

wherein:

a first opposing surface is formed in the joint body so as to be perpendicular to the axial direction,

a second opposing surface is formed in the union nut so as to oppose the first opposing surface,

the pipe joint made of synthetic resin further comprises:

an engagement projection provided in one of the first opposing surface and the second opposing surface so as to project toward the other of the first opposing surface and the second opposing surface; and

an engagement recess provided in the other of the first opposing surface and the second opposing surface, the engagement recess being formed such that the engagement projection engages with the engagement recess when the union nut has been tightened up to an appropriate position,

a regulation portion is disposed, in a circumferential direction, on only part of one of the first opposing surface and the second opposing surface and projects toward the other of the first opposing surface and the second opposing surface, and

the regulation portion regulates screwing in a tightening direction in a state where the engagement projection has engaged with the engagement recess.

2. The pipe joint made of synthetic resin according to claim 1 , wherein the engagement projection contacts the other of the first opposing surface and the second opposing surface immediately before the engagement projection engages with the engagement recess.

3. The pipe joint made of synthetic resin according to claim 1 , further comprising:

a first projection provided at a predetermined position on the outer circumference of the joint body, so as to project radially outward; and

a second projection provided at a predetermined position on an outer circumference of the union nut, so as to project radially outward, wherein

the first projection and the second projection are disposed such that a position of the first projection and a position of the second projection, in the circumferential direction, are the same when the engagement projection has engaged with the engagement recess.

4. The pipe joint made of synthetic resin according to claim 3 , wherein

the first projection has a joint body side end surface which is a portion of the first opposing surface, and

a portion of the engagement projection or the engagement recess provided in the first opposing surface is formed in the joint body side end surface.

5. The pipe joint made of synthetic resin according to claim 3 , wherein

the second projection has a union nut side end surface which is a portion of the second opposing surface, and

a portion of the engagement projection or the engagement recess provided in the second opposing surface is formed in the union nut side end surface.