Method of assembling gas flow control valve

An assembly method of assembling a gas-mass-flow control valve including a valve housing having an inlet for accepting a gas and an outlet for discharging the gas, a primary channel formed in said valve housing in a vicinity of said inlet, two secondary channels that branch off from said primary channel and that are communicated with said outlet, first and second channel openings that are formed between said two secondary channels and said primary channel, respectively, first and second valves that open or close said two channel openings simultaneously by way of first and second valve seats which are disposed in said two channel openings, respectively, a valve shaft having said first and second valves, and an actuator that causes said valve shaft to reciprocate in a direction of an axis of said valve housing, said assembly method comprising the steps of:

• press-fitting said first valve seat to a valve seat press-fitted portion of said first channel opening on a side of said actuator;
• placing oil between an outer surface of a first large-diameter portion of said valve shaft and an inner surface of said first valve;
• press-fitting said first valve to said first large-diameter portion of said valve shaft;
• measuring a distance L1 between a position of said first valve on a side of said primary channel and a position of a valve seat press-fitted portion of said second channel opening on a side of said primary channel in a state in which said valve shaft to which said first valve is press-fitted is temporarily incorporated into said valve housing so that said first valve is adhered to said first valve seat;
• placing oil between an outer surface of a second large-diameter portion of said valve shaft and an inner surface of said second valve after taking out said valve shaft from said valve housing;
• while measuring a distance L2 between a position corresponding to said first valve on the side of said primary channel and a position corresponding to said second valve seat on the side of said primary channel, press-fitting said second valve to said second large-diameter portion of said valve shaft in a state in which said second valve seat is placed in said second large-diameter portion of said valve shaft so that said distance L2 becomes equal to said distance L1, only when an amount of leakage in said second valve seat at ordinary temperatures is set to 0;
• press-fitting said second valve seat to said valve seat press-fitted portion of said second channel opening which is distant from said actuator;
• and
• incorporating said valve shaft into said valve housing.