Method for making resin hollow body and flow measuring device

A method for making a resin hollow body including a hollow portion, a linear space, a recess, and a hollow wall surface defining the hollow portion, the method comprising performing a joining process, wherein the performing of the joining process includes:

• bringing joining edges of at least two resin parts into contact with one another so as to form the hollow portion and the linear space, wherein:
• the at least two resin parts are disposed in a predetermined metal mold in a state where the hollow portion and the linear space are formed;
• and
• the metal mold includes a restraining part that is fitted in the recess provided at a part of surfaces of the at least two resin parts which serves as an outer surface of the resin hollow body;
• filling up the linear space with high-pressure resin fluid which is injected at a predetermined injection pressure;
• and
• joining together the at least two resin parts, wherein:
• the metal mold receives the injection pressure of the resin fluid, with which the linear space is filled up, through the at least two resin parts, and applies pressing force, which pushes back the at least two resin parts toward the linear space, to the at least two resin parts as reaction force against the injection pressure;
• stress is produced on the hollow wall surface in a direction in which the hollow wall surface projects into the hollow portion due to the injection pressure;
• and
• the restraining part applies the pressing force to the at least two resin parts in a direction opposite from the stress projecting the hollow wall surface into the hollow portion.