PUMP

摘要

Disclosed is a pump which is capable of exhibiting an excellent back-suction function by using the features of a push-down head, without impairing the simple push-down operation of the head due to the addition of the back-suction function. A pump comprises a push-down head (D5) and a ring-shaped piston (D4). The push-down head (D5) is mounted so as to be capable of relative vertical movement in an upwardly biased state with respect to a stem (D1). When the push-down head (D5) is pushed down, an open-close valve member (D6) which is biased toward a discharge opening (81) is moved by the action of a lever member (D7) and the discharge opening (81) is opened. The push-down resistance of the push-down head (D5) with respect to the stem is smaller than the push-down resistance of the actual stem. When the ring-shaped piston (D4) is in the uppermost position thereof, a discharge valve (73) comprising a discharge-valve seat (40) protruding from the outer circumference of the stem (D1) is opened, and when the ring-shaped piston (D4) is in the lowermost position thereof, the discharge valve (73) is closed. When the stem (D1) is raised, back suction occurs while the pressure inside the stem (D1) is negative until the ring-shaped piston (D4) closes the discharge-valve seat (40).