Controller

A controller comprising:

• a valve body in which a fluid passage is provided;
• a diaphragm configured to close and open the fluid passage by coming into contact with and separating from an annular valve seat provided to the valve body, respectively;
• a valve stem configured to change a position thereof, thereby deforming the diaphragm in closing and opening directions;
• and a drive device configured to move the position of the valve stem;
• wherein, between a working shaft of the drive device and the valve stem, a power transmission device configured to amplify a force acting on the working shaft and to transmit a resultant force thus amplified to the valve stem is provided,
• the diaphragm is made of metal and is deformable to either state among:
• a fully closed state in which the fluid passage is fully closed;
• a fully open state in which the fluid passage is fully open;
• and
• a partially open state in which the fluid passage is partially open,
• wherein the drive device is a pneumatic cylinder device and comprises:
• a cylinder having a recess that is open at one end side of the cylinder;
• a bonnet configured to close an opening of the cylinder;
• a piston disposed in the recess of the cylinder;
• a rod fixed to a distal end side of the piston and configured to press the working shaft;
• and
• a diaphragm having a center portion fixed to the piston, a peripheral edge portion fixed between the cylinder and the bonnet, and a turn portion between the center portion and the peripheral edge portion both of which are fixed,
• in which compressed air supplied between the bonnet and the diaphragm is caused to press the piston via the diaphragm, thereby moving the rod, and,
• in the partially open state, on a basis of a flow rate of a fluid that flows through the fluid passage, the drive device makes an adjustment to a position of the working shaft such that the flow rate is constant by adjusting the compressed air supplied between the bonnet and the diaphragm.