Fluid control device, fluid supply system, and fluid supply method

A fluid control device comprising:

• a valve device configured to open/close a flow path and adjust a flow rate of a fluid flowing through the flow path,
• a pressure sensor provided upstream of the valve device;
• and
• a control circuit connected to the valve device and the pressure sensor;
• wherein the valve device includes a main valve having a main actuator operated by a driving fluid and a corresponding valve element, and a sub valve having a sub actuator extendable by an electrical drive and a corresponding valve element,
• branch flow paths are formed downstream of the pressure sensor, the main valve being provided at one of the branch flow paths and the sub valve being provided at another one of the branch flow paths, and
• the control circuit controls an operation of the sub actuator of the sub valve based on a pressure measured by the pressure sensor and a reference pressure drop curve, in a state where an upstream side of the fluid control device is closed and the main valve is opened by using the main actuator.