To provide a valve unit control method capable of separating a valve member from a valve seat with smaller driving torque when opening a valve while avoiding the valve member from being excessively compressed against the valve seat when closing the valve seat provided therein.

When the valve member closes the valve seat, more frequent pulses than required for the valve member to close the valve seat are given to a stepping motor to be rotated, whereby a feed screw is displaced at least to a position P1for the valve member to abut on the valve seat and the feed screw is further displaced to a position P2for the valve member to be compressed between the valve seat and itself. Then, pulses are given to the stepping motor to be rotated in the opposite direction to the previous rotating direction, whereby the feed screw has linear motion to a position X in the opposite direction. Thus, the valve member stays at a position of relaxing the compression of the valve member and holding the condition of closing the valve seat.

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