US Patent 7942647 Pump for supplying chemical liquids

An opening 22d of a supply/withdrawal passage 22b is positioned at the center part of the internal wall surface 22c of the operating chamber 26 (concave area 22a), and a pin 24 that protrudes toward the diaphragm 23 is provided in a position that is offset from the center of the wall surface 22c. When the diaphragm 23 is deformed toward the operating chamber 26 by the suction of an operation air into the operating chamber 26 during drawing in the chemical liquid, a part of the diaphragm 23 opposing to the pin 24 rides on the pin 24 and this part becomes a slightly convex shape toward the pump chamber 25. When the operation air is supplied from the opening 22d into the operating chamber 26 during the discharge of the chemical liquid, the deformation begins first from the part of the diaphragm 23 riding on the pin 24.