Diaphragm pump with valve switching device

A diaphragm pump comprising:

• paired diaphragms that define pump chambers and air chambers;
• a main body unit that slidably supports a center rod at a central portion of each diaphragm so as to be capable of reciprocating the center rod;
• and
• a valve body that houses a spool that switches supply of a fluid to the air chambers so as to reciprocate the center rod, the valve body including a sleeve, and the spool is disposed inside the sleeve to be reciprocated in an axial direction,
• wherein the spool includes a third disc-shaped portion S3, a second disc-shaped portion S2, and a first disc-shaped portion S1, a surface area of each disc-shaped portion that receives a compressed air pressure has a relationship that an upper side of the third disc-shaped portion S3>a lower side of the second disc-shaped portion S2>an upper side of the first disc-shaped portion S1,
• wherein each disc-shaped portion of the spool includes a seal ring functioning as a packing, each disc-shaped portion separates a plurality of ports within the sleeve from one another, the sleeve includes, for the diaphragms, two ports that can communicate with an air inlet,
• wherein while the spool moves from a top of the valve body toward a bottom of the valve body in the sleeve, the air inlet is always located between the second disc-shaped portion S2 and the first disc-shaped portion S1, and a port that can communicate with the air inlet is changed depending on a movement of the spool, so that supply of the compressed air supplied from the air inlet is switched from one air chamber to another air chamber, and
• wherein when the spool moves to the bottom of the valve body in the sleeve, because the surface area of the lower side of the second disc-shaped portion S2 is larger than the surface area of the upper side of the first disc-shaped portion S1, a force is applied to the spool so as to move the spool toward the top of the valve body in the sleeve, and when the spool moves to the top of the valve body in the sleeve, the compressed air is supplied to a port which is located on top of the sleeve and the spool is pushed down toward the bottom of the valve body in the sleeve.